On Tue, Mar 02, 2021 at 02:27:46PM +0000, Stefan Hajnoczi wrote:
> Daemons often have a --pidfile option where the pid is written to a file
> so that scripts can stop the daemon by sending a signal.
>
> The pid file also acts as a lock to prevent multiple instances of the
> daemon from launching for a given pid file.
>
> QEMU, qemu-nbd, qemu-ga, virtiofsd, and qemu-pr-helper all support the
> --pidfile option. Add it to qemu-storage-daemon too.
>
> Reported-by: Richard W.M. Jones <rjo...@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> v3:
> * Add --pidfile help output [Kevin]
>
> docs/tools/qemu-storage-daemon.rst | 14 +++++++++++
> storage-daemon/qemu-storage-daemon.c | 36 ++++++++++++++++++++++++++++
> 2 files changed, 50 insertions(+)
>
> diff --git a/docs/tools/qemu-storage-daemon.rst
> b/docs/tools/qemu-storage-daemon.rst
> index f63627eaf6..3d9704d835 100644
> --- a/docs/tools/qemu-storage-daemon.rst
> +++ b/docs/tools/qemu-storage-daemon.rst
> @@ -118,6 +118,20 @@ Standard options:
> List object properties with ``<type>,help``. See the :manpage:`qemu(1)`
> manual page for a description of the object properties.
>
> +.. option:: --pidfile PATH
> +
> + is the path to a file where the daemon writes its pid. This allows scripts
> to
> + stop the daemon by sending a signal::
> +
> + $ kill -SIGTERM $(<path/to/qsd.pid)
> +
> + A file lock is applied to the file so only one instance of the daemon can
> run
> + with a given pid file path. The daemon unlinks its pid file when
> terminating.
> +
> + The pid file is written after chardevs, exports, and NBD servers have been
> + created but before accepting connections. The daemon has started
> successfully
> + when the pid file is written and clients may begin connecting.
> +
> 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 9021a46b3a..4672145df5 100644
> --- a/storage-daemon/qemu-storage-daemon.c
> +++ b/storage-daemon/qemu-storage-daemon.c
> @@ -59,6 +59,7 @@
> #include "sysemu/runstate.h"
> #include "trace/control.h"
>
> +static const char *pid_file;
> static volatile bool exit_requested = false;
>
> void qemu_system_killed(int signal, pid_t pid)
> @@ -115,6 +116,8 @@ static void help(void)
> " See the qemu(1) man page for documentation of
> the\n"
> " objects that can be added.\n"
> "\n"
> +" --pidfile <path> write process ID to a file after startup\n"
> +"\n"
> QEMU_HELP_BOTTOM "\n",
> error_get_progname());
> }
> @@ -126,6 +129,7 @@ enum {
> OPTION_MONITOR,
> OPTION_NBD_SERVER,
> OPTION_OBJECT,
> + OPTION_PIDFILE,
> };
>
> extern QemuOptsList qemu_chardev_opts;
> @@ -164,6 +168,7 @@ static void process_options(int argc, char *argv[])
> {"monitor", required_argument, NULL, OPTION_MONITOR},
> {"nbd-server", required_argument, NULL, OPTION_NBD_SERVER},
> {"object", required_argument, NULL, OPTION_OBJECT},
> + {"pidfile", required_argument, NULL, OPTION_PIDFILE},
> {"trace", required_argument, NULL, 'T'},
> {"version", no_argument, NULL, 'V'},
> {0, 0, 0, 0}
> @@ -275,6 +280,9 @@ static void process_options(int argc, char *argv[])
> qobject_unref(args);
> break;
> }
> + case OPTION_PIDFILE:
> + pid_file = optarg;
> + break;
> default:
> g_assert_not_reached();
> }
> @@ -285,6 +293,27 @@ static void process_options(int argc, char *argv[])
> }
> }
>
> +static void pid_file_cleanup(void)
> +{
> + unlink(pid_file);
> +}
> +
> +static void pid_file_init(void)
> +{
> + Error *err = NULL;
> +
> + if (!pid_file) {
> + return;
> + }
> +
> + if (!qemu_write_pidfile(pid_file, &err)) {
> + error_reportf_err(err, "cannot create PID file: ");
> + exit(EXIT_FAILURE);
> + }
> +
> + atexit(pid_file_cleanup);
> +}
> +
> int main(int argc, char *argv[])
> {
> #ifdef CONFIG_POSIX
> @@ -312,6 +341,13 @@ int main(int argc, char *argv[])
> qemu_init_main_loop(&error_fatal);
> process_options(argc, argv);
>
> + /*
> + * Write the pid file after creating chardevs, exports, and NBD servers
> but
> + * before accepting connections. This ordering is documented. Do not
> change
> + * it.
> + */
> + pid_file_init();
> +
> while (!exit_requested) {
> main_loop_wait(false);
> }
> --
> 2.29.2
>
Reviewed-by: Richard W.M. Jones <rjo...@redhat.com>
Rich.
--
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