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

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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

registered: Amtsgericht Charlottenburg, HRB 108616B
General Management: Rolf Morich, Stefaan Sonck Thiebaut


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