Merge branch 'mv/defer-gc'

* mv/defer-gc:
  contrib/hooks: add an example pre-auto-gc hook
  Documentation/hooks: add pre-auto-gc hook
  git-gc --auto: add pre-auto-gc hook

Documentation/hooks.txt

@@ -276,3 +276,10 @@ probably enable this hook.
 Both standard output and standard error output are forwarded to
 `git-send-pack` on the other end, so you can simply `echo` messages
 for the user.
+
+pre-auto-gc
+-----------
+
+This hook is invoked by `git-gc --auto`. It takes no parameter, and
+exiting with non-zero status from this script causes the `git-gc --auto`
+to abort.

builtin-gc.c

@@ -157,6 +157,34 @@ static int too_many_packs(void)
 	return gc_auto_pack_limit <= cnt;
 }
 
+static int run_hook(void)
+{
+	const char *argv[2];
+	struct child_process hook;
+	int ret;
+
+	argv[0] = git_path("hooks/pre-auto-gc");
+	argv[1] = NULL;
+
+	if (access(argv[0], X_OK) < 0)
+		return 0;
+
+	memset(&hook, 0, sizeof(hook));
+	hook.argv = argv;
+	hook.no_stdin = 1;
+	hook.stdout_to_stderr = 1;
+
+	ret = start_command(&hook);
+	if (ret) {
+		warning("Could not spawn %s", argv[0]);
+		return ret;
+	}
+	ret = finish_command(&hook);
+	if (ret == -ERR_RUN_COMMAND_WAITPID_SIGNAL)
+		warning("%s exited due to uncaught signal", argv[0]);
+	return ret;
+}
+
 static int need_to_gc(void)
 {
 	/*
@@ -176,6 +204,9 @@ static int need_to_gc(void)
 		append_option(argv_repack, "-A", MAX_ADD);
 	else if (!too_many_loose_objects())
 		return 0;
+
+	if (run_hook())
+		return 0;
 	return 1;
 }
 

contrib/hooks/pre-auto-gc-battery

@@ -0,0 +1,36 @@
+#!/bin/sh
+#
+# An example hook script to verify if you are on battery, in case you
+# are running Linux. 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 hook is stored in the contrib/hooks directory. Your distribution
+# may have put this somewhere else. If you want to use this hook, you
+# should make this script executable then link to it in the repository
+# you would like to use it in.
+#
+# For example, if the hook is stored in
+# /usr/share/git-core/contrib/hooks/pre-auto-gc-battery:
+#
+# chmod a+x pre-auto-gc-battery
+# cd /path/to/your/repository.git
+# ln -sf /usr/share/git-core/contrib/hooks/pre-auto-gc-battery \
+#	hooks/pre-auto-gc
+
+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
+fi
+
+echo "Auto packing deferred; not on AC"
+exit 1