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. (It gets even worse with QEMUâs --chroot, but Iâm not sure whether thereâs any trivial fix for that (whether chroot is used or not is confined to os-posix.c, so this would need to be externally visible; and I guess the plain would be to skip the unlink() in that case?), so Iâd rather just skip that for now... :/) 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. (Another way to fix this might be to open the directory the PID file is in, keep the FD around, and use unlinkat() in the exit handler. I couldnât see any real benefit for this, though, so I didnât go that route. It might be beneficial for the --chroot case, but then again, precisely in that case we probably donât want to keep random directory FDs around.) Hanna Reitz (3): qsd: Unlink absolute PID file path vl: Conditionally register PID file unlink notifier vl: Unlink absolute PID file path softmmu/vl.c | 42 +++++++++++++++++++++------- storage-daemon/qemu-storage-daemon.c | 11 +++++++- 2 files changed, 42 insertions(+), 11 deletions(-) -- 2.35.3