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Make sure loop device is setup (#1462150)

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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.
This commit is contained in:
Brian C. Lane 2017-06-21 14:31:35 -07:00
parent 88498263b1
commit 7bc818507c
1 changed files with 27 additions and 0 deletions
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27
src/pylorax/imgutils.py
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@ -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):