vfs: new superblock methods to override /proc/*/mount{s,info}

a) ->show_devname(m, mnt) - what to put into devname columns in mounts,
mountinfo and mountstats
b) ->show_path(m, mnt) - what to put into relative path column in mountinfo

Leaving those NULL gives old behaviour.  NFS switched to using those.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 60 insertions, 9 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index dffe6f49ab93..75d843ae46d2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -978,7 +978,13 @@ static int show_vfsmnt(struct seq_file *m, void *v)
         int err = 0;
         struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
 
-        mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
+        if (mnt->mnt_sb->s_op->show_devname) {
+                err = mnt->mnt_sb->s_op->show_devname(m, mnt);
+                if (err)
+                        goto out;
+        } else {
+                mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
+        }
         seq_putc(m, ' ');
         seq_path(m, &mnt_path, " \t\n\\");
         seq_putc(m, ' ');
@@ -1025,7 +1031,12 @@ static int show_mountinfo(struct seq_file *m, void *v)
 
         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\\");
+        if (sb->s_op->show_path)
+                err = sb->s_op->show_path(m, mnt);
+        else
+                seq_dentry(m, mnt->mnt_root, " \t\n\\");
+        if (err)
+                goto out;
         seq_putc(m, ' ');
         seq_path_root(m, &mnt_path, &root, " \t\n\\");
         if (root.mnt != p->root.mnt || root.dentry != p->root.dentry) {
@@ -1060,7 +1071,12 @@ static int show_mountinfo(struct seq_file *m, void *v)
         seq_puts(m, " - ");
         show_type(m, sb);
         seq_putc(m, ' ');
-        mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
+        if (sb->s_op->show_devname)
+                err = sb->s_op->show_devname(m, mnt);
+        else
+                mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
+        if (err)
+                goto out;
         seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
         err = show_sb_opts(m, sb);
         if (err)
@@ -1086,11 +1102,15 @@ static int show_vfsstat(struct seq_file *m, void *v)
         int err = 0;
 
         /* device */
-        if (mnt->mnt_devname) {
-                seq_puts(m, "device ");
-                mangle(m, mnt->mnt_devname);
-        } else
-                seq_puts(m, "no device");
+        if (mnt->mnt_sb->s_op->show_devname) {
+                err = mnt->mnt_sb->s_op->show_devname(m, mnt);
+        } else {
+                if (mnt->mnt_devname) {
+                        seq_puts(m, "device ");
+                        mangle(m, mnt->mnt_devname);
+                } else
+                        seq_puts(m, "no device");
+        }
 
         /* mount point */
         seq_puts(m, " mounted on ");
@@ -1104,7 +1124,8 @@ static int show_vfsstat(struct seq_file *m, void *v)
         /* optional statistics */
         if (mnt->mnt_sb->s_op->show_stats) {
                 seq_putc(m, ' ');
-                err = mnt->mnt_sb->s_op->show_stats(m, mnt);
+                if (!err)
+                        err = mnt->mnt_sb->s_op->show_stats(m, mnt);
         }
 
         seq_putc(m, '\n');
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index a6ab483c9ad0..79bc61fe2868 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -263,6 +263,8 @@ static match_table_t nfs_local_lock_tokens = {
 static void nfs_umount_begin(struct super_block *);
 static int  nfs_statfs(struct dentry *, struct kstatfs *);
 static int  nfs_show_options(struct seq_file *, struct vfsmount *);
+static int  nfs_show_devname(struct seq_file *, struct vfsmount *);
+static int  nfs_show_path(struct seq_file *, struct vfsmount *);
 static int  nfs_show_stats(struct seq_file *, struct vfsmount *);
 static int nfs_get_sb(struct file_system_type *, int, const char *, void *, struct vfsmount *);
 static struct dentry *nfs_xdev_mount(struct file_system_type *fs_type,
@@ -296,6 +298,8 @@ static const struct super_operations nfs_sops = {
         .evict_inode    = nfs_evict_inode,
         .umount_begin   = nfs_umount_begin,
         .show_options   = nfs_show_options,
+        .show_devname   = nfs_show_devname,
+        .show_path      = nfs_show_path,
         .show_stats     = nfs_show_stats,
         .remount_fs     = nfs_remount,
 };
@@ -366,6 +370,8 @@ static const struct super_operations nfs4_sops = {
         .evict_inode    = nfs4_evict_inode,
         .umount_begin   = nfs_umount_begin,
         .show_options   = nfs_show_options,
+        .show_devname   = nfs_show_devname,
+        .show_path      = nfs_show_path,
         .show_stats     = nfs_show_stats,
         .remount_fs     = nfs_remount,
 };
@@ -726,6 +732,28 @@ static int nfs_show_options(struct seq_file *m, struct vfsmount *mnt)
         return 0;
 }
 
+static int nfs_show_devname(struct seq_file *m, struct vfsmount *mnt)
+{
+        char *page = (char *) __get_free_page(GFP_KERNEL);
+        char *devname, *dummy;
+        int err = 0;
+        if (!page)
+                return -ENOMEM;
+        devname = nfs_path(&dummy, mnt->mnt_root, page, PAGE_SIZE);
+        if (IS_ERR(devname))
+                err = PTR_ERR(devname);
+        else
+                seq_escape(m, devname, " \t\n\\");
+        free_page((unsigned long)page);
+        return err;
+}
+
+static int nfs_show_path(struct seq_file *m, struct vfsmount *mnt)
+{
+        seq_puts(m, "/");
+        return 0;
+}
+
 /*
  * Present statistical information for this VFS mountpoint
  */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 13df14e2c42e..e6d3fe45981b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1632,6 +1632,8 @@ struct super_operations {
         void (*umount_begin) (struct super_block *);
 
         int (*show_options)(struct seq_file *, struct vfsmount *);
+        int (*show_devname)(struct seq_file *, struct vfsmount *);
+        int (*show_path)(struct seq_file *, struct vfsmount *);
         int (*show_stats)(struct seq_file *, struct vfsmount *);
 #ifdef CONFIG_QUOTA
         ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);