ceph-volume: add helper methods to get only first LVM devs

These convenience methods shortens following phrase to
"lv = get_first_lv()" -

lvs = get_lvs()
if len(lvs) >= 1:
	lvs = lv[0]

These methods do the same things as above phrase internall. Rewrite
listing.py to use these new helper methods.

Signed-off-by: Rishabh Dave <ridave@redhat.com>

src/ceph-volume/ceph_volume/api/lvm.py

@@ -1421,6 +1421,16 @@ def get_pvs(fields=PV_FIELDS, sep='";"', filters='', tags=None):
     pvs_report = _output_parser(stdout, fields)
     return [PVolume(**pv_report) for pv_report in pvs_report]
 
+def get_first_pv(fields=PV_FIELDS, sep='";"', filters=None, tags=None):
+    """
+    Wrapper of get_pv meant to be a convenience method to avoid the phrase::
+        pvs = get_pvs()
+        if len(pvs) >= 1:
+            pv = pvs[0]
+    """
+    pvs = get_pvs(fields=fields, sep=sep, filters=filters, tags=tags)
+    return pvs[0] if len(pvs) > 0 else []
+
 def get_vgs(fields=VG_FIELDS, sep='";"', filters='', tags=None):
     """
     Return a list of VGs that are available on the system and match the
@@ -1445,6 +1455,16 @@ def get_vgs(fields=VG_FIELDS, sep='";"', filters='', tags=None):
     vgs_report =_output_parser(stdout, fields)
     return [VolumeGroup(**vg_report) for vg_report in vgs_report]
 
+def get_first_vg(fields=VG_FIELDS, sep='";"', filters=None, tags=None):
+    """
+    Wrapper of get_vg meant to be a convenience method to avoid the phrase::
+        vgs = get_vgs()
+        if len(vgs) >= 1:
+            vg = vgs[0]
+    """
+    vgs = get_vgs(fields=fields, sep=sep, filters=filters, tags=tags)
+    return vgs[0] if len(vgs) > 0 else []
+
 def get_lvs(fields=LV_FIELDS, sep='";"', filters='', tags=None):
     """
     Return a list of LVs that are available on the system and match the
@@ -1468,3 +1488,13 @@ def get_lvs(fields=LV_FIELDS, sep='";"', filters='', tags=None):
     stdout, stderr, returncode = process.call(args, verbose_on_failure=False)
     lvs_report = _output_parser(stdout, fields)
     return [Volume(**lv_report) for lv_report in lvs_report]
+
+def get_first_lv(fields=LV_FIELDS, sep='";"', filters=None, tags=None):
+    """
+    Wrapper of get_lv meant to be a convenience method to avoid the phrase::
+        lvs = get_lvs()
+        if len(lvs) >= 1:
+            lv = lvs[0]
+    """
+    lvs = get_lvs(fields=fields, sep=sep, filters=filters, tags=tags)
+    return lvs[0] if len(lvs) > 0 else []

src/ceph-volume/ceph_volume/devices/lvm/listing.py

@@ -180,21 +180,18 @@ def single_report(self, device, lvs=None):
         volume in the form of vg/lv or a device with an absolute path like
         /dev/sda1 or /dev/sda
         """
-        if lvs is None:
-            lvs = api.Volumes()
         report = {}
-        lv = api.get_lv_from_argument(device)
+        lv = api.get_first_lv(filters={'lv_path': device})
 
         # check if there was a pv created with the
         # name of device
-        pv = api.get_pv(pv_name=device)
-        if pv and not lv:
-            try:
-                lv = api.get_lv(vg_name=pv.vg_name)
-            except MultipleLVsError:
-                lvs.filter(vg_name=pv.vg_name)
-                return self.full_report(lvs=lvs)
+        if not lv:
+            pv = api.get_first_pv(filters={'pv_name': device})
+            if pv:
+                return self.full_report(lvs=api.get_lv(filters={'vg_name':
+                                                                pv.vg_name}))
 
+        # TODO: a call to full_report just might work.
         if lv:
             try:
                 _id = lv.tags['ceph.osd_id']
@@ -206,36 +203,22 @@ def single_report(self, device, lvs=None):
             lv_report = lv.as_dict()
             lv_report['devices'] = self.match_devices(lv.lv_uuid)
             report[_id].append(lv_report)
-
         else:
-            # this has to be a journal/wal/db device (not a logical volume) so try
-            # to find the PARTUUID that should be stored in the OSD logical
-            # volume
-            for device_type in ['journal', 'block', 'wal', 'db']:
-                device_tag_name = 'ceph.%s_device' % device_type
-                device_tag_uuid = 'ceph.%s_uuid' % device_type
-                associated_lv = lvs.get(lv_tags={device_tag_name: device})
-                if associated_lv:
-                    _id = associated_lv.tags['ceph.osd_id']
-                    uuid = associated_lv.tags[device_tag_uuid]
-
-                    report.setdefault(_id, [])
-                    report[_id].append(
-                        {
-                            'tags': {'PARTUUID': uuid},
-                            'type': device_type,
-                            'path': device,
-                        }
-                    )
-        return report
+            # this has to be a journal/wal/db device (not a logical volume)
+            # so try to find the PARTUUID that should be stored in the OSD
+            # logical volume
+            vg_name = os.path.basename(device)
+            lvs = api.get_lvs(filters={'vg_name': vg_name})
+            if lvs:
+                return self.full_report(lvs=lvs)
 
     def full_report(self, lvs=None):
         """
         Generate a report for all the logical volumes and associated devices
         that have been previously prepared by Ceph
         """
         if lvs is None:
-            lvs = api.Volumes()
+            lvs = api.get_lvs()
         report = {}
 
         for lv in lvs:
@@ -257,7 +240,8 @@ def full_report(self, lvs=None):
                     # bluestore will not have a journal, filestore will not have
                     # a block/wal/db, so we must skip if not present
                     continue
-                if not api.get_lv(lv_uuid=device_uuid, lvs=lvs):
+                if not api.get_lvs(filters={'lv_uuid': device_uuid}):
+                    # if not api.get_lv(lv_uuid=device_uuid, lvs=lvs):
                     # means we have a regular device, so query blkid
                     disk_device = disk.get_device_from_partuuid(device_uuid)
                     if disk_device: