AU: Update Downloader to support our image formats.

AU: Update Downloader to support our image formats.

The downloader used to be dumb in the sense that it would pipe output
to either a DirectFileWriter or a DirectFileWriter via a
GzipDecompressingFileWriter, depending on if we were downloading an
update that was compressed or not. Sadly, things have gotten more
complex: we need to download to two partitions (kernel + rootfs), and
we may stream data via a DeltaPerformer (a type of FileWriter) to the
disk. Thus, the Downloader streams to either
1. gzip decompress->split_writer->direct to disk OR
2. delta performer

Other misc changes: Change FilesystemCopierAction to support
optionally copying the kernel partition rather than root partition.

InstallPlan struct: add an entry for destiation kernel partition.

Test Utils: a new ScopedTempFile class

Utils: support for getting the booted kernel partition device.

BUG=None
TEST=attached unittests

[Daniel Erat, 2010-05-02 18:45:53]

LGTM with a few comments

http://codereview.chromium.org/1694025/diff/1/3
File src/platform/update_engine/download_action.h (right):

http://codereview.chromium.org/1694025/diff/1/3#newcode31
src/platform/update_engine/download_action.h:31: // update goes from. In this
case, the updat will be piped into a
s/updat/update/

http://codereview.chromium.org/1694025/diff/1/3#newcode88
src/platform/update_engine/download_action.h:88: // Used to write out the
downloaded file
Should this be something like "Used to apply delta updates" instead?

http://codereview.chromium.org/1694025/diff/1/13
File src/platform/update_engine/utils.h (right):

http://codereview.chromium.org/1694025/diff/1/13#newcode146
src/platform/update_engine/utils.h:146: const std::string BootKernelDevice(const
std::string& boot_device);
making this distinction between testing and non-testing code is kinda ugly. 
could you make the 'boot_device' argument mandatory for real clients too, and
just pass BootDevice() explicitly?

[adlr, 2010-05-03 18:11:23]

Thanks for the review. Fixed and submitted.

http://codereview.chromium.org/1694025/diff/1/3
File src/platform/update_engine/download_action.h (right):

http://codereview.chromium.org/1694025/diff/1/3#newcode31
src/platform/update_engine/download_action.h:31: // update goes from. In this
case, the updat will be piped into a
On 2010/05/02 18:45:53, Daniel Erat wrote:
> s/updat/update/

Done.

http://codereview.chromium.org/1694025/diff/1/3#newcode88
src/platform/update_engine/download_action.h:88: // Used to write out the
downloaded file
On 2010/05/02 18:45:53, Daniel Erat wrote:
> Should this be something like "Used to apply delta updates" instead?

Done. (slight wording change)

http://codereview.chromium.org/1694025/diff/1/13
File src/platform/update_engine/utils.h (right):

http://codereview.chromium.org/1694025/diff/1/13#newcode146
src/platform/update_engine/utils.h:146: const std::string BootKernelDevice(const
std::string& boot_device);
On 2010/05/02 18:45:53, Daniel Erat wrote:
> making this distinction between testing and non-testing code is kinda ugly. 
> could you make the 'boot_device' argument mandatory for real clients too, and
> just pass BootDevice() explicitly?

Done.