Re: [PATCH v5 13/13] io_uring: support buffer registration sharing

[Pavel Begunkov <asml.silence@gmail.com>]

On 12/01/2021 21:33, Bijan Mottahedeh wrote:
> Implement buffer sharing among multiple rings.
> 
> A ring shares its (future) buffer registrations at setup time with
> IORING_SETUP_SHARE_BUF. A ring attaches to another ring's buffer
> registration at setup time with IORING_SETUP_ATTACH_BUF, after
> authenticating with the buffer registration owner's fd. Any updates to
> the owner's buffer registrations become immediately available to the
> attached rings.

I'm thinking it through, but there is an easy to miss potential bug,
so see below a comment to not forget.

> 
> Signed-off-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
> 
> Conflicts:
> 	fs/io_uring.c
> ---
>  fs/io_uring.c                 | 85 +++++++++++++++++++++++++++++++++++++++++--
>  include/uapi/linux/io_uring.h |  2 +
>  2 files changed, 83 insertions(+), 4 deletions(-)
[...]
> +
> +static int io_init_buf_data(struct io_ring_ctx *ctx, struct io_uring_params *p)
> +{
> +	if ((p->flags & (IORING_SETUP_SHARE_BUF | IORING_SETUP_ATTACH_BUF)) ==
> +	    (IORING_SETUP_SHARE_BUF | IORING_SETUP_ATTACH_BUF))
> +		return -EINVAL;
> +
> +	if (p->flags & IORING_SETUP_SHARE_BUF) {
> +		struct fixed_rsrc_data *buf_data;
> +
> +		buf_data = alloc_fixed_rsrc_data(ctx);
> +		if (IS_ERR(buf_data))
> +			return PTR_ERR(buf_data);

Because of sneaked through 5.11 fixes it'll be

if (!buf_data) return -ENOMEM

> +
> +		ctx->buf_data = buf_data;
> +		return 0;
> +	}
> +
> +	if (p->flags & IORING_SETUP_ATTACH_BUF)
> +		return io_attach_buf_data(ctx, p);
> +
> +	return 0;
> +}
> +


-- 
Pavel Begunkov