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/* SPDX-License-Identifier: MIT-0 */
/* Implement the systemd notify protocol without external dependencies.
* Supports both readiness notification on startup and on reloading,
* according to the protocol defined at:
* https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
* This protocol is guaranteed to be stable as per:
* https://systemd.io/PORTABILITY_AND_STABILITY/ */
#include <errno.h>
#include <inttypes.h>
#include <signal.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <time.h>
#include <unistd.h>
#define _cleanup_(f) __attribute__((cleanup(f)))
static void closep(int *fd) {
if (!fd || *fd < 0)
return;
close(*fd);
*fd = -1;
}
static int notify(const char *message) {
union sockaddr_union {
struct sockaddr sa;
struct sockaddr_un sun;
} socket_addr = {
.sun.sun_family = AF_UNIX,
};
size_t path_length, message_length;
_cleanup_(closep) int fd = -1;
const char *socket_path;
socket_path = getenv("NOTIFY_SOCKET");
if (!socket_path)
return 0; /* Not running under systemd? Nothing to do */
if (!message)
return -EINVAL;
message_length = strlen(message);
if (message_length == 0)
return -EINVAL;
/* Only AF_UNIX is supported, with path or abstract sockets */
if (socket_path[0] != '/' && socket_path[0] != '@')
return -EAFNOSUPPORT;
path_length = strlen(socket_path);
/* Ensure there is room for NUL byte */
if (path_length >= sizeof(socket_addr.sun.sun_path))
return -E2BIG;
memcpy(socket_addr.sun.sun_path, socket_path, path_length);
/* Support for abstract socket */
if (socket_addr.sun.sun_path[0] == '@')
socket_addr.sun.sun_path[0] = 0;
fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0);
if (fd < 0)
return -errno;
if (connect(fd, &socket_addr.sa, offsetof(struct sockaddr_un, sun_path) + path_length) != 0)
return -errno;
ssize_t written = write(fd, message, message_length);
if (written != (ssize_t) message_length)
return written < 0 ? -errno : -EPROTO;
return 1; /* Notified! */
}
static int notify_ready(void) {
return notify("READY=1");
}
static int notify_reloading(void) {
/* A buffer with length sufficient to format the maximum UINT64 value. */
char reload_message[sizeof("RELOADING=1\nMONOTONIC_USEC=18446744073709551615")];
struct timespec ts;
uint64_t now;
/* Notify systemd that we are reloading, including a CLOCK_MONOTONIC timestamp in usec
* so that the program is compatible with a Type=notify-reload service. */
if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
return -errno;
if (ts.tv_sec < 0 || ts.tv_nsec < 0 ||
(uint64_t) ts.tv_sec > (UINT64_MAX - (ts.tv_nsec / 1000ULL)) / 1000000ULL)
return -EINVAL;
now = (uint64_t) ts.tv_sec * 1000000ULL + (uint64_t) ts.tv_nsec / 1000ULL;
if (snprintf(reload_message, sizeof(reload_message), "RELOADING=1\nMONOTONIC_USEC=%" PRIu64, now) < 0)
return -EINVAL;
return notify(reload_message);
}
static volatile sig_atomic_t reloading = 0;
static volatile sig_atomic_t terminating = 0;
static void signal_handler(int sig) {
if (sig == SIGHUP)
reloading = 1;
else if (sig == SIGINT || sig == SIGTERM)
terminating = 1;
}
int main(int argc, char **argv) {
struct sigaction sa = {
.sa_handler = signal_handler,
.sa_flags = SA_RESTART,
};
int r;
/* Setup signal handlers */
sigemptyset(&sa.sa_mask);
sigaction(SIGHUP, &sa, NULL);
sigaction(SIGINT, &sa, NULL);
sigaction(SIGTERM, &sa, NULL);
/* Do more service initialization work here … */
/* Now that all the preparations steps are done, signal readiness */
r = notify_ready();
if (r < 0) {
fprintf(stderr, "Failed to notify readiness to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
while (!terminating) {
if (reloading) {
reloading = false;
/* As a separate but related feature, we can also notify the manager
* when reloading configuration. This allows accurate state-tracking,
* and also automated hook-in of 'systemctl reload' without having to
* specify manually an ExecReload= line in the unit file. */
r = notify_reloading();
if (r < 0) {
fprintf(stderr, "Failed to notify reloading to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
/* Do some reconfiguration work here … */
r = notify_ready();
if (r < 0) {
fprintf(stderr, "Failed to notify readiness to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
}
/* Do some daemon work here … */
sleep(5);
}
return EXIT_SUCCESS;
}
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