Repair an error introduced by log_line_prefix patch: it is not acceptable

to assume that the string pointer passed to set_ps_display is good forever.
There's no need to anyway since ps_status.c itself saves the string, and
we already had an API (get_ps_display) to return it.
I believe this explains Jim Nasby's report of intermittent crashes in
elog.c when %i format code is in use in log_line_prefix.
While at it, repair a previously unnoticed problem: on some platforms such as
Darwin, the string returned by get_ps_display was blank-padded to the maximum
length, meaning that lock.c's attempt to append " waiting" to it never worked.

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.443.4.3 2005/10/20 20:06:02 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.443.4.4 2005/11/05 03:05:04 tgl Exp $
  *
  * NOTES
  *
@@ -2638,7 +2638,6 @@ BackendRun(Port *port)
 	/* set these to empty in case they are needed before we set them up */
 	port->remote_host = "";
 	port->remote_port = "";
-	port->commandTag = "";
 
 	/*
 	 * Initialize libpq and enable reporting of ereport errors to the

src/backend/storage/lmgr/lock.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.145.4.1 2005/03/01 21:15:10 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.145.4.2 2005/11/05 03:05:04 tgl Exp $
  *
  * NOTES
  *	  Outside modules can create a lock table and acquire/release
@@ -1074,19 +1074,21 @@ WaitOnLock(LOCKMETHODID lockmethodid, LOCALLOCK *locallock,
 		   ResourceOwner owner)
 {
 	LockMethod	lockMethodTable = LockMethods[lockmethodid];
-	char	   *new_status,
-			   *old_status;
+	const char *old_status;
+	char	   *new_status;
+	int			len;
 
 	Assert(lockmethodid < NumLockMethods);
 
 	LOCK_PRINT("WaitOnLock: sleeping on lock",
 			   locallock->lock, locallock->tag.mode);
 
-	old_status = pstrdup(get_ps_display());
-	new_status = (char *) palloc(strlen(old_status) + 10);
-	strcpy(new_status, old_status);
-	strcat(new_status, " waiting");
+	old_status = get_ps_display(&len);
+	new_status = (char *) palloc(len + 8 + 1);
+	memcpy(new_status, old_status, len);
+	strcpy(new_status + len, " waiting");
 	set_ps_display(new_status);
+	new_status[len] = '\0';		/* truncate off " waiting" */
 
 	awaitedLock = locallock;
 	awaitedOwner = owner;
@@ -1129,8 +1131,7 @@ WaitOnLock(LOCKMETHODID lockmethodid, LOCALLOCK *locallock,
 
 	awaitedLock = NULL;
 
-	set_ps_display(old_status);
-	pfree(old_status);
+	set_ps_display(new_status);
 	pfree(new_status);
 
 	LOCK_PRINT("WaitOnLock: wakeup on lock",

src/backend/utils/error/elog.c

@@ -42,7 +42,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/error/elog.c,v 1.155.4.3 2005/10/14 16:41:13 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/error/elog.c,v 1.155.4.4 2005/11/05 03:05:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -67,6 +67,7 @@
 #include "tcop/tcopprot.h"
 #include "utils/memutils.h"
 #include "utils/guc.h"
+#include "utils/ps_status.h"
 
 
 /* Global variables */
@@ -1461,13 +1462,20 @@ log_line_prefix(StringInfo buf)
 				break;
 			case 'i':
 				if (MyProcPort)
-					appendStringInfo(buf, "%s", MyProcPort->commandTag);
+				{
+					const char *psdisp;
+					int		displen;
+
+					psdisp = get_ps_display(&displen);
+					appendStringInfo(buf, "%.*s", displen, psdisp);
+				}
 				break;
 			case 'r':
-				if (MyProcPort)
+				if (MyProcPort && MyProcPort->remote_host)
 				{
 					appendStringInfo(buf, "%s", MyProcPort->remote_host);
-					if (strlen(MyProcPort->remote_port) > 0)
+					if (MyProcPort->remote_port &&
+						MyProcPort->remote_port[0] != '\0')
 						appendStringInfo(buf, "(%s)",
 										 MyProcPort->remote_port);
 				}

src/backend/utils/misc/ps_status.c

@@ -5,7 +5,7 @@
  * to contain some useful information. Mechanism differs wildly across
  * platforms.
  *
- * $PostgreSQL: pgsql/src/backend/utils/misc/ps_status.c,v 1.23 2005/01/01 05:43:08 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/misc/ps_status.c,v 1.23.4.1 2005/11/05 03:05:05 tgl Exp $
  *
  * Copyright (c) 2000-2005, PostgreSQL Global Development Group
  * various details abducted from various places
@@ -308,10 +308,6 @@ init_ps_display(const char *username, const char *dbname,
 void
 set_ps_display(const char *activity)
 {
-	/* save tag for possible use by elog.c */
-	if (MyProcPort)
-		MyProcPort->commandTag = activity;
-
 #ifndef PS_USE_NONE
 	/* no ps display for stand-alone backend */
 	if (!IsUnderPostmaster)
@@ -367,15 +363,31 @@ set_ps_display(const char *activity)
 
 /*
  * Returns what's currently in the ps display, in case someone needs
- * it.	Note that only the activity part is returned.
+ * it.	Note that only the activity part is returned.  On some platforms
+ * the string will not be null-terminated, so return the effective
+ * length into *displen.
  */
 const char *
-get_ps_display(void)
+get_ps_display(int *displen)
 {
 #ifdef PS_USE_CLOBBER_ARGV
+	size_t		offset;
+
 	/* If ps_buffer is a pointer, it might still be null */
 	if (!ps_buffer)
+	{
+		*displen = 0;
 		return "";
+	}
+
+	/* Remove any trailing spaces to offset the effect of PS_PADDING */
+	offset = ps_buffer_size;
+	while (offset > ps_buffer_fixed_size && ps_buffer[offset-1] == PS_PADDING)
+		offset--;
+
+	*displen = offset - ps_buffer_fixed_size;
+#else
+	*displen = strlen(ps_buffer + ps_buffer_fixed_size);
 #endif
 
 	return ps_buffer + ps_buffer_fixed_size;

src/include/libpq/libpq-be.h

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/libpq/libpq-be.h,v 1.49 2004/12/31 22:03:32 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/libpq/libpq-be.h,v 1.49.4.1 2005/11/05 03:05:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -79,7 +79,6 @@ typedef struct Port
 	 * database_name and other members of this struct, we may as well keep
 	 * it here.
 	 */
-	const char *commandTag;		/* current command tag */
 	struct timeval session_start;		/* for session duration logging */
 
 	/*

src/include/utils/ps_status.h

@@ -4,7 +4,7 @@
  *
  * Declarations for backend/utils/misc/ps_status.c
  *
- * $PostgreSQL: pgsql/src/include/utils/ps_status.h,v 1.25 2004/02/22 21:26:54 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/ps_status.h,v 1.25.4.1 2005/11/05 03:05:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,6 +19,6 @@ extern void init_ps_display(const char *username, const char *dbname,
 
 extern void set_ps_display(const char *activity);
 
-extern const char *get_ps_display(void);
+extern const char *get_ps_display(int *displen);
 
 #endif   /* PS_STATUS_H */