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Date: Wed, 24 Aug 2011 14:58:16 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20110824115816.GA18393@redhat.com>
References: <4E53E328.90601@siemens.com> <20110824100439.GA17255@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] pci: Error on PCI capability collisions
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Alex Williamson <alex.williamson@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On Wed, Aug 24, 2011 at 12:10:32PM +0200, Jan Kiszka wrote:
> On 2011-08-24 12:04, Michael S. Tsirkin wrote:
> > On Tue, Aug 23, 2011 at 07:28:08PM +0200, Jan Kiszka wrote:
> >> From: Alex Williamson <alex.williamson@redhat.com>
> >>
> >> Nothing good can happen when we overlap capabilities
> >>
> >> [ Jan: rebased over qemu, minor formatting ]
> >>
> >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >=20
> > This doesn't build for me:
> >=20
> > /scm/qemu/hw/pci.c: In function =E2=80=98pci_add_capability=E2=80=99:
> > /scm/qemu/hw/pci.c:1970:45: error: =E2=80=98PCIDevice=E2=80=99 has no=
 member named =E2=80=98config_map=E2=80=99
>=20
> Yeah, sorry, forgot to refresh the commit before posting.
>=20
> >=20
> > I think that what that includes is the capability including each give=
n
> > offset, right?  It would be easy to write some code scanning the
> > capability list to figure this value out.
> > Something along the lines of (untested):
> >=20
> > static
> > uint8_t pci_find_capability_at_offset(PCIDevice *pdev, uint8_t offset=
)
> > {                                      =20
> >     uint8_t next, prev, found =3D 0;
> >=20
> >     if (!(pdev->config[PCI_STATUS] & PCI_STATUS_CAP_LIST))
> >         return 0;
> >=20
> >     for (prev =3D PCI_CAPABILITY_LIST; (next =3D pdev->config[prev]);
> >          prev =3D next + PCI_CAP_LIST_NEXT)
> >         if (next <=3D offset && next > found)
> >             found =3D next;
> >=20
> >     return found;
> > }
>=20
> Sounds useful, will enhance the patch.
>=20
> (Originally, I just wanted to reduce the qemu-kvm delta... :) )
>=20
> Jan

Also, let's add a comment documenting the
reason for this check: device assignment
depends on this check to verify that the device
is not broken.

> --=20
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux