[Bug 2003789] Re: Cannot exclude read-only paths from dpkg, as they still cause dpkg to fail

[Ubuntu Foundations Team Bug Bot]

** Tags added: patch

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https://bugs.launchpad.net/bugs/2003789

Title:
  Cannot exclude read-only paths from dpkg, as they still cause dpkg to
  fail

Status in dpkg package in Ubuntu:
  New

Bug description:
  [Impact]

  In certain very specific cases, certain directories on the filesystem
  can be read-only. As-is, this is problematic for dpkg in case some
  package wants to install files there - which is fine and expected. But
  when this situation is 'intentional', one might want to use --path-
  exclude for the selected paths. Currently, dpkg will *still* fail in
  such cases.

  The reason is that dpkg, before starting work on the package, checks
  for any dpkg interrupted transactions. It does that by performing a
  rename() on the dpkg tmp files on the selected path, and if there is
  none (by checking errno for ENOENT and ENOTDIR), it continues the
  operation. But in cases where the file-system is read only, the
  returned errno is EROFS, which is not handled and treated as if the
  file is there but unable to restore it.

  It feels like a valid case though - if the filesystem if readonly, we
  should not consider *this* as an error case. Without path-excludes,
  dpkg will fail at a different moment anyway. While if someone has a
  working setup where this path indeed should be read-only but excluded,
  we should let dpkg continue.

  [Test Case]

  Ideally, creating a setup where some directory (for instance,
  /lib/firmware) is read-only, and trying to install a package like
  alsa-topology-conf. The package installation should succeed without
  any files installed into /lib/firmware.

  [Regression Potential]

  As this is a change in dpkg, there's quite a lot that might go wrong.
  However, the change is rather limited. Problems can appear in handling
  of interrupted transactions, or by breaking package installation in
  overall.

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