+++ /dev/null
-\documentclass{article}
-\def\version{$Id: cdrom-standard.tex,v 1.9 1997/12/28 15:42:49 david Exp $}
-\newcommand{\newsection}[1]{\newpage\section{#1}}
-
-\evensidemargin=0pt
-\oddsidemargin=0pt
-\topmargin=-\headheight \advance\topmargin by -\headsep
-\textwidth=15.99cm \textheight=24.62cm % normal A4, 1'' margin
-
-\def\linux{{\sc Linux}}
-\def\cdrom{{\sc cd-rom}}
-\def\UCD{{\sc Uniform cd-rom Driver}}
-\def\cdromc{{\tt {cdrom.c}}}
-\def\cdromh{{\tt {cdrom.h}}}
-\def\fo{\sl} % foreign words
-\def\ie{{\fo i.e.}}
-\def\eg{{\fo e.g.}}
-
-\everymath{\it} \everydisplay{\it}
-\catcode `\_=\active \def_{\_\penalty100 }
-\catcode`\<=\active \def<#1>{{\langle\hbox{\rm#1}\rangle}}
-
-\begin{document}
-\title{A \linux\ \cdrom\ standard}
-\author{David van Leeuwen\\{\normalsize\tt david@ElseWare.cistron.nl}
-\\{\footnotesize updated by Erik Andersen {\tt(andersee@debian.org)}}
-\\{\footnotesize updated by Jens Axboe {\tt(axboe@image.dk)}}}
-\date{12 March 1999}
-
-\maketitle
-
-\newsection{Introduction}
-
-\linux\ is probably the Unix-like operating system that supports
-the widest variety of hardware devices. The reasons for this are
-presumably
-\begin{itemize}
-\item
- The large list of hardware devices available for the many platforms
- that \linux\ now supports (\ie, i386-PCs, Sparc Suns, etc.)
-\item
- The open design of the operating system, such that anybody can write a
- driver for \linux.
-\item
- There is plenty of source code around as examples of how to write a driver.
-\end{itemize}
-The openness of \linux, and the many different types of available
-hardware has allowed \linux\ to support many different hardware devices.
-Unfortunately, the very openness that has allowed \linux\ to support
-all these different devices has also allowed the behavior of each
-device driver to differ significantly from one device to another.
-This divergence of behavior has been very significant for \cdrom\
-devices; the way a particular drive reacts to a `standard' $ioctl()$
-call varies greatly from one device driver to another. To avoid making
-their drivers totally inconsistent, the writers of \linux\ \cdrom\
-drivers generally created new device drivers by understanding, copying,
-and then changing an existing one. Unfortunately, this practice did not
-maintain uniform behavior across all the \linux\ \cdrom\ drivers.
-
-This document describes an effort to establish Uniform behavior across
-all the different \cdrom\ device drivers for \linux. This document also
-defines the various $ioctl$s, and how the low-level \cdrom\ device
-drivers should implement them. Currently (as of the \linux\ 2.1.$x$
-development kernels) several low-level \cdrom\ device drivers, including
-both IDE/ATAPI and SCSI, now use this Uniform interface.
-
-When the \cdrom\ was developed, the interface between the \cdrom\ drive
-and the computer was not specified in the standards. As a result, many
-different \cdrom\ interfaces were developed. Some of them had their
-own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
-manufacturers adopted an existing electrical interface and changed
-the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
-adapted their drives to one or more of the already existing electrical
-interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
-most of the `NoName' manufacturers). In cases where a new drive really
-brought its own interface or used its own command set and flow control
-scheme, either a separate driver had to be written, or an existing
-driver had to be enhanced. History has delivered us \cdrom\ support for
-many of these different interfaces. Nowadays, almost all new \cdrom\
-drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
-manufacturer will create a new interface. Even finding drives for the
-old proprietary interfaces is getting difficult.
-
-When (in the 1.3.70's) I looked at the existing software interface,
-which was expressed through \cdromh, it appeared to be a rather wild
-set of commands and data formats.\footnote{I cannot recollect what
-kernel version I looked at, then, presumably 1.2.13 and 1.3.34---the
-latest kernel that I was indirectly involved in.} It seemed that many
-features of the software interface had been added to accommodate the
-capabilities of a particular drive, in an {\fo ad hoc\/} manner. More
-importantly, it appeared that the behavior of the `standard' commands
-was different for most of the different drivers: \eg, some drivers
-close the tray if an $open()$ call occurs when the tray is open, while
-others do not. Some drivers lock the door upon opening the device, to
-prevent an incoherent file system, but others don't, to allow software
-ejection. Undoubtedly, the capabilities of the different drives vary,
-but even when two drives have the same capability their drivers'
-behavior was usually different.
-
-I decided to start a discussion on how to make all the \linux\ \cdrom\
-drivers behave more uniformly. I began by contacting the developers of
-the many \cdrom\ drivers found in the \linux\ kernel. Their reactions
-encouraged me to write the \UCD\ which this document is intended to
-describe. The implementation of the \UCD\ is in the file \cdromc. This
-driver is intended to be an additional software layer that sits on top
-of the low-level device drivers for each \cdrom\ drive. By adding this
-additional layer, it is possible to have all the different \cdrom\
-devices behave {\em exactly\/} the same (insofar as the underlying
-hardware will allow).
-
-The goal of the \UCD\ is {\em not\/} to alienate driver developers who
-have not yet taken steps to support this effort. The goal of \UCD\ is
-simply to give people writing application programs for \cdrom\ drives
-{\em one\/} \linux\ \cdrom\ interface with consistent behavior for all
-\cdrom\ devices. In addition, this also provides a consistent interface
-between the low-level device driver code and the \linux\ kernel. Care
-is taken that 100\,\% compatibility exists with the data structures and
-programmer's interface defined in \cdromh. This guide was written to
-help \cdrom\ driver developers adapt their code to use the \UCD\ code
-defined in \cdromc.
-
-Personally, I think that the most important hardware interfaces are
-the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
-of hardware drop continuously, it is also likely that people may have
-more than one \cdrom\ drive, possibly of mixed types. It is important
-that these drives behave in the same way. In December 1994, one of the
-cheapest \cdrom\ drives was a Philips cm206, a double-speed proprietary
-drive. In the months that I was busy writing a \linux\ driver for it,
-proprietary drives became obsolete and IDE/ATAPI drives became the
-standard. At the time of the last update to this document (November
-1997) it is becoming difficult to even {\em find} anything less than a
-16 speed \cdrom\ drive, and 24 speed drives are common.
-
-\newsection{Standardizing through another software level}
-\label{cdrom.c}
-
-At the time this document was conceived, all drivers directly
-implemented the \cdrom\ $ioctl()$ calls through their own routines. This
-led to the danger of different drivers forgetting to do important things
-like checking that the user was giving the driver valid data. More
-importantly, this led to the divergence of behavior, which has already
-been discussed.
-
-For this reason, the \UCD\ was created to enforce consistent \cdrom\
-drive behavior, and to provide a common set of services to the various
-low-level \cdrom\ device drivers. The \UCD\ now provides another
-software-level, that separates the $ioctl()$ and $open()$ implementation
-from the actual hardware implementation. Note that this effort has
-made few changes which will affect a user's application programs. The
-greatest change involved moving the contents of the various low-level
-\cdrom\ drivers' header files to the kernel's cdrom directory. This was
-done to help ensure that the user is only presented with only one cdrom
-interface, the interface defined in \cdromh.
-
-\cdrom\ drives are specific enough (\ie, different from other
-block-devices such as floppy or hard disc drives), to define a set
-of common {\em \cdrom\ device operations}, $<cdrom-device>_dops$.
-These operations are different from the classical block-device file
-operations, $<block-device>_fops$.
-
-The routines for the \UCD\ interface level are implemented in the file
-\cdromc. In this file, the \UCD\ interfaces with the kernel as a block
-device by registering the following general $struct\ file_operations$:
-$$
-\halign{$#$\ \hfil&$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
-struct& file_operations\ cdrom_fops = \{\hidewidth\cr
- &NULL, & lseek \cr
- &block_read, & read---general block-dev read \cr
- &block_write, & write---general block-dev write \cr
- &NULL, & readdir \cr
- &NULL, & select \cr
- &cdrom_ioctl, & ioctl \cr
- &NULL, & mmap \cr
- &cdrom_open, & open \cr
- &cdrom_release, & release \cr
- &NULL, & fsync \cr
- &NULL, & fasync \cr
- &cdrom_media_changed, & media change \cr
- &NULL & revalidate \cr
-\};\cr
-}
-$$
-
-Every active \cdrom\ device shares this $struct$. The routines
-declared above are all implemented in \cdromc, since this file is the
-place where the behavior of all \cdrom-devices is defined and
-standardized. The actual interface to the various types of \cdrom\
-hardware is still performed by various low-level \cdrom-device
-drivers. These routines simply implement certain {\em capabilities\/}
-that are common to all \cdrom\ (and really, all removable-media
-devices).
-
-Registration of a low-level \cdrom\ device driver is now done through
-the general routines in \cdromc, not through the Virtual File System
-(VFS) any more. The interface implemented in \cdromc\ is carried out
-through two general structures that contain information about the
-capabilities of the driver, and the specific drives on which the
-driver operates. The structures are:
-\begin{description}
-\item[$cdrom_device_ops$]
- This structure contains information about the low-level driver for a
- \cdrom\ device. This structure is conceptually connected to the major
- number of the device (although some drivers may have different
- major numbers, as is the case for the IDE driver).
-\item[$cdrom_device_info$]
- This structure contains information about a particular \cdrom\ drive,
- such as its device name, speed, etc. This structure is conceptually
- connected to the minor number of the device.
-\end{description}
-
-Registering a particular \cdrom\ drive with the \UCD\ is done by the
-low-level device driver though a call to:
-$$register_cdrom(struct\ cdrom_device_info * <device>_info)
-$$
-The device information structure, $<device>_info$, contains all the
-information needed for the kernel to interface with the low-level
-\cdrom\ device driver. One of the most important entries in this
-structure is a pointer to the $cdrom_device_ops$ structure of the
-low-level driver.
-
-The device operations structure, $cdrom_device_ops$, contains a list
-of pointers to the functions which are implemented in the low-level
-device driver. When \cdromc\ accesses a \cdrom\ device, it does it
-through the functions in this structure. It is impossible to know all
-the capabilities of future \cdrom\ drives, so it is expected that this
-list may need to be expanded from time to time as new technologies are
-developed. For example, CD-R and CD-R/W drives are beginning to become
-popular, and support will soon need to be added for them. For now, the
-current $struct$ is:
-$$
-\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
- $/*$ \rm# $*/$\hfil\cr
-struct& cdrom_device_ops\ \{ \hidewidth\cr
- &int& (* open)(struct\ cdrom_device_info *, int)\cr
- &void& (* release)(struct\ cdrom_device_info *);\cr
- &int& (* drive_status)(struct\ cdrom_device_info *, int);\cr
- &unsigned\ int& (* check_events)(struct\ cdrom_device_info *, unsigned\ int, int);\cr
- &int& (* media_changed)(struct\ cdrom_device_info *, int);\cr
- &int& (* tray_move)(struct\ cdrom_device_info *, int);\cr
- &int& (* lock_door)(struct\ cdrom_device_info *, int);\cr
- &int& (* select_speed)(struct\ cdrom_device_info *, int);\cr
- &int& (* select_disc)(struct\ cdrom_device_info *, int);\cr
- &int& (* get_last_session) (struct\ cdrom_device_info *,
- struct\ cdrom_multisession *{});\cr
- &int& (* get_mcn)(struct\ cdrom_device_info *, struct\ cdrom_mcn *{});\cr
- &int& (* reset)(struct\ cdrom_device_info *);\cr
- &int& (* audio_ioctl)(struct\ cdrom_device_info *, unsigned\ int,
- void *{});\cr
-\noalign{\medskip}
- &const\ int& capability;& capability flags \cr
- &int& (* generic_packet)(struct\ cdrom_device_info *, struct\ packet_command *{});\cr
-\};\cr
-}
-$$
-When a low-level device driver implements one of these capabilities,
-it should add a function pointer to this $struct$. When a particular
-function is not implemented, however, this $struct$ should contain a
-NULL instead. The $capability$ flags specify the capabilities of the
-\cdrom\ hardware and/or low-level \cdrom\ driver when a \cdrom\ drive
-is registered with the \UCD.
-
-Note that most functions have fewer parameters than their
-$blkdev_fops$ counterparts. This is because very little of the
-information in the structures $inode$ and $file$ is used. For most
-drivers, the main parameter is the $struct$ $cdrom_device_info$, from
-which the major and minor number can be extracted. (Most low-level
-\cdrom\ drivers don't even look at the major and minor number though,
-since many of them only support one device.) This will be available
-through $dev$ in $cdrom_device_info$ described below.
-
-The drive-specific, minor-like information that is registered with
-\cdromc, currently contains the following fields:
-$$
-\halign{$#$\ \hfil&$#$\ \hfil&\hbox to 10em{$#$\hss}&
- $/*$ \rm# $*/$\hfil\cr
-struct& cdrom_device_info\ \{ \hidewidth\cr
- & const\ struct\ cdrom_device_ops *& ops;& device operations for this major\cr
- & struct\ list_head& list;& linked list of all device_info\cr
- & struct\ gendisk *& disk;& matching block layer disk\cr
- & void *& handle;& driver-dependent data\cr
-\noalign{\medskip}
- & int& mask;& mask of capability: disables them \cr
- & int& speed;& maximum speed for reading data \cr
- & int& capacity;& number of discs in a jukebox \cr
-\noalign{\medskip}
- &unsigned\ int& options : 30;& options flags \cr
- &unsigned& mc_flags : 2;& media-change buffer flags \cr
- &unsigned\ int& vfs_events;& cached events for vfs path\cr
- &unsigned\ int& ioctl_events;& cached events for ioctl path\cr
- & int& use_count;& number of times device is opened\cr
- & char& name[20];& name of the device type\cr
-\noalign{\medskip}
- &__u8& sanyo_slot : 2;& Sanyo 3-CD changer support\cr
- &__u8& keeplocked : 1;& CDROM_LOCKDOOR status\cr
- &__u8& reserved : 5;& not used yet\cr
- & int& cdda_method;& see CDDA_* flags\cr
- &__u8& last_sense;& saves last sense key\cr
- &__u8& media_written;& dirty flag, DVD+RW bookkeeping\cr
- &unsigned\ short& mmc3_profile;& current MMC3 profile\cr
- & int& for_data;& unknown:TBD\cr
- & int\ (* exit)\ (struct\ cdrom_device_info *);&& unknown:TBD\cr
- & int& mrw_mode_page;& which MRW mode page is in use\cr
-\}\cr
-}$$
-Using this $struct$, a linked list of the registered minor devices is
-built, using the $next$ field. The device number, the device operations
-struct and specifications of properties of the drive are stored in this
-structure.
-
-The $mask$ flags can be used to mask out some of the capabilities listed
-in $ops\to capability$, if a specific drive doesn't support a feature
-of the driver. The value $speed$ specifies the maximum head-rate of the
-drive, measured in units of normal audio speed (176\,kB/sec raw data or
-150\,kB/sec file system data). The parameters are declared $const$
-because they describe properties of the drive, which don't change after
-registration.
-
-A few registers contain variables local to the \cdrom\ drive. The
-flags $options$ are used to specify how the general \cdrom\ routines
-should behave. These various flags registers should provide enough
-flexibility to adapt to the different users' wishes (and {\em not\/} the
-`arbitrary' wishes of the author of the low-level device driver, as is
-the case in the old scheme). The register $mc_flags$ is used to buffer
-the information from $media_changed()$ to two separate queues. Other
-data that is specific to a minor drive, can be accessed through $handle$,
-which can point to a data structure specific to the low-level driver.
-The fields $use_count$, $next$, $options$ and $mc_flags$ need not be
-initialized.
-
-The intermediate software layer that \cdromc\ forms will perform some
-additional bookkeeping. The use count of the device (the number of
-processes that have the device opened) is registered in $use_count$. The
-function $cdrom_ioctl()$ will verify the appropriate user-memory regions
-for read and write, and in case a location on the CD is transferred,
-it will `sanitize' the format by making requests to the low-level
-drivers in a standard format, and translating all formats between the
-user-software and low level drivers. This relieves much of the drivers'
-memory checking and format checking and translation. Also, the necessary
-structures will be declared on the program stack.
-
-The implementation of the functions should be as defined in the
-following sections. Two functions {\em must\/} be implemented, namely
-$open()$ and $release()$. Other functions may be omitted, their
-corresponding capability flags will be cleared upon registration.
-Generally, a function returns zero on success and negative on error. A
-function call should return only after the command has completed, but of
-course waiting for the device should not use processor time.
-
-\subsection{$Int\ open(struct\ cdrom_device_info * cdi, int\ purpose)$}
-
-$Open()$ should try to open the device for a specific $purpose$, which
-can be either:
-\begin{itemize}
-\item[0] Open for reading data, as done by {\tt {mount()}} (2), or the
-user commands {\tt {dd}} or {\tt {cat}}.
-\item[1] Open for $ioctl$ commands, as done by audio-CD playing
-programs.
-\end{itemize}
-Notice that any strategic code (closing tray upon $open()$, etc.)\ is
-done by the calling routine in \cdromc, so the low-level routine
-should only be concerned with proper initialization, such as spinning
-up the disc, etc. % and device-use count
-
-
-\subsection{$Void\ release(struct\ cdrom_device_info * cdi)$}
-
-
-Device-specific actions should be taken such as spinning down the device.
-However, strategic actions such as ejection of the tray, or unlocking
-the door, should be left over to the general routine $cdrom_release()$.
-This is the only function returning type $void$.
-
-\subsection{$Int\ drive_status(struct\ cdrom_device_info * cdi, int\ slot_nr)$}
-\label{drive status}
-
-The function $drive_status$, if implemented, should provide
-information on the status of the drive (not the status of the disc,
-which may or may not be in the drive). If the drive is not a changer,
-$slot_nr$ should be ignored. In \cdromh\ the possibilities are listed:
-$$
-\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
-CDS_NO_INFO& no information available\cr
-CDS_NO_DISC& no disc is inserted, tray is closed\cr
-CDS_TRAY_OPEN& tray is opened\cr
-CDS_DRIVE_NOT_READY& something is wrong, tray is moving?\cr
-CDS_DISC_OK& a disc is loaded and everything is fine\cr
-}
-$$
-
-\subsection{$Int\ media_changed(struct\ cdrom_device_info * cdi, int\ disc_nr)$}
-
-This function is very similar to the original function in $struct\
-file_operations$. It returns 1 if the medium of the device $cdi\to
-dev$ has changed since the last call, and 0 otherwise. The parameter
-$disc_nr$ identifies a specific slot in a juke-box, it should be
-ignored for single-disc drives. Note that by `re-routing' this
-function through $cdrom_media_changed()$, we can implement separate
-queues for the VFS and a new $ioctl()$ function that can report device
-changes to software (\eg, an auto-mounting daemon).
-
-\subsection{$Int\ tray_move(struct\ cdrom_device_info * cdi, int\ position)$}
-
-This function, if implemented, should control the tray movement. (No
-other function should control this.) The parameter $position$ controls
-the desired direction of movement:
-\begin{itemize}
-\item[0] Close tray
-\item[1] Open tray
-\end{itemize}
-This function returns 0 upon success, and a non-zero value upon
-error. Note that if the tray is already in the desired position, no
-action need be taken, and the return value should be 0.
-
-\subsection{$Int\ lock_door(struct\ cdrom_device_info * cdi, int\ lock)$}
-
-This function (and no other code) controls locking of the door, if the
-drive allows this. The value of $lock$ controls the desired locking
-state:
-\begin{itemize}
-\item[0] Unlock door, manual opening is allowed
-\item[1] Lock door, tray cannot be ejected manually
-\end{itemize}
-This function returns 0 upon success, and a non-zero value upon
-error. Note that if the door is already in the requested state, no
-action need be taken, and the return value should be 0.
-
-\subsection{$Int\ select_speed(struct\ cdrom_device_info * cdi, int\ speed)$}
-
-Some \cdrom\ drives are capable of changing their head-speed. There
-are several reasons for changing the speed of a \cdrom\ drive. Badly
-pressed \cdrom s may benefit from less-than-maximum head rate. Modern
-\cdrom\ drives can obtain very high head rates (up to $24\times$ is
-common). It has been reported that these drives can make reading
-errors at these high speeds, reducing the speed can prevent data loss
-in these circumstances. Finally, some of these drives can
-make an annoyingly loud noise, which a lower speed may reduce. %Finally,
-%although the audio-low-pass filters probably aren't designed for it,
-%more than real-time playback of audio might be used for high-speed
-%copying of audio tracks.
-
-This function specifies the speed at which data is read or audio is
-played back. The value of $speed$ specifies the head-speed of the
-drive, measured in units of standard cdrom speed (176\,kB/sec raw data
-or 150\,kB/sec file system data). So to request that a \cdrom\ drive
-operate at 300\,kB/sec you would call the CDROM_SELECT_SPEED $ioctl$
-with $speed=2$. The special value `0' means `auto-selection', \ie,
-maximum data-rate or real-time audio rate. If the drive doesn't have
-this `auto-selection' capability, the decision should be made on the
-current disc loaded and the return value should be positive. A negative
-return value indicates an error.
-
-\subsection{$Int\ select_disc(struct\ cdrom_device_info * cdi, int\ number)$}
-
-If the drive can store multiple discs (a juke-box) this function
-will perform disc selection. It should return the number of the
-selected disc on success, a negative value on error. Currently, only
-the ide-cd driver supports this functionality.
-
-\subsection{$Int\ get_last_session(struct\ cdrom_device_info * cdi, struct\
- cdrom_multisession * ms_info)$}
-
-This function should implement the old corresponding $ioctl()$. For
-device $cdi\to dev$, the start of the last session of the current disc
-should be returned in the pointer argument $ms_info$. Note that
-routines in \cdromc\ have sanitized this argument: its requested
-format will {\em always\/} be of the type $CDROM_LBA$ (linear block
-addressing mode), whatever the calling software requested. But
-sanitization goes even further: the low-level implementation may
-return the requested information in $CDROM_MSF$ format if it wishes so
-(setting the $ms_info\rightarrow addr_format$ field appropriately, of
-course) and the routines in \cdromc\ will make the transformation if
-necessary. The return value is 0 upon success.
-
-\subsection{$Int\ get_mcn(struct\ cdrom_device_info * cdi, struct\
- cdrom_mcn * mcn)$}
-
-Some discs carry a `Media Catalog Number' (MCN), also called
-`Universal Product Code' (UPC). This number should reflect the number
-that is generally found in the bar-code on the product. Unfortunately,
-the few discs that carry such a number on the disc don't even use the
-same format. The return argument to this function is a pointer to a
-pre-declared memory region of type $struct\ cdrom_mcn$. The MCN is
-expected as a 13-character string, terminated by a null-character.
-
-\subsection{$Int\ reset(struct\ cdrom_device_info * cdi)$}
-
-This call should perform a hard-reset on the drive (although in
-circumstances that a hard-reset is necessary, a drive may very well not
-listen to commands anymore). Preferably, control is returned to the
-caller only after the drive has finished resetting. If the drive is no
-longer listening, it may be wise for the underlying low-level cdrom
-driver to time out.
-
-\subsection{$Int\ audio_ioctl(struct\ cdrom_device_info * cdi, unsigned\
- int\ cmd, void * arg)$}
-
-Some of the \cdrom-$ioctl$s defined in \cdromh\ can be
-implemented by the routines described above, and hence the function
-$cdrom_ioctl$ will use those. However, most $ioctl$s deal with
-audio-control. We have decided to leave these to be accessed through a
-single function, repeating the arguments $cmd$ and $arg$. Note that
-the latter is of type $void*{}$, rather than $unsigned\ long\
-int$. The routine $cdrom_ioctl()$ does do some useful things,
-though. It sanitizes the address format type to $CDROM_MSF$ (Minutes,
-Seconds, Frames) for all audio calls. It also verifies the memory
-location of $arg$, and reserves stack-memory for the argument. This
-makes implementation of the $audio_ioctl()$ much simpler than in the
-old driver scheme. For example, you may look up the function
-$cm206_audio_ioctl()$ in {\tt {cm206.c}} that should be updated with
-this documentation.
-
-An unimplemented ioctl should return $-ENOSYS$, but a harmless request
-(\eg, $CDROMSTART$) may be ignored by returning 0 (success). Other
-errors should be according to the standards, whatever they are. When
-an error is returned by the low-level driver, the \UCD\ tries whenever
-possible to return the error code to the calling program. (We may decide
-to sanitize the return value in $cdrom_ioctl()$ though, in order to
-guarantee a uniform interface to the audio-player software.)
-
-\subsection{$Int\ dev_ioctl(struct\ cdrom_device_info * cdi, unsigned\ int\
- cmd, unsigned\ long\ arg)$}
-
-Some $ioctl$s seem to be specific to certain \cdrom\ drives. That is,
-they are introduced to service some capabilities of certain drives. In
-fact, there are 6 different $ioctl$s for reading data, either in some
-particular kind of format, or audio data. Not many drives support
-reading audio tracks as data, I believe this is because of protection
-of copyrights of artists. Moreover, I think that if audio-tracks are
-supported, it should be done through the VFS and not via $ioctl$s. A
-problem here could be the fact that audio-frames are 2352 bytes long,
-so either the audio-file-system should ask for 75264 bytes at once
-(the least common multiple of 512 and 2352), or the drivers should
-bend their backs to cope with this incoherence (to which I would be
-opposed). Furthermore, it is very difficult for the hardware to find
-the exact frame boundaries, since there are no synchronization headers
-in audio frames. Once these issues are resolved, this code should be
-standardized in \cdromc.
-
-Because there are so many $ioctl$s that seem to be introduced to
-satisfy certain drivers,\footnote{Is there software around that
- actually uses these? I'd be interested!} any `non-standard' $ioctl$s
-are routed through the call $dev_ioctl()$. In principle, `private'
-$ioctl$s should be numbered after the device's major number, and not
-the general \cdrom\ $ioctl$ number, {\tt {0x53}}. Currently the
-non-supported $ioctl$s are: {\it CDROMREADMODE1, CDROMREADMODE2,
- CDROMREADAUDIO, CDROMREADRAW, CDROMREADCOOKED, CDROMSEEK,
- CDROMPLAY\-BLK and CDROM\-READALL}.
-
-
-\subsection{\cdrom\ capabilities}
-\label{capability}
-
-Instead of just implementing some $ioctl$ calls, the interface in
-\cdromc\ supplies the possibility to indicate the {\em capabilities\/}
-of a \cdrom\ drive. This can be done by ORing any number of
-capability-constants that are defined in \cdromh\ at the registration
-phase. Currently, the capabilities are any of:
-$$
-\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
-CDC_CLOSE_TRAY& can close tray by software control\cr
-CDC_OPEN_TRAY& can open tray\cr
-CDC_LOCK& can lock and unlock the door\cr
-CDC_SELECT_SPEED& can select speed, in units of $\sim$150\,kB/s\cr
-CDC_SELECT_DISC& drive is juke-box\cr
-CDC_MULTI_SESSION& can read sessions $>\rm1$\cr
-CDC_MCN& can read Media Catalog Number\cr
-CDC_MEDIA_CHANGED& can report if disc has changed\cr
-CDC_PLAY_AUDIO& can perform audio-functions (play, pause, etc)\cr
-CDC_RESET& hard reset device\cr
-CDC_IOCTLS& driver has non-standard ioctls\cr
-CDC_DRIVE_STATUS& driver implements drive status\cr
-}
-$$
-The capability flag is declared $const$, to prevent drivers from
-accidentally tampering with the contents. The capability fags actually
-inform \cdromc\ of what the driver can do. If the drive found
-by the driver does not have the capability, is can be masked out by
-the $cdrom_device_info$ variable $mask$. For instance, the SCSI \cdrom\
-driver has implemented the code for loading and ejecting \cdrom's, and
-hence its corresponding flags in $capability$ will be set. But a SCSI
-\cdrom\ drive might be a caddy system, which can't load the tray, and
-hence for this drive the $cdrom_device_info$ struct will have set
-the $CDC_CLOSE_TRAY$ bit in $mask$.
-
-In the file \cdromc\ you will encounter many constructions of the type
-$$\it
-if\ (cdo\rightarrow capability \mathrel\& \mathord{\sim} cdi\rightarrow mask
- \mathrel{\&} CDC_<capability>) \ldots
-$$
-There is no $ioctl$ to set the mask\dots The reason is that
-I think it is better to control the {\em behavior\/} rather than the
-{\em capabilities}.
-
-\subsection{Options}
-
-A final flag register controls the {\em behavior\/} of the \cdrom\
-drives, in order to satisfy different users' wishes, hopefully
-independently of the ideas of the respective author who happened to
-have made the drive's support available to the \linux\ community. The
-current behavior options are:
-$$
-\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
-CDO_AUTO_CLOSE& try to close tray upon device $open()$\cr
-CDO_AUTO_EJECT& try to open tray on last device $close()$\cr
-CDO_USE_FFLAGS& use $file_pointer\rightarrow f_flags$ to indicate
- purpose for $open()$\cr
-CDO_LOCK& try to lock door if device is opened\cr
-CDO_CHECK_TYPE& ensure disc type is data if opened for data\cr
-}
-$$
-
-The initial value of this register is $CDO_AUTO_CLOSE \mathrel|
-CDO_USE_FFLAGS \mathrel| CDO_LOCK$, reflecting my own view on user
-interface and software standards. Before you protest, there are two
-new $ioctl$s implemented in \cdromc, that allow you to control the
-behavior by software. These are:
-$$
-\halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
-CDROM_SET_OPTIONS& set options specified in $(int)\ arg$\cr
-CDROM_CLEAR_OPTIONS& clear options specified in $(int)\ arg$\cr
-}
-$$
-One option needs some more explanation: $CDO_USE_FFLAGS$. In the next
-newsection we explain what the need for this option is.
-
-A software package {\tt setcd}, available from the Debian distribution
-and {\tt sunsite.unc.edu}, allows user level control of these flags.
-
-\newsection{The need to know the purpose of opening the \cdrom\ device}
-
-Traditionally, Unix devices can be used in two different `modes',
-either by reading/writing to the device file, or by issuing
-controlling commands to the device, by the device's $ioctl()$
-call. The problem with \cdrom\ drives, is that they can be used for
-two entirely different purposes. One is to mount removable
-file systems, \cdrom s, the other is to play audio CD's. Audio commands
-are implemented entirely through $ioctl$s, presumably because the
-first implementation (SUN?) has been such. In principle there is
-nothing wrong with this, but a good control of the `CD player' demands
-that the device can {\em always\/} be opened in order to give the
-$ioctl$ commands, regardless of the state the drive is in.
-
-On the other hand, when used as a removable-media disc drive (what the
-original purpose of \cdrom s is) we would like to make sure that the
-disc drive is ready for operation upon opening the device. In the old
-scheme, some \cdrom\ drivers don't do any integrity checking, resulting
-in a number of i/o errors reported by the VFS to the kernel when an
-attempt for mounting a \cdrom\ on an empty drive occurs. This is not a
-particularly elegant way to find out that there is no \cdrom\ inserted;
-it more-or-less looks like the old IBM-PC trying to read an empty floppy
-drive for a couple of seconds, after which the system complains it
-can't read from it. Nowadays we can {\em sense\/} the existence of a
-removable medium in a drive, and we believe we should exploit that
-fact. An integrity check on opening of the device, that verifies the
-availability of a \cdrom\ and its correct type (data), would be
-desirable.
-
-These two ways of using a \cdrom\ drive, principally for data and
-secondarily for playing audio discs, have different demands for the
-behavior of the $open()$ call. Audio use simply wants to open the
-device in order to get a file handle which is needed for issuing
-$ioctl$ commands, while data use wants to open for correct and
-reliable data transfer. The only way user programs can indicate what
-their {\em purpose\/} of opening the device is, is through the $flags$
-parameter (see {\tt {open(2)}}). For \cdrom\ devices, these flags aren't
-implemented (some drivers implement checking for write-related flags,
-but this is not strictly necessary if the device file has correct
-permission flags). Most option flags simply don't make sense to
-\cdrom\ devices: $O_CREAT$, $O_NOCTTY$, $O_TRUNC$, $O_APPEND$, and
-$O_SYNC$ have no meaning to a \cdrom.
-
-We therefore propose to use the flag $O_NONBLOCK$ to indicate
-that the device is opened just for issuing $ioctl$
-commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
-subsequent calls to the device don't cause the calling process to
-wait. We could interpret this as ``don't wait until someone has
-inserted some valid data-\cdrom.'' Thus, our proposal of the
-implementation for the $open()$ call for \cdrom s is:
-\begin{itemize}
-\item If no other flags are set than $O_RDONLY$, the device is opened
-for data transfer, and the return value will be 0 only upon successful
-initialization of the transfer. The call may even induce some actions
-on the \cdrom, such as closing the tray.
-\item If the option flag $O_NONBLOCK$ is set, opening will always be
-successful, unless the whole device doesn't exist. The drive will take
-no actions whatsoever.
-\end{itemize}
-
-\subsection{And what about standards?}
-
-You might hesitate to accept this proposal as it comes from the
-\linux\ community, and not from some standardizing institute. What
-about SUN, SGI, HP and all those other Unix and hardware vendors?
-Well, these companies are in the lucky position that they generally
-control both the hardware and software of their supported products,
-and are large enough to set their own standard. They do not have to
-deal with a dozen or more different, competing hardware
-configurations.\footnote{Incidentally, I think that SUN's approach to
-mounting \cdrom s is very good in origin: under Solaris a
-volume-daemon automatically mounts a newly inserted \cdrom\ under {\tt
-{/cdrom/$<volume-name>$/}}. In my opinion they should have pushed this
-further and have {\em every\/} \cdrom\ on the local area network be
-mounted at the similar location, \ie, no matter in which particular
-machine you insert a \cdrom, it will always appear at the same
-position in the directory tree, on every system. When I wanted to
-implement such a user-program for \linux, I came across the
-differences in behavior of the various drivers, and the need for an
-$ioctl$ informing about media changes.}
-
-We believe that using $O_NONBLOCK$ to indicate that a device is being opened
-for $ioctl$ commands only can be easily introduced in the \linux\
-community. All the CD-player authors will have to be informed, we can
-even send in our own patches to the programs. The use of $O_NONBLOCK$
-has most likely no influence on the behavior of the CD-players on
-other operating systems than \linux. Finally, a user can always revert
-to old behavior by a call to $ioctl(file_descriptor, CDROM_CLEAR_OPTIONS,
-CDO_USE_FFLAGS)$.
-
-\subsection{The preferred strategy of $open()$}
-
-The routines in \cdromc\ are designed in such a way that run-time
-configuration of the behavior of \cdrom\ devices (of {\em any\/} type)
-can be carried out, by the $CDROM_SET/CLEAR_OPTIONS$ $ioctls$. Thus, various
-modes of operation can be set:
-\begin{description}
-\item[$CDO_AUTO_CLOSE \mathrel| CDO_USE_FFLAGS \mathrel| CDO_LOCK$] This
-is the default setting. (With $CDO_CHECK_TYPE$ it will be better, in the
-future.) If the device is not yet opened by any other process, and if
-the device is being opened for data ($O_NONBLOCK$ is not set) and the
-tray is found to be open, an attempt to close the tray is made. Then,
-it is verified that a disc is in the drive and, if $CDO_CHECK_TYPE$ is
-set, that it contains tracks of type `data mode 1.' Only if all tests
-are passed is the return value zero. The door is locked to prevent file
-system corruption. If the drive is opened for audio ($O_NONBLOCK$ is
-set), no actions are taken and a value of 0 will be returned.
-\item[$CDO_AUTO_CLOSE \mathrel| CDO_AUTO_EJECT \mathrel| CDO_LOCK$] This
-mimics the behavior of the current sbpcd-driver. The option flags are
-ignored, the tray is closed on the first open, if necessary. Similarly,
-the tray is opened on the last release, \ie, if a \cdrom\ is unmounted,
-it is automatically ejected, such that the user can replace it.
-\end{description}
-We hope that these option can convince everybody (both driver
-maintainers and user program developers) to adopt the new \cdrom\
-driver scheme and option flag interpretation.
-
-\newsection{Description of routines in \cdromc}
-
-Only a few routines in \cdromc\ are exported to the drivers. In this
-new section we will discuss these, as well as the functions that `take
-over' the \cdrom\ interface to the kernel. The header file belonging
-to \cdromc\ is called \cdromh. Formerly, some of the contents of this
-file were placed in the file {\tt {ucdrom.h}}, but this file has now been
-merged back into \cdromh.
-
-\subsection{$Struct\ file_operations\ cdrom_fops$}
-
-The contents of this structure were described in section~\ref{cdrom.c}.
-A pointer to this structure is assigned to the $fops$ field
-of the $struct gendisk$.
-
-\subsection{$Int\ register_cdrom( struct\ cdrom_device_info\ * cdi)$}
-
-This function is used in about the same way one registers $cdrom_fops$
-with the kernel, the device operations and information structures,
-as described in section~\ref{cdrom.c}, should be registered with the
-\UCD:
-$$
-register_cdrom(\&<device>_info));
-$$
-This function returns zero upon success, and non-zero upon
-failure. The structure $<device>_info$ should have a pointer to the
-driver's $<device>_dops$, as in
-$$
-\vbox{\halign{&$#$\hfil\cr
-struct\ &cdrom_device_info\ <device>_info = \{\cr
-& <device>_dops;\cr
-&\ldots\cr
-\}\cr
-}}$$
-Note that a driver must have one static structure, $<device>_dops$, while
-it may have as many structures $<device>_info$ as there are minor devices
-active. $Register_cdrom()$ builds a linked list from these.
-
-\subsection{$Void\ unregister_cdrom(struct\ cdrom_device_info * cdi)$}
-
-Unregistering device $cdi$ with minor number $MINOR(cdi\to dev)$ removes
-the minor device from the list. If it was the last registered minor for
-the low-level driver, this disconnects the registered device-operation
-routines from the \cdrom\ interface. This function returns zero upon
-success, and non-zero upon failure.
-
-\subsection{$Int\ cdrom_open(struct\ inode * ip, struct\ file * fp)$}
-
-This function is not called directly by the low-level drivers, it is
-listed in the standard $cdrom_fops$. If the VFS opens a file, this
-function becomes active. A strategy is implemented in this routine,
-taking care of all capabilities and options that are set in the
-$cdrom_device_ops$ connected to the device. Then, the program flow is
-transferred to the device_dependent $open()$ call.
-
-\subsection{$Void\ cdrom_release(struct\ inode *ip, struct\ file
-*fp)$}
-
-This function implements the reverse-logic of $cdrom_open()$, and then
-calls the device-dependent $release()$ routine. When the use-count has
-reached 0, the allocated buffers are flushed by calls to $sync_dev(dev)$
-and $invalidate_buffers(dev)$.
-
-
-\subsection{$Int\ cdrom_ioctl(struct\ inode *ip, struct\ file *fp,
-unsigned\ int\ cmd, unsigned\ long\ arg)$}
-\label{cdrom-ioctl}
-
-This function handles all the standard $ioctl$ requests for \cdrom\
-devices in a uniform way. The different calls fall into three
-categories: $ioctl$s that can be directly implemented by device
-operations, ones that are routed through the call $audio_ioctl()$, and
-the remaining ones, that are presumable device-dependent. Generally, a
-negative return value indicates an error.
-
-\subsubsection{Directly implemented $ioctl$s}
-\label{ioctl-direct}
-
-The following `old' \cdrom-$ioctl$s are implemented by directly
-calling device-operations in $cdrom_device_ops$, if implemented and
-not masked:
-\begin{description}
-\item[CDROMMULTISESSION] Requests the last session on a \cdrom.
-\item[CDROMEJECT] Open tray.
-\item[CDROMCLOSETRAY] Close tray.
-\item[CDROMEJECT_SW] If $arg\not=0$, set behavior to auto-close (close
-tray on first open) and auto-eject (eject on last release), otherwise
-set behavior to non-moving on $open()$ and $release()$ calls.
-\item[CDROM_GET_MCN] Get the Media Catalog Number from a CD.
-\end{description}
-
-\subsubsection{$Ioctl$s routed through $audio_ioctl()$}
-\label{ioctl-audio}
-
-The following set of $ioctl$s are all implemented through a call to
-the $cdrom_fops$ function $audio_ioctl()$. Memory checks and
-allocation are performed in $cdrom_ioctl()$, and also sanitization of
-address format ($CDROM_LBA$/$CDROM_MSF$) is done.
-\begin{description}
-\item[CDROMSUBCHNL] Get sub-channel data in argument $arg$ of type $struct\
-cdrom_subchnl *{}$.
-\item[CDROMREADTOCHDR] Read Table of Contents header, in $arg$ of type
-$struct\ cdrom_tochdr *{}$.
-\item[CDROMREADTOCENTRY] Read a Table of Contents entry in $arg$ and
-specified by $arg$ of type $struct\ cdrom_tocentry *{}$.
-\item[CDROMPLAYMSF] Play audio fragment specified in Minute, Second,
-Frame format, delimited by $arg$ of type $struct\ cdrom_msf *{}$.
-\item[CDROMPLAYTRKIND] Play audio fragment in track-index format
-delimited by $arg$ of type $struct\ \penalty-1000 cdrom_ti *{}$.
-\item[CDROMVOLCTRL] Set volume specified by $arg$ of type $struct\
-cdrom_volctrl *{}$.
-\item[CDROMVOLREAD] Read volume into by $arg$ of type $struct\
-cdrom_volctrl *{}$.
-\item[CDROMSTART] Spin up disc.
-\item[CDROMSTOP] Stop playback of audio fragment.
-\item[CDROMPAUSE] Pause playback of audio fragment.
-\item[CDROMRESUME] Resume playing.
-\end{description}
-
-\subsubsection{New $ioctl$s in \cdromc}
-
-The following $ioctl$s have been introduced to allow user programs to
-control the behavior of individual \cdrom\ devices. New $ioctl$
-commands can be identified by the underscores in their names.
-\begin{description}
-\item[CDROM_SET_OPTIONS] Set options specified by $arg$. Returns the
-option flag register after modification. Use $arg = \rm0$ for reading
-the current flags.
-\item[CDROM_CLEAR_OPTIONS] Clear options specified by $arg$. Returns
- the option flag register after modification.
-\item[CDROM_SELECT_SPEED] Select head-rate speed of disc specified as
- by $arg$ in units of standard cdrom speed (176\,kB/sec raw data or
- 150\,kB/sec file system data). The value 0 means `auto-select', \ie,
- play audio discs at real time and data discs at maximum speed. The value
- $arg$ is checked against the maximum head rate of the drive found in the
- $cdrom_dops$.
-\item[CDROM_SELECT_DISC] Select disc numbered $arg$ from a juke-box.
- First disc is numbered 0. The number $arg$ is checked against the
- maximum number of discs in the juke-box found in the $cdrom_dops$.
-\item[CDROM_MEDIA_CHANGED] Returns 1 if a disc has been changed since
- the last call. Note that calls to $cdrom_media_changed$ by the VFS
- are treated by an independent queue, so both mechanisms will detect
- a media change once. For juke-boxes, an extra argument $arg$
- specifies the slot for which the information is given. The special
- value $CDSL_CURRENT$ requests that information about the currently
- selected slot be returned.
-\item[CDROM_DRIVE_STATUS] Returns the status of the drive by a call to
- $drive_status()$. Return values are defined in section~\ref{drive
- status}. Note that this call doesn't return information on the
- current playing activity of the drive; this can be polled through an
- $ioctl$ call to $CDROMSUBCHNL$. For juke-boxes, an extra argument
- $arg$ specifies the slot for which (possibly limited) information is
- given. The special value $CDSL_CURRENT$ requests that information
- about the currently selected slot be returned.
-\item[CDROM_DISC_STATUS] Returns the type of the disc currently in the
- drive. It should be viewed as a complement to $CDROM_DRIVE_STATUS$.
- This $ioctl$ can provide \emph {some} information about the current
- disc that is inserted in the drive. This functionality used to be
- implemented in the low level drivers, but is now carried out
- entirely in \UCD.
-
- The history of development of the CD's use as a carrier medium for
- various digital information has lead to many different disc types.
- This $ioctl$ is useful only in the case that CDs have \emph {only
- one} type of data on them. While this is often the case, it is
- also very common for CDs to have some tracks with data, and some
- tracks with audio. Because this is an existing interface, rather
- than fixing this interface by changing the assumptions it was made
- under, thereby breaking all user applications that use this
- function, the \UCD\ implements this $ioctl$ as follows: If the CD in
- question has audio tracks on it, and it has absolutely no CD-I, XA,
- or data tracks on it, it will be reported as $CDS_AUDIO$. If it has
- both audio and data tracks, it will return $CDS_MIXED$. If there
- are no audio tracks on the disc, and if the CD in question has any
- CD-I tracks on it, it will be reported as $CDS_XA_2_2$. Failing
- that, if the CD in question has any XA tracks on it, it will be
- reported as $CDS_XA_2_1$. Finally, if the CD in question has any
- data tracks on it, it will be reported as a data CD ($CDS_DATA_1$).
-
- This $ioctl$ can return:
- $$
- \halign{$#$\ \hfil&$/*$ \rm# $*/$\hfil\cr
- CDS_NO_INFO& no information available\cr
- CDS_NO_DISC& no disc is inserted, or tray is opened\cr
- CDS_AUDIO& Audio disc (2352 audio bytes/frame)\cr
- CDS_DATA_1& data disc, mode 1 (2048 user bytes/frame)\cr
- CDS_XA_2_1& mixed data (XA), mode 2, form 1 (2048 user bytes)\cr
- CDS_XA_2_2& mixed data (XA), mode 2, form 1 (2324 user bytes)\cr
- CDS_MIXED& mixed audio/data disc\cr
- }
- $$
- For some information concerning frame layout of the various disc
- types, see a recent version of \cdromh.
-
-\item[CDROM_CHANGER_NSLOTS] Returns the number of slots in a
- juke-box.
-\item[CDROMRESET] Reset the drive.
-\item[CDROM_GET_CAPABILITY] Returns the $capability$ flags for the
- drive. Refer to section \ref{capability} for more information on
- these flags.
-\item[CDROM_LOCKDOOR] Locks the door of the drive. $arg == \rm0$
- unlocks the door, any other value locks it.
-\item[CDROM_DEBUG] Turns on debugging info. Only root is allowed
- to do this. Same semantics as CDROM_LOCKDOOR.
-\end{description}
-
-\subsubsection{Device dependent $ioctl$s}
-
-Finally, all other $ioctl$s are passed to the function $dev_ioctl()$,
-if implemented. No memory allocation or verification is carried out.
-
-\newsection{How to update your driver}
-
-\begin{enumerate}
-\item Make a backup of your current driver.
-\item Get hold of the files \cdromc\ and \cdromh, they should be in
- the directory tree that came with this documentation.
-\item Make sure you include \cdromh.
-\item Change the 3rd argument of $register_blkdev$ from
-$\&<your-drive>_fops$ to $\&cdrom_fops$.
-\item Just after that line, add the following to register with the \UCD:
- $$register_cdrom(\&<your-drive>_info);$$
- Similarly, add a call to $unregister_cdrom()$ at the appropriate place.
-\item Copy an example of the device-operations $struct$ to your
- source, \eg, from {\tt {cm206.c}} $cm206_dops$, and change all
- entries to names corresponding to your driver, or names you just
- happen to like. If your driver doesn't support a certain function,
- make the entry $NULL$. At the entry $capability$ you should list all
- capabilities your driver currently supports. If your driver
- has a capability that is not listed, please send me a message.
-\item Copy the $cdrom_device_info$ declaration from the same example
- driver, and modify the entries according to your needs. If your
- driver dynamically determines the capabilities of the hardware, this
- structure should also be declared dynamically.
-\item Implement all functions in your $<device>_dops$ structure,
- according to prototypes listed in \cdromh, and specifications given
- in section~\ref{cdrom.c}. Most likely you have already implemented
- the code in a large part, and you will almost certainly need to adapt the
- prototype and return values.
-\item Rename your $<device>_ioctl()$ function to $audio_ioctl$ and
- change the prototype a little. Remove entries listed in the first
- part in section~\ref{cdrom-ioctl}, if your code was OK, these are
- just calls to the routines you adapted in the previous step.
-\item You may remove all remaining memory checking code in the
- $audio_ioctl()$ function that deals with audio commands (these are
- listed in the second part of section~\ref{cdrom-ioctl}). There is no
- need for memory allocation either, so most $case$s in the $switch$
- statement look similar to:
- $$
- case\ CDROMREADTOCENTRY\colon get_toc_entry\bigl((struct\
- cdrom_tocentry *{})\ arg\bigr);
- $$
-\item All remaining $ioctl$ cases must be moved to a separate
- function, $<device>_ioctl$, the device-dependent $ioctl$s. Note that
- memory checking and allocation must be kept in this code!
-\item Change the prototypes of $<device>_open()$ and
- $<device>_release()$, and remove any strategic code (\ie, tray
- movement, door locking, etc.).
-\item Try to recompile the drivers. We advise you to use modules, both
- for {\tt {cdrom.o}} and your driver, as debugging is much easier this
- way.
-\end{enumerate}
-
-\newsection{Thanks}
-
-Thanks to all the people involved. First, Erik Andersen, who has
-taken over the torch in maintaining \cdromc\ and integrating much
-\cdrom-related code in the 2.1-kernel. Thanks to Scott Snyder and
-Gerd Knorr, who were the first to implement this interface for SCSI
-and IDE-CD drivers and added many ideas for extension of the data
-structures relative to kernel~2.0. Further thanks to Heiko Ei{\ss}feldt,
-Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard M\"onkeberg and Andrew
-Kroll, the \linux\ \cdrom\ device driver developers who were kind
-enough to give suggestions and criticisms during the writing. Finally
-of course, I want to thank Linus Torvalds for making this possible in
-the first place.
-
-\vfill
-$ \version\ $
-\eject
-\end{document}
--- /dev/null
+=======================
+A Linux CD-ROM standard
+=======================
+
+:Author: David van Leeuwen <david@ElseWare.cistron.nl>
+:Date: 12 March 1999
+:Updated by: Erik Andersen (andersee@debian.org)
+:Updated by: Jens Axboe (axboe@image.dk)
+
+
+Introduction
+============
+
+Linux is probably the Unix-like operating system that supports
+the widest variety of hardware devices. The reasons for this are
+presumably
+
+- The large list of hardware devices available for the many platforms
+ that Linux now supports (i.e., i386-PCs, Sparc Suns, etc.)
+- The open design of the operating system, such that anybody can write a
+ driver for Linux.
+- There is plenty of source code around as examples of how to write a driver.
+
+The openness of Linux, and the many different types of available
+hardware has allowed Linux to support many different hardware devices.
+Unfortunately, the very openness that has allowed Linux to support
+all these different devices has also allowed the behavior of each
+device driver to differ significantly from one device to another.
+This divergence of behavior has been very significant for CD-ROM
+devices; the way a particular drive reacts to a `standard` *ioctl()*
+call varies greatly from one device driver to another. To avoid making
+their drivers totally inconsistent, the writers of Linux CD-ROM
+drivers generally created new device drivers by understanding, copying,
+and then changing an existing one. Unfortunately, this practice did not
+maintain uniform behavior across all the Linux CD-ROM drivers.
+
+This document describes an effort to establish Uniform behavior across
+all the different CD-ROM device drivers for Linux. This document also
+defines the various *ioctl()'s*, and how the low-level CD-ROM device
+drivers should implement them. Currently (as of the Linux 2.1.\ *x*
+development kernels) several low-level CD-ROM device drivers, including
+both IDE/ATAPI and SCSI, now use this Uniform interface.
+
+When the CD-ROM was developed, the interface between the CD-ROM drive
+and the computer was not specified in the standards. As a result, many
+different CD-ROM interfaces were developed. Some of them had their
+own proprietary design (Sony, Mitsumi, Panasonic, Philips), other
+manufacturers adopted an existing electrical interface and changed
+the functionality (CreativeLabs/SoundBlaster, Teac, Funai) or simply
+adapted their drives to one or more of the already existing electrical
+interfaces (Aztech, Sanyo, Funai, Vertos, Longshine, Optics Storage and
+most of the `NoName` manufacturers). In cases where a new drive really
+brought its own interface or used its own command set and flow control
+scheme, either a separate driver had to be written, or an existing
+driver had to be enhanced. History has delivered us CD-ROM support for
+many of these different interfaces. Nowadays, almost all new CD-ROM
+drives are either IDE/ATAPI or SCSI, and it is very unlikely that any
+manufacturer will create a new interface. Even finding drives for the
+old proprietary interfaces is getting difficult.
+
+When (in the 1.3.70's) I looked at the existing software interface,
+which was expressed through `cdrom.h`, it appeared to be a rather wild
+set of commands and data formats [#f1]_. It seemed that many
+features of the software interface had been added to accommodate the
+capabilities of a particular drive, in an *ad hoc* manner. More
+importantly, it appeared that the behavior of the `standard` commands
+was different for most of the different drivers: e. g., some drivers
+close the tray if an *open()* call occurs when the tray is open, while
+others do not. Some drivers lock the door upon opening the device, to
+prevent an incoherent file system, but others don't, to allow software
+ejection. Undoubtedly, the capabilities of the different drives vary,
+but even when two drives have the same capability their drivers'
+behavior was usually different.
+
+.. [#f1]
+ I cannot recollect what kernel version I looked at, then,
+ presumably 1.2.13 and 1.3.34 --- the latest kernel that I was
+ indirectly involved in.
+
+I decided to start a discussion on how to make all the Linux CD-ROM
+drivers behave more uniformly. I began by contacting the developers of
+the many CD-ROM drivers found in the Linux kernel. Their reactions
+encouraged me to write the Uniform CD-ROM Driver which this document is
+intended to describe. The implementation of the Uniform CD-ROM Driver is
+in the file `cdrom.c`. This driver is intended to be an additional software
+layer that sits on top of the low-level device drivers for each CD-ROM drive.
+By adding this additional layer, it is possible to have all the different
+CD-ROM devices behave **exactly** the same (insofar as the underlying
+hardware will allow).
+
+The goal of the Uniform CD-ROM Driver is **not** to alienate driver developers
+whohave not yet taken steps to support this effort. The goal of Uniform CD-ROM
+Driver is simply to give people writing application programs for CD-ROM drives
+**one** Linux CD-ROM interface with consistent behavior for all
+CD-ROM devices. In addition, this also provides a consistent interface
+between the low-level device driver code and the Linux kernel. Care
+is taken that 100% compatibility exists with the data structures and
+programmer's interface defined in `cdrom.h`. This guide was written to
+help CD-ROM driver developers adapt their code to use the Uniform CD-ROM
+Driver code defined in `cdrom.c`.
+
+Personally, I think that the most important hardware interfaces are
+the IDE/ATAPI drives and, of course, the SCSI drives, but as prices
+of hardware drop continuously, it is also likely that people may have
+more than one CD-ROM drive, possibly of mixed types. It is important
+that these drives behave in the same way. In December 1994, one of the
+cheapest CD-ROM drives was a Philips cm206, a double-speed proprietary
+drive. In the months that I was busy writing a Linux driver for it,
+proprietary drives became obsolete and IDE/ATAPI drives became the
+standard. At the time of the last update to this document (November
+1997) it is becoming difficult to even **find** anything less than a
+16 speed CD-ROM drive, and 24 speed drives are common.
+
+.. _cdrom_api:
+
+Standardizing through another software level
+============================================
+
+At the time this document was conceived, all drivers directly
+implemented the CD-ROM *ioctl()* calls through their own routines. This
+led to the danger of different drivers forgetting to do important things
+like checking that the user was giving the driver valid data. More
+importantly, this led to the divergence of behavior, which has already
+been discussed.
+
+For this reason, the Uniform CD-ROM Driver was created to enforce consistent
+CD-ROM drive behavior, and to provide a common set of services to the various
+low-level CD-ROM device drivers. The Uniform CD-ROM Driver now provides another
+software-level, that separates the *ioctl()* and *open()* implementation
+from the actual hardware implementation. Note that this effort has
+made few changes which will affect a user's application programs. The
+greatest change involved moving the contents of the various low-level
+CD-ROM drivers\' header files to the kernel's cdrom directory. This was
+done to help ensure that the user is only presented with only one cdrom
+interface, the interface defined in `cdrom.h`.
+
+CD-ROM drives are specific enough (i. e., different from other
+block-devices such as floppy or hard disc drives), to define a set
+of common **CD-ROM device operations**, *<cdrom-device>_dops*.
+These operations are different from the classical block-device file
+operations, *<block-device>_fops*.
+
+The routines for the Uniform CD-ROM Driver interface level are implemented
+in the file `cdrom.c`. In this file, the Uniform CD-ROM Driver interfaces
+with the kernel as a block device by registering the following general
+*struct file_operations*::
+
+ struct file_operations cdrom_fops = {
+ NULL, /∗ lseek ∗/
+ block _read , /∗ read—general block-dev read ∗/
+ block _write, /∗ write—general block-dev write ∗/
+ NULL, /∗ readdir ∗/
+ NULL, /∗ select ∗/
+ cdrom_ioctl, /∗ ioctl ∗/
+ NULL, /∗ mmap ∗/
+ cdrom_open, /∗ open ∗/
+ cdrom_release, /∗ release ∗/
+ NULL, /∗ fsync ∗/
+ NULL, /∗ fasync ∗/
+ cdrom_media_changed, /∗ media change ∗/
+ NULL /∗ revalidate ∗/
+ };
+
+Every active CD-ROM device shares this *struct*. The routines
+declared above are all implemented in `cdrom.c`, since this file is the
+place where the behavior of all CD-ROM-devices is defined and
+standardized. The actual interface to the various types of CD-ROM
+hardware is still performed by various low-level CD-ROM-device
+drivers. These routines simply implement certain **capabilities**
+that are common to all CD-ROM (and really, all removable-media
+devices).
+
+Registration of a low-level CD-ROM device driver is now done through
+the general routines in `cdrom.c`, not through the Virtual File System
+(VFS) any more. The interface implemented in `cdrom.c` is carried out
+through two general structures that contain information about the
+capabilities of the driver, and the specific drives on which the
+driver operates. The structures are:
+
+cdrom_device_ops
+ This structure contains information about the low-level driver for a
+ CD-ROM device. This structure is conceptually connected to the major
+ number of the device (although some drivers may have different
+ major numbers, as is the case for the IDE driver).
+
+cdrom_device_info
+ This structure contains information about a particular CD-ROM drive,
+ such as its device name, speed, etc. This structure is conceptually
+ connected to the minor number of the device.
+
+Registering a particular CD-ROM drive with the Uniform CD-ROM Driver
+is done by the low-level device driver though a call to::
+
+ register_cdrom(struct cdrom_device_info * <device>_info)
+
+The device information structure, *<device>_info*, contains all the
+information needed for the kernel to interface with the low-level
+CD-ROM device driver. One of the most important entries in this
+structure is a pointer to the *cdrom_device_ops* structure of the
+low-level driver.
+
+The device operations structure, *cdrom_device_ops*, contains a list
+of pointers to the functions which are implemented in the low-level
+device driver. When `cdrom.c` accesses a CD-ROM device, it does it
+through the functions in this structure. It is impossible to know all
+the capabilities of future CD-ROM drives, so it is expected that this
+list may need to be expanded from time to time as new technologies are
+developed. For example, CD-R and CD-R/W drives are beginning to become
+popular, and support will soon need to be added for them. For now, the
+current *struct* is::
+
+ struct cdrom_device_ops {
+ int (*open)(struct cdrom_device_info *, int)
+ void (*release)(struct cdrom_device_info *);
+ int (*drive_status)(struct cdrom_device_info *, int);
+ unsigned int (*check_events)(struct cdrom_device_info *,
+ unsigned int, int);
+ int (*media_changed)(struct cdrom_device_info *, int);
+ int (*tray_move)(struct cdrom_device_info *, int);
+ int (*lock_door)(struct cdrom_device_info *, int);
+ int (*select_speed)(struct cdrom_device_info *, int);
+ int (*select_disc)(struct cdrom_device_info *, int);
+ int (*get_last_session) (struct cdrom_device_info *,
+ struct cdrom_multisession *);
+ int (*get_mcn)(struct cdrom_device_info *, struct cdrom_mcn *);
+ int (*reset)(struct cdrom_device_info *);
+ int (*audio_ioctl)(struct cdrom_device_info *,
+ unsigned int, void *);
+ const int capability; /* capability flags */
+ int (*generic_packet)(struct cdrom_device_info *,
+ struct packet_command *);
+ };
+
+When a low-level device driver implements one of these capabilities,
+it should add a function pointer to this *struct*. When a particular
+function is not implemented, however, this *struct* should contain a
+NULL instead. The *capability* flags specify the capabilities of the
+CD-ROM hardware and/or low-level CD-ROM driver when a CD-ROM drive
+is registered with the Uniform CD-ROM Driver.
+
+Note that most functions have fewer parameters than their
+*blkdev_fops* counterparts. This is because very little of the
+information in the structures *inode* and *file* is used. For most
+drivers, the main parameter is the *struct* *cdrom_device_info*, from
+which the major and minor number can be extracted. (Most low-level
+CD-ROM drivers don't even look at the major and minor number though,
+since many of them only support one device.) This will be available
+through *dev* in *cdrom_device_info* described below.
+
+The drive-specific, minor-like information that is registered with
+`cdrom.c`, currently contains the following fields::
+
+ struct cdrom_device_info {
+ const struct cdrom_device_ops * ops; /* device operations for this major */
+ struct list_head list; /* linked list of all device_info */
+ struct gendisk * disk; /* matching block layer disk */
+ void * handle; /* driver-dependent data */
+
+ int mask; /* mask of capability: disables them */
+ int speed; /* maximum speed for reading data */
+ int capacity; /* number of discs in a jukebox */
+
+ unsigned int options:30; /* options flags */
+ unsigned mc_flags:2; /* media-change buffer flags */
+ unsigned int vfs_events; /* cached events for vfs path */
+ unsigned int ioctl_events; /* cached events for ioctl path */
+ int use_count; /* number of times device is opened */
+ char name[20]; /* name of the device type */
+
+ __u8 sanyo_slot : 2; /* Sanyo 3-CD changer support */
+ __u8 keeplocked : 1; /* CDROM_LOCKDOOR status */
+ __u8 reserved : 5; /* not used yet */
+ int cdda_method; /* see CDDA_* flags */
+ __u8 last_sense; /* saves last sense key */
+ __u8 media_written; /* dirty flag, DVD+RW bookkeeping */
+ unsigned short mmc3_profile; /* current MMC3 profile */
+ int for_data; /* unknown:TBD */
+ int (*exit)(struct cdrom_device_info *);/* unknown:TBD */
+ int mrw_mode_page; /* which MRW mode page is in use */
+ };
+
+Using this *struct*, a linked list of the registered minor devices is
+built, using the *next* field. The device number, the device operations
+struct and specifications of properties of the drive are stored in this
+structure.
+
+The *mask* flags can be used to mask out some of the capabilities listed
+in *ops->capability*, if a specific drive doesn't support a feature
+of the driver. The value *speed* specifies the maximum head-rate of the
+drive, measured in units of normal audio speed (176kB/sec raw data or
+150kB/sec file system data). The parameters are declared *const*
+because they describe properties of the drive, which don't change after
+registration.
+
+A few registers contain variables local to the CD-ROM drive. The
+flags *options* are used to specify how the general CD-ROM routines
+should behave. These various flags registers should provide enough
+flexibility to adapt to the different users' wishes (and **not** the
+`arbitrary` wishes of the author of the low-level device driver, as is
+the case in the old scheme). The register *mc_flags* is used to buffer
+the information from *media_changed()* to two separate queues. Other
+data that is specific to a minor drive, can be accessed through *handle*,
+which can point to a data structure specific to the low-level driver.
+The fields *use_count*, *next*, *options* and *mc_flags* need not be
+initialized.
+
+The intermediate software layer that `cdrom.c` forms will perform some
+additional bookkeeping. The use count of the device (the number of
+processes that have the device opened) is registered in *use_count*. The
+function *cdrom_ioctl()* will verify the appropriate user-memory regions
+for read and write, and in case a location on the CD is transferred,
+it will `sanitize` the format by making requests to the low-level
+drivers in a standard format, and translating all formats between the
+user-software and low level drivers. This relieves much of the drivers'
+memory checking and format checking and translation. Also, the necessary
+structures will be declared on the program stack.
+
+The implementation of the functions should be as defined in the
+following sections. Two functions **must** be implemented, namely
+*open()* and *release()*. Other functions may be omitted, their
+corresponding capability flags will be cleared upon registration.
+Generally, a function returns zero on success and negative on error. A
+function call should return only after the command has completed, but of
+course waiting for the device should not use processor time.
+
+::
+
+ int open(struct cdrom_device_info *cdi, int purpose)
+
+*Open()* should try to open the device for a specific *purpose*, which
+can be either:
+
+- Open for reading data, as done by `mount()` (2), or the
+ user commands `dd` or `cat`.
+- Open for *ioctl* commands, as done by audio-CD playing programs.
+
+Notice that any strategic code (closing tray upon *open()*, etc.) is
+done by the calling routine in `cdrom.c`, so the low-level routine
+should only be concerned with proper initialization, such as spinning
+up the disc, etc.
+
+::
+
+ void release(struct cdrom_device_info *cdi)
+
+Device-specific actions should be taken such as spinning down the device.
+However, strategic actions such as ejection of the tray, or unlocking
+the door, should be left over to the general routine *cdrom_release()*.
+This is the only function returning type *void*.
+
+.. _cdrom_drive_status:
+
+::
+
+ int drive_status(struct cdrom_device_info *cdi, int slot_nr)
+
+The function *drive_status*, if implemented, should provide
+information on the status of the drive (not the status of the disc,
+which may or may not be in the drive). If the drive is not a changer,
+*slot_nr* should be ignored. In `cdrom.h` the possibilities are listed::
+
+
+ CDS_NO_INFO /* no information available */
+ CDS_NO_DISC /* no disc is inserted, tray is closed */
+ CDS_TRAY_OPEN /* tray is opened */
+ CDS_DRIVE_NOT_READY /* something is wrong, tray is moving? */
+ CDS_DISC_OK /* a disc is loaded and everything is fine */
+
+::
+
+ int media_changed(struct cdrom_device_info *cdi, int disc_nr)
+
+This function is very similar to the original function in $struct
+file_operations*. It returns 1 if the medium of the device *cdi->dev*
+has changed since the last call, and 0 otherwise. The parameter
+*disc_nr* identifies a specific slot in a juke-box, it should be
+ignored for single-disc drives. Note that by `re-routing` this
+function through *cdrom_media_changed()*, we can implement separate
+queues for the VFS and a new *ioctl()* function that can report device
+changes to software (e. g., an auto-mounting daemon).
+
+::
+
+ int tray_move(struct cdrom_device_info *cdi, int position)
+
+This function, if implemented, should control the tray movement. (No
+other function should control this.) The parameter *position* controls
+the desired direction of movement:
+
+- 0 Close tray
+- 1 Open tray
+
+This function returns 0 upon success, and a non-zero value upon
+error. Note that if the tray is already in the desired position, no
+action need be taken, and the return value should be 0.
+
+::
+
+ int lock_door(struct cdrom_device_info *cdi, int lock)
+
+This function (and no other code) controls locking of the door, if the
+drive allows this. The value of *lock* controls the desired locking
+state:
+
+- 0 Unlock door, manual opening is allowed
+- 1 Lock door, tray cannot be ejected manually
+
+This function returns 0 upon success, and a non-zero value upon
+error. Note that if the door is already in the requested state, no
+action need be taken, and the return value should be 0.
+
+::
+
+ int select_speed(struct cdrom_device_info *cdi, int speed)
+
+Some CD-ROM drives are capable of changing their head-speed. There
+are several reasons for changing the speed of a CD-ROM drive. Badly
+pressed CD-ROM s may benefit from less-than-maximum head rate. Modern
+CD-ROM drives can obtain very high head rates (up to *24x* is
+common). It has been reported that these drives can make reading
+errors at these high speeds, reducing the speed can prevent data loss
+in these circumstances. Finally, some of these drives can
+make an annoyingly loud noise, which a lower speed may reduce.
+
+This function specifies the speed at which data is read or audio is
+played back. The value of *speed* specifies the head-speed of the
+drive, measured in units of standard cdrom speed (176kB/sec raw data
+or 150kB/sec file system data). So to request that a CD-ROM drive
+operate at 300kB/sec you would call the CDROM_SELECT_SPEED *ioctl*
+with *speed=2*. The special value `0` means `auto-selection`, i. e.,
+maximum data-rate or real-time audio rate. If the drive doesn't have
+this `auto-selection` capability, the decision should be made on the
+current disc loaded and the return value should be positive. A negative
+return value indicates an error.
+
+::
+
+ int select_disc(struct cdrom_device_info *cdi, int number)
+
+If the drive can store multiple discs (a juke-box) this function
+will perform disc selection. It should return the number of the
+selected disc on success, a negative value on error. Currently, only
+the ide-cd driver supports this functionality.
+
+::
+
+ int get_last_session(struct cdrom_device_info *cdi,
+ struct cdrom_multisession *ms_info)
+
+This function should implement the old corresponding *ioctl()*. For
+device *cdi->dev*, the start of the last session of the current disc
+should be returned in the pointer argument *ms_info*. Note that
+routines in `cdrom.c` have sanitized this argument: its requested
+format will **always** be of the type *CDROM_LBA* (linear block
+addressing mode), whatever the calling software requested. But
+sanitization goes even further: the low-level implementation may
+return the requested information in *CDROM_MSF* format if it wishes so
+(setting the *ms_info->addr_format* field appropriately, of
+course) and the routines in `cdrom.c` will make the transformation if
+necessary. The return value is 0 upon success.
+
+::
+
+ int get_mcn(struct cdrom_device_info *cdi,
+ struct cdrom_mcn *mcn)
+
+Some discs carry a `Media Catalog Number` (MCN), also called
+`Universal Product Code` (UPC). This number should reflect the number
+that is generally found in the bar-code on the product. Unfortunately,
+the few discs that carry such a number on the disc don't even use the
+same format. The return argument to this function is a pointer to a
+pre-declared memory region of type *struct cdrom_mcn*. The MCN is
+expected as a 13-character string, terminated by a null-character.
+
+::
+
+ int reset(struct cdrom_device_info *cdi)
+
+This call should perform a hard-reset on the drive (although in
+circumstances that a hard-reset is necessary, a drive may very well not
+listen to commands anymore). Preferably, control is returned to the
+caller only after the drive has finished resetting. If the drive is no
+longer listening, it may be wise for the underlying low-level cdrom
+driver to time out.
+
+::
+
+ int audio_ioctl(struct cdrom_device_info *cdi,
+ unsigned int cmd, void *arg)
+
+Some of the CD-ROM-\ *ioctl()*\ 's defined in `cdrom.h` can be
+implemented by the routines described above, and hence the function
+*cdrom_ioctl* will use those. However, most *ioctl()*\ 's deal with
+audio-control. We have decided to leave these to be accessed through a
+single function, repeating the arguments *cmd* and *arg*. Note that
+the latter is of type *void*, rather than *unsigned long int*.
+The routine *cdrom_ioctl()* does do some useful things,
+though. It sanitizes the address format type to *CDROM_MSF* (Minutes,
+Seconds, Frames) for all audio calls. It also verifies the memory
+location of *arg*, and reserves stack-memory for the argument. This
+makes implementation of the *audio_ioctl()* much simpler than in the
+old driver scheme. For example, you may look up the function
+*cm206_audio_ioctl()* `cm206.c` that should be updated with
+this documentation.
+
+An unimplemented ioctl should return *-ENOSYS*, but a harmless request
+(e. g., *CDROMSTART*) may be ignored by returning 0 (success). Other
+errors should be according to the standards, whatever they are. When
+an error is returned by the low-level driver, the Uniform CD-ROM Driver
+tries whenever possible to return the error code to the calling program.
+(We may decide to sanitize the return value in *cdrom_ioctl()* though, in
+order to guarantee a uniform interface to the audio-player software.)
+
+::
+
+ int dev_ioctl(struct cdrom_device_info *cdi,
+ unsigned int cmd, unsigned long arg)
+
+Some *ioctl()'s* seem to be specific to certain CD-ROM drives. That is,
+they are introduced to service some capabilities of certain drives. In
+fact, there are 6 different *ioctl()'s* for reading data, either in some
+particular kind of format, or audio data. Not many drives support
+reading audio tracks as data, I believe this is because of protection
+of copyrights of artists. Moreover, I think that if audio-tracks are
+supported, it should be done through the VFS and not via *ioctl()'s*. A
+problem here could be the fact that audio-frames are 2352 bytes long,
+so either the audio-file-system should ask for 75264 bytes at once
+(the least common multiple of 512 and 2352), or the drivers should
+bend their backs to cope with this incoherence (to which I would be
+opposed). Furthermore, it is very difficult for the hardware to find
+the exact frame boundaries, since there are no synchronization headers
+in audio frames. Once these issues are resolved, this code should be
+standardized in `cdrom.c`.
+
+Because there are so many *ioctl()'s* that seem to be introduced to
+satisfy certain drivers [#f2]_, any non-standard *ioctl()*\ s
+are routed through the call *dev_ioctl()*. In principle, `private`
+*ioctl()*\ 's should be numbered after the device's major number, and not
+the general CD-ROM *ioctl* number, `0x53`. Currently the
+non-supported *ioctl()'s* are:
+
+ CDROMREADMODE1, CDROMREADMODE2, CDROMREADAUDIO, CDROMREADRAW,
+ CDROMREADCOOKED, CDROMSEEK, CDROMPLAY-BLK and CDROM-READALL
+
+.. [#f2]
+
+ Is there software around that actually uses these? I'd be interested!
+
+.. _cdrom_capabilities:
+
+CD-ROM capabilities
+-------------------
+
+Instead of just implementing some *ioctl* calls, the interface in
+`cdrom.c` supplies the possibility to indicate the **capabilities**
+of a CD-ROM drive. This can be done by ORing any number of
+capability-constants that are defined in `cdrom.h` at the registration
+phase. Currently, the capabilities are any of::
+
+ CDC_CLOSE_TRAY /* can close tray by software control */
+ CDC_OPEN_TRAY /* can open tray */
+ CDC_LOCK /* can lock and unlock the door */
+ CDC_SELECT_SPEED /* can select speed, in units of * sim*150 ,kB/s */
+ CDC_SELECT_DISC /* drive is juke-box */
+ CDC_MULTI_SESSION /* can read sessions *> rm1* */
+ CDC_MCN /* can read Media Catalog Number */
+ CDC_MEDIA_CHANGED /* can report if disc has changed */
+ CDC_PLAY_AUDIO /* can perform audio-functions (play, pause, etc) */
+ CDC_RESET /* hard reset device */
+ CDC_IOCTLS /* driver has non-standard ioctls */
+ CDC_DRIVE_STATUS /* driver implements drive status */
+
+The capability flag is declared *const*, to prevent drivers from
+accidentally tampering with the contents. The capability fags actually
+inform `cdrom.c` of what the driver can do. If the drive found
+by the driver does not have the capability, is can be masked out by
+the *cdrom_device_info* variable *mask*. For instance, the SCSI CD-ROM
+driver has implemented the code for loading and ejecting CD-ROM's, and
+hence its corresponding flags in *capability* will be set. But a SCSI
+CD-ROM drive might be a caddy system, which can't load the tray, and
+hence for this drive the *cdrom_device_info* struct will have set
+the *CDC_CLOSE_TRAY* bit in *mask*.
+
+In the file `cdrom.c` you will encounter many constructions of the type::
+
+ if (cdo->capability & ∼cdi->mask & CDC _⟨capability⟩) ...
+
+There is no *ioctl* to set the mask... The reason is that
+I think it is better to control the **behavior** rather than the
+**capabilities**.
+
+Options
+-------
+
+A final flag register controls the **behavior** of the CD-ROM
+drives, in order to satisfy different users' wishes, hopefully
+independently of the ideas of the respective author who happened to
+have made the drive's support available to the Linux community. The
+current behavior options are::
+
+ CDO_AUTO_CLOSE /* try to close tray upon device open() */
+ CDO_AUTO_EJECT /* try to open tray on last device close() */
+ CDO_USE_FFLAGS /* use file_pointer->f_flags to indicate purpose for open() */
+ CDO_LOCK /* try to lock door if device is opened */
+ CDO_CHECK_TYPE /* ensure disc type is data if opened for data */
+
+The initial value of this register is
+`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK`, reflecting my own view on user
+interface and software standards. Before you protest, there are two
+new *ioctl()'s* implemented in `cdrom.c`, that allow you to control the
+behavior by software. These are::
+
+ CDROM_SET_OPTIONS /* set options specified in (int)arg */
+ CDROM_CLEAR_OPTIONS /* clear options specified in (int)arg */
+
+One option needs some more explanation: *CDO_USE_FFLAGS*. In the next
+newsection we explain what the need for this option is.
+
+A software package `setcd`, available from the Debian distribution
+and `sunsite.unc.edu`, allows user level control of these flags.
+
+
+The need to know the purpose of opening the CD-ROM device
+=========================================================
+
+Traditionally, Unix devices can be used in two different `modes`,
+either by reading/writing to the device file, or by issuing
+controlling commands to the device, by the device's *ioctl()*
+call. The problem with CD-ROM drives, is that they can be used for
+two entirely different purposes. One is to mount removable
+file systems, CD-ROM's, the other is to play audio CD's. Audio commands
+are implemented entirely through *ioctl()\'s*, presumably because the
+first implementation (SUN?) has been such. In principle there is
+nothing wrong with this, but a good control of the `CD player` demands
+that the device can **always** be opened in order to give the
+*ioctl* commands, regardless of the state the drive is in.
+
+On the other hand, when used as a removable-media disc drive (what the
+original purpose of CD-ROM s is) we would like to make sure that the
+disc drive is ready for operation upon opening the device. In the old
+scheme, some CD-ROM drivers don't do any integrity checking, resulting
+in a number of i/o errors reported by the VFS to the kernel when an
+attempt for mounting a CD-ROM on an empty drive occurs. This is not a
+particularly elegant way to find out that there is no CD-ROM inserted;
+it more-or-less looks like the old IBM-PC trying to read an empty floppy
+drive for a couple of seconds, after which the system complains it
+can't read from it. Nowadays we can **sense** the existence of a
+removable medium in a drive, and we believe we should exploit that
+fact. An integrity check on opening of the device, that verifies the
+availability of a CD-ROM and its correct type (data), would be
+desirable.
+
+These two ways of using a CD-ROM drive, principally for data and
+secondarily for playing audio discs, have different demands for the
+behavior of the *open()* call. Audio use simply wants to open the
+device in order to get a file handle which is needed for issuing
+*ioctl* commands, while data use wants to open for correct and
+reliable data transfer. The only way user programs can indicate what
+their *purpose* of opening the device is, is through the *flags*
+parameter (see `open(2)`). For CD-ROM devices, these flags aren't
+implemented (some drivers implement checking for write-related flags,
+but this is not strictly necessary if the device file has correct
+permission flags). Most option flags simply don't make sense to
+CD-ROM devices: *O_CREAT*, *O_NOCTTY*, *O_TRUNC*, *O_APPEND*, and
+*O_SYNC* have no meaning to a CD-ROM.
+
+We therefore propose to use the flag *O_NONBLOCK* to indicate
+that the device is opened just for issuing *ioctl*
+commands. Strictly, the meaning of *O_NONBLOCK* is that opening and
+subsequent calls to the device don't cause the calling process to
+wait. We could interpret this as don't wait until someone has
+inserted some valid data-CD-ROM. Thus, our proposal of the
+implementation for the *open()* call for CD-ROM s is:
+
+- If no other flags are set than *O_RDONLY*, the device is opened
+ for data transfer, and the return value will be 0 only upon successful
+ initialization of the transfer. The call may even induce some actions
+ on the CD-ROM, such as closing the tray.
+- If the option flag *O_NONBLOCK* is set, opening will always be
+ successful, unless the whole device doesn't exist. The drive will take
+ no actions whatsoever.
+
+And what about standards?
+-------------------------
+
+You might hesitate to accept this proposal as it comes from the
+Linux community, and not from some standardizing institute. What
+about SUN, SGI, HP and all those other Unix and hardware vendors?
+Well, these companies are in the lucky position that they generally
+control both the hardware and software of their supported products,
+and are large enough to set their own standard. They do not have to
+deal with a dozen or more different, competing hardware
+configurations\ [#f3]_.
+
+.. [#f3]
+
+ Incidentally, I think that SUN's approach to mounting CD-ROM s is very
+ good in origin: under Solaris a volume-daemon automatically mounts a
+ newly inserted CD-ROM under `/cdrom/*<volume-name>*`.
+
+ In my opinion they should have pushed this
+ further and have **every** CD-ROM on the local area network be
+ mounted at the similar location, i. e., no matter in which particular
+ machine you insert a CD-ROM, it will always appear at the same
+ position in the directory tree, on every system. When I wanted to
+ implement such a user-program for Linux, I came across the
+ differences in behavior of the various drivers, and the need for an
+ *ioctl* informing about media changes.
+
+We believe that using *O_NONBLOCK* to indicate that a device is being opened
+for *ioctl* commands only can be easily introduced in the Linux
+community. All the CD-player authors will have to be informed, we can
+even send in our own patches to the programs. The use of *O_NONBLOCK*
+has most likely no influence on the behavior of the CD-players on
+other operating systems than Linux. Finally, a user can always revert
+to old behavior by a call to
+*ioctl(file_descriptor, CDROM_CLEAR_OPTIONS, CDO_USE_FFLAGS)*.
+
+The preferred strategy of *open()*
+----------------------------------
+
+The routines in `cdrom.c` are designed in such a way that run-time
+configuration of the behavior of CD-ROM devices (of **any** type)
+can be carried out, by the *CDROM_SET/CLEAR_OPTIONS* *ioctls*. Thus, various
+modes of operation can be set:
+
+`CDO_AUTO_CLOSE | CDO_USE_FFLAGS | CDO_LOCK`
+ This is the default setting. (With *CDO_CHECK_TYPE* it will be better, in
+ the future.) If the device is not yet opened by any other process, and if
+ the device is being opened for data (*O_NONBLOCK* is not set) and the
+ tray is found to be open, an attempt to close the tray is made. Then,
+ it is verified that a disc is in the drive and, if *CDO_CHECK_TYPE* is
+ set, that it contains tracks of type `data mode 1`. Only if all tests
+ are passed is the return value zero. The door is locked to prevent file
+ system corruption. If the drive is opened for audio (*O_NONBLOCK* is
+ set), no actions are taken and a value of 0 will be returned.
+
+`CDO_AUTO_CLOSE | CDO_AUTO_EJECT | CDO_LOCK`
+ This mimics the behavior of the current sbpcd-driver. The option flags are
+ ignored, the tray is closed on the first open, if necessary. Similarly,
+ the tray is opened on the last release, i. e., if a CD-ROM is unmounted,
+ it is automatically ejected, such that the user can replace it.
+
+We hope that these option can convince everybody (both driver
+maintainers and user program developers) to adopt the new CD-ROM
+driver scheme and option flag interpretation.
+
+Description of routines in `cdrom.c`
+====================================
+
+Only a few routines in `cdrom.c` are exported to the drivers. In this
+new section we will discuss these, as well as the functions that `take
+over' the CD-ROM interface to the kernel. The header file belonging
+to `cdrom.c` is called `cdrom.h`. Formerly, some of the contents of this
+file were placed in the file `ucdrom.h`, but this file has now been
+merged back into `cdrom.h`.
+
+::
+
+ struct file_operations cdrom_fops
+
+The contents of this structure were described in cdrom_api_.
+A pointer to this structure is assigned to the *fops* field
+of the *struct gendisk*.
+
+::
+
+ int register_cdrom(struct cdrom_device_info *cdi)
+
+This function is used in about the same way one registers *cdrom_fops*
+with the kernel, the device operations and information structures,
+as described in cdrom_api_, should be registered with the
+Uniform CD-ROM Driver::
+
+ register_cdrom(&<device>_info);
+
+
+This function returns zero upon success, and non-zero upon
+failure. The structure *<device>_info* should have a pointer to the
+driver's *<device>_dops*, as in::
+
+ struct cdrom_device_info <device>_info = {
+ <device>_dops;
+ ...
+ }
+
+Note that a driver must have one static structure, *<device>_dops*, while
+it may have as many structures *<device>_info* as there are minor devices
+active. *Register_cdrom()* builds a linked list from these.
+
+
+::
+
+ void unregister_cdrom(struct cdrom_device_info *cdi)
+
+Unregistering device *cdi* with minor number *MINOR(cdi->dev)* removes
+the minor device from the list. If it was the last registered minor for
+the low-level driver, this disconnects the registered device-operation
+routines from the CD-ROM interface. This function returns zero upon
+success, and non-zero upon failure.
+
+::
+
+ int cdrom_open(struct inode * ip, struct file * fp)
+
+This function is not called directly by the low-level drivers, it is
+listed in the standard *cdrom_fops*. If the VFS opens a file, this
+function becomes active. A strategy is implemented in this routine,
+taking care of all capabilities and options that are set in the
+*cdrom_device_ops* connected to the device. Then, the program flow is
+transferred to the device_dependent *open()* call.
+
+::
+
+ void cdrom_release(struct inode *ip, struct file *fp)
+
+This function implements the reverse-logic of *cdrom_open()*, and then
+calls the device-dependent *release()* routine. When the use-count has
+reached 0, the allocated buffers are flushed by calls to *sync_dev(dev)*
+and *invalidate_buffers(dev)*.
+
+
+.. _cdrom_ioctl:
+
+::
+
+ int cdrom_ioctl(struct inode *ip, struct file *fp,
+ unsigned int cmd, unsigned long arg)
+
+This function handles all the standard *ioctl* requests for CD-ROM
+devices in a uniform way. The different calls fall into three
+categories: *ioctl()'s* that can be directly implemented by device
+operations, ones that are routed through the call *audio_ioctl()*, and
+the remaining ones, that are presumable device-dependent. Generally, a
+negative return value indicates an error.
+
+Directly implemented *ioctl()'s*
+--------------------------------
+
+The following `old` CD-ROM *ioctl()*\ 's are implemented by directly
+calling device-operations in *cdrom_device_ops*, if implemented and
+not masked:
+
+`CDROMMULTISESSION`
+ Requests the last session on a CD-ROM.
+`CDROMEJECT`
+ Open tray.
+`CDROMCLOSETRAY`
+ Close tray.
+`CDROMEJECT_SW`
+ If *arg\not=0*, set behavior to auto-close (close
+ tray on first open) and auto-eject (eject on last release), otherwise
+ set behavior to non-moving on *open()* and *release()* calls.
+`CDROM_GET_MCN`
+ Get the Media Catalog Number from a CD.
+
+*Ioctl*s routed through *audio_ioctl()*
+---------------------------------------
+
+The following set of *ioctl()'s* are all implemented through a call to
+the *cdrom_fops* function *audio_ioctl()*. Memory checks and
+allocation are performed in *cdrom_ioctl()*, and also sanitization of
+address format (*CDROM_LBA*/*CDROM_MSF*) is done.
+
+`CDROMSUBCHNL`
+ Get sub-channel data in argument *arg* of type
+ `struct cdrom_subchnl *`.
+`CDROMREADTOCHDR`
+ Read Table of Contents header, in *arg* of type
+ `struct cdrom_tochdr *`.
+`CDROMREADTOCENTRY`
+ Read a Table of Contents entry in *arg* and specified by *arg*
+ of type `struct cdrom_tocentry *`.
+`CDROMPLAYMSF`
+ Play audio fragment specified in Minute, Second, Frame format,
+ delimited by *arg* of type `struct cdrom_msf *`.
+`CDROMPLAYTRKIND`
+ Play audio fragment in track-index format delimited by *arg*
+ of type `struct cdrom_ti *`.
+`CDROMVOLCTRL`
+ Set volume specified by *arg* of type `struct cdrom_volctrl *`.
+`CDROMVOLREAD`
+ Read volume into by *arg* of type `struct cdrom_volctrl *`.
+`CDROMSTART`
+ Spin up disc.
+`CDROMSTOP`
+ Stop playback of audio fragment.
+`CDROMPAUSE`
+ Pause playback of audio fragment.
+`CDROMRESUME`
+ Resume playing.
+
+New *ioctl()'s* in `cdrom.c`
+----------------------------
+
+The following *ioctl()'s* have been introduced to allow user programs to
+control the behavior of individual CD-ROM devices. New *ioctl*
+commands can be identified by the underscores in their names.
+
+`CDROM_SET_OPTIONS`
+ Set options specified by *arg*. Returns the option flag register
+ after modification. Use *arg = \rm0* for reading the current flags.
+`CDROM_CLEAR_OPTIONS`
+ Clear options specified by *arg*. Returns the option flag register
+ after modification.
+`CDROM_SELECT_SPEED`
+ Select head-rate speed of disc specified as by *arg* in units
+ of standard cdrom speed (176\,kB/sec raw data or
+ 150kB/sec file system data). The value 0 means `auto-select`,
+ i. e., play audio discs at real time and data discs at maximum speed.
+ The value *arg* is checked against the maximum head rate of the
+ drive found in the *cdrom_dops*.
+`CDROM_SELECT_DISC`
+ Select disc numbered *arg* from a juke-box.
+
+ First disc is numbered 0. The number *arg* is checked against the
+ maximum number of discs in the juke-box found in the *cdrom_dops*.
+`CDROM_MEDIA_CHANGED`
+ Returns 1 if a disc has been changed since the last call.
+ Note that calls to *cdrom_media_changed* by the VFS are treated
+ by an independent queue, so both mechanisms will detect a
+ media change once. For juke-boxes, an extra argument *arg*
+ specifies the slot for which the information is given. The special
+ value *CDSL_CURRENT* requests that information about the currently
+ selected slot be returned.
+`CDROM_DRIVE_STATUS`
+ Returns the status of the drive by a call to
+ *drive_status()*. Return values are defined in cdrom_drive_status_.
+ Note that this call doesn't return information on the
+ current playing activity of the drive; this can be polled through
+ an *ioctl* call to *CDROMSUBCHNL*. For juke-boxes, an extra argument
+ *arg* specifies the slot for which (possibly limited) information is
+ given. The special value *CDSL_CURRENT* requests that information
+ about the currently selected slot be returned.
+`CDROM_DISC_STATUS`
+ Returns the type of the disc currently in the drive.
+ It should be viewed as a complement to *CDROM_DRIVE_STATUS*.
+ This *ioctl* can provide *some* information about the current
+ disc that is inserted in the drive. This functionality used to be
+ implemented in the low level drivers, but is now carried out
+ entirely in Uniform CD-ROM Driver.
+
+ The history of development of the CD's use as a carrier medium for
+ various digital information has lead to many different disc types.
+ This *ioctl* is useful only in the case that CDs have \emph {only
+ one} type of data on them. While this is often the case, it is
+ also very common for CDs to have some tracks with data, and some
+ tracks with audio. Because this is an existing interface, rather
+ than fixing this interface by changing the assumptions it was made
+ under, thereby breaking all user applications that use this
+ function, the Uniform CD-ROM Driver implements this *ioctl* as
+ follows: If the CD in question has audio tracks on it, and it has
+ absolutely no CD-I, XA, or data tracks on it, it will be reported
+ as *CDS_AUDIO*. If it has both audio and data tracks, it will
+ return *CDS_MIXED*. If there are no audio tracks on the disc, and
+ if the CD in question has any CD-I tracks on it, it will be
+ reported as *CDS_XA_2_2*. Failing that, if the CD in question
+ has any XA tracks on it, it will be reported as *CDS_XA_2_1*.
+ Finally, if the CD in question has any data tracks on it,
+ it will be reported as a data CD (*CDS_DATA_1*).
+
+ This *ioctl* can return::
+
+ CDS_NO_INFO /* no information available */
+ CDS_NO_DISC /* no disc is inserted, or tray is opened */
+ CDS_AUDIO /* Audio disc (2352 audio bytes/frame) */
+ CDS_DATA_1 /* data disc, mode 1 (2048 user bytes/frame) */
+ CDS_XA_2_1 /* mixed data (XA), mode 2, form 1 (2048 user bytes) */
+ CDS_XA_2_2 /* mixed data (XA), mode 2, form 1 (2324 user bytes) */
+ CDS_MIXED /* mixed audio/data disc */
+
+ For some information concerning frame layout of the various disc
+ types, see a recent version of `cdrom.h`.
+
+`CDROM_CHANGER_NSLOTS`
+ Returns the number of slots in a juke-box.
+`CDROMRESET`
+ Reset the drive.
+`CDROM_GET_CAPABILITY`
+ Returns the *capability* flags for the drive. Refer to section
+ cdrom_capabilities_ for more information on these flags.
+`CDROM_LOCKDOOR`
+ Locks the door of the drive. `arg == 0` unlocks the door,
+ any other value locks it.
+`CDROM_DEBUG`
+ Turns on debugging info. Only root is allowed to do this.
+ Same semantics as CDROM_LOCKDOOR.
+
+
+Device dependent *ioctl()'s*
+----------------------------
+
+Finally, all other *ioctl()'s* are passed to the function *dev_ioctl()*,
+if implemented. No memory allocation or verification is carried out.
+
+How to update your driver
+=========================
+
+- Make a backup of your current driver.
+- Get hold of the files `cdrom.c` and `cdrom.h`, they should be in
+ the directory tree that came with this documentation.
+- Make sure you include `cdrom.h`.
+- Change the 3rd argument of *register_blkdev* from `&<your-drive>_fops`
+ to `&cdrom_fops`.
+- Just after that line, add the following to register with the Uniform
+ CD-ROM Driver::
+
+ register_cdrom(&<your-drive>_info);*
+
+ Similarly, add a call to *unregister_cdrom()* at the appropriate place.
+- Copy an example of the device-operations *struct* to your
+ source, e. g., from `cm206.c` *cm206_dops*, and change all
+ entries to names corresponding to your driver, or names you just
+ happen to like. If your driver doesn't support a certain function,
+ make the entry *NULL*. At the entry *capability* you should list all
+ capabilities your driver currently supports. If your driver
+ has a capability that is not listed, please send me a message.
+- Copy the *cdrom_device_info* declaration from the same example
+ driver, and modify the entries according to your needs. If your
+ driver dynamically determines the capabilities of the hardware, this
+ structure should also be declared dynamically.
+- Implement all functions in your `<device>_dops` structure,
+ according to prototypes listed in `cdrom.h`, and specifications given
+ in cdrom_api_. Most likely you have already implemented
+ the code in a large part, and you will almost certainly need to adapt the
+ prototype and return values.
+- Rename your `<device>_ioctl()` function to *audio_ioctl* and
+ change the prototype a little. Remove entries listed in the first
+ part in cdrom_ioctl_, if your code was OK, these are
+ just calls to the routines you adapted in the previous step.
+- You may remove all remaining memory checking code in the
+ *audio_ioctl()* function that deals with audio commands (these are
+ listed in the second part of cdrom_ioctl_. There is no
+ need for memory allocation either, so most *case*s in the *switch*
+ statement look similar to::
+
+ case CDROMREADTOCENTRY:
+ get_toc_entry\bigl((struct cdrom_tocentry *) arg);
+
+- All remaining *ioctl* cases must be moved to a separate
+ function, *<device>_ioctl*, the device-dependent *ioctl()'s*. Note that
+ memory checking and allocation must be kept in this code!
+- Change the prototypes of *<device>_open()* and
+ *<device>_release()*, and remove any strategic code (i. e., tray
+ movement, door locking, etc.).
+- Try to recompile the drivers. We advise you to use modules, both
+ for `cdrom.o` and your driver, as debugging is much easier this
+ way.
+
+Thanks
+======
+
+Thanks to all the people involved. First, Erik Andersen, who has
+taken over the torch in maintaining `cdrom.c` and integrating much
+CD-ROM-related code in the 2.1-kernel. Thanks to Scott Snyder and
+Gerd Knorr, who were the first to implement this interface for SCSI
+and IDE-CD drivers and added many ideas for extension of the data
+structures relative to kernel~2.0. Further thanks to Heiko Eißfeldt,
+Thomas Quinot, Jon Tombs, Ken Pizzini, Eberhard Mönkeberg and Andrew Kroll,
+the Linux CD-ROM device driver developers who were kind
+enough to give suggestions and criticisms during the writing. Finally
+of course, I want to thank Linus Torvalds for making this possible in
+the first place.
projects / openwrt / staging / blogic.git / commitdiff