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qsd: Add --daemonize

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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>
Message-Id: <20220303164814.284974-4-hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Hanna Reitz 2022-03-03 17:48:13 +01:00 • committed by Kevin Wolf
parent 79d51d7317
commit 2525edd85f
2 changed files with 22 additions and 0 deletions
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15
storage-daemon/qemu-storage-daemon.c
View file

@ -93,6 +93,9 @@ static void help(void)
" --chardev <options> configure a character device backend\n"
" (see the qemu(1) man page for possible options)\n"
"\n"
" --daemonize daemonize the process, and have the parent exit\n"
" once startup is complete\n"
"\n"
" --export [type=]nbd,id=<id>,node-name=<node-name>[,name=<export-name>]\n"
" [,writable=on|off][,bitmap=<name>]\n"
" export the specified block node over NBD\n"
@ -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);