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

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Date:   Tue, 18 Jan 2022 13:54:16 +0000
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
Cc:     Jeff Layton <jlayton@...nel.org>, Jeff Layton <jlayton@...nel.org>,
        dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <smfrench@...il.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        JeffleXu <jefflexu@...ux.alibaba.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 06/11] cachefiles: Explain checks in a comment

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

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