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"
QEMU_HELP_BOTTOM "\n",
error_get_progname());
}
@@ -144,6 +147,7 @@ QEMU_HELP_BOTTOM "\n",
enum {
OPTION_BLOCKDEV = 256,
OPTION_CHARDEV,
+ OPTION_DAEMONIZE,
OPTION_EXPORT,
OPTION_MONITOR,
OPTION_NBD_SERVER,
@@ -200,6 +204,7 @@ static void process_options(int argc, char *argv[], bool pre_init_pass)
static const struct option long_options[] = {
{"blockdev", required_argument, NULL, OPTION_BLOCKDEV},
{"chardev", required_argument, NULL, OPTION_CHARDEV},
+ {"daemonize", no_argument, NULL, OPTION_DAEMONIZE},
{"export", required_argument, NULL, OPTION_EXPORT},
{"help", no_argument, NULL, 'h'},
{"monitor", required_argument, NULL, OPTION_MONITOR},
@@ -225,6 +230,7 @@ static void process_options(int argc, char *argv[], bool pre_init_pass)
c == '?' ||
c == 'h' ||
c == 'V' ||
+ c == OPTION_DAEMONIZE ||
c == OPTION_PIDFILE;
/* Process every option only in its respective pass */
@@ -277,6 +283,12 @@ static void process_options(int argc, char *argv[], bool pre_init_pass)
qemu_opts_del(opts);
break;
}
+ case OPTION_DAEMONIZE:
+ if (os_set_daemonize(true) < 0) {
+ error_report("--daemonize not supported in this build");
+ exit(EXIT_FAILURE);
+ }
+ break;
case OPTION_EXPORT:
{
Visitor *v;
@@ -367,6 +379,8 @@ int main(int argc, char *argv[])
process_options(argc, argv, true);
+ os_daemonize();
+
module_call_init(MODULE_INIT_QOM);
module_call_init(MODULE_INIT_TRACE);
qemu_add_opts(&qemu_trace_opts);
@@ -389,6 +403,7 @@ int main(int argc, char *argv[])
* it.
*/
pid_file_init();
+ os_setup_post();
while (!exit_requested) {
main_loop_wait(false);
--
2.34.1On 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 <hreitz@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 <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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
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