[paludis-dev] [Paludis] #1207: Add xz support to expatch

Paludis trac at pioto.org
Sun Nov 6 18:35:19 UTC 2011


#1207: Add xz support to expatch
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    Reporter:  irishespresso          |      Owner:
        Type:  enhancement            |     Status:  new
    Priority:  Sometime               |  Milestone:
   Component:  repositories/e/ebuild  |    Version:  0.70.1
  Resolution:                         |   Keywords:
  Blocked By:                         |   Blocking:
Distribution:  Exherbo                |
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Comment (by irishespresso):

 Unfortunately, "xz --list" does not show the version information that you
 are looking for.  That said, the xz format is forward-compatible as long
 as one sticks to the defaults.  From the xz maintainer:

 Right now there is no way to get a version number of the format.

 I could make xz -lvv show the oldest XZ Utils version that will decompress
 the file. It can only work for files that are supported by the xz tool, so
 it's not possible to make an old xz tool to display how much newer xz is
 required for a given file; the old tool could only tell that it doesn't
 support it. I don't know if this could be good enough for you.

 To understand the reason for the above, it's good to understand how
 incompatible additions may happen:

 (1) A new filter/method ID may be added into the official .xz format
     specification. Old tools will show that there is an unsupported
     filter ID and cannot decompress such files (will display an error).

 (2) Third-party developers may use custom filter IDs which aren't in
     the official specification and aren't supported by XZ Utils. If
     they don't deviate from the .xz specification in any other way,
     this is OK. Old tools cannot distinguish this situation from (1).

 (3) A new .xz format specification may add new features to the
     container format. The old tools will detect such files as
     unsupported (they won't claim them to be corrupt). With old tools,
     the difference to (1) and (2) is that the old tools won't be able
     to list even the filter IDs.

 If incompatible additions are made, the xz tool won't use them by default.
 Maybe they might become a default after several years have passed and old
 xz versions aren't common anymore. But it won't be done easily, because it
 would make people angry if the default settings created files that many
 wouldn't be able to decompress without extra work.

-- 
Ticket URL: <http://trac.pioto.org/paludis/ticket/1207#comment:11>
Paludis <http://paludis.pioto.org/>
Paludis, the Other Package Mangler


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