[PATCH 1/4] Add platform-independent .git "symlink"

@@ -239,6 +239,40 @@ static int check_repository_format_gently(int *nongit_ok)
 }
 
 /*
+ * Try to read the location of the git directory from the .git file,
+ * return path to git directory if found.
+ * Format of the .git file is
+ *    gitdir: <path>\n
+ */
+static const char *read_gitfile_gently(const char *path)
+{
+	static char buf[PATH_MAX + 9];  /* "gitdir: " + "\n" */
+	struct stat st;
+	int fd;
+	size_t len;
+
+	if (stat(path, &st))
+		return NULL;
+	if (!S_ISREG(st.st_mode) || st.st_size >= sizeof(buf))
+		return NULL;
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+	len = read_in_full(fd, buf, sizeof(buf));
+	close(fd);
+	if (len != st.st_size)
+		return NULL;
+	if (!len || buf[len - 1] != '\n')
+		return NULL;
+	buf[len - 1] = '\0';
+	if (prefixcmp(buf, "gitdir: "))
+		return NULL;
+	if (!is_git_directory(buf + 8))
+		return NULL;
+	return make_absolute_path(buf + 8);
+}
+
+/*
  * We cannot decide in this function whether we are in the work tree or
  * not, since the config can only be read _after_ this function was called.
  */

@@ -247,6 +281,7 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	const char *work_tree_env = getenv(GIT_WORK_TREE_ENVIRONMENT);
 	static char cwd[PATH_MAX+1];
 	const char *gitdirenv;
+	const char *gitfile_dir;
 	int len, offset;
 
 	/*

@@ -302,6 +337,11 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	 */
 	offset = len = strlen(cwd);
 	for (;;) {
+		gitfile_dir = read_gitfile_gently(DEFAULT_GIT_DIR_ENVIRONMENT);
+		if (gitfile_dir) {
+			setenv(GIT_DIR_ENVIRONMENT, gitfile_dir, 1);
+			break;
+		}
 		if (is_git_directory(DEFAULT_GIT_DIR_ENVIRONMENT))
 			break;
 		if (is_git_directory(".")) {