[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>

4 files changed, 144 insertions, 23 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 518ebe609e2b..2cd920f92e5e 100644
--- 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 dfdf51e81c1c..c807b8d5f891 100644
--- 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 a04b3db7a296..c5e412a00b17 100644
--- 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 c078aacc8116..830bbcd449d6 100644
--- 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