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List:       busybox
Subject:    Busybox "tar -c" aborts on failed reads? (GNU tar doesn't)
From:       Joshua Judson Rosen <jrosen () harvestai ! com>
Date:       2013-08-15 17:31:19
Message-ID: 520D1067.8090901 () harvestai ! com
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I noticed that writeFileToTarball() _aborts_ if it fails to read a file that
it's supposed to put into the archive (including if the file changed size);
the code in question being:

     /* If it was a regular file, write out the body */
     if (inputFileFd >= 0) {
         size_t readSize;
         /* Write the file to the archive. */
         /* We record size into header first, */
         /* and then write out file. If file shrinks in between, */
         /* tar will be corrupted. So we don't allow for that. */
         /* NB: GNU tar 1.16 warns and pads with zeroes */
         /* or even seeks back and updates header */
         bb_copyfd_exact_size(inputFileFd, tbInfo->tarFd, statbuf->st_size);
         ////off_t readSize;
         ////readSize = bb_copyfd_size(inputFileFd, tbInfo->tarFd, 
statbuf->st_size);
         ////if (readSize != statbuf->st_size && readSize >= 0) {
         ////    bb_error_msg_and_die("short read from %s, aborting", fileName);
         ////}

I'm running into this problem when trying to tar up files from a failing UBIFS,
so there are occasional read-errors for some files, but I was surprised to find
that an error reading a file early in the fileset will both discard all of the
later files _and_ result in a corrupt tar-stream (when tar just aborts, the
output prematurely truncated).

GNU tar indeed handles this much more gracefully; and it seems like it should be
easy enough for me to fix this issue in busybox, but I wonder if there's any
particular reason that it's handled the way it is rather than like GNU tar does.
Should I fix it and send a patch up, or should I just find a work-around?

-- 
"'tis an ill wind that blows no minds."
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