Re: Request for Comments: libarchive, bsdtar

From: David Schultz (das_at_FreeBSD.ORG)
Date: 01/15/04

  • Next message: Tim Kientzle: "Re: Request for Comments: libarchive, bsdtar" 
    Date: Thu, 15 Jan 2004 12:44:58 -0800
To: Tim Kientzle <kientzle@acm.org>

    On Thu, Jan 15, 2004, Tim Kientzle wrote:
    > David Schultz wrote:
    > >On Tue, Jan 13, 2004, Tim Kientzle wrote:
    > >
    > >Nice! I'm sure [libarchive] will be immensely useful when finished.
    >
    > It should be useful now.

    I didn't mean to imply that it isn't; I just meant to say that it
    will be *really* useful when it becomes the default and has better
    compatibility with the gtar format. I'm really glad you went
    ahead and did this.

    > >- Have you considered extending the API such that it is able to
    > > efficiently support random access archive formats?
    >
    > Yes, and I've chosen not to go that way. In short, random-access
    > is a different problem: tar/gzip and tar/bzip2 do not support
    > random-access at all; uncompressed tar archives do not cleanly
    > support updates; tape drives/stdin/stdout/sockets do not support
    > random access. Random access gains you some things, loses you others.
    >
    > In short, libarchive is for "streaming archive formats."
    >
    > On the other hand, many archive formats can be handled via
    > streaming: it should be possible for libarchive to read
    > zip archives, for example. (However, compressed zip archives
    > can't be written in a pure streaming mode.)
    [...]
    > >- When this is done, I'm wondering what potential impact it might
    > > have on sysinstall and the archive format it uses...
    >
    > Sysinstall uses tar/gzip format, libarchive reads tar/gzip format.
    > This may potentially impact the implementation of sysinstall
    > (which could unpack the base system itself rather than running
    > a separate tar), but I see no potential impact on sysinstall's
    > choice of archive format.

    Okay, so random access is simply not in the scope of your project.
    That's fine. The problem I was hoping could be solved has to do
    with the fact that the package tools don't have an archive format
    that supports random access, so they wind up extracting a
    temporary copy of the whole archive, then processing the parts
    that they want. As I understand, this is one of the reasons that
    sysinstall makes a hard distinction between distributions and
    packages, a distinction that shouldn't exist. However, I don't
    (want to) understand these problems as well as others...
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