linux-kernel - Re: [PATCH] virtio_bt: Fix alignment in configuration struct

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Message-ID: <CABBYNZKfLOxrTAVLRSH+hOwaB5RYkGdjbtfabufUcgR3oy897A@mail.gmail.com>
Date:   Fri, 7 Oct 2022 12:33:46 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Igor Skalkin <igor.skalkin@...nsynergy.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        linux-bluetooth@...r.kernel.org, mgo@...nsynergy.com
Subject: Re: [PATCH] virtio_bt: Fix alignment in configuration struct

Hi Michael,

On Fri, Oct 7, 2022 at 6:03 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Mon, Aug 08, 2022 at 02:04:43PM +0200, Igor Skalkin wrote:
> > On 8/8/22 01:00, Michael S. Tsirkin wrote:
> >
> >     On Mon, Aug 08, 2022 at 12:11:52AM +0200, Igor Skalkin wrote:
> >
> >         According to specification [1], "For the device-specific configuration
> >         space, the driver MUST use 8 bit wide accesses for 8 bit wide fields,
> >         16 bit wide and aligned accesses for 16 bit wide fields and 32 bit wide
> >         and aligned accesses for 32 and 64 bit wide fields.".
> >
> >         Current version of the configuration structure:
> >
> >             struct virtio_bt_config {
> >                 __u8  type;
> >                 __u16 vendor;
> >                 __u16 msft_opcode;
> >             } __attribute__((packed));
> >
> >         has both 16bit fields non-aligned.
> >
> >         This commit fixes it.
> >
> >         [1] https://ddec1-0-en-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdocs.oasis%2dopen.org%2fvirtio%2fvirtio%2fv1.1%2fvirtio%2dv1.1.pdf&umid=d1786ace-e8ea-40e8-9665-96c0949174e5&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-39b15885ceebe9fda9357320aec1ccbac416a470
> >
> >         Signed-off-by: Igor Skalkin <Igor.Skalkin@...nsynergy.com>
> >
> >     This is all true enough, but the problem is
> >     1. changing uapi like this can't be done, will break userspace
> >     2. the driver has more issues and no one seems to want to
> >        maintain it.
> >     I posted a patch "Bluetooth: virtio_bt: mark broken" and intend
> >     to merge it for this release.
> >
> > This is very sad. We already use this driver in our projects.
>
> Ping. If we still have no maintainer I'm marking it broken, users
> should at least be warned.

Please resend.

>
> > Our virtio bluetooth device has two backends - HCI_USER socket backend for one
> > platform and uart backend for the other, and works well (after applying your
> > "[PATCH] Bluetooth: virtio_bt: fix device remove") patch, so this "device
> > removal" problem can probably be considered solved .
> > We could help with the rest of the problems you listed that can be solved
> > (specification, QEMU support).
> > And the only problem that is difficult to solve (because of the need to change
> > UAPI header files) is just this one with unaligned configuration fields.
> > At the moment, it does not reproduce, because without VIRTIO_BT_F_VND_HCI
> > (Indicates vendor command support) feature negotiated, the driver does not
> > read the non-aligned configuration fields.
> >
> > So, what would you advise us to do? Continuing to use the "marked broken"
> > driver, start writing a specification for a new from scratch, better one?
> > Or is there any way to bring this one back to life?
> >
> >
> >
> >         ---
> >          include/uapi/linux/virtio_bt.h | 2 +-
> >          1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >         diff --git a/include/uapi/linux/virtio_bt.h b/include/uapi/linux/virtio_bt.h
> >         index a7bd48daa9a9..adc03709cc4f 100644
> >         --- a/include/uapi/linux/virtio_bt.h
> >         +++ b/include/uapi/linux/virtio_bt.h
> >         @@ -23,9 +23,9 @@ enum virtio_bt_config_vendor {
> >          };
> >
> >          struct virtio_bt_config {
> >         -       __u8  type;
> >                 __u16 vendor;
> >                 __u16 msft_opcode;
> >         +       __u8  type;
> >          } __attribute__((packed));
> >
> >          #endif /* _UAPI_LINUX_VIRTIO_BT_H */
> >         --
> >         2.34.1
> >
> > --
> >
> > Best regards,
> >
> > Igor Skalkin
> > Software Engineer
> >
> > OpenSynergy GmbH
> > Rotherstr. 20, 10245 Berlin
> >
> > igor.skalkin@...nsynergy.com
> > www.opensynergy.com
> >
> > registered: Amtsgericht Charlottenburg, HRB 108616B
> > General Management: Rolf Morich, Stefaan Sonck Thiebaut
> >
> >
> > Please mind our privacy notice pursuant to Art. 13 GDPR. // Unsere Hinweise zum
> > Datenschutz gem. Art. 13 DSGVO finden Sie hier.
>


-- 
Luiz Augusto von Dentz