od --skip (-j) works even on files in /proc, when the kernel lies

* src/od.c (skip): Don't let kernel misinformation (nonempty files
in /proc with stat.st_size == 0) make "od -j N" misbehave.
Patch by Paul Eggert.
* NEWS: Document this work-around.
* tests/misc/od-zero-len: New file, test for the above.

1 files changed, 53 insertions, 0 deletions

diff --git a/tests/misc/od-zero-len b/tests/misc/od-zero-len
new file mode 100755
index 000000000..42008ce8e
--- /dev/null
+++ b/tests/misc/od-zero-len
@@ -0,0 +1,53 @@
+#!/bin/sh
+# ensure that od -j doesn't improperly fseek across a nonempty file in /proc
+
+# Copyright (C) 2007 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  od --version
+fi
+
+pwd=`pwd`
+t0=`echo "$0"|sed 's,.*/,,'`.tmp; tmp=$t0/$$
+trap 'status=$?; cd "$pwd" && chmod -R u+rwx $t0 && rm -rf $t0 && exit $status' 0
+trap '(exit $?); exit $?' 1 2 13 15
+
+framework_failure=0
+mkdir -p $tmp || framework_failure=1
+cd $tmp || framework_failure=1
+printf e > f2 || framework_failure=1
+
+if test $framework_failure = 1; then
+  echo "$0: failure in testing framework" 1>&2
+  (exit 1); exit 1
+fi
+
+# Use a file in /proc whose size is not likely to
+# change between the wc and od invocations.
+f=/proc/version
+test -r $f || f=empty
+
+fail=0
+
+n=`wc -c < $f` || fail=1
+od -An -c -j $n $f f2 > out || fail=1
+echo '   e' > exp || fail=1
+
+cmp out exp || fail=1
+test $fail = 1 && diff out exp 2> /dev/null
+
+(exit $fail); exit $fail