Re: [PATCH 07/19] Add FUSE_MOUNT_FALLBACK_NEEDED define for -2 mount errors

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Mar 23, 2026 at 06:45:02PM +0100, Bernd Schubert wrote:
> From: Bernd Schubert <bschubert@ddn.com>
> 
> Magic numbers in the code are not good - we better use a define.
> 
> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> ---
>  lib/fuse_i.h | 3 +++
>  lib/mount.c  | 6 +++---
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/fuse_i.h b/lib/fuse_i.h
> index 9e3c5dc5021e210a2778e975a37ab609af324010..b4c1d3eef41010287f6c9555ec0b2442d904d192 100644
> --- a/lib/fuse_i.h
> +++ b/lib/fuse_i.h
> @@ -217,6 +217,9 @@ struct fuse_chan *fuse_chan_get(struct fuse_chan *ch);
>   */
>  void fuse_chan_put(struct fuse_chan *ch);
>  
> +/* Special return value for mount functions to indicate fallback to fusermount3 is needed */
> +#define FUSE_MOUNT_FALLBACK_NEEDED -2

...and you might want to put that in parentheses to avoid weird
interactions elsewhere.  Or maybe just make fuse_kern_do_mount return an
enum so that callers have to handle FUSE_MOUNT_{OK,FAIL,FALLBACK} and
can do so via switch statements?

--D

> +
>  struct mount_opts *parse_mount_opts(struct fuse_args *args);
>  void destroy_mount_opts(struct mount_opts *mo);
>  void fuse_mount_version(void);
> diff --git a/lib/mount.c b/lib/mount.c
> index 6e404451cc9edc8e35434cc31f25612cfc4edca1..dec9d52274c13536648cacef959789f472c5682c 100644
> --- a/lib/mount.c
> +++ b/lib/mount.c
> @@ -563,7 +563,7 @@ out_close:
>   * @mo: mount options
>   * @mnt_opts: mount options to pass to the kernel
>   *
> - * Returns: 0 on success, -1 on failure, -2 if fusermount should be used
> + * Returns: 0 on success, -1 on failure, FUSE_MOUNT_FALLBACK_NEEDED if fusermount should be used
>   */
>  static int fuse_kern_do_mount(const char *mnt, struct mount_opts *mo,
>  				  const char *mnt_opts)
> @@ -611,7 +611,7 @@ static int fuse_kern_do_mount(const char *mnt, struct mount_opts *mo,
>  		 * case try falling back to fusermount3
>  		 */
>  		if (errno == EPERM) {
> -			res = -2;
> +			res = FUSE_MOUNT_FALLBACK_NEEDED;
>  		} else {
>  			int errno_save = errno;
>  			if (mo->blkdev && errno == ENODEV &&
> @@ -749,7 +749,7 @@ int fuse_kern_mount(const char *mountpoint, struct mount_opts *mo)
>  			umount2(mountpoint, MNT_DETACH); /* lazy umount */
>  			res = -1;
>  		}
> -	} else if (res == -2) {
> +	} else if (res == FUSE_MOUNT_FALLBACK_NEEDED) {
>  		if (mo->fusermount_opts &&
>  		    fuse_opt_add_opt(&mnt_opts, mo->fusermount_opts) == -1)
>  			goto out;
> 
> -- 
> 2.43.0
> 
>