Re: [Qemu-devel] [Xen-devel] [PATCH] xen_disk: implement BLKIF_OP_FLUSH_DISKCACHE, remove BLKIF_OP_WRITE_BARRIER

[Christoph Hellwig]

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.

Talking about those: the mainline Linux blkback backend also implements
different semantics from what mainline Linux blkfront seems to expect,
as well as different from qemu.  Looking at these three alone I can't see
how Xen ever managed to get data to disk reliably if using the paravirt
interface.
with the implementations in qemu and the Linux kernel frontend and backends,
which

> 
> Ian
> 
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