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[Bug-tar] Tar short read

From: Kevin Fox
Subject: [Bug-tar] Tar short read
Date: Mon, 26 Sep 2011 11:20:26 -0700

I think I've run into a bug in tar. I have grabbed the newest stable
(1.26) version from the website and verified I can see the behavior
there too.

I have a fuse file system that returns data from our archive. It reads
file contents out of the remote network file system in 32mb chunks. If a
request spans multiple chunks, it short returns what is available,
freeing the chunk up for the next read.

I see tar reading out of a file in 10240 byte chunks at a time with an
initial smaller read. On the read that would return the 32m byte, I see
a short read out of the file system as expected. I never see another
read to the file system by tar though. Tar starts padding out the file
with 0's up until the file stat size and returns a message like:
NET.csv: File shrank by 45427965 bytes; padding with zeros

The man page for read says that a short read is normal and expected. End
of file is only handled with a 0 return.

I believe in this case, tar should try to fill its remaining buffer
space with another read and only enter this "File shrank" mode if that
read returns 0 bytes?


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