Re: [PATCH V8 0/8] io_uring: support sqe group and leased group kbuf

[Ming Lei <ming.lei@redhat.com>]

On Thu, Oct 31, 2024 at 09:07:18AM -0600, Jens Axboe wrote:
> Another option is that we fully stick with the per-group buffer concept,
> which could also work just fine with io_rsrc_node. If we stick with the
> OP_GROUP_START thing, then that op could setup group_buf thing that is
> local to that group. This is where an instantiated buffer would appear
> too, keeping it strictly local to that group. That avoids needing any
> kind of ring state for this, and the group_buf would be propagated from
> the group leader to the members. The group_buf lives until all members
> of the group are dead, at which point it's released. I forget if your
> grouping implementation mandated the same scheme I originally had, where
> the group leader completes last? If it does, then it's a natural thing

Yes, the group leader's CQE is posted after all members' CQE are posted,
and the leader request is freed after all member request is freed.

> to have the group_buf live for the duration of the group leader, and it
> can just be normal per-io_kiocb data at that point, nothing special
> needed there.

That is basically what GROUP_KBUF is written, just not using io_rsrc_node.

> 
> As with the previous scheme, each request using one of these
> IORING_RSRC_KBUFFER nodes just assigns it like it would any other fixed
> resource node, and the normal completion path puts it.

Here the thing is simpler, all member can just use leader's io_rsrc_node,
leader's rsrc_node reference is grabbed & leased to member when adding member
to group, and released by the normal io_req_put_rsrc_nodes(). 

Thanks,
Ming