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Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_
From: |
Stefano Stabellini |
Subject: |
Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER |
Date: |
Wed, 25 Apr 2012 12:21:53 +0100 |
User-agent: |
Alpine 2.00 (DEB 1167 2008-08-23) |
On Wed, 25 Apr 2012, Christoph Hellwig wrote:
> On Wed, Apr 25, 2012 at 10:02:45AM +0100, Ian Campbell wrote:
> > The blkif spec was recently much improved, you can find it at
> > http://xenbits.xen.org/docs/unstable/hypercall/include,public,io,blkif.h.html
> >
> > TBH I'm not sure it actually answers your questions wrt
> > BLKIF_OP_FLUSH_DISKCACHE, if not please let us know and we can see about
> > improving it.
>
> That description in there is overly simple, and does not match any of the
> implementations known to me on either end.
That is true, in fact I couldn't figure out what I had to implement just
reading the comment. So I went through the blkback code and tried to
understand what I had to do, but I got it wrong.
Reading the code again it seems to me that BLKIF_OP_FLUSH_DISKCACHE
is supposed to have the same semantics as REQ_FLUSH, that implies a
preflush if nr_segments > 0, not a postflush like I did.
Konrad, can you please confirm this?
- [Qemu-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Stefano Stabellini, 2012/04/16
- Re: [Qemu-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Konrad Rzeszutek Wilk, 2012/04/16
- Re: [Qemu-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Christoph Hellwig, 2012/04/25
- Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Ian Campbell, 2012/04/25
- Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Christoph Hellwig, 2012/04/25
- Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER,
Stefano Stabellini <=
- Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Ian Campbell, 2012/04/25
- Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Christoph Hellwig, 2012/04/25
- Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER, Konrad Rzeszutek Wilk, 2012/04/26