enable full md component detection at the right time

An active md device with an end superblock causes lvm to
enable full md component detection.  This was being done
within the filter loop instead of before, so the full
filtering of some devs could be missed.

Also incorporate the recently added config setting that
controls the md component detection.

lib/device/dev-cache.c

@@ -15,6 +15,7 @@
 
 #include "base/memory/zalloc.h"
 #include "lib/misc/lib.h"
+#include "lib/device/dev-type.h"
 #include "lib/datastruct/btree.h"
 #include "lib/config/config.h"
 #include "lib/commands/toolcontext.h"
@@ -1634,3 +1635,21 @@ const char *dev_name(const struct device *dev)
 	return (dev && dev->aliases.n) ? dm_list_item(dev->aliases.n, struct dm_str_list)->str :
 	    unknown_device_name();
 }
+
+bool dev_cache_has_md_with_end_superblock(struct dev_types *dt)
+{
+	struct btree_iter *iter = btree_first(_cache.devices);
+	struct device *dev;
+
+	while (iter) {
+		dev = btree_get_data(iter);
+
+		if (dev_is_md_with_end_superblock(dt, dev))
+			return true;
+
+		iter = btree_next(iter);
+	}
+
+	return false;
+}
+

lib/device/dev-cache.h

@@ -17,6 +17,7 @@
 #define _LVM_DEV_CACHE_H
 
 #include "lib/device/device.h"
+#include "lib/device/dev-type.h"
 #include "lib/misc/lvm-wrappers.h"
 
 struct cmd_context;
@@ -71,4 +72,6 @@ void dev_reset_error_count(struct cmd_context *cmd);
 
 void dev_cache_failed_path(struct device *dev, const char *path);
 
+bool dev_cache_has_md_with_end_superblock(struct dev_types *dt);
+
 #endif

lib/device/dev-md.c

@@ -302,12 +302,12 @@ static int _md_sysfs_attribute_scanf(struct dev_types *dt,
 		return ret;
 
 	if (!(fp = fopen(path, "r"))) {
-		log_sys_error("fopen", path);
+		log_debug("_md_sysfs_attribute_scanf fopen failed %s", path);
 		return ret;
 	}
 
 	if (!fgets(buffer, sizeof(buffer), fp)) {
-		log_sys_error("fgets", path);
+		log_debug("_md_sysfs_attribute_scanf fgets failed %s", path);
 		goto out;
 	}
 
@@ -449,7 +449,7 @@ int dev_is_md_with_end_superblock(struct dev_types *dt, struct device *dev)
 
 	if (_md_sysfs_attribute_scanf(dt, dev, attribute,
 				      "%s", &version_string) != 1)
-		return -1;
+		return 0;
 
 	log_very_verbose("Device %s %s is %s.",
 			 dev_name(dev), attribute, version_string);

lib/label/label.c

@@ -893,6 +893,20 @@ int label_scan(struct cmd_context *cmd)
 	 */
 	dev_cache_scan();
 
+	/*
+	 * If we know that there will be md components with an end
+	 * superblock, then enable the full md filter before label
+	 * scan begins.  FIXME: we could skip the full md check on
+	 * devs that are not identified as PVs, but then we'd need
+	 * to do something other than using the standard md filter.
+	 */
+	if (cmd->md_component_detection && !cmd->use_full_md_check &&
+	    !strcmp(cmd->md_component_checks, "auto") &&
+	    dev_cache_has_md_with_end_superblock(cmd->dev_types)) {
+		log_debug("Enable full md component check.");
+		cmd->use_full_md_check = 1;
+	}
+
 	/*
 	 * Set up the iterator that is needed to step through each device in
 	 * dev cache.
@@ -931,19 +945,6 @@ int label_scan(struct cmd_context *cmd)
 			bcache_invalidate_fd(scan_bcache, dev->bcache_fd);
 			_scan_dev_close(dev);
 		}
-
-		/*
-		 * When md devices exist that use the old superblock at the
-		 * end of the device, then in order to detect and filter out
-		 * the component devices of those md devs, we enable the full
-		 * md filter which scans both the start and the end of every
-		 * device.  This doubles the amount of scanning i/o, which we
-		 * want to avoid.  FIXME: this forces start+end scanning of
-		 * every device, but it would be more efficient to limit the
-		 * end scan only to PVs.
-		 */
-		if (dev_is_md_with_end_superblock(cmd->dev_types, dev))
-			cmd->use_full_md_check = 1;
 	};
 	dev_iter_destroy(iter);
 

tools/pvscan.c

@@ -938,6 +938,13 @@ int pvscan_cache_cmd(struct cmd_context *cmd, int argc, char **argv)
 	/* Creates a list of dev names from /dev, sysfs, etc; does not read any. */
 	dev_cache_scan();
 
+	if (cmd->md_component_detection && !cmd->use_full_md_check &&
+	    !strcmp(cmd->md_component_checks, "auto") &&
+	    dev_cache_has_md_with_end_superblock(cmd->dev_types)) {
+		log_debug("Enable full md component check.");
+		cmd->use_full_md_check = 1;
+	}
+
 	/*
 	 * For each device command arg (from either position or --major/--minor),
 	 * decide if that device is being added to the system (a dev node exists