Re: [PATCH 0/3] qemu/qsd: Unlink absolute PID file path

[Hanna Reitz]

On 09.06.22 14:26, Hanna Reitz wrote:
> Hi,
>
> QEMU (the system emulator) and the storage daemon (QSD) write their PID
> to the given file when you specify --pidfile.  They keep the path around
> and register exit handlers (QEMU uses an exit notifier, QSD an atexit()
> function) to unlink this file when the process terminates.  These
> handlers unlink precisely the path that the user has specified via
> --pidfile, so if it was a relative path and the process has at any point
> changed its working directory, the path no longer points to the PID
> file, and so the unlink() will fail (or worse).
>
> When using --daemonize, the process will always change its working
> directory to /, so this problem basically always appears when using
> --daemonize and --pidfile in conjunction.

[...]

> We can fix the problem by running realpath() once the PID file has been
> created, so we get an absolute path that we can unlink in the exit
> handler.  This is done here.

Thanks for the review, Dan, I’ve applied the series to my block branch:

https://gitlab.com/hreitz/qemu/-/commits/block