Re: [Bug-tar] tar: do not fail hardly when compressor just warns

[Antonio Diaz Diaz]

Pavel Raiskup wrote:
> Hi Antonio, thanks for comments,

You are welcome. :-)


> Exit value 2 is a general warning exit status among compressors

Then those compressors have a serious problem with their APIs that 
should be fixed, or at least carefully documented. Callers like tar do 
not mind if there were warnings or not, only if the data was succesfully 
compressed or not.


> > if important programs like GNU tar begin accepting an exit status of '2'
> > as success for those compressors, it will prevent them from switching to
> > the correct and sane API
>
> This is not so truth, nobody prevents anyone from switching

Suppose that gzip-1.6 begins returning '2' to mean fatal error, just as 
most compressors are already doing (see below). This would work fine 
with the current tar. But if '-z' is modified to accept '2' as success, 
then the new tar with gzip-1.6 would produce truncated archives without 
a warning. This is far worse than giving an spurious error. Therefore, 
if tar is modified, gzip won't.


> This patch is intended just to make tar work *now* .. don't wait forever.

Passing -f to compress and considering all warnings from gzip as errors 
is the simplest and safest way of making tar work now without 
compromising the future.


> And even if some standard compressor change its API (I see this as an
> highly unlikely), it is very easily configurable on target distribution
> tar (distro maintainers can know, which API its distributed compressor
> uses) - not possible now, thats why I am trying to solve this.

If tar is modified and later some compressor changes its API, user's 
scripts will break and chaos will develop as soon as a partial update is 
made.


> > It seems that pigz does not use the compress API.
>
> Thanks for this info!  Tried to find it in manual page and wasn't
> successful.

I had to look at the source.

In addition to bzip2 and lzip (and all their derivatives and parallel 
versions), it seems that all parallel compressors use the standard API, 
not the compress one.

Pixz, for example, returns '2' in case of fatal error[1].
[1] https://github.com/vasi/pixz/blob/master/pixz.c


Best regards,
Antonio.