lib/cache/lvmcache.c               |  2 +-

 lib/device/dev-md.c                | 27 ++++++++++----

 lib/device/dev-type.h              |  1 +

 lib/filters/filter-md.c            | 74 +++++++++++++++++++-------------------

 lib/label/label.c                  | 14 ++++++++

 test/shell/pvcreate-md-fake-hdr.sh |  3 +-

 6 files changed, 75 insertions(+), 46 deletions(-)

diff --git a/lib/cache/lvmcache.c b/lib/cache/lvmcache.c

index 2fba3ff..f55a14c 100644

--- a/lib/cache/lvmcache.c

+++ b/lib/cache/lvmcache.c

@@ -1002,7 +1002,7 @@ int lvmcache_dev_is_unchosen_duplicate(struct device *dev)

  * unused_duplicate_devs list, and restrict what we allow done with it.

  *

  * In the case of md components, we usually filter these out in filter-md,

- * but in the special case of md superblocks <= 1.0 where the superblock

+ * but in the special case of md superblock version 1.0 where the superblock

  * is at the end of the device, filter-md doesn't always eliminate them

  * first, so we eliminate them here.

  *

diff --git a/lib/device/dev-md.c b/lib/device/dev-md.c

index f5a736f..7196dc0 100644

--- a/lib/device/dev-md.c

+++ b/lib/device/dev-md.c

@@ -142,13 +142,6 @@ static int _native_dev_is_md(struct device *dev, uint64_t *offset_found, int ful

 	 * command if it should do a full check (cmd->use_full_md_check),

 	 * and set it for commands that could possibly write to an md dev

 	 * (pvcreate/vgcreate/vgextend).

-	 *

-	 * For old md versions with magic numbers at the end of devices,

-	 * the md dev components won't be filtered out here when full is 0,

-	 * so they will be scanned, and appear as duplicate PVs in lvmcache.

-	 * The md device itself will be chosen as the primary duplicate,

-	 * and the components are dropped from the list of duplicates in,

-	 * i.e. a kind of post-scan filtering.

 	 */

 	if (!full) {

 		sb_offset = 0;

@@ -414,6 +407,26 @@ unsigned long dev_md_stripe_width(struct dev_types *dt, struct device *dev)

 	return stripe_width_sectors;

 }

+int dev_is_md_with_end_superblock(struct dev_types *dt, struct device *dev)

+{

+	char version_string[MD_MAX_SYSFS_SIZE];

+	const char *attribute = "metadata_version";

+

+	if (MAJOR(dev->dev) != dt->md_major)

+		return 0;

+

+	if (_md_sysfs_attribute_scanf(dt, dev, attribute,

+				      "%s", &version_string) != 1)

+		return -1;

+

+	log_very_verbose("Device %s %s is %s.",

+			 dev_name(dev), attribute, version_string);

+

+	if (!strcmp(version_string, "1.0"))

+		return 1;

+	return 0;

+}

+

 #else

 int dev_is_md(struct device *dev __attribute__((unused)),

diff --git a/lib/device/dev-type.h b/lib/device/dev-type.h

index 843e254..f629a02 100644

--- a/lib/device/dev-type.h

+++ b/lib/device/dev-type.h

@@ -76,6 +76,7 @@ int wipe_known_signatures(struct cmd_context *cmd, struct device *dev, const cha

 /* Type-specific device properties */

 unsigned long dev_md_stripe_width(struct dev_types *dt, struct device *dev);

+int dev_is_md_with_end_superblock(struct dev_types *dt, struct device *dev);

 /* Partitioning */

 int major_max_partitions(struct dev_types *dt, int major);

diff --git a/lib/filters/filter-md.c b/lib/filters/filter-md.c

index ab97b59..ad5b8e4 100644

--- a/lib/filters/filter-md.c

+++ b/lib/filters/filter-md.c

@@ -29,43 +29,43 @@

  *

  * (This is assuming lvm.conf md_component_detection=1.)

  *

- * If lvm does *not* ignore the components, then lvm will read lvm

- * labels from the md dev and from the component devs, and will see

- * them all as duplicates of each other.  LVM duplicate resolution

- * will then kick in and keep the md dev around to use and ignore

- * the components.

- *

- * It is better to exclude the components as early as possible during

- * lvm processing, ideally before lvm even looks for labels on the

- * components, so that duplicate resolution can be avoided.  There are

- * a number of ways that md components can be excluded earlier than

- * the duplicate resolution phase:

- *

- * - When external_device_info_source="udev", lvm discovers a device is

- *   an md component by asking udev during the initial filtering phase.

- *   However, lvm's default is to not use udev for this.  The

- *   alternative is "native" detection in which lvm tries to detect

- *   md components itself.

- *

- * - When using native detection, lvm's md filter looks for the md

- *   superblock at the start of devices.  It will see the md superblock

- *   on the components, exclude them in the md filter, and avoid

- *   handling them later in duplicate resolution.

- *

- * - When using native detection, lvm's md filter will not detect

- *   components when the md device has an older superblock version that

- *   places the superblock at the end of the device.  This case will

- *   fall back to duplicate resolution to exclude components.

- *

- * A variation of the description above occurs for lvm commands that

- * intend to create new PVs on devices (pvcreate, vgcreate, vgextend).

- * For these commands, the native md filter also reads the end of all

- * devices to check for the odd md superblocks.

- *

- * (The reason that external_device_info_source is not set to udev by

- * default is that there have be issues with udev not being promptly

- * or reliably updated about md state changes, causing the udev info

- * that lvm uses to be occasionally wrong.)

+ * If lvm does *not* ignore the components, then lvm may read lvm

+ * labels from the component devs and potentially the md dev,

+ * which can trigger duplicate detection, and/or cause lvm to display

+ * md components as PVs rather than ignoring them.

+ *

+ * If scanning md componenents causes duplicates to be seen, then

+ * the lvm duplicate resolution will exclude the components.

+ *

+ * The lvm md filter has three modes:

+ *

+ * 1. look for md superblock at the start of the device

+ * 2. look for md superblock at the start and end of the device

+ * 3. use udev to detect components

+ *

+ * mode 1 will not detect and exclude components of md devices

+ * that use superblock version 1.0 which is at the end of the device.

+ *

+ * mode 2 will detect these, but mode 2 doubles the i/o done by label

+ * scan, since there's a read at both the start and end of every device.

+ *

+ * mode 3 is used when external_device_info_source="udev".  It does

+ * not require any io from lvm, but this mode is not used by default

+ * because there have been problems getting reliable info from udev.

+ *

+ * lvm uses mode 2 when:

+ *

+ * - the command is pvcreate/vgcreate/vgextend, which format new

+ *   devices, and if the user ran these commands on a component

+ *   device of an md device 1.0, then it would cause problems.

+ *   FIXME: this would only really need to scan the end of the

+ *   devices being formatted, not all devices.

+ *

+ * - it sees an md device on the system using version 1.0.

+ *   The point of this is just to avoid displaying md components

+ *   from the 'pvs' command.

+ *   FIXME: the cost (double i/o) may not be worth the benefit

+ *   (not showing md components).

  */

 /*

diff --git a/lib/label/label.c b/lib/label/label.c

index e7e3997..6fb35ff 100644

--- a/lib/label/label.c

+++ b/lib/label/label.c

@@ -872,6 +872,20 @@ 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 need to 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: it may not be worth the

+		 * cost of double i/o just to avoid displaying md component

+		 * devs in 'pvs', which is a pretty harmless effect from a

+		 * pretty uncommon situation.

+		 */

+		if (dev_is_md_with_end_superblock(cmd->dev_types, dev))

+			cmd->use_full_md_check = 1;

 	};

 	dev_iter_destroy(iter);

diff --git a/test/shell/pvcreate-md-fake-hdr.sh b/test/shell/pvcreate-md-fake-hdr.sh

index b89fe43..4c9ac7c 100644

--- a/test/shell/pvcreate-md-fake-hdr.sh

+++ b/test/shell/pvcreate-md-fake-hdr.sh

@@ -89,6 +89,7 @@ sleep 1

 # (when mdadm supports repair)

 if mdadm --action=repair "$mddev" ; then

 	sleep 1

+	pvscan -vvvv

 	# should be showing correctly PV3 & PV4

-	pvs

+	pvs -vvvv "$dev3" "$dev4"

 fi