The sequence is:
exec growpart
exec sgdisk --info # read-only
exec sgdisk --pretend # read-only
exec sgdisk --backup # read-only copy
# modification of disk starts
exec sgdisk --move-second-header \
--delete=PART \
--new=PART \
--typecode --partition-guid --change-name
# now that sgdisk has *closed* the filehandle on the disk, systemd-udevd will
# get an inotify signal and trigger udevd to run udev scripts on the disk.
# this includes the *removal* of symlinks due to the --delete portion of
sgdisk call
# and following the removal, the -new will trigger the add run on the rules
which would
# recreate the symlinks.
# update kernel partition sizes; this is an ioctl so it does not trigger an
udev events
exec partx --update
# the kernel has the new partition sizes, and udev scripts/events are all
queued (and possibly in flight)
exit growpart
cloud-init invokes get_size() operation which:
# this is where the race occurs if the symlink created by udev is *not*
present
os.open(/dev/disk/by-id/fancy-symlink-with-partuuid-points-to-sdb1)
Dan had put a udevadm settle in this spot like so
def get_size(filename)
util.subp(['udevadm', 'settle'])
os.open(....)
So, you're suggesting that somehow _not all_ of the uevents triggered by
the sgdisk command in growpart *wouldn't* have been queued before we
call udevadm settle?
If some other events are happening how is cloud-init to know such that
it can take action to "handle this race" more robustly?
Lastly if there is a *race* in the symlink creation/remove/delay in
uevent propigation; why is that a userspace let alone a cloud-init
issue. This isn't universally reproducible, rather it's pretty narrow
circumstances between certain kernels and udevs all the while the
growpart/cloud-init code remains the same.
** Changed in: cloud-init
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1834875
Title:
cloud-init growpart race with udev
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