[PATCH AUTOSEL 5.11 01/44] virtiofs: Fail dax mount if device does not support it

From: Vivek Goyal <vgoyal@redhat.com>

[ Upstream commit 3f9b9efd82a84f27e95d0414f852caf1fa839e83 ]

Right now "mount -t virtiofs -o dax myfs /mnt/virtiofs" succeeds even
if filesystem deivce does not have a cache window and hence DAX can't
be supported.

This gives a false sense to user that they are using DAX with virtiofs
but fact of the matter is that they are not.

Fix this by returning error if dax can't be supported and user has asked
for it.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Miklos Szeredi <redacted>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/fuse/virtio_fs.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 8868ac31a3c0..4ee6f734ba83 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c

@@ -1324,8 +1324,15 @@ static int virtio_fs_fill_super(struct super_block *sb, struct fs_context *fsc)
 
 	/* virtiofs allocates and installs its own fuse devices */
 	ctx->fudptr = NULL;
-	if (ctx->dax)
+	if (ctx->dax) {
+		if (!fs->dax_dev) {
+			err = -EINVAL;
+			pr_err("virtio-fs: dax can't be enabled as filesystem"
+			       " device does not support it.\n");
+			goto err_free_fuse_devs;
+		}
 		ctx->dax_dev = fs->dax_dev;
+	}
 	err = fuse_fill_super_common(sb, ctx);
 	if (err < 0)
 		goto err_free_fuse_devs;

-- 
2.30.1

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