Bug#986289: libcache-fastmmap-perl: autopkgtest fails on t/21.t if a large tmpfs is present

[Sebastien Delafond]

Source: libcache-fastmmap-perl
Version: 1.56-1
Severity: normal
User: devel at kali.org
Usertags: origin-kali

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

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.10.0-4-amd64 (SMP w/36 CPU threads)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled