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Re: [Qemu-devel] [PATCH 00/33] Qtest driver framework

From: Emanuele
Subject: Re: [Qemu-devel] [PATCH 00/33] Qtest driver framework
Date: Thu, 16 Aug 2018 20:16:38 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 15/08/2018 14:38, Markus Armbruster wrote:
Emanuele Giuseppe Esposito <address@hidden> writes:

Qgraph API for the qtest driver framework

This series of patches introduce a different qtest driver
organization, viewing machines, drivers and tests as node in a
graph, each having one or multiple edges relations.

The idea is to have a framework where each test asks for a specific
driver, and the framework takes care of allocating the proper devices
required and passing the correct command line arguments to QEMU.

A node can be of four types:
- MACHINE:   for example "arm/raspi2"
- DRIVER:    for example "generic-sdhci"
- INTERFACE: for example "sdhci" (interface for all "-sdhci" drivers)
- TEST:      for example "sdhci-test", consumes an interface and tests
              the functions provided

An edge relation between two nodes (drivers or machines) X and Y can be:
- X CONSUMES Y: Y can be plugged into X
- X PRODUCES Y: X provides the interface Y
- X CONTAINS Y: Y is part of X component

Basic framework steps are the following:
- All nodes and edges are created in their respective machine/driver/test files
- The framework starts QEMU and asks for a list of available devices
   and machines
- The framework walks the graph starting from the available machines and
   performs a Depth First Search for tests
- Once a test is found, the path is walked again and all drivers are
   allocated accordingly and the final interface is passed to the test
- The test is executed
- Unused objects are cleaned and the path discovery is continued

Depending on the QEMU binary used, only some drivers/machines will be available
and only test that are reached by them will be executed.

This work is being done as Google Summer of Code 2018 project for QEMU,
my mentors are Paolo Bonzini and Laurent Vivier.
Additional infos on the project can be found at:
You've likely answered this question somewhere already, but it should be
answered right here: what does this framework buy us?

I figure the main benefit is running tests in all possible contexts,
with automated context setup.  Instead, you feed the framework
declarations of how things are related (the graph stuff described
You're right, that is the main benefit: running tests in all possible contexts, with automated context setup. Before, tests where basically hard-coded to run on a single architecture, or even a single machine type. Now, qgraph allows this kind of higher level view of the devices and their relationships, where tests generally consume an interface that hides the underneath implementation (for example, for sdhci-pci device, it consumes a "pci-bus", without knowing that the bus can be a pci-pc or pci-spapr).

This allows developers to add test without knowing or forcing the machine/architecture/additional required devices, they just need to know what interface the test can consume (and if not present, implement a node representing the device they want to test). For example, if you look at virtio-9p-test, you can see that the old test was just testing "virtio-9p-pci", while using the qgraph I was able to add "virtio-9p-device" too, without any additional change to the test, improving test coverage.

The other benefit is the automated context setup: as Paolo said once, every test basically re-invented the wheel in its own way. Every test had a main function, a section where qemu was started with proper devices, and a section where everything was cleaned up and shut down. Qgraph handles all these operations automatically, so the developer does not need to care about that. Just add the test function to the graph, and it will take care of running the test with the proper setup.

Of course this requires a minimal knowledge of the graph and the relationships you are going to use, since each test will receive structures representing device from the other nodes in the graph.
Taking a step back: your cover letter describes a solution at a high
level.  That's good.  But it should *first* describe the problem you're
trying to solve.
Do you think this explanation of the problem is fine?

I am not very experienced with patches, so in case it is, should I re-write the cover letter adding the above explanations or is fine like this? In case I should do it, should I submit the whole series again?
- Minor fixes regarding memory leaks and naming

Signed-off-by: Emanuele Giuseppe Esposito <address@hidden>

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