bug#80583: "dd" fails to account for short final write
Paul Eggert <[email protected]> Wed, 11 Mar 2026 12:12:51 -0700
| Newsgroups | gmane.comp.gnu.core-utils.bugs |
|---|---|
| Organization | UCLA Computer Science Department |
| Message-ID | <[email protected]> |
On 2026-03-11 08:49, Pádraig Brady wrote:
> +(
> + ulimit -S -f 1024 || skip_ 'unable to set file size ulimit'
> + trap '' XFSZ || skip_ 'unable to ignore SIGXFSZ'
> + dd if=/dev/zero of=f bs=768K count=2 2>err
> + echo $? > dd.ret
> +)
> +
> +if test "$(cat dd.ret)" = 1; then
> + grep -F '+1 records out' err || { cat err; fail=1; }
> +fi
Not clear why we have to put the exit status into dd.ret; can't we just
inspect $? after the (...) finishes?
There's a problem with doing a ulimit -f in a test script: it also
limits the size of the test trace output by the shell. Although 768K
should be safe, better to place the limit where it actually should be,
for safety in a subsidiary shell invocation. Something like this, perhaps?
> cat <<\EOF > experr-XFSZ || framework_failure_
> dd: error writing 'out-XFSZ': File too large
> 2+0 records in
> 1+1 records out
> EOF
> dd ibs=2048 obs=2048 count=1 if=/dev/zero of=exp-XFSZ &&
> ! $SHELL -c '
> ulimit -S -f 4 && trap "" XFSZ && \
> exec dd bs=1536 status=noxfer if=/dev/zero of=out-XFSZ 2>err-XFSZ
> ' &&
> compare exp-XFSZ out-XFSZ &&
> compare experr-XFSZ err-XFSZ || fail=1