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    Subject[patch 6/7] vfs: mountinfo: add /proc/<pid>/mountinfo
    From: Ram Pai <linuxram@us.ibm.com>

    [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>
    ---
    Documentation/filesystems/proc.txt | 33 ++++++++++
    fs/namespace.c | 121 +++++++++++++++++++++++++++++--------
    fs/proc/base.c | 15 ++++
    include/linux/mnt_namespace.h | 1
    4 files changed, 147 insertions(+), 23 deletions(-)
    Index: vfs-2.6/Documentation/filesystems/proc.txt
    ===================================================================
    --- vfs-2.6.orig/Documentation/filesystems/proc.txt 2008-03-26 21:37:52.000000000 +0100
    +++ vfs-2.6/Documentation/filesystems/proc.txt 2008-03-26 21:43:05.000000000 +0100
    @@ -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 +2349,36 @@ 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 rw master:1 - ext3 /dev/root,errors=continue
    +(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
    +
    +(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) super options: filesystem type independent, per super block options
    +(8) optional fields: zero or more fields of the form "tag[:value]"
    +(9) separator: marks the end of the optional fields
    +(10) filesystem type: name of filesystem of the form "type[.subtype]"
    +(11) mount source: filesystem specific information or "none"
    +(12) filesystem options: filesystem type dependent 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
    +
    ------------------------------------------------------------------------------
    Index: vfs-2.6/fs/namespace.c
    ===================================================================
    --- vfs-2.6.orig/fs/namespace.c 2008-03-26 21:43:03.000000000 +0100
    +++ vfs-2.6/fs/namespace.c 2008-03-26 21:43:05.000000000 +0100
    @@ -753,20 +753,30 @@ static void m_stop(struct seq_file *m, 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" },
    @@ -775,27 +785,37 @@ static int show_vfsmnt(struct seq_file *
    { 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");
    @@ -809,6 +829,61 @@ 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;
    + size_t count_save = m->count;
    + 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, rewind seq_file. Ugly,
    + * but necessary for race-free detection of unreachable
    + * mountpoints.
    + */
    + m->count = count_save;
    + return 0;
    + }
    + seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
    + show_mnt_opts(m, mnt);
    + seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
    + show_sb_opts(m, sb);
    +
    + /* 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");
    + 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);
    @@ -829,7 +904,7 @@ static int show_vfsstat(struct seq_file

    /* 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) {
    Index: vfs-2.6/fs/proc/base.c
    ===================================================================
    --- vfs-2.6.orig/fs/proc/base.c 2008-03-26 21:43:03.000000000 +0100
    +++ vfs-2.6/fs/proc/base.c 2008-03-26 21:43:05.000000000 +0100
    @@ -604,6 +604,19 @@ static const struct file_operations proc
    .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);
    @@ -2285,6 +2298,7 @@ static const struct pid_entry tgid_base_
    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),
    @@ -2616,6 +2630,7 @@ static const struct pid_entry tid_base_s
    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),
    Index: vfs-2.6/include/linux/mnt_namespace.h
    ===================================================================
    --- vfs-2.6.orig/include/linux/mnt_namespace.h 2008-03-26 21:43:03.000000000 +0100
    +++ vfs-2.6/include/linux/mnt_namespace.h 2008-03-26 21:43:05.000000000 +0100
    @@ -46,6 +46,7 @@ static inline void get_mnt_ns(struct mnt
    }

    extern const struct seq_operations mounts_op;
    +extern const struct seq_operations mountinfo_op;
    extern const struct seq_operations mountstats_op;

    #endif
    --


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