Re: [PATCH v1 22/30] io_uring/rsrc: refactor io_buffer_register_bvec()/io_buffer_unregister_bvec()

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

On Tue, Dec 2, 2025 at 4:37 PM Joanne Koong <joannelkoong@gmail.com> wrote:
>
> Changes:
> - Rename io_buffer_register_bvec() to io_buffer_register_request()
> - Rename io_buffer_unregister_bvec() to io_buffer_unregister()
> - Add cmd wrappers for io_buffer_register_request() and
>   io_buffer_unregister() for ublk to use

I agree these names seem clearer.

>
> This is in preparation for supporting kernel-populated buffers in fuse
> io-uring, which will need to register bvecs directly (not through a
> block-based request) and will need to do unregistration through an
> io_ring_ctx directly.
>
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> ---
>  Documentation/block/ublk.rst | 15 ++++++++-------
>  drivers/block/ublk_drv.c     | 20 +++++++++++---------
>  include/linux/io_uring/cmd.h | 13 ++++++++-----
>  io_uring/rsrc.c              | 14 +++++---------
>  io_uring/rsrc.h              |  7 +++++++
>  io_uring/uring_cmd.c         | 21 +++++++++++++++++++++
>  6 files changed, 60 insertions(+), 30 deletions(-)
>
> diff --git a/Documentation/block/ublk.rst b/Documentation/block/ublk.rst
> index 8c4030bcabb6..1546477e768b 100644
> --- a/Documentation/block/ublk.rst
> +++ b/Documentation/block/ublk.rst
> @@ -326,16 +326,17 @@ Zero copy
>  ---------
>
>  ublk zero copy relies on io_uring's fixed kernel buffer, which provides
> -two APIs: `io_buffer_register_bvec()` and `io_buffer_unregister_bvec`.
> +two APIs: `io_uring_cmd_buffer_register_request()` and
> +`io_uring_cmd_buffer_unregister`.
>
>  ublk adds IO command of `UBLK_IO_REGISTER_IO_BUF` to call
> -`io_buffer_register_bvec()` for ublk server to register client request
> -buffer into io_uring buffer table, then ublk server can submit io_uring
> +`io_uring_cmd_buffer_register_request()` for ublk server to register client
> +request buffer into io_uring buffer table, then ublk server can submit io_uring
>  IOs with the registered buffer index. IO command of `UBLK_IO_UNREGISTER_IO_BUF`
> -calls `io_buffer_unregister_bvec()` to unregister the buffer, which is
> -guaranteed to be live between calling `io_buffer_register_bvec()` and
> -`io_buffer_unregister_bvec()`. Any io_uring operation which supports this
> -kind of kernel buffer will grab one reference of the buffer until the
> +calls `io_uring_cmd_buffer_unregister()` to unregister the buffer, which is
> +guaranteed to be live between calling `io_uring_cmd_buffer_register_request()`
> +and `io_uring_cmd_buffer_unregister()`. Any io_uring operation which supports
> +this kind of kernel buffer will grab one reference of the buffer until the
>  operation is completed.
>
>  ublk server implementing zero copy or user copy has to be CAP_SYS_ADMIN and
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index e0c601128efa..d671d08533c9 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -1246,8 +1246,9 @@ static bool ublk_auto_buf_reg(const struct ublk_queue *ubq, struct request *req,
>  {
>         int ret;
>
> -       ret = io_buffer_register_bvec(io->cmd, req, ublk_io_release,
> -                                     io->buf.index, issue_flags);
> +       ret = io_uring_cmd_buffer_register_request(io->cmd, req,
> +                                                  ublk_io_release,
> +                                                  io->buf.index, issue_flags);
>         if (ret) {
>                 if (io->buf.flags & UBLK_AUTO_BUF_REG_FALLBACK) {
>                         ublk_auto_buf_reg_fallback(ubq, io);
> @@ -2204,8 +2205,8 @@ static int ublk_register_io_buf(struct io_uring_cmd *cmd,
>         if (!req)
>                 return -EINVAL;
>
> -       ret = io_buffer_register_bvec(cmd, req, ublk_io_release, index,
> -                                     issue_flags);
> +       ret = io_uring_cmd_buffer_register_request(cmd, req, ublk_io_release,
> +                                                  index, issue_flags);
>         if (ret) {
>                 ublk_put_req_ref(io, req);
>                 return ret;
> @@ -2236,8 +2237,8 @@ ublk_daemon_register_io_buf(struct io_uring_cmd *cmd,
>         if (!ublk_dev_support_zero_copy(ub) || !ublk_rq_has_data(req))
>                 return -EINVAL;
>
> -       ret = io_buffer_register_bvec(cmd, req, ublk_io_release, index,
> -                                     issue_flags);
> +       ret = io_uring_cmd_buffer_register_request(cmd, req, ublk_io_release,
> +                                                  index, issue_flags);
>         if (ret)
>                 return ret;
>
> @@ -2252,7 +2253,7 @@ static int ublk_unregister_io_buf(struct io_uring_cmd *cmd,
>         if (!(ub->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY))
>                 return -EINVAL;
>
> -       return io_buffer_unregister_bvec(cmd, index, issue_flags);
> +       return io_uring_cmd_buffer_unregister(cmd, index, issue_flags);
>  }
>
>  static int ublk_check_fetch_buf(const struct ublk_device *ub, __u64 buf_addr)
> @@ -2386,7 +2387,7 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
>                 goto out;
>
>         /*
> -        * io_buffer_unregister_bvec() doesn't access the ubq or io,
> +        * io_uring_cmd_buffer_unregister() doesn't access the ubq or io,
>          * so no need to validate the q_id, tag, or task
>          */
>         if (_IOC_NR(cmd_op) == UBLK_IO_UNREGISTER_IO_BUF)
> @@ -2456,7 +2457,8 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd,
>
>                 /* can't touch 'ublk_io' any more */
>                 if (buf_idx != UBLK_INVALID_BUF_IDX)
> -                       io_buffer_unregister_bvec(cmd, buf_idx, issue_flags);
> +                       io_uring_cmd_buffer_unregister(cmd, buf_idx,
> +                                                      issue_flags);
>                 if (req_op(req) == REQ_OP_ZONE_APPEND)
>                         req->__sector = addr;
>                 if (compl)
> diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
> index 795b846d1e11..fc956f8f7ed2 100644
> --- a/include/linux/io_uring/cmd.h
> +++ b/include/linux/io_uring/cmd.h
> @@ -185,10 +185,13 @@ static inline void io_uring_cmd_done32(struct io_uring_cmd *ioucmd, s32 ret,
>         return __io_uring_cmd_done(ioucmd, ret, res2, issue_flags, true);
>  }
>
> -int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq,
> -                           void (*release)(void *), unsigned int index,
> -                           unsigned int issue_flags);
> -int io_buffer_unregister_bvec(struct io_uring_cmd *cmd, unsigned int index,
> -                             unsigned int issue_flags);
> +int io_uring_cmd_buffer_register_request(struct io_uring_cmd *cmd,
> +                                        struct request *rq,
> +                                        void (*release)(void *),
> +                                        unsigned int index,
> +                                        unsigned int issue_flags);
> +
> +int io_uring_cmd_buffer_unregister(struct io_uring_cmd *cmd, unsigned int index,
> +                                  unsigned int issue_flags);
>
>  #endif /* _LINUX_IO_URING_CMD_H */
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index b6dd62118311..59cafe63d187 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -941,11 +941,10 @@ int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
>         return ret;
>  }
>
> -int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq,
> -                           void (*release)(void *), unsigned int index,
> -                           unsigned int issue_flags)
> +int io_buffer_register_request(struct io_ring_ctx *ctx, struct request *rq,
> +                              void (*release)(void *), unsigned int index,
> +                              unsigned int issue_flags)
>  {
> -       struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
>         struct io_rsrc_data *data = &ctx->buf_table;
>         struct req_iterator rq_iter;
>         struct io_mapped_ubuf *imu;
> @@ -1003,12 +1002,10 @@ int io_buffer_register_bvec(struct io_uring_cmd *cmd, struct request *rq,
>         io_ring_submit_unlock(ctx, issue_flags);
>         return ret;
>  }
> -EXPORT_SYMBOL_GPL(io_buffer_register_bvec);
>
> -int io_buffer_unregister_bvec(struct io_uring_cmd *cmd, unsigned int index,
> -                             unsigned int issue_flags)
> +int io_buffer_unregister(struct io_ring_ctx *ctx, unsigned int index,
> +                        unsigned int issue_flags)
>  {
> -       struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
>         struct io_rsrc_data *data = &ctx->buf_table;
>         struct io_rsrc_node *node;
>         int ret = 0;
> @@ -1036,7 +1033,6 @@ int io_buffer_unregister_bvec(struct io_uring_cmd *cmd, unsigned int index,
>         io_ring_submit_unlock(ctx, issue_flags);
>         return ret;
>  }
> -EXPORT_SYMBOL_GPL(io_buffer_unregister_bvec);
>
>  static int validate_fixed_range(u64 buf_addr, size_t len,
>                                 const struct io_mapped_ubuf *imu)
> diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
> index 658934f4d3ff..d1ca33f3319a 100644
> --- a/io_uring/rsrc.h
> +++ b/io_uring/rsrc.h
> @@ -91,6 +91,13 @@ int io_validate_user_buf_range(u64 uaddr, u64 ulen);
>  bool io_check_coalesce_buffer(struct page **page_array, int nr_pages,
>                               struct io_imu_folio_data *data);
>
> +int io_buffer_register_request(struct io_ring_ctx *ctx, struct request *rq,
> +                              void (*release)(void *), unsigned int index,
> +                              unsigned int issue_flags);
> +
> +int io_buffer_unregister(struct io_ring_ctx *ctx, unsigned int index,
> +                        unsigned int issue_flags);
> +
>  static inline struct io_rsrc_node *io_rsrc_node_lookup(struct io_rsrc_data *data,
>                                                        int index)
>  {
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 3eb10bbba177..3922ac86b481 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -383,6 +383,27 @@ struct io_br_sel io_uring_cmd_buffer_select(struct io_uring_cmd *ioucmd,
>  }
>  EXPORT_SYMBOL_GPL(io_uring_cmd_buffer_select);
>
> +int io_uring_cmd_buffer_register_request(struct io_uring_cmd *cmd,
> +                                        struct request *rq,
> +                                        void (*release)(void *),
> +                                        unsigned int index,
> +                                        unsigned int issue_flags)
> +{
> +       struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
> +
> +       return io_buffer_register_request(ctx, rq, release, index, issue_flags);
> +}
> +EXPORT_SYMBOL_GPL(io_uring_cmd_buffer_register_request);
> +
> +int io_uring_cmd_buffer_unregister(struct io_uring_cmd *cmd, unsigned int index,
> +                                  unsigned int issue_flags)
> +{
> +       struct io_ring_ctx *ctx = cmd_to_io_kiocb(cmd)->ctx;
> +
> +       return io_buffer_unregister(ctx, index, issue_flags);
> +}
> +EXPORT_SYMBOL_GPL(io_uring_cmd_buffer_unregister);

It would be nice to avoid these additional function calls that can't
be inlined. I guess we probably don't want to include the
io_uring-internal header io_uring/rsrc.h in the external header
linux/io_uring/cmd.h, which is probably why the functions were
declared in linux/io_uring/cmd.h but defined in io_uring/rsrc.c
previously. Maybe it would make sense to move the definitions of
io_uring_cmd_buffer_register_request() and
io_uring_cmd_buffer_unregister() to io_uring/rsrc.c so
io_buffer_register_request()/io_buffer_unregister() can be inlined
into them?

Best,
Caleb

> +
>  /*
>   * Return true if this multishot uring_cmd needs to be completed, otherwise
>   * the event CQE is posted successfully.
> --
> 2.47.3
>