coredump: make sure we vacuum by default

Only if both keep_free and max_use are actually 0 we can shortcut things
and avoid vacuuming. If either are positive or -1 we need to execute the
vacuuming.

http://lists.freedesktop.org/archives/systemd-devel/2015-April/031382.html

man/coredump.conf.xml

@@ -134,7 +134,9 @@
         by coredumps might temporarily exceed these limits while
         coredumps are processed. Note that old coredumps are also
         removed based on time via
-        <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem>
+        <citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Set
+        either value to 0 to turn off size based
+        clean-up.</para></listitem>
       </varlistentry>
     </variablelist>
 

src/journal/coredump-vacuum.c

@@ -103,8 +103,7 @@ static bool vacuum_necessary(int fd, off_t sum, off_t keep_free, off_t max_use)
 
                         if (max_use < DEFAULT_MAX_USE_LOWER)
                                 max_use = DEFAULT_MAX_USE_LOWER;
-                }
-                else
+                } else
                         max_use = DEFAULT_MAX_USE_LOWER;
         } else
                 max_use = PAGE_ALIGN(max_use);
@@ -135,7 +134,7 @@ int coredump_vacuum(int exclude_fd, off_t keep_free, off_t max_use) {
         struct stat exclude_st;
         int r;
 
-        if (keep_free <= 0 && max_use <= 0)
+        if (keep_free == 0 && max_use == 0)
                 return 0;
 
         if (exclude_fd >= 0) {