Make it possible to get core dumps on Linux too

When starting as root and then setuid-ing, we need to set the dumpable
bit to get core dumps on Linux.  Do so.


git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3145 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/mgt_child.c

@@ -50,6 +50,10 @@
 #include "compat/setproctitle.h"
 #endif
 
+#ifdef __linux__
+#include <sys/prctl.h>
+#endif
+
 #include "heritage.h"
 #include "mgt.h"
 #include "cli.h"
@@ -283,6 +287,15 @@ start_child(struct cli *cli)
 			XXXAZ(setuid(params->uid));
 		}
 
+		/* On Linux >= 2.4, you need to set the dumpable flag
+		   to get core dumps after you have done a setuid. */
+#ifdef __linux__
+		if (prctl(PR_SET_DUMPABLE, 1) != 0) {
+		  printf("Could not set dumpable bit.  Core dumps turned "
+			 "off\n");
+		}
+#endif
+
 		/* Redirect stdin/out/err */
 		AZ(close(STDIN_FILENO));
 		assert(open("/dev/null", O_RDONLY) == STDIN_FILENO);