GNU tar bug reading multi-volumes from a pipe

[Vincent Stemen]

Dear GNU tar maintainers:

I am the author of bu, the NFS based backup tool
(http://www.hightek.org/bu).  In the process of adding multi-volume
compressed CDRW backup capability to bu, using tar, I have encountered
a bug in GNU tar that has become a show stopper in my project when it
comes to extracting the data from the CD's.  Since tar does not handle
compressed multiple volumes, I am making use of the
"--new-volume-script" feature, uncompressing each archive in the
external script and attaching it to a named pipe for tar to read on
the other end, then running tar with the "--read-full-blocks" to open
and read the pipe for each volume.

The problem is, tar will not properly read a multi-volume tar file
through a named pipe.  The file that is split between two volumes is
corrupted when read back.  The resulting file has part of the next tar
file just appended to it, tar header and all.  This has been the case
for tar versions ranging from at least 1.13 to 1.13.25.  I am
currently testing on FreeBSD-4.4.

Dr. Jan Bredereke <address@hidden> reported this same bug about a
year ago under similar conditions using Linux and sent both a patch
against version 1.13.17 to fix it and a Makefile that, when run in an
empty directory, will demonstrate the bug.  He says he never got any
response about it.

His patch fixes the initial problem of reading the split file
incorrectly but, unfortunately in my tests, it generates another
bug, causing it to not continue reading past the split file and read
the rest of the second volume.  However, it seems to be a step in the
right direction and may be useful in completing a fix.

He has posted his comments, Makefile, and patch on a web page at

http://www.tzi.de/~brederek/tar-bugfix/index.html

I, and Dr. Bredereke I'm sure, will be happy to provide any additional
information you may need to assist in fixing this problem.  I have
already written a bunch of code for bu to utilize this feature before
I discovered this bug and I would like to be able to complete this
project without finding an entirely different approach.

Thank you.
Please reply.

- Vincent