[lvm-devel] [PATCH 2/3] Add find_vgname_from_pvname() function using lvmcache functions.

[Dave Wysochanski]

Some commands start with a pvname, but we'd like to force users to
start with a vg handle to obtain a pv handle.  Our best option seems
to be providing a way to look up the vgname from the pvname, and then
requiring them to use vg_read/vg_open.  This find function first
does an intial scan, then asks lvmcache for the vgname.  If the
vgname is an orphan, we then check to see if there's metadata areas,
and if not, we scan every PV on the system by calling
scan_vgs_for_pvs().  In most cases we should not need to do this,
and by using the info->mdas count, we avoid calling pv_read() as
prior code did.  So this patch is a bit cleaner IMO and should
allow us to refactor more of the pv code.

Signed-off-by: Dave Wysochanski <dwysocha at redhat.com>
---
 lib/metadata/metadata-exported.h |    1 +
 lib/metadata/metadata.c          |   42 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/lib/metadata/metadata-exported.h b/lib/metadata/metadata-exported.h
index f8329d5..597b913 100644
--- a/lib/metadata/metadata-exported.h
+++ b/lib/metadata/metadata-exported.h
@@ -605,6 +605,7 @@ struct logical_volume *find_lv(const struct volume_group *vg,
 struct physical_volume *find_pv_by_name(struct cmd_context *cmd,
 					const char *pv_name);
 
+char *find_vgname_from_pvname(struct cmd_context *cmd, const char *pvname);
 /* Find LV segment containing given LE */
 struct lv_segment *first_seg(const struct logical_volume *lv);
 
diff --git a/lib/metadata/metadata.c b/lib/metadata/metadata.c
index 28c7c47..cec0b7e 100644
--- a/lib/metadata/metadata.c
+++ b/lib/metadata/metadata.c
@@ -2971,6 +2971,48 @@ out:
 	return NULL;
 }
 
+
+char *find_vgname_from_pvname(struct cmd_context *cmd, const char *pvname)
+{
+	char *vgname;
+	struct lvmcache_info *info;
+
+	/*
+	 * Initially, all we have is a pv name - we don't know the VG name.
+	 * Try to look the name up in lvmcache.
+	 */
+	lvmcache_label_scan(cmd, 0);
+	vgname = lvmcache_vgname_from_pvname(cmd, pvname);
+
+	if (is_orphan_vg(vgname)) {
+		/*
+		 * If it's an orphan though, we need to do more work,
+		 * if there's no mdas.
+		 */
+		if (!(info = info_from_pvname(pvname, 1))) {
+			return_NULL;
+		}
+		/*
+		 * If a PV has no MDAs it may appear to be an
+		 * orphan until the metadata is read off
+		 * another PV in the same VG.  Detecting this
+		 * means checking every VG by scanning every
+		 * PV on the system.
+		 */
+		if (!dm_list_size(&info->mdas)) {
+			if (!scan_vgs_for_pvs(cmd)) {
+				log_error("Rescan for PVs without "
+					  "metadata areas failed.");
+				return NULL;
+			}
+		}
+		/* Ask lvmcache again - we may have a non-orphan name now */
+		vgname = lvmcache_vgname_from_pvname(cmd, pvname);
+	}
+
+	return vgname;
+}
+
 /**
  * pv_read - read and return a handle to a physical volume
  * @cmd: LVM command initiating the pv_read
-- 
1.6.0.6