MDEV-18611: mariabackup silently ended during xtrabackup_copy_logfile()

log_group_read_log_seg(): Always return false when returning
before reading end_lsn.

xtrabackup_copy_logfile(): On error, indicate whether
a corrupt log record was encountered.

Only xtrabackup_copy_logfile() in Mariabackup cared about the
return value of the function. InnoDB crash recovery was not
affected by this bug.

extra/mariabackup/xtrabackup.cc

@@ -2756,7 +2756,10 @@ static bool xtrabackup_copy_logfile(bool last = false)
 		log_mutex_exit();
 
 		if (!start_lsn) {
-			die("xtrabackup_copy_logfile() failed.");
+			msg(recv_sys->found_corrupt_log
+			    ? "xtrabackup_copy_logfile() failed: corrupt log."
+			    : "xtrabackup_copy_logfile() failed.");
+			return true;
 		}
 	} while (start_lsn == end_lsn);
 

storage/innobase/log/log0recv.cc

@@ -2,7 +2,7 @@
 
 Copyright (c) 1997, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2013, 2018, MariaDB Corporation.
+Copyright (c) 2013, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -807,7 +807,9 @@ loop:
 			happen when InnoDB was killed while it was
 			writing redo log. We simply treat this as an
 			abrupt end of the redo log. */
+fail:
 			end_lsn = *start_lsn;
+			success = false;
 			break;
 		}
 
@@ -829,9 +831,7 @@ loop:
 					    << log_block_get_checkpoint_no(buf)
 					    << " expected: " << crc
 					    << " found: " << cksum;
-				end_lsn = *start_lsn;
-				success = false;
-				break;
+				goto fail;
 			}
 
 			if (group->is_encrypted()) {
@@ -845,8 +845,7 @@ loop:
 		    || (dl > OS_FILE_LOG_BLOCK_SIZE - LOG_BLOCK_TRL_SIZE
 			&& dl != OS_FILE_LOG_BLOCK_SIZE)) {
 			recv_sys->found_corrupt_log = true;
-			end_lsn = *start_lsn;
-			break;
+			goto fail;
 		}
 	}