watchdog: always prefer /dev/watchdog0 over /dev/watchdog

diff --git a/man/systemd-system.conf.xml b/man/systemd-system.conf.xml
index 2307a8f5c951d8ba7d1280007c580d4f63d1c039..3805a010e2e779a558fb47c1f93c54c0ef90e6d1 100644 (file)
--- a/man/systemd-system.conf.xml
+++ b/man/systemd-system.conf.xml
@@ -144,7 +144,7 @@
         depending on hardware capabilities).</para>
 
         <para>If <varname>RuntimeWatchdogSec=</varname> is set to a non-zero value, the watchdog hardware
-        (<filename>/dev/watchdog</filename> or the path specified with <varname>WatchdogDevice=</varname> or
+        (<filename>/dev/watchdog0</filename> or the path specified with <varname>WatchdogDevice=</varname> or
         the kernel option <varname>systemd.watchdog-device=</varname>) will be programmed to automatically
         reboot the system if it is not contacted within the specified timeout interval. The system manager
         will ensure to contact it at least once in half the specified timeout interval. This feature requires
@@ -182,7 +182,7 @@
 
         <listitem><para>Configure the hardware watchdog device that the
         runtime and shutdown watchdog timers will open and use. Defaults
-        to <filename>/dev/watchdog</filename>. This setting has no
+        to <filename>/dev/watchdog0</filename>. This setting has no
         effect if a hardware watchdog is not available.</para></listitem>
       </varlistentry>
 

diff --git a/src/shared/watchdog.c b/src/shared/watchdog.c
index 8a551fb5c8674952c71f4716cba1262f50402e82..c23a4cbac4c07ed4f1c365871846f937d9a6a8f5 100644 (file)
--- a/src/shared/watchdog.c
+++ b/src/shared/watchdog.c
@@ -10,6 +10,7 @@
 #include "errno-util.h"
 #include "fd-util.h"
 #include "log.h"
+#include "path-util.h"
 #include "string-util.h"
 #include "time-util.h"
 #include "watchdog.h"
@@ -127,7 +128,13 @@ static int open_watchdog(void) {
         if (watchdog_fd >= 0)
                 return 0;
 
-        fn = watchdog_device ?: "/dev/watchdog";
+        /* Let's prefer new-style /dev/watchdog0 (i.e. kernel 3.5+) over classic /dev/watchdog. The former
+         * has the benefit that we can easily find the matching directory in sysfs from it, as the relevant
+         * sysfs attributes can only be found via /sys/dev/char/<major>:<minor> if the new-style device
+         * major/minor is used, not the old-style. */
+        fn = !watchdog_device || path_equal(watchdog_device, "/dev/watchdog") ?
+                "/dev/watchdog0" : watchdog_device;
+
         watchdog_fd = open(fn, O_WRONLY|O_CLOEXEC);
         if (watchdog_fd < 0)
                 return log_debug_errno(errno, "Failed to open watchdog device %s, ignoring: %m", fn);