From: Stefano Stabellini <sstabellini@kernel.org>
To: Juergen Gross <jgross@suse.com>
Cc: "Anthony PERARD" <anthony.perard@citrix.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Roger Pau Monné" <roger.pau@citrix.com>,
xen-devel@lists.xen.org
Subject: Re: potential problem with qdisk backend
Date: Mon, 16 May 2016 12:59:04 +0100 (BST) [thread overview]
Message-ID: <alpine.DEB.2.10.1605161250490.2494@sstabellini-ThinkPad-X260> (raw)
In-Reply-To: <5733395D.5060905@suse.com>
On Wed, 11 May 2016, Juergen Gross wrote:
> On 06/05/16 13:41, Juergen Gross wrote:
> > Looking at the qdisk backend implementation I wondered whether
> > blkif_get_x86_32_req() is really correct, especially for the
> > BLKIF_OP_DISCARD case. The Linux kernel based blk backend seems to
> > distinguish 32- and 64-bit layouts of blkif_request_discard while
> > qemu treats them to be the same.
> >
> > Am I completely wrong here?
>
> Adding some maintainers.
Yes, it seems to me that the internal alignment of the fields in struct
blkif_request_discard (as declared by xen/include/public/io/blkif.h)
differs between x86_32 and x86_64. The two different alignments are both
specified explicitly in Linux, by using __packed__ and explicit
padding.
On the other hand QEMU uses Xen's declaration of struct
blkif_request_discard without paying attention to the word size in the
guest. As a consequence it will work correctly only if the guest bitness
and the dom0 bitness match.
The discard struct should have two implementations in QEMU, like
blkif_x86_32_request and blkif_x86_64_request.
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next prev parent reply other threads:[~2016-05-16 11:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-06 11:41 potential problem with qdisk backend Juergen Gross
2016-05-11 13:53 ` Juergen Gross
2016-05-16 11:59 ` Stefano Stabellini [this message]
2016-05-13 15:42 ` Jan Beulich
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