From 8750ac02381be5f0b3ebbcc0131779553fa7ce52 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Fri, 9 Mar 2018 09:32:03 +0100
Subject: [PATCH] pid1: make use of high rt signals on hppa with newer kernels

Back in 4dffec1459f50ac9f8f67ccfcb79836b4ed5a50e we stopped using SIGRTMIN+26
and higher on hppa because they were not available. Then they became available
in linux 3.18:

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1f25df2eff5b25f52c139d3ff31bc883eee9a0ab

Instead of hard-coding the list based on architecture, let's use a runtime
check like signal(7) says.

(A note about implementation: RTSIG_IF_AVAILABLE is defined to take the full
signal and not just an offset from SIGRTMIN so that it's still possible to
grep for SIGRTMIN\+.)

Add a simple "test" to print the signal values.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=84931.
---
 src/core/manager.c          | 28 +++++++++++++++-------------
 src/test/test-signal-util.c | 12 ++++++++++++
 2 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/src/core/manager.c b/src/core/manager.c
index 84adb9c6660..3c662ffdefb 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -426,6 +426,8 @@ static int enable_special_signals(Manager *m) {
         return 0;
 }
 
+#define RTSIG_IF_AVAILABLE(signum) (signum <= SIGRTMAX ? signum : -1)
+
 static int manager_setup_signals(Manager *m) {
         struct sigaction sa = {
                 .sa_handler = SIG_DFL,
@@ -479,22 +481,22 @@ static int manager_setup_signals(Manager *m) {
 
                         /* .. one free signal here ... */
 
-#if !defined(__hppa64__) && !defined(__hppa__)
-                        /* Apparently Linux on hppa has fewer RT
-                         * signals (SIGRTMAX is SIGRTMIN+25 there),
-                         * hence let's not try to make use of them
-                         * here. Since these commands are accessible
-                         * by different means and only really a safety
-                         * net, the missing functionality on hppa
-                         * shouldn't matter. */
+                        /* Apparently Linux on hppa had fewer RT signals until v3.18,
+                         * SIGRTMAX was SIGRTMIN+25, and then SIGRTMIN was lowered,
+                         * see commit v3.17-7614-g1f25df2eff.
+                         *
+                         * We cannot unconditionally make use of those signals here,
+                         * so let's use a runtime check. Since these commands are
+                         * accessible by different means and only really a safety
+                         * net, the missing functionality on hppa shouldn't matter.
+                         */
 
-                        SIGRTMIN+26, /* systemd: set log target to journal-or-kmsg */
-                        SIGRTMIN+27, /* systemd: set log target to console */
-                        SIGRTMIN+28, /* systemd: set log target to kmsg */
-                        SIGRTMIN+29, /* systemd: set log target to syslog-or-kmsg (obsolete) */
+                        RTSIG_IF_AVAILABLE(SIGRTMIN+26), /* systemd: set log target to journal-or-kmsg */
+                        RTSIG_IF_AVAILABLE(SIGRTMIN+27), /* systemd: set log target to console */
+                        RTSIG_IF_AVAILABLE(SIGRTMIN+28), /* systemd: set log target to kmsg */
+                        RTSIG_IF_AVAILABLE(SIGRTMIN+29), /* systemd: set log target to syslog-or-kmsg (obsolete) */
 
                         /* ... one free signal here SIGRTMIN+30 ... */
-#endif
                         -1);
         assert_se(sigprocmask(SIG_SETMASK, &mask, NULL) == 0);
 
diff --git a/src/test/test-signal-util.c b/src/test/test-signal-util.c
index f4b19ed69d3..d2640824783 100644
--- a/src/test/test-signal-util.c
+++ b/src/test/test-signal-util.c
@@ -21,10 +21,21 @@
 #include <signal.h>
 #include <unistd.h>
 
+#include "log.h"
 #include "macro.h"
 #include "signal-util.h"
 #include "process-util.h"
 
+#define info(sig) log_info(#sig " = " STRINGIFY(sig) " = %d", sig)
+
+static void test_rt_signals(void) {
+        info(SIGRTMIN);
+        info(SIGRTMAX);
+
+        /* We use signals SIGRTMIN+0 to SIGRTMIN+24 unconditionally */
+        assert(SIGRTMAX - SIGRTMIN >= 24);
+}
+
 static void test_block_signals(void) {
         sigset_t ss;
 
@@ -62,6 +73,7 @@ static void test_ignore_signals(void) {
 }
 
 int main(int argc, char *argv[]) {
+        test_rt_signals();
         test_block_signals();
         test_ignore_signals();