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

Bug-Debian: https://bugs.debian.org/863290
Origin: https://bugs.debian.org/863290#5

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]

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 681594df7334f4b95a18688d45e40c80cea7cf1c..9729a750a097ad63e27456e16e15dd829cc1c898 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3444,6 +3444,15 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
                btrfs_set_and_info(fs_info, SSD, "enabling ssd optimizations");
        }
 
+       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