[gentoo-dev] digest + manifest = new file format

[Alec Warner]

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This is basically a resubmission of Genone's file format merger [1].

The code to handle digests and manifests is currently being designed and
rewritten.  As such we need two things from the developer community.
One is a decision of what the new format will entail.  Two is a firm
agreement on the migration plan.

1.  The file format is specified in Genone's original mail, but I'll go
over it again to save you the extra linkage ;)

Inside of the digest-manifest we have:
EBUILD Filename SIZE 1234567 MD5 A4FD085FF SHA-256 A7439FDB1
<type> <filename> <size-tag> <size> <hash-tag> <value> <hash-tag>
<value>....
Where type is the type of file (DIGEST, SRC_URI, EBUILD, PATCH, etc)

*Note, that the size-tag was added to make the human parsing easier.

2.  If you didn't notice by now, this format breaks versions of portage
that don't support it ( ie 2.0.X ).  This leads us to a few options as
users migrate to a version of portage that supports the new file format.

	A.  Write some code into the final stable version to do both kind of
formats and/or use the new format style but fall back to the old style (
since at release time the new style format probably won't be in the tree
yet ).  Either way, the last release of 2.0.X should work with the new
file format in enough of a fashion to not break.  This means that when
the old manifest + digests are combined in the tree, most users should
be ok even if they aren't upgraded to 2.1.X.

	B.  Have a migration time where both formats are in the tree.  For a
while the tree will be larger, and many people will have issues with
this.  However, old portage will use the old files, and new releases
will use the new files.  Then after a period of however long ( 6 months?
) announce loudly beforehand that portage-2.0.X will no longer be
supported and pull the old digests/manifests out of the tree.

	C.  The Carpaski way ;)[2]  Add support for the new format in 2.1,
while also adding support for current format.  Force everyone to upgrade
to 2.1.X, while announcing that 2.0.X will not work in the future.  When
we have confidence that most users are upgraded, pull the old format and
add the new format to the tree.

	Problems with all of these include the same problems as the cascaded
profiles, some goofball doesn't upgrade for a year, syncs with new
digests...how does he get his portage upgraded?  An upgrade path should
be provided and documented in this case.

The best route is probably some combination of the above.  Pre-emptively
add support for the new format to stable, while announcing the death of
the old format after 2.1's release.  When most users upgrade normally to
the latest 2.0.X series ( perhaps fearing the changes of 2.1.X ) they
will gain support for the new file format (or if not support, merely a
working portage instead of broken).  We should catch the majority of
users who upgrade with either the last 2.0.X release or the new release
of 2.1.X.

Suggestions, criticisms, etc... welcome.

[1] http://marc.theaimsgroup.com/?l=gentoo-dev&m=109725383228494&w=2
[2] http://marc.theaimsgroup.com/?l=gentoo-dev&m=109725779909405&w=2
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