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Re: [Qemu-block] [PATCH 0/6] QTests: use Python to run complex tests

From: Nir Soffer
Subject: Re: [Qemu-block] [PATCH 0/6] QTests: use Python to run complex tests
Date: Thu, 14 Dec 2017 15:39:12 +0000

On Thu, Dec 14, 2017 at 1:36 PM Paolo Bonzini <address@hidden> wrote:
On 14/12/2017 10:39, Stefan Hajnoczi wrote:
>>             # verify Card ID
>>             data = ""> >>             oid, pnm, psn = struct.unpack(">x2s5sxLxxx", data)
>>             self.assertEqual(oid, "XY") # QEMU default
>>             self.assertEqual(pnm, "QEMU!") # QEMU default
>>             self.assertEqual(psn, 0xdeadbeef) # QEMU default
> Device qtests are better done in C than Python.  Python is not good at
> binary I/O and porting this to Python 3 will be extra work later (Python
> 2 is set for End-of-Life in 2020, see https://pythonclock.org/).
> More importantly, we already have libqos in C with a guest memory
> allocator, PCI, and virtio support.  Fragmenting the small amount effort
> that goes into device testing will delay libqos reaching critical mass.
> Critical mass is where libqos provides all the infrastructure you need
> to set up a device and focus on your actual test instead of machine,
> bus, or device initialization.  Starting a Python device testing effort
> will just lead to duplication and 2 underdeveloped device testing
> frameworks.

I agree that fragmentation is bad.  However, libqos is small (about 4k
lines of code, maybe 3k in Python).

I also agree that any qtest written in Python should be written in
Python 3 from the beginning (in fact we should consider dropping Python
2.x support in 2.12).  Doing so should not make binary I/O much
different than C.

Using python 3 will make it hard to develop and test qemu on RHEL/CentOS
which do not provide python 3 yet.

Doing binary io in python 2 and 3 is the same, there is no need to use
python 3 for this. The only advantage is not having to backport code
later from 2 to 3.


>From my point of view, the main advantage of Python is the reflection
mechanisms.  Those would make it possible to automatically discover the
set of runnable tests; for example, based on:

- two machine descriptions (including malloc) for ARM -M virt and x86 -M q35

- a driver for the generic PCIe host bridge

- a driver for virtio-pci

- a driver for virtio-scsi

- a set of SCSI tests

... it should be possible to run the same tests as either ARM or x86
qtests.  This would be a very different framework compared to the C libqos.



> Is there a specific reason why adding SD Card support to libqos is not
> possible in C?

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