config: read system-wide defaults from /etc/gitconfig

The settings in /etc/gitconfig can be overridden in ~/.gitconfig,
which in turn can be overridden in .git/config.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/config.txt

@@ -5,7 +5,8 @@ The git configuration file contains a number of variables that affect
 the git command's behavior. `.git/config` file for each repository
 is used to store the information for that repository, and
 `$HOME/.gitconfig` is used to store per user information to give
-fallback values for `.git/config` file.
+fallback values for `.git/config` file. The file `/etc/gitconfig`
+can be used to store system-wide defaults.
 
 They can be used by both the git plumbing
 and the porcelains. The variables are divided into sections, where

Makefile

@@ -124,6 +124,7 @@ prefix = $(HOME)
 bindir = $(prefix)/bin
 gitexecdir = $(bindir)
 template_dir = $(prefix)/share/git-core/templates/
+ETC_GITCONFIG = $(prefix)/etc/gitconfig
 # DESTDIR=
 
 # default configuration for gitweb
@@ -584,6 +585,7 @@ endif
 # Shell quote (do not use $(call) to accommodate ancient setups);
 
 SHA1_HEADER_SQ = $(subst ','\'',$(SHA1_HEADER))
+ETC_GITCONFIG_SQ = $(subst ','\'',$(ETC_GITCONFIG))
 
 DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
 bindir_SQ = $(subst ','\'',$(bindir))
@@ -596,7 +598,8 @@ PERL_PATH_SQ = $(subst ','\'',$(PERL_PATH))
 
 LIBS = $(GITLIBS) $(EXTLIBS)
 
-BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' $(COMPAT_CFLAGS)
+BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
+	-DETC_GITCONFIG='"$(ETC_GITCONFIG_SQ)"' $(COMPAT_CFLAGS)
 LIB_OBJS += $(COMPAT_OBJS)
 
 ALL_CFLAGS += $(BASIC_CFLAGS)

builtin-config.c

@@ -64,7 +64,7 @@ static int get_value(const char* key_, const char* regex_)
 	int ret = -1;
 	char *tl;
 	char *global = NULL, *repo_config = NULL;
-	const char *local;
+	const char *system_wide = NULL, *local;
 
 	local = getenv(CONFIG_ENVIRONMENT);
 	if (!local) {
@@ -74,6 +74,7 @@ static int get_value(const char* key_, const char* regex_)
 			local = repo_config = xstrdup(git_path("config"));
 		if (home)
 			global = xstrdup(mkpath("%s/.gitconfig", home));
+		system_wide = ETC_GITCONFIG;
 	}
 
 	key = xstrdup(key_);
@@ -103,11 +104,15 @@ static int get_value(const char* key_, const char* regex_)
 		}
 	}
 
+	if (do_all && system_wide)
+		git_config_from_file(show_config, system_wide);
 	if (do_all && global)
 		git_config_from_file(show_config, global);
 	git_config_from_file(show_config, local);
 	if (!do_all && !seen && global)
 		git_config_from_file(show_config, global);
+	if (!do_all && !seen && system_wide)
+		git_config_from_file(show_config, system_wide);
 
 	free(key);
 	if (regexp) {
@@ -147,7 +152,10 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 			} else {
 				die("$HOME not set");
 			}
-		} else if (!strcmp(argv[1], "--rename-section")) {
+		}
+		else if (!strcmp(argv[1], "--system"))
+			setenv("GIT_CONFIG", ETC_GITCONFIG, 1);
+		else if (!strcmp(argv[1], "--rename-section")) {
 			int ret;
 			if (argc != 4)
 				usage(git_config_set_usage);
@@ -159,7 +167,8 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 				return 1;
 			}
 			return 0;
-		} else
+		}
+		else
 			break;
 		argc--;
 		argv++;

config.c

@@ -383,6 +383,8 @@ int git_config(config_fn_t fn)
 	 * config file otherwise. */
 	filename = getenv(CONFIG_ENVIRONMENT);
 	if (!filename) {
+		if (!access(ETC_GITCONFIG, R_OK))
+			ret += git_config_from_file(fn, ETC_GITCONFIG);
 		home = getenv("HOME");
 		filename = getenv(CONFIG_LOCAL_ENVIRONMENT);
 		if (!filename)