Binary diffs for deb files

[Scott James Remnant]

On Tue, 2006-05-02 at 15:26 -0700, Matt Zimmerman wrote:

> On Tue, May 02, 2006 at 11:10:08PM +0100, Colin Watson wrote:
> > On Tue, May 02, 2006 at 02:50:50PM -0700, Matt Zimmerman wrote:
> > > On Tue, May 02, 2006 at 10:14:50PM +0100, James Hall wrote:
> > > > Some other issues I have with zsync are:
> > > > 
> > > > 1. How easy would it be to recompress all the packages with the gzip
> > > > --rsync flag?
> > > 
> > > Trivial.  At the appropriate time, we enable this flag by default for
> > > dpkg-deb, and all builds from that point forward produce rsyncable debs.
> > 
> > dpkg-deb uses zlib for compression, not gzip. Last time I talked to
> > Scott about this, I seem to remember that he said that it was
> > non-trivial to enable rsyncability because the gzip --rsyncable patch
> > was done in gzip rather than in zlib, and would require some moderately
> > complex porting work.
> 
> Good point; it wouldn't quite be trivial.  We could recompress the debs
> using gzip after the build, I suppose, but is there any particular reason
> why dpkg needs to use zlib?  It already relies on external tools of similar
> ubiquity (e.g., GNU tar), and forking gzip is typically faster on
> multiprocessor machines like our buildds.
> 
Actually dpkg has its own internal implementation of tar too.

This is all for decompression of a deb, obviously; for compression of
one, dpkg-deb could theoretically call out to external tools -- the risk
there is that when the tools are changed, dpkg is no longer able to
decompress the debs it created.

cf. the time a few months ago when the tar format changed slightly

Scott
-- 
Scott James Remnant
scott at ubuntu.com
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