Add timeline and checkpoint checks to backup.

Add the following checks:

* Checkpoint is updated in pg_control after pg_start_backup(). This helps ensure that PostgreSQL and pgBackRest have a consistent view of the storage and that PGDATA paths match.
* Timeline of backup start WAL file matches pg_control. Hard to see how this one could get hit, but we have the power...
* Standby is on the same timeline as the primary. If not, this standby is not following the primary.
* Last standby checkpoint is not greater than the backup checkpoint. If so, this standby is not following the primary.

This also requires some additional plumbing to read/write timeline/checkpoint from pg_control and parse timelines from WAL filenames. There were some changes in the backup tests caused by the fact that pg_control now has different contents for each backup.

The check to ensure that the required checkpoint was reached on the standby should also be updated to use pg_control (it currently uses pg_control_checkpoint()), but that requires non-trivial changes to the test harness and will need to wait.

src/postgres/interface.c

@@ -540,6 +540,25 @@ pgLsnFromWalSegment(const String *walSegment, unsigned int walSegmentSize)
         (cvtZToUInt64Base(strZ(strSubN(walSegment, 16, 8)), 16) * walSegmentSize));
 }
 
+/**********************************************************************************************************************************/
+uint32_t
+pgTimelineFromWalSegment(const String *const walSegment)
+{
+    FUNCTION_TEST_BEGIN();
+        FUNCTION_TEST_PARAM(STRING, walSegment);
+    FUNCTION_TEST_END();
+
+    ASSERT(walSegment != NULL);
+    ASSERT(strSize(walSegment) == 24);
+
+    char buffer[9];
+
+    strncpy(buffer, strZ(walSegment), sizeof(buffer) - 1);
+    buffer[sizeof(buffer) - 1] = '\0';
+
+    FUNCTION_TEST_RETURN(cvtZToUIntBase(buffer, 16));
+}
+
 /**********************************************************************************************************************************/
 StringList *
 pgLsnRangeToWalSegmentList(

src/postgres/interface.h

@@ -105,6 +105,9 @@ typedef struct PgControl
     uint64_t systemId;
     unsigned int catalogVersion;
 
+    uint64_t checkpoint;                                            // Last checkpoint LSN
+    uint32_t timeline;                                              // Current timeline
+
     unsigned int pageSize;
     unsigned int walSegmentSize;
 
@@ -149,6 +152,9 @@ String *pgLsnToStr(uint64_t lsn);
 String *pgLsnToWalSegment(uint32_t timeline, uint64_t lsn, unsigned int walSegmentSize);
 uint64_t pgLsnFromWalSegment(const String *walSegment, unsigned int walSegmentSize);
 
+// Get timeline from WAL segment name
+uint32_t pgTimelineFromWalSegment(const String *walSegment);
+
 // Convert a timeline and lsn range to a list of wal segments
 StringList *pgLsnRangeToWalSegmentList(
     unsigned int pgVersion, uint32_t timeline, uint64_t lsnStart, uint64_t lsnStop, unsigned int walSegmentSize);

src/postgres/interface/version.intern.h

@@ -73,6 +73,8 @@ Read the version specific pg_control into a general data structure
         {                                                                                                                          \
             .systemId = ((ControlFileData *)controlFile)->system_identifier,                                                       \
             .catalogVersion = ((ControlFileData *)controlFile)->catalog_version_no,                                                \
+            .checkpoint = ((ControlFileData *)controlFile)->checkPoint,                                                            \
+            .timeline = ((ControlFileData *)controlFile)->checkPointCopy.ThisTimeLineID,                                           \
             .pageSize = ((ControlFileData *)controlFile)->blcksz,                                                                  \
             .walSegmentSize = ((ControlFileData *)controlFile)->xlog_seg_size,                                                     \
             .pageChecksum = ((ControlFileData *)controlFile)->data_checksum_version != 0,                                          \
@@ -92,6 +94,10 @@ Read the version specific pg_control into a general data structure
         {                                                                                                                          \
             .systemId = ((ControlFileData *)controlFile)->system_identifier,                                                       \
             .catalogVersion = ((ControlFileData *)controlFile)->catalog_version_no,                                                \
+            .checkpoint =                                                                                                          \
+                (uint64_t)((ControlFileData *)controlFile)->checkPoint.xlogid << 32 |                                              \
+                ((ControlFileData *)controlFile)->checkPoint.xrecoff,                                                              \
+            .timeline = ((ControlFileData *)controlFile)->checkPointCopy.ThisTimeLineID,                                           \
             .pageSize = ((ControlFileData *)controlFile)->blcksz,                                                                  \
             .walSegmentSize = ((ControlFileData *)controlFile)->xlog_seg_size,                                                     \
         };                                                                                                                         \