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

Igor Skalkin
2022-10-11T12:23:25Z

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@redhat.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=b1110db2-819d-4f27-b35e-18ac23ce0ab4&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-2c53002097633a932e7d67b899e6bf6999cdc899
>>>
>>> Signed-off-by: Igor Skalkin <Igor.Skalkin@opensynergy.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@opensynergy.com
>>> www.opensynergy.com
>>>
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>>> General Management: Rolf Morich, Stefaan Sonck Thiebaut
>>>
>>>
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>>
>
>

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