btrfs: warn about RAID5/6 being experimental at mount time (Closes: #863290)

debian/changelog

@@ -414,6 +414,7 @@ linux (4.9.30-1) UNRELEASED; urgency=medium
   * debian/control: Fix compiler build-dependencies for cross-building
     (Closes: #863907)
   * Add Debian package version to "hung task" log messages
+  * btrfs: warn about RAID5/6 being experimental at mount time (Closes: #863290)
 
   [ Salvatore Bonaccorso ]
   * tracing: Use strlcpy() instead of strcpy() in __trace_find_cmdline()

debian/patches/debian/btrfs-warn-about-raid5-6-being-experimental-at-mount.patch

@@ -0,0 +1,35 @@
+From: Adam Borowski <kilobyte@angband.pl>
+Date: Tue, 28 Mar 2017 16:55:05 +0200
+Subject: 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]
+---
+ fs/btrfs/disk-io.c | 8 ++++++++
+ 1 file changed, 8 insertions(+)
+
+--- 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

debian/patches/series

@@ -46,6 +46,7 @@ debian/fjes-disable-autoload.patch
 
 # Taint if dangerous features are used
 debian/fanotify-taint-on-use-of-fanotify_access_permissions.patch
+debian/btrfs-warn-about-raid5-6-being-experimental-at-mount.patch
 
 # Reduce noise for bug #852324
 debian/amd64-don-t-warn-about-expected-w+x-pages-on-xen.patch