reiserfs: ignore on disk s_bmap_nr value

Implement support for file systems larger than 8 TiB.

The reiserfs superblock contains a 16 bit value for counting the number of
bitmap blocks.  The rest of the disk format supports file systems up to 2^32
blocks, but the bitmap block limitation artificially limits this to 8 TiB with
a 4KiB block size.

Rather than trust the superblock's 16-bit bitmap block count, we calculate it
dynamically based on the number of blocks in the file system.  When an
incorrect value is observed in the superblock, it is zeroed out, ensuring that
older kernels will not be able to mount the file system.

Userspace support has already been implemented and shipped in reiserfsprogs
3.6.20.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index b82897ae090b..57adfe90d5ae 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -1725,6 +1725,21 @@ static int reiserfs_fill_super(struct super_block *s, void *data, int silent)
                 set_sb_umount_state(rs, REISERFS_ERROR_FS);
                 set_sb_fs_state(rs, 0);
 
+                /* Clear out s_bmap_nr if it would wrap. We can handle this
+                 * case, but older revisions can't. This will cause the
+                 * file system to fail mount on those older implementations,
+                 * avoiding corruption. -jeffm */
+                if (bmap_would_wrap(reiserfs_bmap_count(s)) &&
+                    sb_bmap_nr(rs) != 0) {
+                        reiserfs_warning(s, "super-2030: This file system "
+                                        "claims to use %u bitmap blocks in "
+                                        "its super block, but requires %u. "
+                                        "Clearing to zero.", sb_bmap_nr(rs),
+                                        reiserfs_bmap_count(s));
+
+                        set_sb_bmap_nr(rs, 0);
+                }
+
                 if (old_format_only(s)) {
                         /* filesystem of format 3.5 either with standard or non-standard
                            journal */