Re: [PATCH] Fuse: Add backing file support for uring_cmd

[Bernd Schubert <bernd@bsbernd.com>]

On 2/21/25 16:36, Moinak Bhattacharyya wrote:
> Sorry about that. Correctly-formatted patch follows. Should I send out a
> V2 instead?
> 
> Add support for opening and closing backing files in the fuse_uring_cmd
> callback. Store backing_map (for open) and backing_id (for close) in the
> uring_cmd data.
> ---
>  fs/fuse/dev_uring.c       | 50 +++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/fuse.h |  6 +++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index ebd2931b4f2a..df73d9d7e686 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -1033,6 +1033,40 @@ fuse_uring_create_ring_ent(struct io_uring_cmd *cmd,
>      return ent;
>  }
> 
> +/*
> + * Register new backing file for passthrough, getting backing map from
> URING_CMD data
> + */
> +static int fuse_uring_backing_open(struct io_uring_cmd *cmd,
> +    unsigned int issue_flags, struct fuse_conn *fc)
> +{
> +    const struct fuse_backing_map *map = io_uring_sqe_cmd(cmd->sqe);
> +    int ret = fuse_backing_open(fc, map);

Do you have the libfuse part somewhere? I need to hurry up to split and
clean up my uring branch. Not promised, but maybe this weekend. 
What we need to be careful here about is that in my current 'uring'
libfuse always expects to get a CQE - here you introduce a 2nd user
for CQEs - it needs credit management.


> +
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    io_uring_cmd_done(cmd, ret, 0, issue_flags);
> +    return 0;
> +}
> +
> +/*
> + * Remove file from passthrough tracking, getting backing_id from
> URING_CMD data
> + */
> +static int fuse_uring_backing_close(struct io_uring_cmd *cmd,
> +    unsigned int issue_flags, struct fuse_conn *fc)
> +{
> +    const int *backing_id = io_uring_sqe_cmd(cmd->sqe);
> +    int ret = fuse_backing_close(fc, *backing_id);
> +
> +    if (ret < 0) {
> +        return ret;
> +    }


Both functions don't have the check for 

	if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
		return -EOPNOTSUPP;

but their ioctl counter parts have that.


Thanks,
Bernd