MDEV-14425 deprecate and ignore innodb_log_files_in_group

Now there can be only one log file instead of several which
logically work as a single file.

Possible names of redo log files: ib_logfile0,
ib_logfile101 (for just created one)

innodb_log_fiels_in_group: value of this variable is not used
by InnoDB. Possible values are still 1..100, to not break upgrade

LOG_FILE_NAME: add constant of value "ib_logfile0"
LOG_FILE_NAME_PREFIX: add constant of value "ib_logfile"

get_log_file_path(): convenience function that returns full
path of a redo log file

SRV_N_LOG_FILES_MAX: removed

srv_n_log_files: we can't remove this for compatibility reasons,
but now server doesn't use this variable

log_sys_t::file::fd: now just one, not std::vector

log_sys_t::log_capacity: removed word 'group'

find_and_check_log_file(): part of logic from huge srv_start()
moved here

recv_sys_t::files: file descriptors of redo log files.
There can be several of those in case we're upgrading
from older MariaDB version.

recv_sys_t::remove_extra_log_files: whether to remove
ib_logfile{1,2,3...} after successfull upgrade.

recv_sys_t::read(): open if needed and read from one
of several log files

recv_sys_t::files_size(): open if needed and return files count

redo_file_sizes_are_correct(): check that redo log files
sizes are equal. Just to log an error for a user.
Corresponding check was moved from srv0start.cc

namespace deprecated: put all deprecated variables here to
prevent usage of it by us, developers

3 files changed, 24 insertions, 60 deletions

diff --git a/extra/mariabackup/backup_copy.cc b/extra/mariabackup/backup_copy.cc
index c1e96422dec..edcbb94c20f 100644
--- a/extra/mariabackup/backup_copy.cc
+++ b/extra/mariabackup/backup_copy.cc
@@ -1863,24 +1863,25 @@ copy_back()
 	dst_dir = (srv_log_group_home_dir && *srv_log_group_home_dir)
 		? srv_log_group_home_dir : mysql_data_home;
 
-	/* --backup generates a single ib_logfile0, which we must copy
+	/* --backup generates a single LOG_FILE_NAME, which we must copy
 	if it exists. */
 
 	ds_data = ds_create(dst_dir, DS_TYPE_LOCAL);
 	MY_STAT stat_arg;
-	if (!my_stat("ib_logfile0", &stat_arg, MYF(0)) || !stat_arg.st_size) {
+	if (!my_stat(LOG_FILE_NAME, &stat_arg, MYF(0)) || !stat_arg.st_size) {
 		/* After completed --prepare, redo log files are redundant.
 		We must delete any redo logs at the destination, so that
 		the database will not jump to a different log sequence number
 		(LSN). */
 
-		for (uint i = 0; i <= SRV_N_LOG_FILES_MAX + 1; i++) {
-			char filename[FN_REFLEN];
-			snprintf(filename, sizeof filename, "%s/ib_logfile%u",
-				 dst_dir, i);
-			unlink(filename);
-		}
-	} else if (!(ret = copy_or_move_file("ib_logfile0", "ib_logfile0",
+		char filename[FN_REFLEN];
+		snprintf(filename, sizeof filename, "%s/%s0", dst_dir,
+			 LOG_FILE_NAME_PREFIX);
+		unlink(filename);
+		snprintf(filename, sizeof filename, "%s/%s101", dst_dir,
+			 LOG_FILE_NAME_PREFIX);
+		unlink(filename);
+	} else if (!(ret = copy_or_move_file(LOG_FILE_NAME, LOG_FILE_NAME,
 					     dst_dir, 1))) {
 		goto cleanup;
 	}
@@ -1972,7 +1973,7 @@ copy_back()
 		}
 
 		/* skip the redo log (it was already copied) */
-		if (!strcmp(filename, "ib_logfile0")) {
+		if (!strcmp(filename, LOG_FILE_NAME)) {
 			continue;
 		}
 
diff --git a/extra/mariabackup/backup_mysql.cc b/extra/mariabackup/backup_mysql.cc
index 9cac43dd6f8..df8d1c0956b 100644
--- a/extra/mariabackup/backup_mysql.cc
+++ b/extra/mariabackup/backup_mysql.cc
@@ -483,9 +483,7 @@ get_mysql_vars(MYSQL *connection)
 	}
 
 	if (innodb_log_files_in_group_var) {
-		srv_n_log_files = strtol(
-			innodb_log_files_in_group_var, &endptr, 10);
-		ut_ad(*endptr == 0);
+		// deprecated
 	}
 
 	if (innodb_log_file_size_var) {
@@ -1573,7 +1571,6 @@ bool write_backup_config_file()
 		"[mysqld]\n"
 		"innodb_checksum_algorithm=%s\n"
 		"innodb_data_file_path=%s\n"
-		"innodb_log_files_in_group=%lu\n"
 		"innodb_log_file_size=%llu\n"
 		"innodb_page_size=%lu\n"
 		"innodb_undo_directory=%s\n"
@@ -1583,7 +1580,6 @@ bool write_backup_config_file()
 		"%s\n",
 		innodb_checksum_algorithm_names[srv_checksum_algorithm],
 		make_local_paths(innobase_data_file_path).c_str(),
-		srv_n_log_files,
 		srv_log_file_size,
 		srv_page_size,
 		srv_undo_dir,
diff --git a/extra/mariabackup/xtrabackup.cc b/extra/mariabackup/xtrabackup.cc
index 70ddc933fe3..a17aace794b 100644
--- a/extra/mariabackup/xtrabackup.cc
+++ b/extra/mariabackup/xtrabackup.cc
@@ -1166,6 +1166,10 @@ uint xb_client_options_count = array_elements(xb_client_options);
 static const char *dbug_option;
 #endif
 
+namespace deprecated {
+extern ulong srv_n_log_files;
+}
+
 struct my_option xb_server_options[] =
 {
   {"datadir", 'h', "Path to the database root.", (G_PTR*) &mysql_data_home,
@@ -1274,7 +1278,7 @@ struct my_option xb_server_options[] =
    UNIV_PAGE_SIZE_MAX, 0},
   {"innodb_log_files_in_group", OPT_INNODB_LOG_FILES_IN_GROUP,
    "Ignored for mysqld option compatibility",
-   &srv_n_log_files, &srv_n_log_files,
+   &deprecated::srv_n_log_files, &deprecated::srv_n_log_files,
    0, GET_LONG, REQUIRED_ARG, 1, 1, 100, 0, 1, 0},
   {"innodb_log_group_home_dir", OPT_INNODB_LOG_GROUP_HOME_DIR,
    "Path to InnoDB log files.", &srv_log_group_home_dir,
@@ -2894,7 +2898,7 @@ Initialize the appropriate datasink(s). Both local backups and streaming in the
 
 Otherwise (i.e. when streaming in the 'tar' format) we need 2 separate datasinks
 for the data stream (and don't allow parallel data copying) and for metainfo
-files (including ib_logfile0). The second datasink writes to temporary
+files (including LOG_FILE_NAME). The second datasink writes to temporary
 files first, and then streams them in a serialized way when closed. */
 static void
 xtrabackup_init_datasinks(void)
@@ -3760,36 +3764,6 @@ xb_filters_free()
 	}
 }
 
-/**Create log file metadata.
-@param[in]	i		log file number in group
-@param[in,out]	file_names	redo log file names */
-static
-void
-open_or_create_log_file(
-	ulint	i,
-	std::vector<std::string> &file_names)
-{
-	char	name[FN_REFLEN];
-	ulint	dirnamelen;
-
-	os_normalize_path(srv_log_group_home_dir);
-
-	dirnamelen = strlen(srv_log_group_home_dir);
-	ut_a(dirnamelen < (sizeof name) - 10 - sizeof "ib_logfile");
-	memcpy(name, srv_log_group_home_dir, dirnamelen);
-
-	/* Add a path separator if needed. */
-	if (dirnamelen && name[dirnamelen - 1] != OS_PATH_SEPARATOR) {
-		name[dirnamelen++] = OS_PATH_SEPARATOR;
-	}
-
-	sprintf(name + dirnamelen, "%s%zu", "ib_logfile", i);
-
-	ut_a(fil_validate());
-
-	file_names.emplace_back(name);
-}
-
 /***********************************************************************
 Set the open files limit. Based on set_max_open_files().
 
@@ -4046,15 +4020,8 @@ fail:
 		    SRV_MAX_N_PENDING_SYNC_IOS);
 
 	log_sys.create();
-	log_sys.log.create(srv_n_log_files);
-
-	std::vector<std::string> file_names;
-
-	for (ulint i = 0; i < srv_n_log_files; i++) {
-		open_or_create_log_file(i, file_names);
-	}
-
-	log_sys.log.open_files(std::move(file_names));
+	log_sys.log.create();
+	log_sys.log.open_file(get_log_file_path());
 
 	/* create extra LSN dir if it does not exist. */
 	if (xtrabackup_extra_lsndir
@@ -4123,10 +4090,10 @@ reread_log_header:
 
 	/* open the log file */
 	memset(&stat_info, 0, sizeof(MY_STAT));
-	dst_log_file = ds_open(ds_redo, "ib_logfile0", &stat_info);
+	dst_log_file = ds_open(ds_redo, LOG_FILE_NAME, &stat_info);
 	if (dst_log_file == NULL) {
-		msg("Error: failed to open the target stream for "
-		    "'ib_logfile0'.");
+		msg("Error: failed to open the target stream for '%s'.",
+		    LOG_FILE_NAME);
 		goto fail;
 	}
 
@@ -4147,7 +4114,7 @@ reread_log_header:
 	log_hdr_field +=
 		(log_sys.next_checkpoint_no & 1) ? LOG_CHECKPOINT_2 : LOG_CHECKPOINT_1;
 	/* The least significant bits of LOG_CHECKPOINT_OFFSET must be
-	stored correctly in the copy of the ib_logfile. The most significant
+	stored correctly in the copy of the LOG_FILE_NAME. The most significant
 	bits, which identify the start offset of the log block in the file,
 	we did choose freely, as LOG_FILE_HDR_SIZE. */
 	ut_ad(!((log_sys.log.get_lsn() ^ checkpoint_lsn_start)