config: introduce validate_metadata

Add lvm.conf  config/validate_metadata  configurable setting.
Allows to disable validation of volume_group structure before
writing to disk.
Call of vg_validate() is supposed to catch any inconsistency
of in-memory volume group structure and possibly early aborting
commnand before making any more 'damage' in case the VG struct
is found insistent after some metadata manipulation.

This is almost always useful for devel - and also for normal user
as for small metadata size this doesn't add too much overhead.

However if the volume_group size is large and operations are just
adding removing simple LVs - this validation time may add noticable
to final command running time.

So if the user seeks the highest perfomance of command and does
not do any 'complex' metadata manipulation - it's reasonably safe
to disable validation (with the use of setting "none") here.

conf/example.conf.in

@@ -36,6 +36,19 @@ config {
 	# This configuration option has an automatic default value.
 	# checks = 1
 
+	# Configuration option config/validate_metadata.
+	# Allows to select the level of validation after metadata transformation.
+	# Validation takes extra CPU time to verify internal consistency.
+	# Accepted values:
+	#   full
+	#     Do a full metadata validation before disk write.
+	#   none
+	#     Skip any checks (unrecommended, slightly faster).
+	#
+	# This configuration option is advanced.
+	# This configuration option has an automatic default value.
+	# validate_metadata = "full"
+
 	# Configuration option config/abort_on_errors.
 	# Abort the LVM process if a configuration mismatch is found.
 	# This configuration option has an automatic default value.

lib/commands/toolcontext.c

@@ -658,7 +658,7 @@ static int _process_config(struct cmd_context *cmd)
 {
 	mode_t old_umask;
 	const char *dev_ext_info_src = NULL;
-	const char *read_ahead;
+	const char *read_ahead, *validate_metadata;
 	struct stat st;
 	const struct dm_config_node *cn;
 	const struct dm_config_value *cv;
@@ -744,6 +744,15 @@ static int _process_config(struct cmd_context *cmd)
 		return 0;
 	}
 
+	cmd->vg_write_validates_vg = 1;
+	if ((validate_metadata = find_config_tree_str(cmd, config_validate_metadata_CFG, NULL))) {
+		if (!strcasecmp(validate_metadata, "none"))
+			cmd->vg_write_validates_vg = 0;
+		else if (strcasecmp(validate_metadata, "full"))
+			log_warn("WARNING: Ignoring unknown validate_metadata setting: %s.",
+				 validate_metadata);
+	}
+
 	/*
 	 * If udev is disabled using DM_DISABLE_UDEV environment
 	 * variable, override existing config and hardcode these:

lib/commands/toolcontext.h

@@ -218,6 +218,7 @@ struct cmd_context {
 	unsigned device_ids_invalid:1;
 	unsigned device_ids_auto_import:1;
 	unsigned get_vgname_from_options:1;     /* used by lvconvert */
+	unsigned vg_write_validates_vg:1;
 
 	/*
 	 * Devices and filtering.

lib/config/config_settings.h

@@ -214,6 +214,16 @@ cfg(config_checks_CFG, "checks", config_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_
 	"without any warning (a message about the configuration key not being\n"
 	"found is issued in verbose mode only).\n")
 
+cfg(config_validate_metadata_CFG, "validate_metadata", config_CFG_SECTION, CFG_DEFAULT_COMMENTED | CFG_ADVANCED, CFG_TYPE_STRING, DEFAULT_VALIDATE_METADATA, vsn(2, 3, 28), NULL, 0, NULL,
+	"Allows to select the level of validation after metadata transformation.\n"
+	"Validation takes extra CPU time to verify internal consistency.\n"
+	"Accepted values:\n"
+	"  full\n"
+	"    Do a full metadata validation before disk write.\n"
+	"  none\n"
+	"    Skip any checks (unrecommended, slightly faster).\n"
+	"#\n")
+
 cfg(config_abort_on_errors_CFG, "abort_on_errors", config_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_TYPE_BOOL, 0, vsn(2,2,99), NULL, 0, NULL,
 	"Abort the LVM process if a configuration mismatch is found.\n")
 

lib/config/defaults.h

@@ -33,6 +33,7 @@
 
 #define DEFAULT_ARCHIVE_ENABLED 1
 #define DEFAULT_BACKUP_ENABLED 1
+#define DEFAULT_VALIDATE_METADATA "full"    /* full | none */
 
 #define DEFAULT_CACHE_FILE_PREFIX ""
 

lib/metadata/metadata.c

@@ -2951,8 +2951,13 @@ int vg_write(struct volume_group *vg)
 		return 0;
 	}
 
-	if (!vg_validate(vg))
-		return_0;
+	if (vg->cmd->vg_write_validates_vg) {
+		log_debug_metadata("Validating volume group structure.");
+		if (!vg_validate(vg))
+			return_0;
+	} else
+		log_debug_metadata("Skipping validation of volume group structure.");
+
 
 	if (vg->status & PARTIAL_VG) {
 		log_error("Cannot update partial volume group %s.", vg->name);