From: Jeff Layton Date: Mon, 29 Jan 2018 11:41:30 +0000 (-0500) Subject: fs: new API for handling inode->i_version X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=ae5e165d855dd978a461b22175531b07f54fb61f;p=openwrt%2Fstaging%2Fblogic.git fs: new API for handling inode->i_version Add a documentation blob that explains what the i_version field is, how it is expected to work, and how it is currently implemented by various filesystems. We already have inode_inc_iversion. Add several other functions for manipulating and accessing the i_version counter. For now, the implementation is trivial and basically works the way that all of the open-coded i_version accesses work today. Future patches will convert existing users of i_version to use the new API, and then convert the backend implementation to do things more efficiently. Signed-off-by: Jeff Layton Reviewed-by: Jan Kara --- diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index eb1bac7c8553..c95d7b2efefb 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -31,6 +31,7 @@ #include #include #include +#include #include "ctree.h" #include "disk-io.h" #include "transaction.h" diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index e1a7f3cb5be9..27f008b33fc1 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -43,6 +43,7 @@ #include #include #include +#include #include "ctree.h" #include "disk-io.h" #include "transaction.h" diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 2ef8acaac688..aa452c9e2eff 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -43,6 +43,7 @@ #include #include #include +#include #include "ctree.h" #include "disk-io.h" #include "transaction.h" diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c index 2c7e53f9ff1b..5258c1714830 100644 --- a/fs/btrfs/xattr.c +++ b/fs/btrfs/xattr.c @@ -23,6 +23,7 @@ #include #include #include +#include #include "ctree.h" #include "btrfs_inode.h" #include "transaction.h" diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 7df2c5644e59..fa5d8bc52d2d 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -39,6 +39,7 @@ #include #include #include +#include #include "ext4_jbd2.h" #include "xattr.h" diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 798b3ac680db..bcf0dff517be 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -34,6 +34,7 @@ #include #include #include +#include #include "ext4.h" #include "ext4_jbd2.h" diff --git a/fs/inode.c b/fs/inode.c index 03102d6ef044..19e72f500f71 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -18,6 +18,7 @@ #include /* for inode_has_buffers */ #include #include +#include #include #include "internal.h" diff --git a/include/linux/fs.h b/include/linux/fs.h index 511fbaabf624..76382c24e9d0 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2036,21 +2036,6 @@ static inline void inode_dec_link_count(struct inode *inode) mark_inode_dirty(inode); } -/** - * inode_inc_iversion - increments i_version - * @inode: inode that need to be updated - * - * Every time the inode is modified, the i_version field will be incremented. - * The filesystem has to be mounted with i_version flag - */ - -static inline void inode_inc_iversion(struct inode *inode) -{ - spin_lock(&inode->i_lock); - inode->i_version++; - spin_unlock(&inode->i_lock); -} - enum file_time_flags { S_ATIME = 1, S_MTIME = 2, diff --git a/include/linux/iversion.h b/include/linux/iversion.h new file mode 100644 index 000000000000..d61e063f7c75 --- /dev/null +++ b/include/linux/iversion.h @@ -0,0 +1,242 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_IVERSION_H +#define _LINUX_IVERSION_H + +#include + +/* + * The change attribute (i_version) is mandated by NFSv4 and is mostly for + * knfsd, but is also used for other purposes (e.g. IMA). The i_version must + * appear different to observers if there was a change to the inode's data or + * metadata since it was last queried. + * + * Observers see the i_version as a 64-bit number that never decreases. If it + * remains the same since it was last checked, then nothing has changed in the + * inode. If it's different then something has changed. Observers cannot infer + * anything about the nature or magnitude of the changes from the value, only + * that the inode has changed in some fashion. + * + * Not all filesystems properly implement the i_version counter. Subsystems that + * want to use i_version field on an inode should first check whether the + * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro). + * + * Those that set SB_I_VERSION will automatically have their i_version counter + * incremented on writes to normal files. If the SB_I_VERSION is not set, then + * the VFS will not touch it on writes, and the filesystem can use it how it + * wishes. Note that the filesystem is always responsible for updating the + * i_version on namespace changes in directories (mkdir, rmdir, unlink, etc.). + * We consider these sorts of filesystems to have a kernel-managed i_version. + * + * It may be impractical for filesystems to keep i_version updates atomic with + * respect to the changes that cause them. They should, however, guarantee + * that i_version updates are never visible before the changes that caused + * them. Also, i_version updates should never be delayed longer than it takes + * the original change to reach disk. + * + * Note that some filesystems (e.g. NFS and AFS) just use the field to store + * a server-provided value (for the most part). For that reason, those + * filesystems do not set SB_I_VERSION. These filesystems are considered to + * have a self-managed i_version. + */ + +/** + * inode_set_iversion_raw - set i_version to the specified raw value + * @inode: inode to set + * @new: new i_version value to set + * + * Set @inode's i_version field to @new. This function is for use by + * filesystems that self-manage the i_version. + * + * For example, the NFS client stores its NFSv4 change attribute in this way, + * and the AFS client stores the data_version from the server here. + */ +static inline void +inode_set_iversion_raw(struct inode *inode, u64 new) +{ + inode->i_version = new; +} + +/** + * inode_set_iversion - set i_version to a particular value + * @inode: inode to set + * @new: new i_version value to set + * + * Set @inode's i_version field to @new. This function is for filesystems with + * a kernel-managed i_version. + * + * For now, this just does the same thing as the _raw variant. + */ +static inline void +inode_set_iversion(struct inode *inode, u64 new) +{ + inode_set_iversion_raw(inode, new); +} + +/** + * inode_set_iversion_queried - set i_version to a particular value and set + * flag to indicate that it has been viewed + * @inode: inode to set + * @new: new i_version value to set + * + * When loading in an i_version value from a backing store, we typically don't + * know whether it was previously viewed before being stored or not. Thus, we + * must assume that it was, to ensure that any changes will result in the + * value changing. + * + * This function will set the inode's i_version, and possibly flag the value + * as if it has already been viewed at least once. + * + * For now, this just does what inode_set_iversion does. + */ +static inline void +inode_set_iversion_queried(struct inode *inode, u64 new) +{ + inode_set_iversion(inode, new); +} + +/** + * inode_maybe_inc_iversion - increments i_version + * @inode: inode with the i_version that should be updated + * @force: increment the counter even if it's not necessary + * + * Every time the inode is modified, the i_version field must be seen to have + * changed by any observer. + * + * In this implementation, we always increment it after taking the i_lock to + * ensure that we don't race with other incrementors. + * + * Returns true if counter was bumped, and false if it wasn't. + */ +static inline bool +inode_maybe_inc_iversion(struct inode *inode, bool force) +{ + spin_lock(&inode->i_lock); + inode->i_version++; + spin_unlock(&inode->i_lock); + return true; +} + +/** + * inode_inc_iversion - forcibly increment i_version + * @inode: inode that needs to be updated + * + * Forcbily increment the i_version field. This always results in a change to + * the observable value. + */ +static inline void +inode_inc_iversion(struct inode *inode) +{ + inode_maybe_inc_iversion(inode, true); +} + +/** + * inode_iversion_need_inc - is the i_version in need of being incremented? + * @inode: inode to check + * + * Returns whether the inode->i_version counter needs incrementing on the next + * change. + * + * For now, we assume that it always does. + */ +static inline bool +inode_iversion_need_inc(struct inode *inode) +{ + return true; +} + +/** + * inode_peek_iversion_raw - grab a "raw" iversion value + * @inode: inode from which i_version should be read + * + * Grab a "raw" inode->i_version value and return it. The i_version is not + * flagged or converted in any way. This is mostly used to access a self-managed + * i_version. + * + * With those filesystems, we want to treat the i_version as an entirely + * opaque value. + */ +static inline u64 +inode_peek_iversion_raw(const struct inode *inode) +{ + return inode->i_version; +} + +/** + * inode_inc_iversion_raw - forcibly increment raw i_version + * @inode: inode that needs to be updated + * + * Forcbily increment the raw i_version field. This always results in a change + * to the raw value. + * + * NFS will use the i_version field to store the value from the server. It + * mostly treats it as opaque, but in the case where it holds a write + * delegation, it must increment the value itself. This function does that. + */ +static inline void +inode_inc_iversion_raw(struct inode *inode) +{ + inode_inc_iversion(inode); +} + +/** + * inode_peek_iversion - read i_version without flagging it to be incremented + * @inode: inode from which i_version should be read + * + * Read the inode i_version counter for an inode without registering it as a + * query. + * + * This is typically used by local filesystems that need to store an i_version + * on disk. In that situation, it's not necessary to flag it as having been + * viewed, as the result won't be used to gauge changes from that point. + */ +static inline u64 +inode_peek_iversion(const struct inode *inode) +{ + return inode_peek_iversion_raw(inode); +} + +/** + * inode_query_iversion - read i_version for later use + * @inode: inode from which i_version should be read + * + * Read the inode i_version counter. This should be used by callers that wish + * to store the returned i_version for later comparison. This will guarantee + * that a later query of the i_version will result in a different value if + * anything has changed. + * + * This implementation just does a peek. + */ +static inline u64 +inode_query_iversion(struct inode *inode) +{ + return inode_peek_iversion(inode); +} + +/** + * inode_cmp_iversion_raw - check whether the raw i_version counter has changed + * @inode: inode to check + * @old: old value to check against its i_version + * + * Compare the current raw i_version counter with a previous one. Returns 0 if + * they are the same or non-zero if they are different. + */ +static inline s64 +inode_cmp_iversion_raw(const struct inode *inode, u64 old) +{ + return (s64)inode_peek_iversion_raw(inode) - (s64)old; +} + +/** + * inode_cmp_iversion - check whether the i_version counter has changed + * @inode: inode to check + * @old: old value to check against its i_version + * + * Compare an i_version counter with a previous one. Returns 0 if they are + * the same or non-zero if they are different. + */ +static inline s64 +inode_cmp_iversion(const struct inode *inode, u64 old) +{ + return (s64)inode_peek_iversion(inode) - (s64)old; +} +#endif