Re: [PATCHv5 1/4] liburing: provide uring_cmd prep function

[Keith Busch <kbusch@kernel.org>]

On Sun, Oct 19, 2025 at 09:24:10AM -0700, Caleb Sander Mateos wrote:
> On Mon, Oct 13, 2025 at 11:00 AM Keith Busch <kbusch@meta.com> wrote:
> > +                                          int fd)
> > +       LIBURING_NOEXCEPT
> > +{
> > +       sqe->opcode = (__u8) IORING_OP_URING_CMD;
> 
> Casting the constant seems unnecessary. Do compilers really warn about this?

Oh, not necessary here, but the next patch wants the cast. This was
copied from io_uring_prep_rw(), which passes the 'opcode' as an 'int'
type. I don't know why that type was used, so just trying to match the
local convention.

But I digress, I'll move the cast to the next patch where it is actually
needed.
 
> > +                       io_uring_prep_uring_cmd(sqe, NVME_URING_CMD_IO, use_fd);
> 
> I guess this works because io_uring_prep_uring_cmd() doesn't touch
> sqe->buf_index or sqe->flags, but it seems like it would be less
> brittle to call io_uring_prep_uring_cmd() before setting any of the
> other sqe fields.

Good point, it happens to be "okay", but is safer to move the generic
init before initializing command specific fields.