[Xen-devel] Re: More virtio users

[Jens Axboe <jens.axboe@xxxxxxxxxx>]

On Tue, Jun 12 2007, Rusty Russell wrote:
> On Tue, 2007-06-12 at 08:24 +0200, Jens Axboe wrote:
> > On Tue, Jun 12 2007, Rusty Russell wrote:
> > > On Mon, 2007-06-11 at 09:33 +0200, Jens Axboe wrote:
> > > > 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?
> > 
> > They are SCSI commands!
> > 
> > > Q: Who puts them in my queue?
> > 
> > If you want to support SG_IO for instance, you'd have to deal with SCSI
> > commands.
> 
> I do not.  If someone wants to implement a SCSI layer over virtio, I
> think that's wonderful.  Fortunately, that's not the problem I'm trying
> to solve.

Then you can blissfully ignore blk_pc_request() and just keep your
current code for rejecting !blk_fs_request().

> > -o barrier=1 for ext3, it doesn't use barriers by default.
> 
> That's, um, a little disturbing.
> 
> But, it works.  Thanks!

Well, feel free to send a patch making barrier=1 the default, then I'll
make sure that mails from users that are confused because performance is
suddenly much worse get redirected to you :-)

Kudos to XFS for making it the default, though!

-- 
Jens Axboe


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