raw_syscalls: define __NR_pidfd_send_signal if missing

src/lxc/commands.c

@@ -689,7 +689,7 @@ static int lxc_cmd_stop_callback(int fd, struct lxc_cmd_req *req,
 		stopsignal = handler->conf->stopsignal;
 	memset(&rsp, 0, sizeof(rsp));
 
-	if (handler-> pidfd >= 0)
+	if (handler->pidfd >= 0)
 		rsp.ret = lxc_raw_pidfd_send_signal(handler->pidfd, stopsignal, NULL, 0);
 	else
 		rsp.ret = kill(handler->pid, stopsignal);

src/lxc/raw_syscalls.c

@@ -123,13 +123,13 @@ pid_t lxc_raw_clone_cb(int (*fn)(void *), void *args, unsigned long flags,
 	return pid;
 }
 
+/* For all the architectures we care about it's the same syscall number. */
+#ifndef __NR_pidfd_send_signal
+#define __NR_pidfd_send_signal 424
+#endif
+
 int lxc_raw_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
 			      unsigned int flags)
 {
-#ifdef __NR_pidfd_send_signal
 	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
-#else
-	errno = ENOSYS;
-	return -1;
-#endif
 }

src/lxc/utils.c

@@ -1833,5 +1833,9 @@ bool lxc_can_use_pidfd(int pidfd)
 	if (ret < 0)
 		return log_error_errno(false, errno, "Kernel does not support waiting on processes through pidfds");
 
+	ret = lxc_raw_pidfd_send_signal(pidfd, 0, NULL, 0);
+	if (ret)
+		return log_error_errno(false, errno, "Kernel does not support sending singals through pidfds");
+
 	return log_trace(true, "Kernel supports pidfds");
 }