glance-common post-install script breaks in Ussuri when /var/lib/glance/images is a PureStorage-hosted NFS share.

[Paul Goins]

Hi,

I recently upgraded from Stein to Train successfully, and am now in the process of upgrading from Train to Ussuri. This bug hit me specifically on Ussuri.

I found that while trying to perform upgrades to switch to the bionic/ussuri packages for glance, I hit this error:

---
Setting up glance-common (2:20.0.1-0ubuntu1~cloud0) ...
chmod: changing permissions of '/var/lib/glance/images/.snapshot': Read-only file system
dpkg: error processing package glance-common (--configure):
 installed glance-common package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of python3-glance:
 python3-glance depends on glance-common (= 2:20.0.1-0ubuntu1~cloud0); however:
  Package glance-common is not configured yet.
---

/var/lib/glance/images/ is an NFS mount from a PureStorage device. It has a /var/lib/glance/images/.snapshot/ directory, and while I'm not a PureStorage expert, any attempt to write any file to that .snapshot/ directory returns "Read-only file system" errors.

Upon investigation of the postinst scripts, I noticed a delta which I believe is responsible for this.

In 19.0.4 (train):
    find /var/lib/glance -xdev -type d -exec chown glance:glance {} \;

In 20.0.1 (ussuri):
    find /var/lib/glance -exec chown glance:glance "{}" +
    find /var/lib/glance -type f -exec chmod 0640 "{}" + -o -type d -exec chmod 0750 "{}" +

I believe the "-xdev" flag likely prevented this from occuring previously, as /var/lib/glance/images/ would have been on a different filesystem than /var/lib/glance/, thus it would have been skipped.

However, the new version makes no such exclusion. And while it's OK for the images within /var/lib/glance/images/ to be chown'd/chmod'd, this fails and crashes because it also tries to modify the .snapshot directory.

[Paul Goins (vultaire)]

As a workaround, I had to perform the following:

* I verified that everything aside from the .snapshot directory had the correct owner and permissions, as the post-install script would have otherwise set.

* I edited /var/lib/dpkg/info/glance-common.postinst, commenting out those 2 lines.

* I ran "sudo dpkg --configure glance-common" to allow the modified post-install hook to run, and for the package to complete installation. This then allowed for packages that depended on glance-common to be upgraded afterwards.