[PATCH 2/2] shmem: allow reporting fanotify events with file handles on tmpfs

From: Amir Goldstein <amir73il@gmail.com>
To: Jan Kara <jack@suse.cz>
Cc: Hugh Dickins <hughd@google.com>, Theodore Tso <tytso@mit.edu>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	linux-fsdevel@vger.kernel.org
Subject: [PATCH 2/2] shmem: allow reporting fanotify events with file handles on tmpfs
Date: Mon, 22 Mar 2021 19:39:44 +0200	[thread overview]
Message-ID: <20210322173944.449469-3-amir73il@gmail.com> (raw)
In-Reply-To: <20210322173944.449469-1-amir73il@gmail.com>

Since kernel v5.1, fanotify_init(2) supports the flag FAN_REPORT_FID
for identifying objects using file handle and fsid in events.

fanotify_mark(2) fails with -ENODEV when trying to set a mark on
filesystems that report null f_fsid in stasfs(2).

Use the digest of uuid as f_fsid for tmpfs to uniquely identify tmpfs
objects as best as possible and allow setting an fanotify mark that
reports events with file handles on tmpfs.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 mm/shmem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index b2db4ed0fbc7..162d8f8993bb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2846,6 +2846,9 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
 		buf->f_ffree = sbinfo->free_inodes;
 	}
 	/* else leave those fields 0 like simple_statfs */
+
+	buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
+
 	return 0;
 }
 
-- 
2.25.1

