btrfs: warn about RAID5/6 being experimental at mount time

Too many people come complaining about losing their data -- and indeed,
there's no warning outside a wiki and the mailing list tribal knowledge.
Message severity chosen for consistency with XFS -- "alert" makes dmesg
produce nice red background which should get the point across.

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
[bwh: Also add_taint() so this is flagged in bug reports]

Gbp-Pq: Topic debian
Gbp-Pq: Name btrfs-warn-about-raid5-6-being-experimental-at-mount.patch

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1cd325765aaa8cd49be5100250c00e69561a0126..44981fa948a670723937110da0321b0e587908e3 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3098,6 +3098,15 @@ retry_root_backup:
                btrfs_set_opt(fs_info->mount_opt, SSD);
        }
 
+       if ((fs_info->avail_data_alloc_bits |
+            fs_info->avail_metadata_alloc_bits |
+            fs_info->avail_system_alloc_bits) &
+           BTRFS_BLOCK_GROUP_RAID56_MASK) {
+               btrfs_alert(fs_info,
+               "btrfs RAID5/6 is EXPERIMENTAL and has known data-loss bugs");
+               add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+       }
+
        /*
         * Mount does not set all options immediately, we can do it now and do
         * not have to wait for transaction commit