[patch 6/7] vfs: mountinfo: add /proc/<pid>/mountinfo

[mszeredi@suse.cz] rewrite and split big patch into managable chunks

/proc/mounts in its current form lacks important information:

 - propagation state
 - root of mount for bind mounts
 - the st_dev value used within the filesystem
 - identifier for each mount and it's parent

It also suffers from the following problems:

 - not easily extendable
 - ambiguity of mountpoints within a chrooted environment
 - doesn't distinguish between filesystem dependent and independent options
 - doesn't distinguish between per mount and per super block options

This patch introduces /proc/<pid>/mountinfo which attempts to address
all these deficiencies.

Code shared between /proc/<pid>/mounts and /proc/<pid>/mountinfo is
extracted into separate functions.

Thanks to Al Viro for the help in getting the design right.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 518ebe609e2b1c9392580c9ae840d5da4aa84e68..2cd920f92e5e8f1e39de64b860e3562cc7f5de6e 100644 (file)
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -43,6 +43,7 @@ Table of Contents
   2.13 /proc/<pid>/oom_score - Display current oom-killer score
   2.14 /proc/<pid>/io - Display the IO accounting fields
   2.15 /proc/<pid>/coredump_filter - Core dump filtering settings
+  2.16 /proc/<pid>/mountinfo - Information about mounts
 
 ------------------------------------------------------------------------------
 Preface
@@ -2348,4 +2349,35 @@ For example:
   $ echo 0x7 > /proc/self/coredump_filter
   $ ./some_program
 
+2.16   /proc/<pid>/mountinfo - Information about mounts
+--------------------------------------------------------
+
+This file contains lines of the form:
+
+36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
+(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
+
+(1) mount ID:  unique identifier of the mount (may be reused after umount)
+(2) parent ID:  ID of parent (or of self for the top of the mount tree)
+(3) major:minor:  value of st_dev for files on filesystem
+(4) root:  root of the mount within the filesystem
+(5) mount point:  mount point relative to the process's root
+(6) mount options:  per mount options
+(7) optional fields:  zero or more fields of the form "tag[:value]"
+(8) separator:  marks the end of the optional fields
+(9) filesystem type:  name of filesystem of the form "type[.subtype]"
+(10) mount source:  filesystem specific information or "none"
+(11) super options:  per super block options
+
+Parsers should ignore all unrecognised optional fields.  Currently the
+possible optional fields are:
+
+shared:X  mount is shared in peer group X
+master:X  mount is slave to peer group X
+unbindable  mount is unbindable
+
+For more information on mount propagation see:
+
+  Documentation/filesystems/sharedsubtree.txt
+
 ------------------------------------------------------------------------------

diff --git a/fs/namespace.c b/fs/namespace.c
index dfdf51e81c1c298fca3cf66da8aef2193fb47e24..c807b8d5f89176aba3c927839a89a3fd51fa5b35 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -746,20 +746,30 @@ static void m_stop(struct seq_file *m, void *v)
        up_read(&namespace_sem);
 }
 
-static int show_vfsmnt(struct seq_file *m, void *v)
+struct proc_fs_info {
+       int flag;
+       const char *str;
+};
+
+static void show_sb_opts(struct seq_file *m, struct super_block *sb)
 {
-       struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
-       int err = 0;
-       static struct proc_fs_info {
-               int flag;
-               char *str;
-       } fs_info[] = {
+       static const struct proc_fs_info fs_info[] = {
                { MS_SYNCHRONOUS, ",sync" },
                { MS_DIRSYNC, ",dirsync" },
                { MS_MANDLOCK, ",mand" },
                { 0, NULL }
        };
-       static struct proc_fs_info mnt_info[] = {
+       const struct proc_fs_info *fs_infop;
+
+       for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
+               if (sb->s_flags & fs_infop->flag)
+                       seq_puts(m, fs_infop->str);
+       }
+}
+
+static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
+{
+       static const struct proc_fs_info mnt_info[] = {
                { MNT_NOSUID, ",nosuid" },
                { MNT_NODEV, ",nodev" },
                { MNT_NOEXEC, ",noexec" },
@@ -768,27 +778,37 @@ static int show_vfsmnt(struct seq_file *m, void *v)
                { MNT_RELATIME, ",relatime" },
                { 0, NULL }
        };
-       struct proc_fs_info *fs_infop;
+       const struct proc_fs_info *fs_infop;
+
+       for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
+               if (mnt->mnt_flags & fs_infop->flag)
+                       seq_puts(m, fs_infop->str);
+       }
+}
+
+static void show_type(struct seq_file *m, struct super_block *sb)
+{
+       mangle(m, sb->s_type->name);
+       if (sb->s_subtype && sb->s_subtype[0]) {
+               seq_putc(m, '.');
+               mangle(m, sb->s_subtype);
+       }
+}
+
+static int show_vfsmnt(struct seq_file *m, void *v)
+{
+       struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
+       int err = 0;
        struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
 
        mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
        seq_putc(m, ' ');
        seq_path(m, &mnt_path, " \t\n\\");
        seq_putc(m, ' ');
-       mangle(m, mnt->mnt_sb->s_type->name);
-       if (mnt->mnt_sb->s_subtype && mnt->mnt_sb->s_subtype[0]) {
-               seq_putc(m, '.');
-               mangle(m, mnt->mnt_sb->s_subtype);
-       }
+       show_type(m, mnt->mnt_sb);
        seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
-       for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
-               if (mnt->mnt_sb->s_flags & fs_infop->flag)
-                       seq_puts(m, fs_infop->str);
-       }
-       for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
-               if (mnt->mnt_flags & fs_infop->flag)
-                       seq_puts(m, fs_infop->str);
-       }
+       show_sb_opts(m, mnt->mnt_sb);
+       show_mnt_opts(m, mnt);
        if (mnt->mnt_sb->s_op->show_options)
                err = mnt->mnt_sb->s_op->show_options(m, mnt);
        seq_puts(m, " 0 0\n");
@@ -802,6 +822,59 @@ const struct seq_operations mounts_op = {
        .show   = show_vfsmnt
 };
 
+static int show_mountinfo(struct seq_file *m, void *v)
+{
+       struct proc_mounts *p = m->private;
+       struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
+       struct super_block *sb = mnt->mnt_sb;
+       struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
+       struct path root = p->root;
+       int err = 0;
+
+       seq_printf(m, "%i %i %u:%u ", mnt->mnt_id, mnt->mnt_parent->mnt_id,
+                  MAJOR(sb->s_dev), MINOR(sb->s_dev));
+       seq_dentry(m, mnt->mnt_root, " \t\n\\");
+       seq_putc(m, ' ');
+       seq_path_root(m, &mnt_path, &root, " \t\n\\");
+       if (root.mnt != p->root.mnt || root.dentry != p->root.dentry) {
+               /*
+                * Mountpoint is outside root, discard that one.  Ugly,
+                * but less so than trying to do that in iterator in a
+                * race-free way (due to renames).
+                */
+               return SEQ_SKIP;
+       }
+       seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
+       show_mnt_opts(m, mnt);
+
+       /* Tagged fields ("foo:X" or "bar") */
+       if (IS_MNT_SHARED(mnt))
+               seq_printf(m, " shared:%i", mnt->mnt_group_id);
+       if (IS_MNT_SLAVE(mnt))
+               seq_printf(m, " master:%i", mnt->mnt_master->mnt_group_id);
+       if (IS_MNT_UNBINDABLE(mnt))
+               seq_puts(m, " unbindable");
+
+       /* Filesystem specific data */
+       seq_puts(m, " - ");
+       show_type(m, sb);
+       seq_putc(m, ' ');
+       mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
+       seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
+       show_sb_opts(m, sb);
+       if (sb->s_op->show_options)
+               err = sb->s_op->show_options(m, mnt);
+       seq_putc(m, '\n');
+       return err;
+}
+
+const struct seq_operations mountinfo_op = {
+       .start  = m_start,
+       .next   = m_next,
+       .stop   = m_stop,
+       .show   = show_mountinfo,
+};
+
 static int show_vfsstat(struct seq_file *m, void *v)
 {
        struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
@@ -822,7 +895,7 @@ static int show_vfsstat(struct seq_file *m, void *v)
 
        /* file system type */
        seq_puts(m, "with fstype ");
-       mangle(m, mnt->mnt_sb->s_type->name);
+       show_type(m, mnt->mnt_sb);
 
        /* optional statistics */
        if (mnt->mnt_sb->s_op->show_stats) {

diff --git a/fs/proc/base.c b/fs/proc/base.c
index a04b3db7a296f8017913adbbbada28569241e587..c5e412a00b170e5294964505726b85f6cff93309 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -604,6 +604,19 @@ static const struct file_operations proc_mounts_operations = {
        .poll           = mounts_poll,
 };
 
+static int mountinfo_open(struct inode *inode, struct file *file)
+{
+       return mounts_open_common(inode, file, &mountinfo_op);
+}
+
+static const struct file_operations proc_mountinfo_operations = {
+       .open           = mountinfo_open,
+       .read           = seq_read,
+       .llseek         = seq_lseek,
+       .release        = mounts_release,
+       .poll           = mounts_poll,
+};
+
 static int mountstats_open(struct inode *inode, struct file *file)
 {
        return mounts_open_common(inode, file, &mountstats_op);
@@ -2303,6 +2316,7 @@ static const struct pid_entry tgid_base_stuff[] = {
        LNK("root",       root),
        LNK("exe",        exe),
        REG("mounts",     S_IRUGO, mounts),
+       REG("mountinfo",  S_IRUGO, mountinfo),
        REG("mountstats", S_IRUSR, mountstats),
 #ifdef CONFIG_PROC_PAGE_MONITOR
        REG("clear_refs", S_IWUSR, clear_refs),
@@ -2635,6 +2649,7 @@ static const struct pid_entry tid_base_stuff[] = {
        LNK("root",      root),
        LNK("exe",       exe),
        REG("mounts",    S_IRUGO, mounts),
+       REG("mountinfo",  S_IRUGO, mountinfo),
 #ifdef CONFIG_PROC_PAGE_MONITOR
        REG("clear_refs", S_IWUSR, clear_refs),
        REG("smaps",     S_IRUGO, smaps),

diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
index c078aacc8116477d6e3569972396b086150b9706..830bbcd449d6c97c9e09a51bce33fabcd163d087 100644 (file)
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -46,6 +46,7 @@ static inline void get_mnt_ns(struct mnt_namespace *ns)
 }
 
 extern const struct seq_operations mounts_op;
+extern const struct seq_operations mountinfo_op;
 extern const struct seq_operations mountstats_op;
 
 #endif