ceph-disk: Adding retry loop in get_partition_dev()

There is very rare cases where get_partition_dev() is called before the actual partition is available in /sys/block/<device>.

It appear that waiting a very short is usually enough to get the partition beein populated.

Analysis:
update_partition() is supposed to be enough to avoid any racing between events sent by parted/sgdisk/partprobe and
the actual creation on the /sys/block/<device>/* entrypoint.
On our CI that race occurs pretty often but trying to reproduce it locally never been possible.

This patch is almost a workaround rather than a fix to the real problem.
It offer retrying after a very short to be make a chance the device to appear.
This approach have been succesful on the CI.

Note his patch is not changing the timing when the device is perfectly created on time and just differ by a 1/5th up to 2 seconds when the bug occurs.

A typical output from the build running on a CI with that code.
	command_check_call: Running command: /usr/bin/udevadm settle --timeout=600
	get_dm_uuid: get_dm_uuid /dev/sda uuid path is /sys/dev/block/8:0/dm/uuid
	get_partition_dev: Try 1/10 : partition 2 for /dev/sda does not in /sys/block/sda
	get_partition_dev: Found partition 2 for /dev/sda after 1 tries
        get_dm_uuid: get_dm_uuid /dev/sda uuid path is /sys/dev/block/8:0/dm/uuid
	get_dm_uuid: get_dm_uuid /dev/sda2 uuid path is /sys/dev/block/8:2/dm/uuid

fixes: #19428

Signed-off-by: Erwan Velu <erwan@redhat.com>
(cherry picked from commit 93e7b95)

src/ceph-disk/ceph_disk/main.py

@@ -702,25 +702,36 @@ def get_partition_dev(dev, pnum):
        sda 1 -> sda1
        cciss/c0d1 1 -> cciss!c0d1p1
     """
-    partname = None
-    error_msg = ""
-    if is_mpath(dev):
-        partname = get_partition_mpath(dev, pnum)
-    else:
-        name = get_dev_name(os.path.realpath(dev))
-        sys_entry = os.path.join('/sys/block', name)
-        error_msg = " in %s" % sys_entry
-        for f in os.listdir(sys_entry):
-            if f.startswith(name) and f.endswith(str(pnum)):
-                # we want the shortest name that starts with the base name
-                # and ends with the partition number
-                if not partname or len(f) < len(partname):
-                    partname = f
-    if partname:
-        return get_dev_path(partname)
-    else:
-        raise Error('partition %d for %s does not appear to exist%s' %
-                    (pnum, dev, error_msg))
+    max_retry = 10
+    for retry in range(0, max_retry + 1):
+        partname = None
+        error_msg = ""
+        if is_mpath(dev):
+            partname = get_partition_mpath(dev, pnum)
+        else:
+            name = get_dev_name(os.path.realpath(dev))
+            sys_entry = os.path.join('/sys/block', name)
+            error_msg = " in %s" % sys_entry
+            for f in os.listdir(sys_entry):
+                if f.startswith(name) and f.endswith(str(pnum)):
+                    # we want the shortest name that starts with the base name
+                    # and ends with the partition number
+                    if not partname or len(f) < len(partname):
+                        partname = f
+        if partname:
+            if retry:
+                LOG.info('Found partition %d for %s after %d tries' %
+                         (pnum, dev, retry))
+            return get_dev_path(partname)
+        else:
+            if retry < max_retry:
+                LOG.info('Try %d/%d : partition %d for %s does not exist%s' %
+                         (retry + 1, max_retry, pnum, dev, error_msg))
+                time.sleep(.2)
+                continue
+            else:
+                raise Error('partition %d for %s does not appear to exist%s' %
+                            (pnum, dev, error_msg))
 
 
 def list_all_partitions():