sd-daemon,man: ignore missing $WATCHDOG_PID

Systemd 209 started setting $WATCHDOG_PID, and sd-daemon watch was
modified to check for this variable. This means that
sd_watchdog_enabled() stopped working with previous versions of
systemd. But sd-event is a public library and API and we must keep it
working even when a program compiled with a newer version of the
libary is used on a system running an older version of the manager.

getenv() and unsetenv() are fairly expensive calls, so optimize
sd_watchdog_enabled() by not calling them when unnecessary.

man: centralize the description of $WATCHDOG_PID and $WATCHDOG_USEC in
the sd_watchdog_enabled manpage. It is better not to repeat the same
stuff in two places.

1 files changed, 22 insertions, 26 deletions

diff --git a/src/libsystemd/sd-daemon/sd-daemon.c b/src/libsystemd/sd-daemon/sd-daemon.c
index 46241f77ff..1f2a53393f 100644
--- a/src/libsystemd/sd-daemon/sd-daemon.c
+++ b/src/libsystemd/sd-daemon/sd-daemon.c
@@ -491,39 +491,35 @@ _public_ int sd_booted(void) {
 }
 
 _public_ int sd_watchdog_enabled(int unset_environment, uint64_t *usec) {
-        const char *e;
+        const char *s, *p = ""; /* p is set to dummy value to do unsetting */
         uint64_t u;
-        pid_t pid;
-        int r;
+        int r = 0;
 
-        e = getenv("WATCHDOG_PID");
-        if (!e) {
-                r = 0;
+        s = getenv("WATCHDOG_USEC");
+        if (!s)
                 goto finish;
-        }
 
-        r = parse_pid(e, &pid);
+        r = safe_atou64(s, &u);
         if (r < 0)
                 goto finish;
-
-        /* Is this for us? */
-        if (getpid() != pid) {
-                r = 0;
-                goto finish;
-        }
-
-        e = getenv("WATCHDOG_USEC");
-        if (!e) {
+        if (u <= 0) {
                 r = -EINVAL;
                 goto finish;
         }
 
-        r = safe_atou64(e, &u);
-        if (r < 0)
-                goto finish;
-        if (u <= 0) {
-                r = -EINVAL;
-                goto finish;
+        p = getenv("WATCHDOG_PID");
+        if (p) {
+                pid_t pid;
+
+                r = parse_pid(p, &pid);
+                if (r < 0)
+                        goto finish;
+
+                /* Is this for us? */
+                if (getpid() != pid) {
+                        r = 0;
+                        goto finish;
+                }
         }
 
         if (usec)
@@ -532,10 +528,10 @@ _public_ int sd_watchdog_enabled(int unset_environment, uint64_t *usec) {
         r = 1;
 
 finish:
-        if (unset_environment) {
-                unsetenv("WATCHDOG_PID");
+        if (unset_environment && s)
                 unsetenv("WATCHDOG_USEC");
-        }
+        if (unset_environment && p)
+                unsetenv("WATCHDOG_PID");
 
         return r;
 }