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xen-devel
[Xen-devel] Re: More virtio users
On Mon, 2007-06-11 at 09:33 +0200, Jens Axboe wrote:
> On Mon, Jun 11 2007, Rusty Russell wrote:
> > So the problem is that I'd like to handle all of them, but I'm not clear
> > what requests my device can get. I can't see a source of any other type
> > of request.
>
> The other main request type is blk_pc_request(). In the data setup it's
> indentical to blk_fs_request(), there's a bio chain off ->bio. It's a
> byte granularity entity though, so you should check ->data_len for the
> size of it. ->cmd[] holds a SCSI cdb, which is the command you are
> supposed to handle.
SCSI? I'm even more lost now.
Q: So what *are* the commands?
Q: Who puts them in my queue?
I have *never* seen anything but an fs request come through to my
driver.
> Perhaps you are misunderstanding what the tag is? The tag is a unique
> identifier for a pending request, so you will by definition never have
> requests sharing a tag value.
Yes, I started to suspect that.
> But the tag is not to be considered as
> ordered, unless it has the barrier flag set as well. So you only need to
> serialize on the device side when blk_barrier_rq() is true.
blk_barrier_rq(req) is never true. I put a BUG_ON(blk_barrier_rq(req))
in my code and booted. This is using the device as a root ext3
filesystem.
I reverted all the tag changes, still no barriers. I added
"blk_queue_ordered(vblk->disk->queue, QUEUE_ORDERED_DRAIN, NULL);",
still no barriers.
Dazed and confused,
Rusty.
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