On 2/10/20 10:01 PM, Collin Walling wrote:
Hello,
Apart from what Laine said, this looks like your test binary is missing
event loop. The way sending QMP commands work is that you have one
thread, that wants to send a QMP command. It will construct the command,
format JSON string out of it and notifies the other thread (where the
event loop is running) and goes to sleep. The other thread waits until
QMP socket becomes writable (poll()) and then writes the JSON string
into it. Then it waits until the socket becomes readable and when it
does so, it reads incoming data (which is a reply to the command). Once
the full reply was received it will wake up the original thread [1].
Adding an event loop to your program should be easy. Just see what
tests/qemucapsprobe.c is doing. Important bits are eventLoop() function
and virEventRegisterDefaultImpl() and virThreadCreate() calls.
However, as Laine says, we don't want our test suite to spawn any qemu
process. Not only it would create a non-reproducible environment for the
tests (developers might run different version of qemu), it might also
not work at all - when building libvirt we don't require qemu to be
installed (as we don't link with it, there is no library to link with
anyways). But we want our test suite to run successfully.
When we want to test something that talks on QMP monitor (e.g.
qemumonitorjsontest), we create two threads and provide an alternative
implementation for the event loop - instead of actually touching any
real QMP monitor socket, it discards all writes, and provides well
defined replies (crafted before). Look into the source file and you will
understand.
Michal
1: In fact, the event loop always poll()-s for socket to be readable,
because QEMU can send us an event asynchronously, but let's not
complicate things right now.
