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

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Message-ID: <d41ec1d3-e262-3be6-17f2-a9495c55b868@opensynergy.com>
Date:   Tue, 11 Oct 2022 14:23:13 +0200
From:   Igor Skalkin <igor.skalkin@...nsynergy.com>
To:     Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     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 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@...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=b1110db2-819d-4f27-b35e-18ac23ce0ab4&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-2c53002097633a932e7d67b899e6bf6999cdc899
>>>
>>>          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
>>>
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>>> General Management: Rolf Morich, Stefaan Sonck Thiebaut
>>>
>>>
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>>
>
>

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