1 files changed, 121 insertions, 0 deletions
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index ef827dbc404..1a21dac8538 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -456,6 +456,127 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
 	return buffer;
 }
 
+/*
+ * Restore a full-page image from a backup block attached to an XLOG record.
+ *
+ * lsn: LSN of the XLOG record being replayed
+ * record: the complete XLOG record
+ * block_index: which backup block to restore (0 .. XLR_MAX_BKP_BLOCKS - 1)
+ * get_cleanup_lock: TRUE to get a cleanup rather than plain exclusive lock
+ * keep_buffer: TRUE to return the buffer still locked and pinned
+ *
+ * Returns the buffer number containing the page.  Note this is not terribly
+ * useful unless keep_buffer is specified as TRUE.
+ *
+ * Note: when a backup block is available in XLOG, we restore it
+ * unconditionally, even if the page in the database appears newer.
+ * This is to protect ourselves against database pages that were partially
+ * or incorrectly written during a crash.  We assume that the XLOG data
+ * must be good because it has passed a CRC check, while the database
+ * page might not be.  This will force us to replay all subsequent
+ * modifications of the page that appear in XLOG, rather than possibly
+ * ignoring them as already applied, but that's not a huge drawback.
+ *
+ * If 'get_cleanup_lock' is true, a cleanup lock is obtained on the buffer,
+ * else a normal exclusive lock is used.  During crash recovery, that's just
+ * pro forma because there can't be any regular backends in the system, but
+ * in hot standby mode the distinction is important.
+ *
+ * If 'keep_buffer' is true, return without releasing the buffer lock and pin;
+ * then caller is responsible for doing UnlockReleaseBuffer() later.  This
+ * is needed in some cases when replaying XLOG records that touch multiple
+ * pages, to prevent inconsistent states from being visible to other backends.
+ * (Again, that's only important in hot standby mode.)
+ */
+Buffer
+RestoreBackupBlock(XLogRecPtr lsn, XLogRecord *record, int block_index,
+				   bool get_cleanup_lock, bool keep_buffer)
+{
+	BkpBlock	bkpb;
+	char	   *blk;
+	int			i;
+
+	/* Locate requested BkpBlock in the record */
+	blk = (char *) XLogRecGetData(record) + record->xl_len;
+	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
+	{
+		if (!(record->xl_info & XLR_BKP_BLOCK(i)))
+			continue;
+
+		memcpy(&bkpb, blk, sizeof(BkpBlock));
+		blk += sizeof(BkpBlock);
+
+		if (i == block_index)
+		{
+			/* Found it, apply the update */
+			return RestoreBackupBlockContents(lsn, bkpb, blk, get_cleanup_lock,
+											  keep_buffer);
+		}
+
+		blk += BLCKSZ - bkpb.hole_length;
+	}
+
+	/* Caller specified a bogus block_index */
+	elog(ERROR, "failed to restore block_index %d", block_index);
+	return InvalidBuffer;		/* keep compiler quiet */
+}
+
+/*
+ * Workhorse for RestoreBackupBlock usable without an xlog record
+ *
+ * Restores a full-page image from BkpBlock and a data pointer.
+ */
+Buffer
+RestoreBackupBlockContents(XLogRecPtr lsn, BkpBlock bkpb, char *blk,
+						   bool get_cleanup_lock, bool keep_buffer)
+{
+	Buffer		buffer;
+	Page		page;
+
+	buffer = XLogReadBufferExtended(bkpb.node, bkpb.fork, bkpb.block,
+									RBM_ZERO);
+	Assert(BufferIsValid(buffer));
+	if (get_cleanup_lock)
+		LockBufferForCleanup(buffer);
+	else
+		LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+
+	page = (Page) BufferGetPage(buffer);
+
+	if (bkpb.hole_length == 0)
+	{
+		memcpy((char *) page, blk, BLCKSZ);
+	}
+	else
+	{
+		memcpy((char *) page, blk, bkpb.hole_offset);
+		/* must zero-fill the hole */
+		MemSet((char *) page + bkpb.hole_offset, 0, bkpb.hole_length);
+		memcpy((char *) page + (bkpb.hole_offset + bkpb.hole_length),
+			   blk + bkpb.hole_offset,
+			   BLCKSZ - (bkpb.hole_offset + bkpb.hole_length));
+	}
+
+	/*
+	 * The checksum value on this page is currently invalid. We don't need to
+	 * reset it here since it will be set before being written.
+	 */
+
+	/*
+	 * The page may be uninitialized. If so, we can't set the LSN because that
+	 * would corrupt the page.
+	 */
+	if (!PageIsNew(page))
+	{
+		PageSetLSN(page, lsn);
+	}
+	MarkBufferDirty(buffer);
+
+	if (!keep_buffer)
+		UnlockReleaseBuffer(buffer);
+
+	return buffer;
+}
 
 /*
  * Struct actually returned by XLogFakeRelcacheEntry, though the declared