vgchange -aay: optimize device list using pvs_online files

Port another optimization from pvscan -aay to vgchange -aay:
  "pvscan: only add device args to dev cache"

This optimization avoids doing a full dev_cache_scan, and
instead populates dev-cache with only the devices in the
VG being activated.

This involves shifting the use of pvs_online files from
the hints interface up to the higher level label_scan
interface.  This specialized label_scan is structured
around creating a list of devices from the pvs_online
files.  Previously, a list of all devices was created
first, and then reduced based on the pvs_online files.
The initial step of listing all devices was slow when
thousands of devices are present on the system.

This optimization extends the previous optimization that
used pvs_online files to limit the devices that were
actually scanned (i.e. reading to identify the device):
  "vgchange -aay: optimize device scan using pvs_online files"

2 files changed, 12 insertions, 0 deletions

diff --git a/lib/cache/lvmcache.c b/lib/cache/lvmcache.c
index bee63ebb4..81b9b0ec9 100644
--- a/lib/cache/lvmcache.c
+++ b/lib/cache/lvmcache.c
@@ -572,6 +572,16 @@ static const char *_get_pvsummary_device_id(const char *pvid_arg, const char **d
 	return NULL;
 }
 
+int lvmcache_pvsummary_count(const char *vgname)
+{
+	struct lvmcache_vginfo *vginfo;
+
+	if (!(vginfo = lvmcache_vginfo_from_vgname(vgname, NULL)))
+		return_0;
+
+	return dm_list_size(&vginfo->pvsummaries);
+}
+
 /*
  * Check if any PVs in vg->pvs have the same PVID as any
  * entries in _unused_duplicates.
diff --git a/lib/cache/lvmcache.h b/lib/cache/lvmcache.h
index 9511bb9e9..4c4903136 100644
--- a/lib/cache/lvmcache.h
+++ b/lib/cache/lvmcache.h
@@ -229,4 +229,6 @@ void lvmcache_extra_md_component_checks(struct cmd_context *cmd);
 
 unsigned int lvmcache_vg_info_count(void);
 
+int lvmcache_pvsummary_count(const char *vgname);
+
 #endif