Re: [PATCH] io_uring/net: use REQ_F_IMPORT_BUFFER for send_zc

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

On Tue, Mar 25, 2025 at 6:30 AM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> On 3/24/25 15:11, Caleb Sander Mateos wrote:
> > Instead of a bool field in struct io_sr_msg, use REQ_F_IMPORT_BUFFER to
> > track whether io_send_zc() has already imported the buffer. This flag
> > already serves a similar purpose for sendmsg_zc and {read,write}v_fixed.
> >
> > Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
> > Suggested-by: Pavel Begunkov <asml.silence@gmail.com>
> > ---
> >   include/linux/io_uring_types.h | 5 ++++-
> >   io_uring/net.c                 | 8 +++-----
> >   2 files changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> > index c17d2eedf478..699e2c0895ae 100644
> > --- a/include/linux/io_uring_types.h
> > +++ b/include/linux/io_uring_types.h
> > @@ -583,11 +583,14 @@ enum {
> >       REQ_F_BUFFERS_COMMIT    = IO_REQ_FLAG(REQ_F_BUFFERS_COMMIT_BIT),
> >       /* buf node is valid */
> >       REQ_F_BUF_NODE          = IO_REQ_FLAG(REQ_F_BUF_NODE_BIT),
> >       /* request has read/write metadata assigned */
> >       REQ_F_HAS_METADATA      = IO_REQ_FLAG(REQ_F_HAS_METADATA_BIT),
> > -     /* resolve padded iovec to registered buffers */
> > +     /*
> > +      * For vectored fixed buffers, resolve iovec to registered buffers.
> > +      * For SEND_ZC, whether to import buffers (i.e. the first issue).
> > +      */
> >       REQ_F_IMPORT_BUFFER     = IO_REQ_FLAG(REQ_F_IMPORT_BUFFER_BIT),
> >   };
> >
> >   typedef void (*io_req_tw_func_t)(struct io_kiocb *req, io_tw_token_t tw);
> >
> > diff --git a/io_uring/net.c b/io_uring/net.c
> > index c87af980b98e..b221abe2600e 100644
> > --- a/io_uring/net.c
> > +++ b/io_uring/net.c
> > @@ -75,11 +75,10 @@ struct io_sr_msg {
> >       unsigned                        nr_multishot_loops;
> >       u16                             flags;
> >       /* initialised and used only by !msg send variants */
> >       u16                             buf_group;
> >       bool                            retry;
> > -     bool                            imported; /* only for io_send_zc */
> >       void __user                     *msg_control;
> >       /* used only for send zerocopy */
> >       struct io_kiocb                 *notif;
> >   };
> >
> > @@ -1305,12 +1304,11 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> >       struct io_ring_ctx *ctx = req->ctx;
> >       struct io_kiocb *notif;
> >
> >       zc->done_io = 0;
> >       zc->retry = false;
> > -     zc->imported = false;
> > -     req->flags |= REQ_F_POLL_NO_LAZY;
> > +     req->flags |= REQ_F_POLL_NO_LAZY | REQ_F_IMPORT_BUFFER;
>
> This function is shared with sendmsg_zc, so if we set it here,
> it'll trigger io_import_reg_vec() in io_sendmsg_zc() even for
> non register buffer request.

Good catch. I keep forgetting which prep and issue functions are
shared between which opcodes.

Thanks,
Caleb