[PATCH 2/2] btrfs: document special case error codes for fs errors

[Josef Bacik <josef@toxicpanda.com>]

We've had some discussions about what to do in certain scenarios for
error codes, specifically -EUCLEAN and -EROFS.  Document these near the
error handling code so its clear what their intentions are.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/super.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 58f890f73650..688d1ab95b2b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -67,6 +67,21 @@ static struct file_system_type btrfs_root_fs_type;
 
 static int btrfs_remount(struct super_block *sb, int *flags, char *data);
 
+/*
+ * Generally the error codes correspond to their respective errors, but there's
+ * a few special cases.
+ *
+ * -EUCLEAN: Any sort of corruption that we encounter.  The tree-checker for
+ *  instance will return -EUCLEAN if any of the blocks are corrupted in a way
+ *  that is problematic.  We want to reserve -EUCLEAN for these sort of
+ *  corruptions.
+ *
+ * -EROFS: If we check BTRFS_FS_STATE_ERROR and fail out with a return error, we
+ *  need to use -EROFS for this case.  We will have no idea of the original
+ *  failure, that will have been reported at the time we tripped over the error.
+ *  Each subsequent error that doesn't have any context of the original error
+ *  should use -EROFS when handling BTRFS_FS_STATE_ERROR.
+ */
 const char * __attribute_const__ btrfs_decode_error(int errno)
 {
 	char *errstr = "unknown";
-- 
2.24.1