Re: [PATCH] io_uring/rsrc: replace reg buffer bit field with flags

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

On Mon, Feb 9, 2026 at 6:33 AM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> I'll need a flag in the registered buffer struct for dmabuf work, and
> it'll be more convenient to have a flags field rather than bit fields,
> especially for io_mapped_ubuf initialisation.
>
> We might want to add more flags in the future as well. For example, it
> might be useful for debugging and potentially optimisations to split out
> a flag indicating the shape of the buffer to gate iov_iter_advance()
> walks vs bit/mask arithmetics. It can also be combined with the
> direction mask field.
>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  io_uring/rsrc.c | 12 ++++++------
>  io_uring/rsrc.h |  6 +++++-
>  io_uring/rw.c   |  3 ++-
>  3 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index 95ce553fff8d..05f00bdb02d7 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -828,7 +828,7 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
>         imu->folio_shift = PAGE_SHIFT;
>         imu->release = io_release_ubuf;
>         imu->priv = imu;
> -       imu->is_kbuf = false;
> +       imu->flags = 0;
>         imu->dir = IO_IMU_DEST | IO_IMU_SOURCE;
>         if (coalesced)
>                 imu->folio_shift = data.folio_shift;
> @@ -985,7 +985,7 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq,
>         refcount_set(&imu->refs, 1);
>         imu->release = release;
>         imu->priv = rq;
> -       imu->is_kbuf = true;
> +       imu->flags = IO_REGBUF_F_KBUF;
>         imu->dir = 1 << rq_data_dir(rq);
>
>         rq_for_each_bvec(bv, rq, rq_iter)
> @@ -1020,7 +1020,7 @@ int io_buffer_unregister_bvec(struct io_uring_cmd *cmd, unsigned int index,
>                 ret = -EINVAL;
>                 goto unlock;
>         }
> -       if (!node->buf->is_kbuf) {
> +       if (!(node->buf->flags & IO_REGBUF_F_KBUF)) {
>                 ret = -EBUSY;
>                 goto unlock;
>         }
> @@ -1076,7 +1076,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
>
>         offset = buf_addr - imu->ubuf;
>
> -       if (imu->is_kbuf)
> +       if (imu->flags & IO_REGBUF_F_KBUF)
>                 return io_import_kbuf(ddir, iter, imu, len, offset);
>
>         /*
> @@ -1496,7 +1496,7 @@ int io_import_reg_vec(int ddir, struct iov_iter *iter,
>         iovec_off = vec->nr - nr_iovs;
>         iov = vec->iovec + iovec_off;
>
> -       if (imu->is_kbuf) {
> +       if (imu->flags & IO_REGBUF_F_KBUF) {
>                 int ret = io_kern_bvec_size(iov, nr_iovs, imu, &nr_segs);
>
>                 if (unlikely(ret))
> @@ -1534,7 +1534,7 @@ int io_import_reg_vec(int ddir, struct iov_iter *iter,
>                 req->flags |= REQ_F_NEED_CLEANUP;
>         }
>
> -       if (imu->is_kbuf)
> +       if (imu->flags & IO_REGBUF_F_KBUF)
>                 return io_vec_fill_kern_bvec(ddir, iter, imu, iov, nr_iovs, vec);
>
>         return io_vec_fill_bvec(ddir, iter, imu, iov, nr_iovs, vec);
> diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
> index 4a5db2ad1af2..cff0f8834c35 100644
> --- a/io_uring/rsrc.h
> +++ b/io_uring/rsrc.h
> @@ -28,6 +28,10 @@ enum {
>         IO_IMU_SOURCE   = 1 << ITER_SOURCE,
>  };
>
> +enum {
> +       IO_REGBUF_F_KBUF                = 1,

1 << 0 if this is intended to be extended with more flag bits in the future?

Best,
Caleb

> +};
> +
>  struct io_mapped_ubuf {
>         u64             ubuf;
>         unsigned int    len;
> @@ -37,7 +41,7 @@ struct io_mapped_ubuf {
>         unsigned long   acct_pages;
>         void            (*release)(void *);
>         void            *priv;
> -       bool            is_kbuf;
> +       u8              flags;
>         u8              dir;
>         struct bio_vec  bvec[] __counted_by(nr_bvecs);
>  };
> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index d10386f56d49..b3971171c342 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -702,7 +702,8 @@ static ssize_t loop_rw_iter(int ddir, struct io_rw *rw, struct iov_iter *iter)
>         if ((kiocb->ki_flags & IOCB_NOWAIT) &&
>             !(kiocb->ki_filp->f_flags & O_NONBLOCK))
>                 return -EAGAIN;
> -       if ((req->flags & REQ_F_BUF_NODE) && req->buf_node->buf->is_kbuf)
> +       if ((req->flags & REQ_F_BUF_NODE) &&
> +            (req->buf_node->buf->flags & IO_REGBUF_F_KBUF))
>                 return -EFAULT;
>
>         ppos = io_kiocb_ppos(kiocb);
> --
> 2.52.0
>
>