Install a default pre-auto-gc hook in all repositories

This hook is evaluated by `git gc --auto` to determine if it is a
good idea to execute a GC at this time, or defer it to some later
date.  When working on a laptop its a good idea to avoid GC if you
are on battery power as the extra CPU and disk IO would consume a
decent amount of the charge.

The hook is the standard sample hook from git.git contrib/hooks,
last modified in git.git by 84ed4c5d117d72f02cc918e413b9861a9d2846d7.
I added the GPLv2 header to the script to ensure the license notice
is clear, as it does not match repo's own APLv2 license.

We only update hooks during initial repository creation or on
a repo sync.  This way we don't incur huge overheads from the
hook stat operations during "repo status" or even the normal
"repo sync" cases.

Signed-off-by: Shawn O. Pearce <sop@google.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/hooks/pre-auto-gc b/hooks/pre-auto-gc
new file mode 100755
index 00000000..110e3194
--- /dev/null
+++ b/hooks/pre-auto-gc
@@ -0,0 +1,44 @@
+#!/bin/sh
+#
+# An example hook script to verify if you are on battery, in case you
+# are running Linux or OS X. Called by git-gc --auto with no arguments.
+# The hook should exit with non-zero status after issuing an appropriate
+# message if it wants to stop the auto repacking.
+
+# 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 2 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, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+if test -x /sbin/on_ac_power && /sbin/on_ac_power
+then
+        exit 0
+elif test "$(cat /sys/class/power_supply/AC/online 2>/dev/null)" = 1
+then
+        exit 0
+elif grep -q 'on-line' /proc/acpi/ac_adapter/AC/state 2>/dev/null
+then
+        exit 0
+elif grep -q '0x01$' /proc/apm 2>/dev/null
+then
+        exit 0
+elif grep -q "AC Power \+: 1" /proc/pmu/info 2>/dev/null
+then
+        exit 0
+elif test -x /usr/bin/pmset && /usr/bin/pmset -g batt |
+        grep -q "Currently drawing from 'AC Power'"
+then
+        exit 0
+fi
+
+echo "Auto packing deferred; not on AC"
+exit 1