Re: [Bug-tar] tar 1.23: Problem under Solaris 10 - incorrect GNU header contents

[Joerg Schilling]

"Armistead, Jason" <address@hidden> wrote:

> Dustin wrote:
>
> >The entire original email was focused on ustar functionality, by my
> >read.  Perhaps you can repeat your experiment, bearing in mind that
> >you're expecting a GNU Tar archive, and let us know what happens?
>
> My original experiment WAS with GNU formatted tar archives.  Some work, and 
> some don't.  I have far larger tar files that are working OK.  But this one, 
> from a very important filesystem, is not.  That is what led me to look more 
> closely at the bytes in the file header records.

GNU tar archives by default have vendor specific extension from a definition
in POSIX.1-1988.

As POSIX.1-1988 does not include a way to to associate extensions to a 
specific vendor, implementing POSIX.1-1988 extensions cause a risk of 
missinterpreting archive content. 

> With regard to my e-mail, I made a newbie blunder (having never looked under 
> the hood of tar before), and assumed that because the resulting files 
> contained "ustar" in the header, they must have been in Ustar format.
>
> If I'm correct it my understanding, a GNU formatted achive should also 
> contain "ustar" (followd by a null) at offset 257 and "00" at offset 263.  Is 
> this correct for GNU format archives ?

No, a GNU tar archive is not even compliant to POSIX.1-1988 as it
does not implement long path names acording to POSIX.1-1988. GNU tar
archives are identified by "ustar  " and careful tar implementations
only decode GNU tar vendor specific extensions if the archive can
be identified as a GNU tar archive.

> >Also, 7-zip claims to support "TAR" format, but doesn't say which
> >format - are you sure it's designed to support GNU Tar archives?  If
> >you create a tar file with --format=ustar, can you read it with 7-zip?
>
> 7-Zip is decidedly vague on what sort of TAR it supports.  I now have the 
> source code, but it still doesn't explain what TAR format(s) it supports. 
> Time permitting, I'll try to instrument it to figure out where it's breaking, 
> and to understand what format(s) it supports.  7-Zip's author didn't leave 
> many comments in his code, and doesn't have the ability to conditionally add 
> in debugging.  It could take me some time.

I recommend to use star, star supports 7z compression.

Jörg

-- 
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