t/21.t is executed only if a tmpfs larger than 8G is found on the
system:

```
my $fs;
BEGIN {
    my @fs = map { { /(\w+)="([^"]*)"/g } } split /\n/, `findmnt -t tmpfs -P -b -o TARGET,AVAIL | grep /tmp`;
    ($fs) = grep { $_->{AVAIL} > 2**33 } @fs;
    if (!$fs) {
      plan skip_all => 'Large file tests need tmpfs with at least 8G';
    }
}
```

When that condition is met, the creation of a cache file will be
attempted on that tmpfs, and in an autopkgtest testbed including a user
with a uid greater than 1000 this call will fail as there is no
`Restrictions: need-root` annotation.

Here's a short sequence of calls exhibiting the issue:

  $ debci setup --suite sid --arch amd64 --backend lxc
  $ mkdir -p /srv/tmpfs
  $ mount -t tmpfs -o size=9G,rw tmpfs /srv/tmpfs
  $ TMPDIR=/srv/tmpfs autopkgtest -U -B libcache-fastmmap-perl -- lxc autopkgtest-sid-amd64
  [...]
  t/21.t ..
  1..6
  ok 1 - use Cache::FastMmap;
  Create of share file /srv/tmpfs/autopkgtest-lxc.2sfvvv_r/largecachetest.cache failed: Permission denied at /usr/lib/x86_64-linux-gnu/perl5/5.32/Cache/FastMmap.pm line 762.
  [...]
  autodep8-perl-build-deps FAIL non-zero exit status 1
  [...]
  $ TMPDIR=/srv/tmpfs autopkgtest -u root -U -B libcache-fastmmap-perl -- lxc autopkgtest-sid-amd64
  [...]
  $ echo $?
  0

Hello,

Bug #986289 in libcache-fastmmap-perl reported by you has been fixed in the
Git repository and is awaiting an upload. You can see the commit
message below and you can check the diff of the fix at:

https://salsa.debian.org/perl-team/modules/packages/libcache-fastmmap-perl/-/commit/57b0968300f8d83e26ddaaa9babd7726896a9240
------------------------------------------------------------------------
Skip t/21.t during build and autopkgtests.

It needs not only a tmpfs >= 8GB but also appropriate permissions.

Thanks: Sebastien Delafond for the detailed bug report.
Closes: #986289
------------------------------------------------------------------------

(this message was generated automatically)
-- 
Greetings

https://bugs.debian.org/986289

We believe that the bug you reported is fixed in the latest version of
libcache-fastmmap-perl, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 986289@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
gregor herrmann <gregoa@debian.org> (supplier of updated libcache-fastmmap-perl package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Thu, 14 Jul 2022 16:35:41 +0200
Source: libcache-fastmmap-perl
Architecture: source
Version: 1.57-2
Distribution: unstable
Urgency: medium
Maintainer: Debian Perl Group <pkg-perl-maintainers@lists.alioth.debian.org>
Changed-By: gregor herrmann <gregoa@debian.org>
Closes: 986289
Changes:
 libcache-fastmmap-perl (1.57-2) unstable; urgency=medium
 .
   * Skip t/21.t during build and autopkgtests.
     It needs not only a tmpfs >= 8GB but also appropriate permissions.
     Thanks to Sebastien Delafond for the detailed bug report.
     (Closes: #986289)
   * Update years of packaging copyright.
   * Declare compliance with Debian Policy 4.6.1.
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