Arrange for the postmaster (and standalone backends, initdb, etc) to

chdir into PGDATA and subsequently use relative paths instead of absolute
paths to access all files under PGDATA.  This seems to give a small
performance improvement, and it should make the system more robust
against naive DBAs doing things like moving a database directory that
has a live postmaster in it.  Per recent discussion.

1 files changed, 44 insertions, 28 deletions

diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index be1f6e70496..ffe7db5f7e5 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/init/miscinit.c,v 1.144 2005/06/28 22:16:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/init/miscinit.c,v 1.145 2005/07/04 04:51:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,10 +41,11 @@
 #include "utils/syscache.h"
 
 
+#define DIRECTORY_LOCK_FILE		"postmaster.pid"
+
 ProcessingMode Mode = InitProcessing;
 
-/* Note: we rely on these to initialize as zeroes */
-static char directoryLockFile[MAXPGPATH];
+/* Note: we rely on this to initialize as zeroes */
 static char socketLockFile[MAXPGPATH];
 
 
@@ -178,15 +179,32 @@ SetDataDir(const char *dir)
 }
 
 /*
+ * Change working directory to DataDir.  Most of the postmaster and backend
+ * code assumes that we are in DataDir so it can use relative paths to access
+ * stuff in and under the data directory.  For convenience during path
+ * setup, however, we don't force the chdir to occur during SetDataDir.
+ */
+void
+ChangeToDataDir(void)
+{
+	AssertState(DataDir);
+
+	if (chdir(DataDir) < 0)
+		ereport(FATAL,
+				(errcode_for_file_access(),
+				 errmsg("could not change directory to \"%s\": %m",
+						DataDir)));
+}
+
+/*
  * If the given pathname isn't already absolute, make it so, interpreting
  * it relative to the current working directory.
  *
  * Also canonicalizes the path.  The result is always a malloc'd copy.
  *
- * Note: it is probably unwise to use this in running backends, since they
- * have chdir'd to a database-specific subdirectory; the results would not be
- * consistent across backends.  Currently this is used only during postmaster
- * or standalone-backend startup.
+ * Note: interpretation of relative-path arguments during postmaster startup
+ * should happen before doing ChangeToDataDir(), else the user will probably
+ * not like the results.
  */
 char *
 make_absolute_path(const char *path)
@@ -713,17 +731,22 @@ CreateLockFile(const char *filename, bool amPostmaster,
 	on_proc_exit(UnlinkLockFile, PointerGetDatum(strdup(filename)));
 }
 
+/*
+ * Create the data directory lockfile.
+ *
+ * When this is called, we must have already switched the working
+ * directory to DataDir, so we can just use a relative path.  This
+ * helps ensure that we are locking the directory we should be.
+ */
 void
-CreateDataDirLockFile(const char *datadir, bool amPostmaster)
+CreateDataDirLockFile(bool amPostmaster)
 {
-	char		lockfile[MAXPGPATH];
-
-	snprintf(lockfile, sizeof(lockfile), "%s/postmaster.pid", datadir);
-	CreateLockFile(lockfile, amPostmaster, true, datadir);
-	/* Save name of lockfile for RecordSharedMemoryInLockFile */
-	strcpy(directoryLockFile, lockfile);
+	CreateLockFile(DIRECTORY_LOCK_FILE, amPostmaster, true, DataDir);
 }
 
+/*
+ * Create a lockfile for the specified Unix socket file.
+ */
 void
 CreateSocketLockFile(const char *socketfile, bool amPostmaster)
 {
@@ -777,7 +800,7 @@ TouchSocketLockFile(void)
 
 /*
  * Append information about a shared memory segment to the data directory
- * lock file (if we have created one).
+ * lock file.
  *
  * This may be called multiple times in the life of a postmaster, if we
  * delete and recreate shmem due to backend crash.	Therefore, be prepared
@@ -793,20 +816,13 @@ RecordSharedMemoryInLockFile(unsigned long id1, unsigned long id2)
 	char	   *ptr;
 	char		buffer[BLCKSZ];
 
-	/*
-	 * Do nothing if we did not create a lockfile (probably because we are
-	 * running standalone).
-	 */
-	if (directoryLockFile[0] == '\0')
-		return;
-
-	fd = open(directoryLockFile, O_RDWR | PG_BINARY, 0);
+	fd = open(DIRECTORY_LOCK_FILE, O_RDWR | PG_BINARY, 0);
 	if (fd < 0)
 	{
 		ereport(LOG,
 				(errcode_for_file_access(),
 				 errmsg("could not open file \"%s\": %m",
-						directoryLockFile)));
+						DIRECTORY_LOCK_FILE)));
 		return;
 	}
 	len = read(fd, buffer, sizeof(buffer) - 100);
@@ -815,7 +831,7 @@ RecordSharedMemoryInLockFile(unsigned long id1, unsigned long id2)
 		ereport(LOG,
 				(errcode_for_file_access(),
 				 errmsg("could not read from file \"%s\": %m",
-						directoryLockFile)));
+						DIRECTORY_LOCK_FILE)));
 		close(fd);
 		return;
 	}
@@ -828,7 +844,7 @@ RecordSharedMemoryInLockFile(unsigned long id1, unsigned long id2)
 	if (ptr == NULL ||
 		(ptr = strchr(ptr + 1, '\n')) == NULL)
 	{
-		elog(LOG, "bogus data in \"%s\"", directoryLockFile);
+		elog(LOG, "bogus data in \"%s\"", DIRECTORY_LOCK_FILE);
 		close(fd);
 		return;
 	}
@@ -855,7 +871,7 @@ RecordSharedMemoryInLockFile(unsigned long id1, unsigned long id2)
 		ereport(LOG,
 				(errcode_for_file_access(),
 				 errmsg("could not write to file \"%s\": %m",
-						directoryLockFile)));
+						DIRECTORY_LOCK_FILE)));
 		close(fd);
 		return;
 	}
@@ -864,7 +880,7 @@ RecordSharedMemoryInLockFile(unsigned long id1, unsigned long id2)
 		ereport(LOG,
 				(errcode_for_file_access(),
 				 errmsg("could not write to file \"%s\": %m",
-						directoryLockFile)));
+						DIRECTORY_LOCK_FILE)));
 	}
 }