"tar tfv /dev/cd0" speedup patch

[Joerg Sonnenberger]

On Thu, Feb 18, 2010 at 09:03:33PM -0800, Tim Kientzle wrote:
> Joerg Sonnenberger wrote:
> >On Thu, Feb 18, 2010 at 07:34:59PM +0100, Juergen Lock wrote:
> >> Ok here is a new version of the patch with these things fixed and the
> >>Linux case added:  (Linux case not tested yet, and yes I did this on
> >>stable/8.)
> >
> >Why the check at all? Shouldn't devices that don't allow seek fail that?
> >E.g. for devices, just try to seek ahead and fallback to normal reading?
> 
> That was the initial implementation in libarchive, but
> I had a number of reports of that not working for
> tape drives.  I recently dug out and connected an
> old DDS drive I had in the closet, so I should
> probably try again and see if I misunderstood
> something along the way.

I can think of some complications that for block devices the seek is to
be a multiple of the block size (just like reads), but that's all I can
think of in terms of portable problems.

Joerg