Re: [Qemu-devel] [PATCH V20 8/8] Add fd parameter for TPM passthrough driver

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 01/19/2013 10:31 AM, Eric Blake wrote:
> On 01/18/2013 05:55 PM, Stefan Berger wrote:
>> On 01/18/2013 07:14 PM, Stefan Berger wrote:
>>> On 01/18/2013 01:18 PM, Eric Blake wrote:
>>>> On 01/18/2013 09:02 AM, Stefan Berger wrote:
>>> When libvirt forks, the child process inherits the file descriptors,
>>> among them those of the taps and /dev/tpm0. The subsequent execve
>>> keeps the file descriptor open. QEMU then reads the TPM file
>>> descriptor from the command line into above TPMInfo->fd. This also
>>> works with 'exec 100<>/dev/tpm0' via command line.
>>> Similar to the SELinux labeling of all the other file descriptors I
>>> also use the one for the TPM device for SELinux labeling.
>>>
>> I have to correct this: The libvirt patches for this use path= on the
>> command line and also apply the SELinux label on the path rather than
>> the fd. So, this patch then adds file descriptor passing support to have
>> equivalent functionality to other devices.
> You _still_ don't need extra handling for fd passing; neither on the
> command line, nor in QMP.  Remember, we added --add-fd to the command
> line, precisely so we could use:
>
> qemu -add-fd set=1,fd=100 -tpmdev passthrough,path=/dev/fdset/1 \
>    100<>/dev/tpm0
This helps. /dev/fdset/1 is just a string and not a real device 
following what I see in the code. Then the problem seems to be solved by 
replacing open() with qemu_open() and we can drop this patch. Thanks for 
the hint. Obviously I don't follow all the developments in QEMU close 
enough...

Regards,
     Stefan