Re: [PATCH for-next v12 02/12] io_uring: introduce fixed buffer support for io_uring_cmd

[Anuj gupta <anuj1072538@gmail.com>]

On Fri, Sep 30, 2022 at 7:28 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 9/30/22 12:27 AM, Anuj Gupta wrote:
> > Add IORING_URING_CMD_FIXED flag that is to be used for sending io_uring
> > command with previously registered buffers. User-space passes the buffer
> > index in sqe->buf_index, same as done in read/write variants that uses
> > fixed buffers.
> >
> > Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> > Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> > ---
> >  include/linux/io_uring.h      |  2 +-
> >  include/uapi/linux/io_uring.h |  9 +++++++++
> >  io_uring/uring_cmd.c          | 18 +++++++++++++++++-
> >  3 files changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
> > index 1dbf51115c30..e10c5cc81082 100644
> > --- a/include/linux/io_uring.h
> > +++ b/include/linux/io_uring.h
> > @@ -28,7 +28,7 @@ struct io_uring_cmd {
> >               void *cookie;
> >       };
> >       u32             cmd_op;
> > -     u32             pad;
> > +     u32             flags;
> >       u8              pdu[32]; /* available inline for free use */
> >  };
> >
> > diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> > index 92f29d9505a6..ab7458033ee3 100644
> > --- a/include/uapi/linux/io_uring.h
> > +++ b/include/uapi/linux/io_uring.h
> > @@ -56,6 +56,7 @@ struct io_uring_sqe {
> >               __u32           hardlink_flags;
> >               __u32           xattr_flags;
> >               __u32           msg_ring_flags;
> > +             __u32           uring_cmd_flags;
> >       };
> >       __u64   user_data;      /* data to be passed back at completion time */
> >       /* pack this to avoid bogus arm OABI complaints */
> > @@ -219,6 +220,14 @@ enum io_uring_op {
> >       IORING_OP_LAST,
> >  };
> >
> > +/*
> > + * sqe->uring_cmd_flags
> > + * IORING_URING_CMD_FIXED    use registered buffer; pass thig flag
> > + *                           along with setting sqe->buf_index.
> > + */
> > +#define IORING_URING_CMD_FIXED       (1U << 0)
> > +
> > +
> >  /*
> >   * sqe->fsync_flags
> >   */
> > diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> > index 6a6d69523d75..05e8ad8cef87 100644
> > --- a/io_uring/uring_cmd.c
> > +++ b/io_uring/uring_cmd.c
> > @@ -4,6 +4,7 @@
> >  #include <linux/file.h>
> >  #include <linux/io_uring.h>
> >  #include <linux/security.h>
> > +#include <linux/nospec.h>
> >
> >  #include <uapi/linux/io_uring.h>
> >
> > @@ -77,7 +78,22 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> >  {
> >       struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
> >
> > -     if (sqe->rw_flags || sqe->__pad1)
> > +     if (sqe->__pad1)
> > +             return -EINVAL;
> > +
> > +     ioucmd->flags = READ_ONCE(sqe->uring_cmd_flags);
> > +     if (ioucmd->flags & IORING_URING_CMD_FIXED) {
> > +             struct io_ring_ctx *ctx = req->ctx;
> > +             u16 index;
> > +
> > +             req->buf_index = READ_ONCE(sqe->buf_index);
> > +             if (unlikely(req->buf_index >= ctx->nr_user_bufs))
> > +                     return -EFAULT;
> > +             index = array_index_nospec(req->buf_index, ctx->nr_user_bufs);
> > +             req->imu = ctx->user_bufs[index];
> > +             io_req_set_rsrc_node(req, ctx, 0);
> > +     }
> > +     if (ioucmd->flags & ~IORING_URING_CMD_FIXED)
> >               return -EINVAL;
>
> Not that it _really_ matters, but why isn't this check the first thing
> that is done after reading the flags? No need to respin, I can just move
> it myself.
>
Right, checking this condition should have been the first thing to do after
reading the flags. Thanks for taking care of it.

> --
> Jens Axboe

--
Anuj Gupta