cp: work around linux kernel bug: short-read != EOF on /proc

Remove the optimization that avoided up to 50% of cp's read syscalls.
Do not assume that a short read on a regular file indicates EOF.
When reading from a file in /proc on linux [at least 2.6.9 - 2.6.29]
into a 4k-byte buffer or larger, a short read does not
always indicate EOF.  For example, "cp /proc/slabinfo /tmp"
copies only 4068 of the total 7493 bytes.  This optimization
(25719a33154f0c62ea9881f0c79ae312dd4cec7a, Improve performance a bit
by optimizing away; 2005-11-24) appears to have been worth less than
a 2% speed-up (and usually much less), so the impact of removing it
is negligible.

* src/copy.c (copy_reg): Don't exit the loop early.
* tests/cp/proc-short-read: New test, lightly based on a suggestion
from Mike Frysinger, to exercise this fix.
* tests/Makefile.am (TESTS): Add cp/proc-short-read.
* NEWS (Improve robustness): Mention this change.

2 files changed, 46 insertions, 0 deletions

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 8ce6a2118..c02f2de93 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -281,6 +281,7 @@ TESTS =						\
   cp/parent-perm-race				\
   cp/perm					\
   cp/preserve-2					\
+  cp/proc-short-read				\
   cp/proc-zero-len				\
   cp/r-vs-symlink				\
   cp/same-file					\
diff --git a/tests/cp/proc-short-read b/tests/cp/proc-short-read
new file mode 100755
index 000000000..e06143c9f
--- /dev/null
+++ b/tests/cp/proc-short-read
@@ -0,0 +1,45 @@
+#!/bin/sh
+# exercise cp's short-read failure when operating on >4KB files in /proc
+
+# Copyright (C) 2009 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
+  cp --version
+fi
+
+. $srcdir/test-lib.sh
+
+fail=0
+kall=/proc/kallsyms
+
+test -r $kall || skip_test_ "your system lacks $kall"
+
+# Before coreutils-7.3, cp would copy less than 4KiB of this 1MB+ file.
+cp $kall 1    || fail=1
+cat $kall > 2 || fail=1
+compare 1 2   || fail=1
+
+# Also check md5sum, just for good measure.
+md5sum $kall > 3 || fail=1
+md5sum 2     > 4 || fail=1
+
+# Remove each file name before comparing checksums.
+sed 's/ .*//' 3 > sum.proc || fail=1
+sed 's/ .*//' 4 > sum.2    || fail=1
+compare sum.proc sum.2 || fail=1
+
+Exit $fail