Debian 3.0 (native/quilt) and the kernel packages

[Andy Whitcroft]

At UDS it was decided we should investigate the new Debian source formats
3.0 (native) and 3.0 (quilt) to see if there were any advantages for
the kernel switching to them.  The short answer appears to be no at the
current time.  As we use an orig.tar.gz from upstream Linus' tree we would
need to use 3.0 (quilt) format, and that provides basically no advantage
for us.  Therefore the recommendation is that we stay with the existing
1.0 format.  To do this we are recommended to explicitly indicate the
version we are using.  I will push a patch to the list shortly to do this.

A fuller writeup of the pros and cons of these new formats is below.

-apw

= Background =

The debian archive is switching to a pair of new formats; 3.0 (native)
and 3.0 (quilt).  These are becoming the preferred formats for upload.
As part of the process soyuz has gained the ability to accept uploads in
this format.  See here for further background:

    http://wiki.debian.org/Projects/DebSrc3.0

== 3.0 (native) ==

This format is essentially a raw tarball format.  However there is no
support for an orig tarball in this format.  The entire contents of the
source directory excluding the .git directory are picked up, including
all of the permissions.  This would be appropriate for the kernel as
the resultant build tree is completely identicle to the git checkout.
This lack of support for an orig tarball renders the format unsuitable
for the kernel as they are used heavily to reduce upload times.

== 3.0 (quilt) ==

This format supports an orig tarball and so there are two forms.
Without an orig tarball the format is essentially identicle to the 3.0
(native) format.  With an orig tarball the source form is made up of two
tarballs the orig tarball as normal and a second tarball representing
the debian directory.  This second tarball is a clean tarball of the
debian directory contents.  Any quilt patches listed in debian/patches
are applied to the tree.  Finally any delta in the remainder of the tree
is encoded as a patch in the debian/patches directory.  This makes it
very similar to the current orig+diff format except that permissions and
empty files are correctly encoded for the debian directory.  If we did
convert over to this format we might want to move the branch specific
changes into the debian directory, to debian/master for example.

= Advantages =

Permissions would be maintained correctly in the debian directory.
Also the source as obtained by apt-get source would be more readily
manipulated as it would already by ready for use with quilt.  Other than
this there is no compelling reason to convert to any of the new formats.
There does not appear to be any compelling drive to remove the existing
1.0 format we are already using.

= Conversion =

For our use case we are not going to be able to sensibly turn the patches
into a quilt set, though there is some work ongoing to provide tooling to
produce such a quilt stack from git history.  So we would most likely make
use of the automatically created patch mode of the quilt.  Conversion is
as simple as creating debian/source/format containing '3.0 (quilt)'.
If we do not convert we are advised to specify '1.0' format explicitly.

= Caveats =

This functionality was added under Bug:293106, some of the write up
implies this feature may only be enabled for lucid and later.