Adjust lo_open() so that specifying INV_READ without INV_WRITE creates

a descriptor that uses the current transaction snapshot, rather than
SnapshotNow as it did before (and still does if INV_WRITE is set).
This means pg_dump will now dump a consistent snapshot of large object
contents, as it never could do before.  Also, add a lo_create() function
that is similar to lo_creat() but allows the desired OID of the large
object to be specified.  This will simplify pg_restore considerably
(but I'll fix that in a separate commit).

src/interfaces/libpq/exports.txt

@@ -1,4 +1,4 @@
-# $PostgreSQL: pgsql/src/interfaces/libpq/exports.txt,v 1.3 2004/10/30 23:11:26 tgl Exp $
+# $PostgreSQL: pgsql/src/interfaces/libpq/exports.txt,v 1.4 2005/06/13 02:26:53 tgl Exp $
 # Functions to be exported by libpq DLLs
 PQconnectdb               1
 PQsetdbLogin              2
@@ -122,3 +122,4 @@ PQsendPrepare             119
 PQgetCancel               120
 PQfreeCancel              121
 PQcancel                  122
+lo_create                 123

src/interfaces/libpq/fe-lobj.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-lobj.c,v 1.52 2004/12/31 22:03:50 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-lobj.c,v 1.53 2005/06/13 02:26:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -266,12 +266,11 @@ lo_lseek(PGconn *conn, int fd, int offset, int whence)
 /*
  * lo_creat
  *	  create a new large object
- * the mode is a bitmask describing different attributes of the new object
+ * the mode is ignored (once upon a time it had a use)
  *
  * returns the oid of the large object created or
  * InvalidOid upon failure
  */
-
 Oid
 lo_creat(PGconn *conn, int mode)
 {
@@ -303,6 +302,53 @@ lo_creat(PGconn *conn, int mode)
 	}
 }
 
+/*
+ * lo_create
+ *	  create a new large object
+ * if lobjId isn't InvalidOid, it specifies the OID to (attempt to) create
+ *
+ * returns the oid of the large object created or
+ * InvalidOid upon failure
+ */
+Oid
+lo_create(PGconn *conn, Oid lobjId)
+{
+	PQArgBlock	argv[1];
+	PGresult   *res;
+	int			retval;
+	int			result_len;
+
+	if (conn->lobjfuncs == NULL)
+	{
+		if (lo_initialize(conn) < 0)
+			return InvalidOid;
+	}
+
+	/* Must check this on-the-fly because it's not there pre-8.1 */
+	if (conn->lobjfuncs->fn_lo_create == 0)
+	{
+		printfPQExpBuffer(&conn->errorMessage,
+		   libpq_gettext("cannot determine OID of function lo_create\n"));
+		return InvalidOid;
+	}
+
+	argv[0].isint = 1;
+	argv[0].len = 4;
+	argv[0].u.integer = lobjId;
+	res = PQfn(conn, conn->lobjfuncs->fn_lo_create,
+			   &retval, &result_len, 1, argv, 1);
+	if (PQresultStatus(res) == PGRES_COMMAND_OK)
+	{
+		PQclear(res);
+		return (Oid) retval;
+	}
+	else
+	{
+		PQclear(res);
+		return InvalidOid;
+	}
+}
+
 
 /*
  * lo_tell
@@ -560,7 +606,8 @@ lo_initialize(PGconn *conn)
 
 	/*
 	 * Execute the query to get all the functions at once.	In 7.3 and
-	 * later we need to be schema-safe.
+	 * later we need to be schema-safe.  lo_create only exists in 8.1
+	 * and up.
 	 */
 	if (conn->sversion >= 70300)
 		query = "select proname, oid from pg_catalog.pg_proc "
@@ -568,6 +615,7 @@ lo_initialize(PGconn *conn)
 			"'lo_open', "
 			"'lo_close', "
 			"'lo_creat', "
+			"'lo_create', "
 			"'lo_unlink', "
 			"'lo_lseek', "
 			"'lo_tell', "
@@ -615,6 +663,8 @@ lo_initialize(PGconn *conn)
 			lobjfuncs->fn_lo_close = foid;
 		else if (!strcmp(fname, "lo_creat"))
 			lobjfuncs->fn_lo_creat = foid;
+		else if (!strcmp(fname, "lo_create"))
+			lobjfuncs->fn_lo_create = foid;
 		else if (!strcmp(fname, "lo_unlink"))
 			lobjfuncs->fn_lo_unlink = foid;
 		else if (!strcmp(fname, "lo_lseek"))
@@ -631,7 +681,7 @@ lo_initialize(PGconn *conn)
 
 	/*
 	 * Finally check that we really got all large object interface
-	 * functions.
+	 * functions --- except lo_create, which may not exist.
 	 */
 	if (lobjfuncs->fn_lo_open == 0)
 	{

src/interfaces/libpq/libpq-fe.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.117 2005/06/09 20:01:16 tgl Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.118 2005/06/13 02:26:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -480,6 +480,7 @@ extern int	lo_read(PGconn *conn, int fd, char *buf, size_t len);
 extern int	lo_write(PGconn *conn, int fd, char *buf, size_t len);
 extern int	lo_lseek(PGconn *conn, int fd, int offset, int whence);
 extern Oid	lo_creat(PGconn *conn, int mode);
+extern Oid	lo_create(PGconn *conn, Oid lobjId);
 extern int	lo_tell(PGconn *conn, int fd);
 extern int	lo_unlink(PGconn *conn, Oid lobjId);
 extern Oid	lo_import(PGconn *conn, const char *filename);

src/interfaces/libpq/libpq-int.h

@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.102 2005/06/12 00:00:21 neilc Exp $
+ * $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.103 2005/06/13 02:26:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -229,6 +229,7 @@ typedef struct pgLobjfuncs
 	Oid			fn_lo_open;		/* OID of backend function lo_open		*/
 	Oid			fn_lo_close;	/* OID of backend function lo_close		*/
 	Oid			fn_lo_creat;	/* OID of backend function lo_creat		*/
+	Oid			fn_lo_create;	/* OID of backend function lo_create	*/
 	Oid			fn_lo_unlink;	/* OID of backend function lo_unlink	*/
 	Oid			fn_lo_lseek;	/* OID of backend function lo_lseek		*/
 	Oid			fn_lo_tell;		/* OID of backend function lo_tell		*/