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

Bug-Debian: https://bugs.debian.org/863290
Origin: https://bugs.debian.org/863290#5
Forwarded: https://lore.kernel.org/linux-btrfs/4105665.mVaztBssJx@bagend/

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]
[2023-01-10: still accurate according to btrfs-progs own manpage:
https://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git/commit/?id=922797e15590b836e377d6dc47b828356cafc2a9]
[2024-03-17: still accurate; manpage is now in Documentation/btrfs-man5.rst
implementation went from disk-io.c to super.c; forwarded the issue]

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

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 6119a06b0569386926809b6227380a66664a6c14..96737d03f99b2438f43d2d82be5228bd56fb9d21 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -768,6 +768,18 @@ static void set_device_specific_options(struct btrfs_fs_info *fs_info)
            !fs_info->fs_devices->rotating)
                btrfs_set_opt(fs_info->mount_opt, SSD);
 
+       /*
+        * Warn about RAID5/6 being experimental at mount time
+        */
+       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_AUX, LOCKDEP_STILL_OK);
+       }
+
        /*
         * For devices supporting discard turn on discard=async automatically,
         * unless it's already set or disabled. This could be turned off by