[PATCH v3 0/5] Improving apt cache

[Uladzimir Bely <ubely@ilbers.de>]

Currently, apt cache (e.g. `var/cache/apt/archives`) import and export
functions are not optimal. Multiple files are copied from global
DL_DIR to package WORKDIR, increasing disk IO and space needed.

Also, various chroots (bootstrap, buildchroot, sbuild chroot) include
their apt caches to sstate cache files.

This patchset switches to hardlinks instead of copies and removes apt
cache from bootstrapped images ans sstate caches.

Changes since v2:
 - Don't use CACHEDIR.TAG, simply exclude var/cache/apt directory
when creating rootfs tarball for sstate-cache.
 - Use symlinks when exchanging deb files between WORKDIR/rootfs
and /var/cache/apt/archives inside sbuild chroot

Changes since v1:
 - Simplified cleanup of apt cache in debootstrap rootfs.
 - Now "ln" instead of "cp -l" used.
 - Removed apt cache contents from sstate cache. The idea is proposed
in patch 3, but it was reworked and fixed. Firstly, CACHEDIR.TAG can't
be just a file (e.g. created by 'touch'), it should include some
specific signature [1]. Secondly, it's easier to just create this tag
in bootstrapped rootfs and it will be automatically used in all
derivatives (sbuild-chroot/buildchroot/image). So, the original patch
from Roberto A. Foglietta was simplified.

This patchset includes (or absorbs) the logic from p1..p3 patches of
the series Roberto prosposed. What concerns additional patches, they
don't let us benefit much, but require quite significant changes
in Isar, so we should check twice if they are worth including.

Uladzimir Bely (5):
  Clean apt cache from debootstrapped rootfs dirs
  Use hardlinks in deb-dl-dir import/export
  Exclude apt cache from sstate caches
  Use symlinks when importing debian packages to sbuild chroot
  Lightweight copy of rootfs directories if possible

 meta/classes/deb-dl-dir.bbclass                     | 4 ++--
 meta/classes/dpkg.bbclass                           | 4 ++--
 meta/classes/imagetypes_container.bbclass           | 2 +-
 meta/classes/rootfs.bbclass                         | 7 ++++---
 meta/classes/sdk.bbclass                            | 2 +-
 meta/recipes-core/isar-bootstrap/isar-bootstrap.inc | 6 +++++-
 6 files changed, 15 insertions(+), 10 deletions(-)

-- 
2.20.1