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List:       gentoo-dev
Subject:    Re: [gentoo-dev] [pre-GLEP r2] Gentoo binary package container format
From:       Michał_Górny <mgorny () gentoo ! org>
Date:       2018-11-21 14:21:48
Message-ID: 1542810108.4480.2.camel () gentoo ! org
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On Wed, 2018-11-21 at 14:10 +0100, Fabian Groffen wrote:
> On 20-11-2018 21:33:17 +0100, Michał Górny wrote:
> > The volume label
> > ----------------
> > 
> > The volume label provides an easy way for users to identify the binary
> > package without dedicated tooling or specific format knowledge.
> > 
> > The implementations should include a volume label consisting of fixed
> > string ``gpkg:``, followed by a single space, followed by full package
> > identifier.  However, the implementations must not rely on the volume
> > label being present or attempt to parse its value when it is.
> > 
> > Furthermore, since the volume label is included in the .tar archive
> > as the first member, it provides a magic string at a fixed location
> > that can be used by tools such as file(1) to easily distinguish Gentoo
> > binary packages from regular .tar archives.
> 
> Just for clarity on this point.
> Are you proposing that we patch file(1) to print the Volume Header here?
> file-5.35 seems to not say much but "tar archive" or "POSIX tar archive"
> for tar-files containing a Volume Header as shown by tar -tv.

I'm wondering about that as well, yes.  However, my main idea is to
specifically detect 'gpkg:' there and use it to explicitly identify
the file as Gentoo binary package (and print package name).

> 
> > Container and archive formats
> > -----------------------------
> > 
> > During the debate, the actual archive formats to use were considered.
> > The .tar format seemed an obvious choice for the image archive since
> > it is the only widely deployed archive format that stores all kinds
> > of file metadata on POSIX systems.  However, multiple options for
> > the outer format has been debated.
> 
> You mention POSIX, which triggered me.  I think it would be good to
> specify which tar format to use.
> 
> POSIX.1-2001/pax format doesn't have a 100/256 char filename length
> restriction, which is good but it is not (yet) used by default by GNU
> tar.  busybox tar can read pax tars, it seems.
> 

I think the modern GNU tar format is the obvious choice here.  I think
it doesn't suffer any portability problems these days, and is more
compact than the PAX format.


-- 
Best regards,
Michał Górny

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