Re: [Qemu-devel] [PATCH] qga: implement guest-file-ioctl

[Paolo Bonzini]

On 01/02/2017 06:43, Eric Blake wrote:
>>> It would be possible to design a ioctl API that is more usable if you
>>> didn't try to do generic passthrough of arbitrary ioctl commands. Instead
>>> provide a QAPI schema that uses a union to provide strongly typed arguments
>>> for the ioctl commands you care about using. Or completely separate QAPI
>>> commands instead of multiplexing everything into an ioctl command.
>>
>> I can add a QAPI command for my specific use case if it's acceptable,
> 
> Certainly more palatable, and more likely to gain my acceptance.
> 
>> that's not a problem. Although at that point I would probably just go
>> back to my plan b and use regular file I/O and guest-file-read. I just
>> wanted to be as generic as possible to benefit other use cases as well
>> and I ended up with what's basically my stab at RPC ioctl.
> 
> The problem is that RPC ioctl is not sanely possible.

Windows ioctl (DeviceIoControl) is a little different from POSIX ioctl,
more RPC and less one-size-fits-all bucket for syscallish stuff.  It is
still a leaky abstraction though.

Paolo