Test at compile time whether siginfo_t is usable for --remote (#119).

configure.ac

@@ -60,6 +60,43 @@ AC_TYPE_SIZE_T
 AC_TYPE_SSIZE_T
 AC_TYPE_UID_T
 
+dnl Check that a signal handler can't see the PID of the sender.
+AC_MSG_CHECKING([siginfo_t provides a signal sender's PID])
+AC_RUN_IFELSE(
+[AC_LANG_PROGRAM([[
+#include <string.h>
+#include <signal.h>
+#include <unistd.h>
+
+static pid_t signalSender = 0;
+
+#ifdef SA_SIGINFO
+static void receiveUSR2( __attribute__((unused))
+			int sig, siginfo_t * info, __attribute__((unused))
+			void *ucontext)
+{
+	if (NULL != info)
+		signalSender = info->si_pid;
+}
+#endif
+]], [[
+	struct sigaction sa;
+	memset(&sa, 0, sizeof(sa));
+#ifdef SA_SIGINFO
+	sa.sa_sigaction = receiveUSR2;
+	(void) sigemptyset(&(sa.sa_mask));
+	sa.sa_flags = SA_SIGINFO;
+	(void) sigaction(SIGUSR2, &sa, NULL);
+	raise(SIGUSR2);
+#endif
+	return signalSender == 0 ? 1 : 0;
+]])], [
+AC_MSG_RESULT([yes])
+AC_DEFINE([SIGINFO_PROVIDES_PID], [1], [Signal handlers can determine the sending PID])
+], [
+AC_MSG_RESULT([no])
+])
+
 AH_BOTTOM([#include "config-aux.h"])
 
 AC_ARG_ENABLE([debugging],

src/include/config.h.in

@@ -223,6 +223,9 @@
 /* Define to the version of this package. */
 #undef PACKAGE_VERSION
 
+/* Signal handlers can determine the sending PID */
+#undef SIGINFO_PROVIDES_PID
+
 /* Define to 1 if all of the C90 standard headers exist (not just the ones
    required in a freestanding environment). This macro is provided for
    backward compatibility; new code need not use it. */

src/include/pv-internal.h

@@ -154,13 +154,13 @@ struct pvstate_s {
 		struct sigaction old_sigint;
 		struct sigaction old_sighup;
 		struct sigaction old_sigterm;
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 		struct sigaction old_sigusr2;
 #endif
 		struct sigaction old_sigalrm;
 		struct timespec tstp_time;	 /* see pv_sig_tstp() / __cont() */
 		struct timespec toffset;	 /* total time spent stopped */
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 		volatile sig_atomic_t rxusr2;	 /* whether SIGUSR2 was received */
 		volatile pid_t sender;		 /* PID of sending process for SIGUSR2 */
 #endif

src/include/pv.h

@@ -237,7 +237,7 @@ extern off_t pv_calc_total_size(pvstate_t);
  */
 extern void pv_sig_init(pvstate_t);
 
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 /*
  * Return true if SIGUSR2 has been received, and indicate the sender.
  */

src/main/help.c

@@ -399,11 +399,11 @@ void display_help(void)
 		{ "-U", "--store-and-forward", N_("FILE"),
 		 N_("write all input to FILE before writing to output"),
 		 { 0, 0, 0, 0} },
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 		{ "-R", "--remote", N_("PID"),
 		 N_("update settings of process PID"),
 		 { 0, 0, 0, 0} },
-#endif				/* SA_SIGINFO */
+#endif				/* SIGINFO_PROVIDES_PID */
 		{ "", NULL, NULL, NULL, { 0, 0, 0, 0} },
 		{ "-P", "--pidfile", N_("FILE"),
 		 N_("save process ID in FILE"),

src/main/remote.c

@@ -21,7 +21,7 @@
 #include <sys/time.h>
 #include <sys/stat.h>
 
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 void pv_error(pvstate_t, char *, ...);
 
 struct remote_msg {
@@ -405,10 +405,10 @@ void pv_remote_fini(void)
 {
 }
 
-#else				/* !SA_SIGINFO */
+#else				/* !SIGINFO_PROVIDES_PID */
 
 /*
- * Dummy stubs for remote control when we don't have SA_SIGINFO.
+ * Dummy stubs for remote control when we don't have SIGINFO_PROVIDES_PID.
  */
 void pv_remote_init(void)
 {

src/pv/signal.c

@@ -226,7 +226,7 @@ static void pv_sig_term( /*@unused@ */  __attribute__((unused))
 }
 
 
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 /*
  * Handle a SIGUSR2 by setting a flag to say we received it, after recording
  * the sending PID.
@@ -375,7 +375,7 @@ void pv_sig_init(pvstate_t state)
 	sa.sa_flags = 0;
 	(void) sigaction(SIGTERM, &sa, &(pv_sig_state->signal.old_sigterm));
 
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 	/*
 	 * Handle SIGUSR2 by setting a flag to say the signal has been
 	 * received, and storing the sending process's PID.
@@ -431,7 +431,7 @@ void pv_sig_fini( /*@unused@ */  __attribute__((unused)) pvstate_t state)
 	(void) sigaction(SIGINT, &(pv_sig_state->signal.old_sigint), NULL);
 	(void) sigaction(SIGHUP, &(pv_sig_state->signal.old_sighup), NULL);
 	(void) sigaction(SIGTERM, &(pv_sig_state->signal.old_sigterm), NULL);
-#ifdef SA_SIGINFO
+#ifdef SIGINFO_PROVIDES_PID
 	(void) sigaction(SIGUSR2, &(pv_sig_state->signal.old_sigusr2), NULL);
 #endif
 	(void) sigaction(SIGALRM, &(pv_sig_state->signal.old_sigalrm), NULL);