Re: [Bug-tar] Proposed enhancements to "Sparse format 1.0"

[Tim Kientzle]

Sergey Poznyakoff wrote:
> Tim Kientzle <address@hidden> ha escrit:
>
> > [I] ... have a couple of suggestions
> > you might consider if you ever create a format 1.1:
>
> >   * Include a format specifier ("magic number")
> > in the prepended block description.  ...
> >
> >    #!gnu_sparse_file
> >    #format=1.1
>
> It is possible. But this information is already stored in PAX variables
> `GNU.sparse.major' and `GNU.sparse.minor'. Why it is necessary to
> duplicate it? 

Because you cannot assume those PAX variables are
available to a post-processing program.

Yes, POSIX does require that compliant tar and pax
implementations store "unrecognized" file types as
plain files.  But a program that *does* support the
'x' file type is under no obligation to store the
GNU.sparse.major/minor values on disk.

It is also generally polite to try to ensure that
any new file format you invent can be eventually
identified with standard tools such as "file."

Cheers,

Tim Kientzle