From 7bc818507cdfe57e34284cbba4b0b4bddf16a3a4 Mon Sep 17 00:00:00 2001
From: "Brian C. Lane" <bcl@redhat.com>
Date: Wed, 21 Jun 2017 14:31:35 -0700
Subject: [PATCH] Make sure loop device is setup (#1462150)

It seems that on rare occasions losetup can return before the /dev/loopX
is ready for use, causing problems with mkfs. This tries to make sure
that the loop device really is associated with the backing file before
continuing.

NOTE that using losetup --list -O to return the backing store
associated with the loop device can fail due to losetup truncating
the output filename if sysfs isn't setup. Instead of printing the full
path it will truncate it to 64 characters with a * at the end.

See util-linux lib/loopdev.c for the code that does this.

Use the existing get_loop_name function, which uses losetup -j, to lookup
the loop device associated with the backing store which should work the
same, just in the opposite direction.
---
 src/pylorax/imgutils.py | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/pylorax/imgutils.py b/src/pylorax/imgutils.py
index d501347c..85345bc6 100644
--- a/src/pylorax/imgutils.py
+++ b/src/pylorax/imgutils.py
@@ -24,6 +24,7 @@ import os, tempfile
 from os.path import join, dirname
 from subprocess import Popen, PIPE, CalledProcessError
 import sys
+import time
 import traceback
 import multiprocessing
 from time import sleep
@@ -148,10 +149,36 @@ def mkqemu_img(outfile, size, options=None):
         options.extend(["-f", "qcow2"])
     runcmd(["qemu-img", "create"] + options + [outfile, str(size)])
 
+def loop_waitfor(loop_dev, outfile):
+    """Make sure the loop device is attached to the outfile.
+
+    It seems that on rare occasions losetup can return before the /dev/loopX is
+    ready for use, causing problems with mkfs. This tries to make sure that the
+    loop device really is associated with the backing file before continuing.
+
+    Raise RuntimeError if it isn't setup after 5 tries.
+    """
+    for _x in range(0,5):
+        runcmd(["udevadm", "settle", "--timeout", "300"])
+        ## XXX Note that losetup --list output can be truncated to 64 bytes in some
+        ##     situations. Don't use it to lookup backing file, go the other way
+        ##     and lookup the loop for the backing file. See util-linux lib/loopdev.c
+        ##     loopcxt_get_backing_file()
+        if get_loop_name(outfile) == os.path.basename(loop_dev):
+            return
+
+        # If this really is a race, give it some time to settle down
+        time.sleep(1)
+
+    raise RuntimeError("Unable to setup %s on %s" % (loop_dev, outfile))
+
 def loop_attach(outfile):
     '''Attach a loop device to the given file. Return the loop device name.
     Raises CalledProcessError if losetup fails.'''
     dev = runcmd_output(["losetup", "--find", "--show", outfile])
+
+    # Sometimes the loop device isn't ready yet, make extra sure before returning
+    loop_waitfor(dev.strip(), outfile)
     return dev.strip()
 
 def loop_detach(loopdev):