nilfs2: disallow remount of snapshot from/to a regular mount

Snapshots and regular ro/rw mounts are essentially-different within
the meaning whether the checkpoint is static or not and is marked with
a snapshot flag or not.

The current implemenation, however, allows to remount a snapshot to a
regular rw-mount if the checkpoint number equals the latest one.

This transition is actually impossible since changing a checkpoint to
a snapshot makes another checkpoint, thus the condition is never
satisfied.

This fixes the weird state of affairs, and specifically separates
snapshots and regular rw/ro-mounts.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 23 insertions, 34 deletions

diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index c88e66417330..03b34b738993 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -754,9 +754,7 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
                                 goto failed_sbi;
                         }
                         cno = sbi->s_snapshot_cno;
-                } else
-                        /* Read-only mount */
-                        sbi->s_snapshot_cno = cno;
+                }
         }
 
         err = nilfs_attach_checkpoint(sbi, cno);
@@ -825,7 +823,7 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
         struct the_nilfs *nilfs = sbi->s_nilfs;
         unsigned long old_sb_flags;
         struct nilfs_mount_options old_opts;
-        int err;
+        int was_snapshot, err;
 
         lock_kernel();
 
@@ -833,6 +831,7 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
         old_sb_flags = sb->s_flags;
         old_opts.mount_opt = sbi->s_mount_opt;
         old_opts.snapshot_cno = sbi->s_snapshot_cno;
+        was_snapshot = nilfs_test_opt(sbi, SNAPSHOT);
 
         if (!parse_options(data, sb)) {
                 err = -EINVAL;
@@ -840,20 +839,32 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
         }
         sb->s_flags = (sb->s_flags & ~MS_POSIXACL);
 
-        if ((*flags & MS_RDONLY) &&
-            sbi->s_snapshot_cno != old_opts.snapshot_cno) {
-                printk(KERN_WARNING "NILFS (device %s): couldn't "
-                       "remount to a different snapshot.\n",
-                       sb->s_id);
-                err = -EINVAL;
-                goto restore_opts;
+        err = -EINVAL;
+        if (was_snapshot) {
+                if (!(*flags & MS_RDONLY)) {
+                        printk(KERN_ERR "NILFS (device %s): cannot remount "
+                               "snapshot read/write.\n",
+                               sb->s_id);
+                        goto restore_opts;
+                } else if (sbi->s_snapshot_cno != old_opts.snapshot_cno) {
+                        printk(KERN_ERR "NILFS (device %s): cannot "
+                               "remount to a different snapshot.\n",
+                               sb->s_id);
+                        goto restore_opts;
+                }
+        } else {
+                if (nilfs_test_opt(sbi, SNAPSHOT)) {
+                        printk(KERN_ERR "NILFS (device %s): cannot change "
+                               "a regular mount to a snapshot.\n",
+                               sb->s_id);
+                        goto restore_opts;
+                }
         }
 
         if (!nilfs_valid_fs(nilfs)) {
                 printk(KERN_WARNING "NILFS (device %s): couldn't "
                        "remount because the filesystem is in an "
                        "incomplete recovery state.\n", sb->s_id);
-                err = -EINVAL;
                 goto restore_opts;
         }
 
@@ -864,9 +875,6 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
                 nilfs_detach_segment_constructor(sbi);
                 sb->s_flags |= MS_RDONLY;
 
-                sbi->s_snapshot_cno = nilfs_last_cno(nilfs);
-                /* nilfs_set_opt(sbi, SNAPSHOT); */
-
                 /*
                  * Remounting a valid RW partition RDONLY, so set
                  * the RDONLY flag and then mark the partition as valid again.
@@ -885,24 +893,7 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
                  * store the current valid flag.  (It may have been changed
                  * by fsck since we originally mounted the partition.)
                  */
-                if (nilfs->ns_current && nilfs->ns_current != sbi) {
-                        printk(KERN_WARNING "NILFS (device %s): couldn't "
-                               "remount because an RW-mount exists.\n",
-                               sb->s_id);
-                        err = -EBUSY;
-                        goto restore_opts;
-                }
-                if (sbi->s_snapshot_cno != nilfs_last_cno(nilfs)) {
-                        printk(KERN_WARNING "NILFS (device %s): couldn't "
-                               "remount because the current RO-mount is not "
-                               "the latest one.\n",
-                               sb->s_id);
-                        err = -EINVAL;
-                        goto restore_opts;
-                }
                 sb->s_flags &= ~MS_RDONLY;
-                nilfs_clear_opt(sbi, SNAPSHOT);
-                sbi->s_snapshot_cno = 0;
 
                 err = nilfs_attach_segment_constructor(sbi);
                 if (err)
@@ -911,8 +902,6 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
                 down_write(&nilfs->ns_sem);
                 nilfs_setup_super(sbi);
                 up_write(&nilfs->ns_sem);
-
-                nilfs->ns_current = sbi;
         }
  out:
         up_write(&nilfs->ns_super_sem);