Re: [PATCH v1 23/30] io_uring/rsrc: split io_buffer_register_request() logic

[Caleb Sander Mateos <csander@purestorage.com>]

On Tue, Dec 2, 2025 at 4:37 PM Joanne Koong <joannelkoong@gmail.com> wrote:
>
> Split the main initialization logic in io_buffer_register_request() into
> a helper function.
>
> This is a preparatory patch for supporting kernel-populated buffers in
> fuse io-uring, which will be reusing this logic.
>
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> ---
>  io_uring/rsrc.c | 80 +++++++++++++++++++++++++++++--------------------
>  1 file changed, 48 insertions(+), 32 deletions(-)
>
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index 59cafe63d187..18abba6f6b86 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -941,63 +941,79 @@ int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
>         return ret;
>  }
>
> -int io_buffer_register_request(struct io_ring_ctx *ctx, struct request *rq,
> -                              void (*release)(void *), unsigned int index,
> -                              unsigned int issue_flags)
> +static int io_buffer_init(struct io_ring_ctx *ctx, unsigned int nr_bvecs,

Consider adding "kernel" somewhere in the name to distinguish this
from the userspace registered buffer initialization

> +                         unsigned int total_bytes, u8 dir,
> +                         void (*release)(void *), void *priv,
> +                         unsigned int index)
>  {
>         struct io_rsrc_data *data = &ctx->buf_table;
> -       struct req_iterator rq_iter;
>         struct io_mapped_ubuf *imu;
>         struct io_rsrc_node *node;
> -       struct bio_vec bv;
> -       unsigned int nr_bvecs = 0;
> -       int ret = 0;
>
> -       io_ring_submit_lock(ctx, issue_flags);
> -       if (index >= data->nr) {
> -               ret = -EINVAL;
> -               goto unlock;
> -       }
> +       if (index >= data->nr)
> +               return -EINVAL;
>         index = array_index_nospec(index, data->nr);
>
> -       if (data->nodes[index]) {
> -               ret = -EBUSY;
> -               goto unlock;
> -       }
> +       if (data->nodes[index])
> +               return -EBUSY;
>
>         node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
> -       if (!node) {
> -               ret = -ENOMEM;
> -               goto unlock;
> -       }
> +       if (!node)
> +               return -ENOMEM;
>
> -       /*
> -        * blk_rq_nr_phys_segments() may overestimate the number of bvecs
> -        * but avoids needing to iterate over the bvecs
> -        */
> -       imu = io_alloc_imu(ctx, blk_rq_nr_phys_segments(rq));
> +       imu = io_alloc_imu(ctx, nr_bvecs);
>         if (!imu) {
>                 kfree(node);
> -               ret = -ENOMEM;
> -               goto unlock;
> +               return -ENOMEM;
>         }
>
>         imu->ubuf = 0;
> -       imu->len = blk_rq_bytes(rq);
> +       imu->len = total_bytes;
>         imu->acct_pages = 0;
>         imu->folio_shift = PAGE_SHIFT;
> +       imu->nr_bvecs = nr_bvecs;
>         refcount_set(&imu->refs, 1);
>         imu->release = release;
> -       imu->priv = rq;
> +       imu->priv = priv;
>         imu->is_kbuf = true;
> -       imu->dir = 1 << rq_data_dir(rq);
> +       imu->dir = 1 << dir;
> +
> +       node->buf = imu;
> +       data->nodes[index] = node;
> +
> +       return 0;
> +}
> +
> +int io_buffer_register_request(struct io_ring_ctx *ctx, struct request *rq,
> +                              void (*release)(void *), unsigned int index,
> +                              unsigned int issue_flags)
> +{
> +       struct req_iterator rq_iter;
> +       struct io_mapped_ubuf *imu;
> +       struct bio_vec bv;
> +       unsigned int nr_bvecs;
> +       unsigned int total_bytes;
> +       int ret;
> +
> +       io_ring_submit_lock(ctx, issue_flags);
> +
> +       /*
> +        * blk_rq_nr_phys_segments() may overestimate the number of bvecs
> +        * but avoids needing to iterate over the bvecs
> +        */
> +       nr_bvecs = blk_rq_nr_phys_segments(rq);
> +       total_bytes = blk_rq_bytes(rq);

These could be initialized before io_ring_submit_lock()

> +       ret = io_buffer_init(ctx, nr_bvecs, total_bytes, rq_data_dir(rq), release, rq,
> +                            index);
> +       if (ret)
> +               goto unlock;
>
> +       imu = ctx->buf_table.nodes[index]->buf;

It would be nice to avoid all these additional dereferences. Could
io_buffer_init() return the struct io_mapped_ubuf *, using ERR_PTR()
to return any error code?

Best,
Caleb

> +       nr_bvecs = 0;
>         rq_for_each_bvec(bv, rq, rq_iter)
>                 imu->bvec[nr_bvecs++] = bv;
>         imu->nr_bvecs = nr_bvecs;
>
> -       node->buf = imu;
> -       data->nodes[index] = node;
>  unlock:
>         io_ring_submit_unlock(ctx, issue_flags);
>         return ret;
> --
> 2.47.3
>