On Thu, Mar 03, 2022 at 05:48:13PM +0100, Hanna Reitz wrote: > To implement this, we reuse the existing daemonizing functions from the > system emulator, which mainly do the following: > - Fork off a child process, and set up a pipe between parent and child > - The parent process waits until the child sends a status byte over the > pipe (0 means that the child was set up successfully; anything else > (including errors or EOF) means that the child was not set up > successfully), and then exits with an appropriate exit status > - The child process enters a new session (forking off again), changes > the umask, and will ignore terminal signals from then on > - Once set-up is complete, the child will chdir to /, redirect all > standard I/O streams to /dev/null, and tell the parent that set-up has > been completed successfully > > In contrast to qemu-nbd's --fork implementation, during the set up > phase, error messages are not piped through the parent process. > qemu-nbd mainly does this to detect errors, though (while os_daemonize() > has the child explicitly signal success after set up); because we do not > redirect stderr after forking, error messages continue to appear on > whatever the parent's stderr was (until set up is complete). > > Signed-off-by: Hanna Reitz <hre...@redhat.com> > --- > docs/tools/qemu-storage-daemon.rst | 7 +++++++ > storage-daemon/qemu-storage-daemon.c | 15 +++++++++++++++ > 2 files changed, 22 insertions(+) >
Reviewed-by: Eric Blake <ebl...@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
