tree bd78c7fd410543e3ae0b2f90af34641ff3986a15
parent a376a6e9007539531e99d3e879bc72ad1273f72f
author Alex Deymo <deymo@chromium.org> 1427355307 -0700
committer ChromeOS Commit Bot <chromeos-commit-bot@chromium.org> 1434127065 +0000

update_engine: Introduce FilesystemInterface abstraction.

The interaction with the filesystem in the payload generation process
is hard-coded in several places, making it hard to mock out or use a
different filesystem like squashfs for delta generation. For example,
the metadata, regular file data and non-file data are handled by three
different functions in a similar way, but with different code.

This patch introcudes a filesystem abstraction to map files or
pseudo-files (like the metadata, free-space, etc) into the same interface.
The interface includes three implementations: for parsing ext2 filesystems
using ext2fs (already used by the metadata parsing but not by the file
data processing), a raw one for monolitic partitions like the kernel
and a fake one used for testing without requiring to build/parse a real
ext2 filesystem.

BUG=chromium:331965
TEST=FEATURES=test emerge-link update_engine

Change-Id: I1e14cf8f3883c8e9a1d471c8193c8da60776aa7c
Reviewed-on: https://chromium-review.googlesource.com/275803
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>