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

Michael S. Tsirkin
2022-10-07T13:03:46Z

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@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.

> 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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