Re: [PATCH v2 3/4] qsd: Add --daemonize

[Kevin Wolf <kwolf@redhat.com>]

Am 03.03.2022 um 17:48 hat Hanna Reitz geschrieben:
> 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 <hreitz@redhat.com>
> ---
>  docs/tools/qemu-storage-daemon.rst   |  7 +++++++
>  storage-daemon/qemu-storage-daemon.c | 15 +++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/docs/tools/qemu-storage-daemon.rst b/docs/tools/qemu-storage-daemon.rst
> index 878e6a5c5c..8b97592663 100644
> --- a/docs/tools/qemu-storage-daemon.rst
> +++ b/docs/tools/qemu-storage-daemon.rst
> @@ -154,6 +154,13 @@ Standard options:
>    created but before accepting connections. The daemon has started successfully
>    when the pid file is written and clients may begin connecting.
>  
> +.. option:: --daemonize
> +
> +  Daemonize the process. The parent process will exit once startup is complete
> +  (i.e., after the pid file has been or would have been written) or failure
> +  occurs. Its exit code reflects whether the child has started up successfully
> +  or failed to do so.
> +
>  Examples
>  --------
>  Launch the daemon with QMP monitor socket ``qmp.sock`` so clients can execute
> diff --git a/storage-daemon/qemu-storage-daemon.c b/storage-daemon/qemu-storage-daemon.c
> index b798954edb..9f2c3332bf 100644
> --- a/storage-daemon/qemu-storage-daemon.c
> +++ b/storage-daemon/qemu-storage-daemon.c
> @@ -137,6 +137,9 @@ static void help(void)
>  "\n"
>  "  --pidfile <path>       write process ID to a file after startup\n"
>  "\n"
> +"  --daemonize            daemonize the process, and have the parent exit\n"
> +"                         once startup is complete\n"
> +"\n"

So far the long options in the help text are sorted alphabetically. Do
we want to keep this?

Kevin