linux-kernel - [PATCH] Provide control over core name even for multithreaded processes

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Message-ID: <20080829152215.2cdb1438@kartuli>
Date:	Fri, 29 Aug 2008 15:22:15 -0400
From:	"La Monte H.P. Yarroll" <piggy@...relnetworks.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] Provide control over core name even for multithreaded
 processes

Our system explicitly sets core_pattern to force a relatively small
limit on the number of different core dump names.

Unfortunately, the kernel unconditionally appends .<tid> for
multithreaded processes.

The attached patch introduces "%T" to the core_pattern language, which
expands to ".<tid>" for multithreaded processes. It then changes the
default core_pattern to "core%T" replicating the current default
behavior.

Signed-off-by: La Monte H.P. Yarroll <piggy@...relnetworks.com> 74-256740

diff -Naur linux-2.6.26.3/Documentation/sysctl/kernel.txt linux-2.6.26.3-new/Documentation/sysctl/kernel.txt
--- linux-2.6.26.3/Documentation/sysctl/kernel.txt	2008-08-20 14:11:37.000000000 -0400
+++ linux-2.6.26.3-new/Documentation/sysctl/kernel.txt	2008-08-28 13:27:50.239325000 -0400
@@ -88,7 +88,7 @@
 core_pattern:
 
 core_pattern is used to specify a core dumpfile pattern name.
-. max length 128 characters; default value is "core"
+. max length 128 characters; default value is "core%T"
 . core_pattern is used as a pattern template for the output filename;
   certain string patterns (beginning with '%') are substituted with
   their actual values.
@@ -104,6 +104,7 @@
 	%g	gid
 	%s	signal number
 	%t	UNIX time of dump
+	%T      .tgid or nothing if process is not threaded
 	%h	hostname
 	%e	executable filename
 	%<OTHER> both are dropped
diff -Naur linux-2.6.26.3/fs/exec.c linux-2.6.26.3-new/fs/exec.c
--- linux-2.6.26.3/fs/exec.c	2008-08-20 14:11:37.000000000 -0400
+++ linux-2.6.26.3-new/fs/exec.c	2008-08-28 13:46:57.919768000 -0400
@@ -66,7 +66,7 @@
 #endif
 
 int core_uses_pid;
-char core_pattern[CORENAME_MAX_SIZE] = "core";
+char core_pattern[CORENAME_MAX_SIZE] = "core%T";
 int suid_dumpable = 0;
 
 /* The maximal length of core_pattern is also specified in sysctl.c */
@@ -1415,7 +1415,7 @@
 			case 'p':
 				pid_in_pattern = 1;
 				rc = snprintf(out_ptr, out_end - out_ptr,
-					      "%d", task_tgid_vnr(current));
+					      "%d", task_pid_vnr(current));
 				if (rc > out_end - out_ptr)
 					goto out;
 				out_ptr += rc;
@@ -1455,6 +1455,17 @@
 				out_ptr += rc;
 				break;
 			}
+			/* Conditional tgid */
+			case 'T': {
+			  if (atomic_read(&current->mm->mm_users) != 1) {
+			    rc = snprintf(out_ptr, out_end - out_ptr,
+					  ".%d", task_tgid_vnr(current));
+			    if (rc > out_end - out_ptr)
+			      goto out;
+			    out_ptr += rc;
+			  }
+			  break;
+			}
 			/* hostname */
 			case 'h':
 				down_read(&uts_sem);
@@ -1492,10 +1503,9 @@
 	 * If core_pattern does not include a %p (as is the default)
 	 * and core_uses_pid is set, then .%pid will be appended to
 	 * the filename. Do not do this for piped commands. */
-	if (!ispipe && !pid_in_pattern
-            && (core_uses_pid || atomic_read(&current->mm->mm_users) != 1)) {
+	if (!ispipe && !pid_in_pattern && core_uses_pid) {
 		rc = snprintf(out_ptr, out_end - out_ptr,
-			      ".%d", task_tgid_vnr(current));
+			      ".%d", current->pid);
 		if (rc > out_end - out_ptr)
 			goto out;
 		out_ptr += rc;
--
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