install: add --compare (-C) option to install file only when necessary

* src/install.c (have_same_content): New function to compare files
content.
(extra_mode): New function checking for non-permission bits in mode.
(need_copy): New function to check if copy is necessary.
(main): Handle new option --compare (-C).
(copy_file): Skip file copying if not necessary.
(usage): Show new option --compare (-C) in --help.
* tests/install/install-C: Basic tests for install --compare (-C).
* tests/install/install-C-root: Tests requiring root privileges.
* tests/install/install-C-selinux: Tests requiring SELinux.
* tests/Makefile.am: Add new tests for install --compare (-C).
* doc/coreutils.texi: Document new install option --compare (-C).
* NEWS: Mention the change.

1 files changed, 56 insertions, 0 deletions

diff --git a/tests/install/install-C-selinux b/tests/install/install-C-selinux
new file mode 100755
index 000000000..d1d954085
--- /dev/null
+++ b/tests/install/install-C-selinux
@@ -0,0 +1,56 @@
+#!/bin/sh
+# Ensure "install -C" compares SELinux context.
+
+# Copyright (C) 2008 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
+  ginstall --version
+fi
+
+. $srcdir/test-lib.sh
+require_selinux_
+
+fail=0
+
+echo test > a || framework_failure
+chcon -u system_u a || skip_test_ "chcon doesn't work"
+
+echo "\`a' -> \`b'" > out_installed_first
+echo "removed \`b'
+\`a' -> \`b'" > out_installed_second
+> out_empty
+
+# destination file does not exist
+ginstall -Cv --preserve-context a b > out || fail=1
+compare out out_installed_first || fail=1
+
+# destination file exists
+ginstall -Cv --preserve-context a b > out || fail=1
+compare out out_empty || fail=1
+
+# destination file exists but -C is not given
+ginstall -v --preserve-context a b > out || fail=1
+compare out out_installed_second || fail=1
+
+# destination file exists but SELinux context differs
+chcon -u unconfined_u a || skip_test_ "chcon doesn't work"
+ginstall -Cv --preserve-context a b > out || fail=1
+compare out out_installed_second || fail=1
+ginstall -Cv --preserve-context a b > out || fail=1
+compare out out_empty || fail=1
+
+Exit $fail