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

[Bernd Schubert <bernd@bsbernd.com>]

On 2/21/25 17:14, Bernd Schubert wrote:
> 
> 
> 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.
> 

In order to avoid code dup, maybe that check could be moved
into fuse_backing_open() / fuse_backing_close() as preparation
patch? Amir?

Thanks,
Bernd