Refactor creation of backup_label and backup history files

This change simplifies some of the logic related to the generation and
creation of the backup_label and backup history files, which has become
unnecessarily complicated since the removal of the exclusive backup mode
in commit 39969e2.  The code was previously generating the contents of
these files as a string (start phase for the backup_label and stop phase
for the backup history file), one problem being that the contents of the
backup_label string were scanned to grab some of its internal contents
at the stop phase.

This commit changes the logic so as we store the data required to build
these files in an intermediate structure named BackupState.  The
backup_label file and backup history file strings are generated when
they are ready to be sent back to the client.  Both files are now
generated with the same code path.  While on it, this commit renames
some variables for clarity.

Two new files named xlogbackup.{c,h} are introduced in this commit, to
remove from xlog.c some of the logic around base backups.  Note that
more could be moved to this new set of files.

Author: Bharath Rupireddy, Michael Paquier
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/CALj2ACXWwTDgJqCjdaPyfR7djwm6SrybGcrZyrvojzcsmt4FFw@mail.gmail.com

1 files changed, 42 insertions, 0 deletions

diff --git a/src/include/access/xlogbackup.h b/src/include/access/xlogbackup.h
new file mode 100644
index 00000000000..cb15b8b80a3
--- /dev/null
+++ b/src/include/access/xlogbackup.h
@@ -0,0 +1,42 @@
+/*-------------------------------------------------------------------------
+ *
+ * xlogbackup.h
+ *		Definitions for internals of base backups.
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/include/access/xlogbackup.h
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef XLOG_BACKUP_H
+#define XLOG_BACKUP_H
+
+#include "access/xlogdefs.h"
+#include "lib/stringinfo.h"
+#include "pgtime.h"
+
+/* Structure to hold backup state. */
+typedef struct BackupState
+{
+	/* Fields saved at backup start */
+	/* Backup label name one extra byte for null-termination */
+	char		name[MAXPGPATH + 1];
+	XLogRecPtr	startpoint;		/* backup start WAL location */
+	TimeLineID	starttli;		/* backup start TLI */
+	XLogRecPtr	checkpointloc;	/* last checkpoint location */
+	pg_time_t	starttime;		/* backup start time */
+	bool		started_in_recovery;	/* backup started in recovery? */
+
+	/* Fields saved at the end of backup */
+	XLogRecPtr	stoppoint;		/* backup stop WAL location */
+	TimeLineID	stoptli;		/* backup stop TLI */
+	pg_time_t	stoptime;		/* backup stop time */
+} BackupState;
+
+extern StringInfo build_backup_content(BackupState *state,
+									   bool ishistoryfile);
+
+#endif							/* XLOG_BACKUP_H */