[PATCH 06/11] cachefiles: Explain checks in a comment

[David Howells]

Add a comment to explain the checks that cachefiles is making of the
backing filesystem[1].

Suggested-by: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
Link: https://lore.kernel.org/r/568749bd7cc02908ecf6f3d6a611b6f9cf5c4afd.camel@xxxxxxxxxx/ [1]
---

 fs/cachefiles/cache.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/cachefiles/cache.c b/fs/cachefiles/cache.c
index 1e9c71666c6a..2b2879c5d1d2 100644
--- a/fs/cachefiles/cache.c
+++ b/fs/cachefiles/cache.c
@@ -49,7 +49,13 @@ int cachefiles_add_cache(struct cachefiles_cache *cache)
 		goto error_unsupported;
 	}
 
-	/* check parameters */
+	/* Check features of the backing filesystem:
+	 * - Directories must support looking up and directory creation
+	 * - We use xattrs to store metadata
+	 * - We need to be able to query the amount of space available
+	 * - We want to be able to sync the filesystem when stopping the cache
+	 * - We use DIO to/from pages, so the blocksize mustn't be too big.
+	 */
 	ret = -EOPNOTSUPP;
 	if (d_is_negative(root) ||
 	    !d_backing_inode(root)->i_op->lookup ||