Comment 5 for bug 1877384

Good! Then just for the case ...

Compiling the 9pfs test cases:

cd build
make tests/qtest/qos-test

Running the test cases:

export QTEST_QEMU_BINARY=x86_64-softmmu/qemu-system-x86_64
tests/qtest/qos-test

All 9pfs test cases are in:
tests/qtest/virtio-9p-test.c

The 9pfs test cases are using a simulated filesystem driver called 'synth' driver:
hw/9pfs/9p-synth.c
That 'synth' driver is exclusively used for the 9pfs test cases, it is not used for anything else, so you can add there whatever you need to simulate any file system behaviour required for your test case.