Exec git programs without using PATH.

The git suite may not be in PATH (and thus programs such as
git-send-pack could not exec git-rev-list).  Thus there is a need for
logic that will locate these programs.  Modifying PATH is not
desirable as it result in behavior differing from the user's
intentions, as we may end up prepending "/usr/bin" to PATH.

- git C programs will use exec*_git_cmd() APIs to exec sub-commands.
- exec*_git_cmd() will execute a git program by searching for it in
  the following directories:
	1. --exec-path (as used by "git")
	2. The GIT_EXEC_PATH environment variable.
	3. $(gitexecdir) as set in Makefile (default value $(bindir)).
- git wrapper will modify PATH as before to enable shell scripts to
  invoke "git-foo" commands.

Ideally, shell scripts should use the git wrapper to become independent
of PATH, and then modifying PATH will not be necessary.

[jc: with minor updates after a brief review.]

Signed-off-by: Michal Ostrowski <mostrows@watson.ibm.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

12 files changed, 176 insertions, 62 deletions

diff --git a/Makefile b/Makefile
index 3738811952..c48ae3bc65 100644
--- a/Makefile
+++ b/Makefile
@@ -69,6 +69,7 @@ STRIP ?= strip
 
 prefix = $(HOME)
 bindir = $(prefix)/bin
+gitexecdir = $(prefix)/bin
 template_dir = $(prefix)/share/git-core/templates/
 GIT_PYTHON_DIR = $(prefix)/share/git-core/python
 # DESTDIR=
@@ -142,7 +143,7 @@ PROGRAMS = \
 	git-describe$X
 
 # what 'all' will build and 'install' will install.
-ALL_PROGRAMS = $(PROGRAMS) $(SIMPLE_PROGRAMS) $(SCRIPTS) git$X
+ALL_PROGRAMS = $(PROGRAMS) $(SIMPLE_PROGRAMS) $(SCRIPTS)
 
 # Backward compatibility -- to be removed after 1.0
 PROGRAMS += git-ssh-pull$X git-ssh-push$X
@@ -174,7 +175,7 @@ DIFF_OBJS = \
 
 LIB_OBJS = \
 	blob.o commit.o connect.o count-delta.o csum-file.o \
-	date.o diff-delta.o entry.o ident.o index.o \
+	date.o diff-delta.o entry.o exec_cmd.o ident.o index.o \
 	object.o pack-check.o patch-delta.o path.o pkt-line.o \
 	quote.o read-cache.o refs.o run-command.o \
 	server-info.o setup.o sha1_file.o sha1_name.o strbuf.o \
@@ -367,7 +368,7 @@ LIB_OBJS += $(COMPAT_OBJS)
 export prefix TAR INSTALL DESTDIR SHELL_PATH template_dir
 ### Build rules
 
-all: $(ALL_PROGRAMS)
+all: $(ALL_PROGRAMS) git$X
 
 all:
 	$(MAKE) -C templates
@@ -376,7 +377,7 @@ strip: $(PROGRAMS) git$X
 	$(STRIP) $(STRIP_OPTS) $(PROGRAMS) git$X
 
 git$X: git.c $(LIB_FILE)
-	$(CC) -DGIT_EXEC_PATH='"$(bindir)"' -DGIT_VERSION='"$(GIT_VERSION)"' \
+	$(CC) -DGIT_VERSION='"$(GIT_VERSION)"' \
 		$(CFLAGS) $(COMPAT_CFLAGS) -o $@ $(filter %.c,$^) $(LIB_FILE)
 
 $(patsubst %.sh,%,$(SCRIPT_SH)) : % : %.sh
@@ -416,6 +417,8 @@ git$X git.spec \
 %.o: %.S
 	$(CC) -o $*.o -c $(ALL_CFLAGS) $<
 
+exec_cmd.o: ALL_CFLAGS += -DGIT_EXEC_PATH=\"$(gitexecdir)\"
+
 git-%$X: %.o $(LIB_FILE)
 	$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) $(LIBS)
 
@@ -472,7 +475,9 @@ check:
 
 install: all
 	$(INSTALL) -d -m755 $(call shellquote,$(DESTDIR)$(bindir))
+	$(INSTALL) -d -m755 $(call shellquote,$(DESTDIR)$(gitexecdir))
 	$(INSTALL) $(ALL_PROGRAMS) $(call shellquote,$(DESTDIR)$(bindir))
+	$(INSTALL) git$X $(call shellquote,$(DESTDIR)$(gitexecdir))
 	$(MAKE) -C templates install
 	$(INSTALL) -d -m755 $(call shellquote,$(DESTDIR)$(GIT_PYTHON_DIR))
 	$(INSTALL) $(PYMODULES) $(call shellquote,$(DESTDIR)$(GIT_PYTHON_DIR))
diff --git a/daemon.c b/daemon.c
index 3bd14269d7..bb014fa9c2 100644
--- a/daemon.c
+++ b/daemon.c
@@ -9,6 +9,7 @@
 #include <syslog.h>
 #include "pkt-line.h"
 #include "cache.h"
+#include "exec_cmd.h"
 
 static int log_syslog;
 static int verbose;
@@ -227,7 +228,7 @@ static int upload(char *dir)
 	snprintf(timeout_buf, sizeof timeout_buf, "--timeout=%u", timeout);
 
 	/* git-upload-pack only ever reads stuff, so this is safe */
-	execlp("git-upload-pack", "git-upload-pack", "--strict", timeout_buf, ".", NULL);
+	execl_git_cmd("upload-pack", "--strict", timeout_buf, ".", NULL);
 	return -1;
 }
 
diff --git a/exec_cmd.c b/exec_cmd.c
new file mode 100644
index 0000000000..55af33bb7e
--- /dev/null
+++ b/exec_cmd.c
@@ -0,0 +1,117 @@
+#include "cache.h"
+#include "exec_cmd.h"
+#define MAX_ARGS	32
+
+extern char **environ;
+static const char *builtin_exec_path = GIT_EXEC_PATH;
+static const char *current_exec_path = NULL;
+
+void git_set_exec_path(const char *exec_path)
+{
+	current_exec_path = exec_path;
+}
+
+
+/* Returns the highest-priority, location to look for git programs. */
+const char *git_exec_path()
+{
+	const char *env;
+
+	if (current_exec_path)
+		return current_exec_path;
+
+	env = getenv("GIT_EXEC_PATH");
+	if (env) {
+		return env;
+	}
+
+	return builtin_exec_path;
+}
+
+
+int execv_git_cmd(char **argv)
+{
+	char git_command[PATH_MAX + 1];
+	char *tmp;
+	int len, err, i;
+	const char *paths[] = { current_exec_path,
+				getenv("GIT_EXEC_PATH"),
+				builtin_exec_path };
+
+	for (i = 0; i < sizeof(paths)/sizeof(paths[0]); ++i) {
+		const char *exec_dir = paths[i];
+		if (!exec_dir) continue;
+
+		if (*exec_dir != '/') {
+			if (!getcwd(git_command, sizeof(git_command))) {
+				fprintf(stderr, "git: cannot determine "
+					"current directory\n");
+				exit(1);
+			}
+			len = strlen(git_command);
+
+			/* Trivial cleanup */
+			while (!strncmp(exec_dir, "./", 2)) {
+				exec_dir += 2;
+				while (*exec_dir == '/')
+					exec_dir++;
+			}
+			snprintf(git_command + len, sizeof(git_command) - len,
+				 "/%s", exec_dir);
+		} else {
+			strcpy(git_command, exec_dir);
+		}
+
+		len = strlen(git_command);
+		len += snprintf(git_command + len, sizeof(git_command) - len,
+				"/git-%s", argv[0]);
+
+		if (sizeof(git_command) <= len) {
+			fprintf(stderr,
+				"git: command name given is too long.\n");
+			break;
+		}
+
+		/* argv[0] must be the git command, but the argv array
+		 * belongs to the caller, and my be reused in
+		 * subsequent loop iterations. Save argv[0] and
+		 * restore it on error.
+		 */
+
+		tmp = argv[0];
+		argv[0] = git_command;
+
+		/* execve() can only ever return if it fails */
+		execve(git_command, argv, environ);
+
+		err = errno;
+
+		argv[0] = tmp;
+	}
+	return -1;
+
+}
+
+
+int execl_git_cmd(char *cmd,...)
+{
+	int argc;
+	char *argv[MAX_ARGS + 1];
+	char *arg;
+	va_list param;
+
+	va_start(param, cmd);
+	argv[0] = cmd;
+	argc = 1;
+	while (argc < MAX_ARGS) {
+		arg = argv[argc++] = va_arg(param, char *);
+		if (!arg)
+			break;
+	}
+	va_end(param);
+	if (MAX_ARGS <= argc)
+		return error("too many args to run %s", cmd);
+
+	argv[argc] = NULL;
+	return execv_git_cmd(argv);
+}
diff --git a/exec_cmd.h b/exec_cmd.h
new file mode 100644
index 0000000000..5150ee29f7
--- /dev/null
+++ b/exec_cmd.h
@@ -0,0 +1,10 @@
+#ifndef __GIT_EXEC_CMD_H_
+#define __GIT_EXEC_CMD_H_
+
+extern void git_set_exec_path(const char *exec_path);
+extern const char* git_exec_path(void);
+extern int execv_git_cmd(char **argv); /* NULL terminated */
+extern int execl_git_cmd(char *cmd, ...);
+
+
+#endif /* __GIT_EXEC_CMD_H_ */
diff --git a/fetch-clone.c b/fetch-clone.c
index f46fe6ecbb..859f400941 100644
--- a/fetch-clone.c
+++ b/fetch-clone.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "exec_cmd.h"
 #include <sys/wait.h>
 
 static int finish_pack(const char *pack_tmp_name, const char *me)
@@ -27,8 +28,7 @@ static int finish_pack(const char *pack_tmp_name, const char *me)
 		dup2(pipe_fd[1], 1);
 		close(pipe_fd[0]);
 		close(pipe_fd[1]);
-		execlp("git-index-pack","git-index-pack",
-		       "-o", idx, pack_tmp_name, NULL);
+		execl_git_cmd("index-pack", "-o", idx, pack_tmp_name, NULL);
 		error("cannot exec git-index-pack <%s> <%s>",
 		      idx, pack_tmp_name);
 		exit(1);
@@ -105,8 +105,7 @@ int receive_unpack_pack(int fd[2], const char *me, int quiet)
 		dup2(fd[0], 0);
 		close(fd[0]);
 		close(fd[1]);
-		execlp("git-unpack-objects", "git-unpack-objects",
-		       quiet ? "-q" : NULL, NULL);
+		execl_git_cmd("unpack-objects", quiet ? "-q" : NULL, NULL);
 		die("git-unpack-objects exec failed");
 	}
 	close(fd[0]);
diff --git a/git.c b/git.c
index 5e7da74b68..4616df6e62 100644
--- a/git.c
+++ b/git.c
@@ -10,6 +10,7 @@
 #include <stdarg.h>
 #include <sys/ioctl.h>
 #include "git-compat-util.h"
+#include "exec_cmd.h"
 
 #ifndef PATH_MAX
 # define PATH_MAX 4096
@@ -233,14 +234,11 @@ int main(int argc, char **argv, char **envp)
 {
 	char git_command[PATH_MAX + 1];
 	char wd[PATH_MAX + 1];
-	int i, len, show_help = 0;
-	char *exec_path = getenv("GIT_EXEC_PATH");
+	int i, show_help = 0;
+	const char *exec_path;
 
 	getcwd(wd, PATH_MAX);
 
-	if (!exec_path)
-		exec_path = GIT_EXEC_PATH;
-
 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];
 
@@ -256,10 +254,11 @@ int main(int argc, char **argv, char **envp)
 
 		if (!strncmp(arg, "exec-path", 9)) {
 			arg += 9;
-			if (*arg == '=')
+			if (*arg == '=') {
 				exec_path = arg + 1;
-			else {
-				puts(exec_path);
+				git_set_exec_path(exec_path);
+			} else {
+				puts(git_exec_path());
 				exit(0);
 			}
 		}
@@ -275,42 +274,15 @@ int main(int argc, char **argv, char **envp)
 
 	if (i >= argc || show_help) {
 		if (i >= argc)
-			cmd_usage(exec_path, NULL);
+			cmd_usage(git_exec_path(), NULL);
 
 		show_man_page(argv[i]);
 	}
 
-	if (*exec_path != '/') {
-		if (!getcwd(git_command, sizeof(git_command))) {
-			fprintf(stderr,
-				"git: cannot determine current directory\n");
-			exit(1);
-		}
-		len = strlen(git_command);
-
-		/* Trivial cleanup */
-		while (!strncmp(exec_path, "./", 2)) {
-			exec_path += 2;
-			while (*exec_path == '/')
-				exec_path++;
-		}
-		snprintf(git_command + len, sizeof(git_command) - len,
-			 "/%s", exec_path);
-	}
-	else
-		strcpy(git_command, exec_path);
-	len = strlen(git_command);
-	prepend_to_path(git_command, len);
-
-	len += snprintf(git_command + len, sizeof(git_command) - len,
-			"/git-%s", argv[i]);
-	if (sizeof(git_command) <= len) {
-		fprintf(stderr, "git: command name given is too long.\n");
-		exit(1);
-	}
+	exec_path = git_exec_path();
+	prepend_to_path(exec_path, strlen(exec_path));
 
-	/* execve() can only ever return if it fails */
-	execve(git_command, &argv[i], envp);
+	execv_git_cmd(argv + i);
 
 	if (errno == ENOENT)
 		cmd_usage(exec_path, "'%s' is not a git-command", argv[i]);
diff --git a/receive-pack.c b/receive-pack.c
index f847ec2b54..eae31e370d 100644
--- a/receive-pack.c
+++ b/receive-pack.c
@@ -6,7 +6,7 @@
 
 static const char receive_pack_usage[] = "git-receive-pack <git-dir>";
 
-static const char unpacker[] = "git-unpack-objects";
+static char *unpacker[] = { "unpack-objects", NULL };
 
 static int report_status = 0;
 
@@ -257,7 +257,7 @@ static void read_head_info(void)
 
 static const char *unpack(int *error_code)
 {
-	int code = run_command(unpacker, NULL);
+	int code = run_command_v_opt(1, unpacker, RUN_GIT_CMD);
 
 	*error_code = 0;
 	switch (code) {
diff --git a/run-command.c b/run-command.c
index 8bf5922fc3..b3d287e97e 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "run-command.h"
 #include <sys/wait.h>
+#include "exec_cmd.h"
 
 int run_command_v_opt(int argc, char **argv, int flags)
 {
@@ -13,9 +14,13 @@ int run_command_v_opt(int argc, char **argv, int flags)
 			int fd = open("/dev/null", O_RDWR);
 			dup2(fd, 0);
 			dup2(fd, 1);
-			close(fd);			
+			close(fd);
+		}
+		if (flags & RUN_GIT_CMD) {
+			execv_git_cmd(argv);
+		} else {
+			execvp(argv[0], (char *const*) argv);
 		}
-		execvp(argv[0], (char *const*) argv);
 		die("exec %s failed.", argv[0]);
 	}
 	for (;;) {
diff --git a/run-command.h b/run-command.h
index 2469eeaefb..ef3ee053de 100644
--- a/run-command.h
+++ b/run-command.h
@@ -12,7 +12,7 @@ enum {
 };
 
 #define RUN_COMMAND_NO_STDIO 1
-
+#define RUN_GIT_CMD	     2	/*If this is to be git sub-command */
 int run_command_v_opt(int argc, char **argv, int opt);
 int run_command_v(int argc, char **argv);
 int run_command(const char *cmd, ...);
diff --git a/send-pack.c b/send-pack.c
index cd36193444..990be3f1a3 100644
--- a/send-pack.c
+++ b/send-pack.c
@@ -3,6 +3,7 @@
 #include "tag.h"
 #include "refs.h"
 #include "pkt-line.h"
+#include "exec_cmd.h"
 
 static const char send_pack_usage[] =
 "git-send-pack [--all] [--exec=git-receive-pack] <remote> [<head>...]\n"
@@ -26,11 +27,11 @@ static int is_zero_sha1(const unsigned char *sha1)
 static void exec_pack_objects(void)
 {
 	static char *args[] = {
-		"git-pack-objects",
+		"pack-objects",
 		"--stdout",
 		NULL
 	};
-	execvp("git-pack-objects", args);
+	execv_git_cmd(args);
 	die("git-pack-objects exec failed (%s)", strerror(errno));
 }
 
@@ -39,7 +40,7 @@ static void exec_rev_list(struct ref *refs)
 	static char *args[1000];
 	int i = 0;
 
-	args[i++] = "git-rev-list";	/* 0 */
+	args[i++] = "rev-list";	/* 0 */
 	args[i++] = "--objects";	/* 1 */
 	while (refs) {
 		char *buf = malloc(100);
@@ -58,7 +59,7 @@ static void exec_rev_list(struct ref *refs)
 		refs = refs->next;
 	}
 	args[i] = NULL;
-	execvp("git-rev-list", args);
+	execv_git_cmd(args);
 	die("git-rev-list exec failed (%s)", strerror(errno));
 }
 
diff --git a/shell.c b/shell.c
index cd316185e9..fc0c73cde7 100644
--- a/shell.c
+++ b/shell.c
@@ -1,5 +1,6 @@
 #include "cache.h"
 #include "quote.h"
+#include "exec_cmd.h"
 
 static int do_generic_cmd(const char *me, char *arg)
 {
@@ -7,12 +8,14 @@ static int do_generic_cmd(const char *me, char *arg)
 
 	if (!arg || !(arg = sq_dequote(arg)))
 		die("bad argument");
+	if (strncmp(me, "git-", 4))
+		die("bad command");
 
-	my_argv[0] = me;
+	my_argv[0] = me + 4;
 	my_argv[1] = arg;
 	my_argv[2] = NULL;
 
-	return execvp(me, (char**) my_argv);
+	return execv_git_cmd((char**) my_argv);
 }
 
 static struct commands {
diff --git a/upload-pack.c b/upload-pack.c
index 1834b6ba8c..d1980556ca 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -4,6 +4,7 @@
 #include "tag.h"
 #include "object.h"
 #include "commit.h"
+#include "exec_cmd.h"
 
 static const char upload_pack_usage[] = "git-upload-pack [--strict] [--timeout=nn] <dir>";
 
@@ -60,7 +61,7 @@ static void create_pack_file(void)
 		close(0);
 		close(fd[0]);
 		close(fd[1]);
-		*p++ = "git-rev-list";
+		*p++ = "rev-list";
 		*p++ = "--objects";
 		if (create_full_pack || MAX_NEEDS <= nr_needs)
 			*p++ = "--all";
@@ -79,13 +80,13 @@ static void create_pack_file(void)
 				buf += 41;
 			}
 		*p++ = NULL;
-		execvp("git-rev-list", argv);
+		execv_git_cmd(argv);
 		die("git-upload-pack: unable to exec git-rev-list");
 	}
 	dup2(fd[0], 0);
 	close(fd[0]);
 	close(fd[1]);
-	execlp("git-pack-objects", "git-pack-objects", "--stdout", NULL);
+	execl_git_cmd("pack-objects", "--stdout", NULL);
 	die("git-upload-pack: unable to exec git-pack-objects");
 }