Re: [Qemu-devel] [PATCH] backends: Introduce chr-testdev

[Paolo Bonzini <pbonzini@redhat.com>]

Il 11/07/2014 17:30, Eric Blake ha scritto:
> On 07/11/2014 01:44 AM, Andrew Jones wrote:
>> From: Paolo Bonzini <pbonzini@redhat.com>
>>
>> From: Paolo Bonzini <pbonzini@redhat.com>
>>
>> chr-testdev enables a virtio serial channel to be used for guest
>> initiated qemu exits. hw/misc/debugexit already enables guest
>> initiated qemu exits, but only for PC targets. chr-testdev supports
>> any virtio-capable target. kvm-unit-tests/arm is already making use
>> of this backend.
>>
>> Currently there is a single command implemented, "q".  It takes a
>> (prefix) argument for the exit code, thus an exit is implemented by
>> writing, e.g. "1q", to the virtio-serial port.
>>
>> It can be used as:
>>    $QEMU ... \
>>      -device virtio-serial-device \
>>      -device virtserialport,chardev=ctd -chardev testdev,id=ctd
>>
>> or, use:
>>    $QEMU ... \
>>      -device virtio-serial-device \
>>      -device virtconsole,chardev=ctd -chardev testdev,id=ctd
>>
>> to bind it to virtio-serial port0.
>>
>
>> +
>> +    switch (c) {
>> +    case 'q':
>> +        exit((arg << 1) | 1);
>> +        break;
>
> I'm trying to figure out the motive for only exiting with odd numbers.
> That is, 'q' => 1, '1q' => 3, '2q' => 5, '3q' => 7.  It means that at
> most, I can do '127q' => 255 before I suffer from exit() limiting things
> to 8 bits.  This wasn't explained in the commit message.

It's just for parity with isa-debugexit.

Paolo