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

[Luiz Augusto von Dentz]

Hi Igor,

On Tue, Oct 11, 2022 at 5:23 AM Igor Skalkin
<igor.skalkin@xxxxxxxxxxxxxxx> wrote:
>
> 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.

Thanks for the update, I will wait for the next version then.

> 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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> >>>
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> >>
> >
> >
>
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-- 
Luiz Augusto von Dentz