Re: [PATCH 1/1] qemu_tpm: Get swtpm pid without binary validation

Firstly, this fixes the problem only for swtpm case, but there is one other place where the same problem can happen (qemuVhostUserGPUGetPid()).

From conceptual POV, what may now happen is that when PID wrapped we may wrongly detect another process as swtpm.

I'm wondering whether we can ditch the @binPath argument of virPidFileReadPathIfAlive() completely. A pid file should be locked by the process owning it [1], therefore what we could do is read given file and try to lock it. If we succeeded it means that the process is dead and we read a stale PID. If locking fails then the process is still running and the PID we read is valid. 1: This is how libvirt treats pidfiles (see virPidFileAcquirePath()). Question is whether other tools which use their own pidfiles do the same. For instance, swtpm is given '--pid file=/some/path' argument but I haven't checked whether it behaves as expected. Also, to make things worse there are at least two types of file locks on Linux and both are independent of each other, so question then is what type of lock does given tool use.

But this could all be mitigated by using virCommandSetPidFile() when spawning the command instead of passing arbitrary --pid arguments.