[PATCH 3/3] /dev/null: add IORING_OP_URING_CMD support

[Paul Moore]

On Mon, Aug 22, 2022 at 6:36 PM Jens Axboe <axboe at kernel.dk> wrote:
> On 8/22/22 3:21 PM, Paul Moore wrote:
> > This patch adds support for the io_uring command pass through, aka
> > IORING_OP_URING_CMD, to the /dev/null driver.  As with all of the
> > /dev/null functionality, the implementation is just a simple sink
> > where commands go to die, but it should be useful for developers who
> > need a simple IORING_OP_URING_CMD test device that doesn't require
> > any special hardware.
> >
> > Cc: Arnd Bergmann <arnd at arndb.de>
> > Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> > Signed-off-by: Paul Moore <paul at paul-moore.com>
> > ---
> >  drivers/char/mem.c |    6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> > index 84ca98ed1dad..32a932a065a6 100644
> > --- a/drivers/char/mem.c
> > +++ b/drivers/char/mem.c
> > @@ -480,6 +480,11 @@ static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
> >       return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
> >  }
> >
> > +static int uring_cmd_null(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
> > +{
> > +     return 0;
> > +}
>
> This would be better as:
>
>         return IOU_OK;
>
> using the proper return values for the uring_cmd hook.

The only problem I see with that is that IOU_OK is defined under
io_uring/io_uring.h and not include/linux/io_uring.h so the #include
macro is kinda ugly:

  #include "../../io_uring/io_uring.h"

I'm not sure I want to submit that upstream looking like that.  Are
you okay with leaving the return code as 0 for now and changing it at
a later date?  I'm trying to keep this patchset relatively small since
we are in the -rcX stage, but if you're okay with a simple cut-n-paste
of the enum to linux/io_uring.h I can do that.

> With that:
>
> Acked-by: Jens Axboe <axboe at kernel.dk>

-- 
paul-moore.com