Re: [PATCH] virtio_bt: Fix alignment in configuration struct

[Igor Skalkin]

Hi Luiz,

Current version of this patch is wrong [q]changing uapi like this can't
be done, will break userspace[/q], next version is in process, will be
sent in few days.
Best regards,
Igor
On 10/7/22 21:33, Luiz Augusto von Dentz wrote:
> Hi Michael,
>
> On Fri, Oct 7, 2022 at 6:03 AM Michael S. Tsirkin <mst@xxxxxxxxxx> 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=b1110db2-819d-4f27-b35e-18ac23ce0ab4&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-2c53002097633a932e7d67b899e6bf6999cdc899
> > >
> > >          Signed-off-by: Igor Skalkin <Igor.Skalkin@xxxxxxxxxxxxxxx>
> > >
> > >      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@xxxxxxxxxxxxxxx
> > > www.opensynergy.com
> > >
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> > > General Management: Rolf Morich, Stefaan Sonck Thiebaut
> > >
> > >
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