1 files changed, 49 insertions, 1 deletions
diff --git a/src/include/postmaster/syslogger.h b/src/include/postmaster/syslogger.h
index 3e8b59dbacf..72c14c99cdd 100644
--- a/src/include/postmaster/syslogger.h
+++ b/src/include/postmaster/syslogger.h
@@ -5,13 +5,61 @@
  *
  * Copyright (c) 2004-2007, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/include/postmaster/syslogger.h,v 1.8 2007/01/05 22:19:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/postmaster/syslogger.h,v 1.9 2007/06/14 01:48:51 adunstan Exp $
  *
  *-------------------------------------------------------------------------
  */
 #ifndef _SYSLOGGER_H
 #define _SYSLOGGER_H
 
+#include <limits.h>				/* for PIPE_BUF */
+
+
+/* 
+ * Primitive protocol structure for writing to syslogger pipe(s).  The idea
+ * here is to divide long messages into chunks that are not more than
+ * PIPE_BUF bytes long, which according to POSIX spec must be written into
+ * the pipe atomically.  The pipe reader then uses the protocol headers to
+ * reassemble the parts of a message into a single string.  The reader can
+ * also cope with non-protocol data coming down the pipe, though we cannot
+ * guarantee long strings won't get split apart.
+ *
+ * We use 't' or 'f' instead of a bool for is_last to make the protocol a tiny
+ * bit more robust against finding a false double nul byte prologue.  But we
+ * still might find it in the len and/or pid bytes unless we're careful.
+ */
+
+#ifdef PIPE_BUF
+/* Are there any systems with PIPE_BUF > 64K?  Unlikely, but ... */
+#if PIPE_BUF > 65536
+#define PIPE_CHUNK_SIZE  65536
+#else
+#define PIPE_CHUNK_SIZE  ((int) PIPE_BUF)
+#endif
+#else  /* not defined */
+/* POSIX says the value of PIPE_BUF must be at least 512, so use that */
+#define PIPE_CHUNK_SIZE  512
+#endif
+
+typedef struct 
+{
+	char		nuls[2];		/* always \0\0 */
+	uint16		len;			/* size of this chunk (counts data only) */
+	int32		pid;			/* writer's pid */
+	char		is_last;		/* last chunk of message? 't' or 'f' */
+	char		data[1];		/* data payload starts here */
+} PipeProtoHeader;
+
+typedef union
+{
+	PipeProtoHeader proto;
+	char		filler[PIPE_CHUNK_SIZE];
+} PipeProtoChunk;
+
+#define PIPE_HEADER_SIZE  offsetof(PipeProtoHeader, data)
+#define PIPE_MAX_PAYLOAD  ((int) (PIPE_CHUNK_SIZE - PIPE_HEADER_SIZE))
+
+
 /* GUC options */
 extern bool Redirect_stderr;
 extern int	Log_RotationAge;