Re: [PATCH 2/2] libfuse: always send the subtype to the kernel when using fsconfig()

[Bernd Schubert <bernd@bsbernd.com>]

On 5/5/26 07:23, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Although it's possible to supply a filesystem subtype when calling
> fsopen(), it does not pass the stuff after the dot to the mount option
> parsing mechanism like the legacy mount() call does.  Therefore, it's
> necessary to pass the subtype explicitly via fsconfig() or else the
> subtype will be missing from the /proc/mounts output.
> 
> For example, fuse4fs with the old mount API produces this:
> 
> /dev/sda /mnt fuse.ext4 rw,nosuid,nodev,relatime,user_id=0,group_id=0 0 0
> 
> But with the new mount API, we only get:
> 
> /dev/sda /mnt fuse rw,nosuid,nodev,relatime,user_id=0,group_id=0 0 0
> 
> ...which breaks fstests, which requires the fsname to match the string
> that it passes to mount -t.  Update the comment in mount_service.c to
> match this requirement.
> 
> Fixes: 14cb7b93bb9688 ("Add support for the new linux mount API")
> Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> ---
>  lib/mount_fsmount.c  |   13 +++++++++++++
>  util/mount_service.c |    3 ++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> 
> diff --git a/lib/mount_fsmount.c b/lib/mount_fsmount.c
> index 615271b09758c3..5e13b34ccfc610 100644
> --- a/lib/mount_fsmount.c
> +++ b/lib/mount_fsmount.c
> @@ -359,6 +359,19 @@ int fuse_kern_fsmount(const char *mnt, unsigned long flags, int blkdev,
>  		goto out_free;
>  	}
>  
> +	/* Configure subtype */
> +	if (subtype) {
> +		res = fsconfig(fsfd, FSCONFIG_SET_STRING, "subtype",
> +			       subtype, 0);
> +		if (res) {
> +			err = -errno;
> +			log_fsconfig_kmsg(fsfd);
> +			fprintf(stderr, "fuse: fsconfig subtype failed: %s\n",
> +				strerror(-err));
> +			goto out_free;
> +		}
> +	}
> +
>  	/* Configure source */
>  	res = fsconfig(fsfd, FSCONFIG_SET_STRING, "source", source, 0);
>  	if (res == -1) {

Oh yes, that had slipped through. Going to apply this.

> diff --git a/util/mount_service.c b/util/mount_service.c
> index bc5940bc900dad..3fbabfdd69300d 100644
> --- a/util/mount_service.c
> +++ b/util/mount_service.c
> @@ -821,7 +821,8 @@ static void try_fsopen(struct mount_service *mo)
>  	/*
>  	 * As of Linux 7.0 you can pass subtypes to fsopen, but the manpage for
>  	 * fsopen only says that you can pass any value of the second column of
> -	 * /proc/filesystems into fsopen.
> +	 * /proc/filesystems into fsopen.  You must still call fsconfig() for
> +	 * the subtype separately, however.
>  	 */
>  	mo->fsopenfd = fsopen(fsname(mo), FSOPEN_CLOEXEC);
>  }
> 

Can we integrate that into you series separately, as it is not merged yet?


Thanks,
Bernd