Re: [PATCH v2 5.15] io_uring: auto-removal for direct open/accept

[Jens Axboe <axboe@kernel.dk>]

On 9/14/21 9:12 AM, Pavel Begunkov wrote:
> It might be inconvenient that direct open/accept deviates from the
> update semantics and fails if the slot is taken instead of removing a
> file sitting there. Implement this auto-removal.
> 
> Note that removal might need to allocate and so may fail. However, if an
> empty slot is specified, it's guaraneed to not fail on the fd
> installation side for valid userspace programs. It's needed for users
> who can't tolerate such failures, e.g. accept where the other end
> never retries.
> 
> Suggested-by: Franz-B. Tuneke <franz-bernhard.tuneke@tu-dortmund.de>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> 
> v2: simplify io_rsrc_node_switch_start() handling
> 
>  fs/io_uring.c | 52 +++++++++++++++++++++++++++++++++------------------
>  1 file changed, 34 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index a864a94364c6..58c0cbfdd128 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -8287,11 +8287,27 @@ static int io_sqe_file_register(struct io_ring_ctx *ctx, struct file *file,
>  #endif
>  }
>  
> +static int io_queue_rsrc_removal(struct io_rsrc_data *data, unsigned idx,
> +				 struct io_rsrc_node *node, void *rsrc)
> +{
> +	struct io_rsrc_put *prsrc;
> +
> +	prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
> +	if (!prsrc)
> +		return -ENOMEM;
> +
> +	prsrc->tag = *io_get_tag_slot(data, idx);
> +	prsrc->rsrc = rsrc;
> +	list_add(&prsrc->list, &node->rsrc_list);
> +	return 0;
> +}

I know this code is just being moved, but I tend to like making the
expected/fast path inline:

prsrc = kzalloc(sizeof(*prsrc), GFP_KERNEL);
if (prsrc) {
	prsrc->tag = *io_get_tag_slot(data, idx);
	prsrc->rsrc = rsrc;
	list_add(&prsrc->list, &node->rsrc_list);
	return 0;
}
return -ENOMEM;

-- 
Jens Axboe