Improve error messages in md.c. When a filesystem operation like open() or

fsync() fails, say "file" rather than "relation" when printing the filename.

This makes messages that display block numbers a bit confusing. For example,
in message 'could not read block 150000 of file "base/1234/5678.1"', 150000
is the block number from the beginning of the relation, ie. segment 0, not
150000th block within that segment. Per discussion, users aren't usually
interested in the exact location within the file, so we can live with that.

To ease constructing error messages, add FilePathName(File) function to
return the pathname of a virtual fd.

src/backend/storage/file/fd.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.149 2009/06/11 14:49:01 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/file/fd.c,v 1.150 2009/08/05 18:01:54 heikki Exp $
  *
  * NOTES:
  *
@@ -1319,6 +1319,20 @@ FileTruncate(File file, off_t offset)
 	return returnCode;
 }
 
+/*
+ * Return the pathname associated with an open file.
+ *
+ * The returned string points to an internal buffer, which is valid until
+ * the file is closed.
+ */
+char *
+FilePathName(File file)
+{
+	Assert(FileIsValid(file));
+
+	return VfdCache[file].fileName;
+}
+
 
 /*
  * Routines that want to use stdio (ie, FILE*) should use AllocateFile

src/include/storage/fd.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/fd.h,v 1.64 2009/01/12 05:10:45 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/fd.h,v 1.65 2009/08/05 18:01:54 heikki Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -68,6 +68,7 @@ extern int	FileWrite(File file, char *buffer, int amount);
 extern int	FileSync(File file);
 extern off_t FileSeek(File file, off_t offset, int whence);
 extern int	FileTruncate(File file, off_t offset);
+extern char *FilePathName(File file);
 
 /* Operations that allow use of regular stdio --- USE WITH CAUTION */
 extern FILE *AllocateFile(const char *name, const char *mode);