Re: [Bug-tar] [PATCH] Do not fail when 'compress' is unable to provide sufficient compress ratio

[Antonio Diaz Diaz]

Paul Eggert wrote:
> I think I'd rather have tar assume the gzip exit-status
> convention, and depart from that only for bzip2 and lzip
> (which don't use the convention).  That's a bit simpler
> and is more likely to match some random future compressor.

Only if the "random future compressor" continues repeating the errors of 
the past.

Bzip2 and lzip follow a deeper convention; that any non-zero exit status 
means failure[1]:

[1]http://www.gnu.org/software/bash/manual/html_node/Exit-Status.html#Exit-Status

"For the shell's purposes, a command which exits with a zero exit status 
has succeeded. A non-zero exit status indicates failure. This seemingly 
counter-intuitive scheme is used so there is one well-defined way to 
indicate success and a variety of ways to indicate various failure modes."


Routing around gzip's quirks may be necessary, but if we begin 
considering some non-zero exit statuses as success, chaos will develop. 
The "--use-compress-program" is a general mechanism, not only for 
compressors[2]:

[2]http://www.gnu.org/software/tar/manual/html_node/gzip.html#SEC132

"The '--use-compress-program' option, in particular, lets you implement 
your own filters, not necessarily dealing with 
compression/decompression. For example, suppose you wish to implement 
PGP encryption on top of compression, using gpg"


And it happens that '2' is in the range gpg reserves for fatal errors[3]:

[3]http://www.gnupg.org/documentation/manuals/gnupg/GPG-Examples.html#GPG-Examples

"The program returns 0 if everything was fine, 1 if at least a signature 
was bad, and other error codes for fatal errors."


So, please, don't break "--use-compress-program".


Best regards,
Antonio.