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

[Greg Kroah-Hartman]

On Tue, Aug 23, 2022 at 01:02:08PM -0400, Paul Moore wrote:
> On Tue, Aug 23, 2022 at 2:52 AM Greg Kroah-Hartman
> <gregkh at linuxfoundation.org> wrote:
> > On Mon, Aug 22, 2022 at 05:21:19PM -0400, 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.
> >
> > Also, shouldn't you document this somewhere?
> >
> > At least in the code itself saying "this is here so that /dev/null works
> > as a io_uring sink" or something like that?  Otherwise it just looks
> > like it does nothing at all.
> 
> What about read_null() and write_null()?  I can definitely add a
> comment (there is no /dev/null documentation in the kernel source tree
> that I can see), but there is clearly precedence for /dev/null having
> "do nothing" file_operations functions.

Yes, they should "do nothing".  write_null() does report that it
consumed everything, why doesn't this function have to also do that?

thanks,

greg k-h