On Sun, Jun 10 2007, Rusty Russell wrote:
> On Sun, 2007-06-10 at 11:16 +0300, Avi Kivity wrote:
> > Rusty Russell wrote:
> > > Lguest doesn't have a framebuffer, so maybe this is a good thing for me
> > > to hack on, but I promised myself I'd finish NAPI for the net device,
> > > and tag for block device first.
> > >
> >
> > If you're touching the block device, passing a request's io priority to
> > the host can be useful.
>
> OK, here's the interdiff. I still don't handle non-fs requests, but I
> haven't seen any yet. I should probably BUG_ON() there and wait for
> Jens to scream...
Ehm no, that would certainly cause screaming :-)
Checking for blk_fs_request() and terminating the request if you don't
know how to handle it is the correct thing to do, a BUG() would
definitely not be.
Patch looks good to me, though:
> + blk_queue_prep_rq(vblk->disk->queue, blk_queue_start_tag);
> +
is quite a novel way, I actually had to look that code up to check
whether it was correct. I'd much prefer a little wrapper around that,
ala:
static int virtio_block_prep(request_queue_t *q, struct request *rq)
{
if (!blk_queue_start_tag(q, rq))
return BLKPREP_OK;
return BLKPREP_DEFER;
}
That is much easier to read, and as a bonus it wont eat your request
just because you run out of tags! The fact that blk_queue_start_tag()
just happens to share the prep_rq_fn definition is by coincidence only.
--
Jens Axboe
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