Merge branch 'bs/lock'

* bs/lock:
  Add test for symlinked configuration file updates.
  use lockfile.c routines in git_commit_set_multivar()
  fully resolve symlinks when creating lockfiles

config.c

@@ -715,7 +715,7 @@ int git_config_set_multivar(const char* key, const char* value,
 	int fd = -1, in_fd;
 	int ret;
 	char* config_filename;
-	char* lock_file;
+	struct lock_file *lock = NULL;
 	const char* last_dot = strrchr(key, '.');
 
 	config_filename = getenv(CONFIG_ENVIRONMENT);
@@ -725,7 +725,6 @@ int git_config_set_multivar(const char* key, const char* value,
 			config_filename  = git_path("config");
 	}
 	config_filename = xstrdup(config_filename);
-	lock_file = xstrdup(mkpath("%s.lock", config_filename));
 
 	/*
 	 * Since "key" actually contains the section name and the real
@@ -770,11 +769,12 @@ int git_config_set_multivar(const char* key, const char* value,
 	store.key[i] = 0;
 
 	/*
-	 * The lock_file serves a purpose in addition to locking: the new
+	 * The lock serves a purpose in addition to locking: the new
 	 * contents of .git/config will be written into it.
 	 */
-	fd = open(lock_file, O_WRONLY | O_CREAT | O_EXCL, 0666);
-	if (fd < 0 || adjust_shared_perm(lock_file)) {
+	lock = xcalloc(sizeof(struct lock_file), 1);
+	fd = hold_lock_file_for_update(lock, config_filename, 0);
+	if (fd < 0) {
 		fprintf(stderr, "could not lock config file\n");
 		free(store.key);
 		ret = -1;
@@ -914,25 +914,31 @@ int git_config_set_multivar(const char* key, const char* value,
 				goto write_err_out;
 
 		munmap(contents, contents_sz);
-		unlink(config_filename);
 	}
 
-	if (rename(lock_file, config_filename) < 0) {
-		fprintf(stderr, "Could not rename the lock file?\n");
+	if (close(fd) || commit_lock_file(lock) < 0) {
+		fprintf(stderr, "Cannot commit config file!\n");
 		ret = 4;
 		goto out_free;
 	}
 
+	/* fd is closed, so don't try to close it below. */
+	fd = -1;
+	/*
+	 * lock is committed, so don't try to roll it back below.
+	 * NOTE: Since lockfile.c keeps a linked list of all created
+	 * lock_file structures, it isn't safe to free(lock).  It's
+	 * better to just leave it hanging around.
+	 */
+	lock = NULL;
 	ret = 0;
 
 out_free:
 	if (0 <= fd)
 		close(fd);
+	if (lock)
+		rollback_lock_file(lock);
 	free(config_filename);
-	if (lock_file) {
-		unlink(lock_file);
-		free(lock_file);
-	}
 	return ret;
 
 write_err_out:

lockfile.c

@@ -25,23 +25,111 @@ static void remove_lock_file_on_signal(int signo)
 	raise(signo);
 }
 
+/*
+ * p = absolute or relative path name
+ *
+ * Return a pointer into p showing the beginning of the last path name
+ * element.  If p is empty or the root directory ("/"), just return p.
+ */
+static char *last_path_elm(char *p)
+{
+	/* r starts pointing to null at the end of the string */
+	char *r = strchr(p, '\0');
+
+	if (r == p)
+		return p; /* just return empty string */
+
+	r--; /* back up to last non-null character */
+
+	/* back up past trailing slashes, if any */
+	while (r > p && *r == '/')
+		r--;
+
+	/*
+	 * then go backwards until I hit a slash, or the beginning of
+	 * the string
+	 */
+	while (r > p && *(r-1) != '/')
+		r--;
+	return r;
+}
+
+
+/* We allow "recursive" symbolic links. Only within reason, though */
+#define MAXDEPTH 5
+
+/*
+ * p = path that may be a symlink
+ * s = full size of p
+ *
+ * If p is a symlink, attempt to overwrite p with a path to the real
+ * file or directory (which may or may not exist), following a chain of
+ * symlinks if necessary.  Otherwise, leave p unmodified.
+ *
+ * This is a best-effort routine.  If an error occurs, p will either be
+ * left unmodified or will name a different symlink in a symlink chain
+ * that started with p's initial contents.
+ *
+ * Always returns p.
+ */
+
+static char *resolve_symlink(char *p, size_t s)
+{
+	int depth = MAXDEPTH;
+
+	while (depth--) {
+		char link[PATH_MAX];
+		int link_len = readlink(p, link, sizeof(link));
+		if (link_len < 0) {
+			/* not a symlink anymore */
+			return p;
+		}
+		else if (link_len < sizeof(link))
+			/* readlink() never null-terminates */
+			link[link_len] = '\0';
+		else {
+			warning("%s: symlink too long", p);
+			return p;
+		}
+
+		if (link[0] == '/') {
+			/* absolute path simply replaces p */
+			if (link_len < s)
+				strcpy(p, link);
+			else {
+				warning("%s: symlink too long", p);
+				return p;
+			}
+		} else {
+			/*
+			 * link is a relative path, so I must replace the
+			 * last element of p with it.
+			 */
+			char *r = (char*)last_path_elm(p);
+			if (r - p + link_len < s)
+				strcpy(r, link);
+			else {
+				warning("%s: symlink too long", p);
+				return p;
+			}
+		}
+	}
+	return p;
+}
+
+
 static int lock_file(struct lock_file *lk, const char *path)
 {
 	int fd;
-	struct stat st;
 
-	if ((!lstat(path, &st)) && S_ISLNK(st.st_mode)) {
-		ssize_t sz;
-		static char target[PATH_MAX];
-		sz = readlink(path, target, sizeof(target));
-		if (sz < 0)
-			warning("Cannot readlink %s", path);
-		else if (target[0] != '/')
-			warning("Cannot lock target of relative symlink %s", path);
-		else
-			path = target;
-	}
-	sprintf(lk->filename, "%s.lock", path);
+	if (strlen(path) >= sizeof(lk->filename)) return -1;
+	strcpy(lk->filename, path);
+	/*
+	 * subtract 5 from size to make sure there's room for adding
+	 * ".lock" for the lock file name
+	 */
+	resolve_symlink(lk->filename, sizeof(lk->filename)-5);
+	strcat(lk->filename, ".lock");
 	fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
 	if (0 <= fd) {
 		if (!lock_file_list) {

t/t1300-repo-config.sh

@@ -595,4 +595,19 @@ echo >>result
 
 test_expect_success '--null --get-regexp' 'cmp result expect'
 
+test_expect_success 'symlinked configuration' '
+
+	ln -s notyet myconfig &&
+	GIT_CONFIG=myconfig git config test.frotz nitfol &&
+	test -h myconfig &&
+	test -f notyet &&
+	test "z$(GIT_CONFIG=notyet git config test.frotz)" = znitfol &&
+	GIT_CONFIG=myconfig git config test.xyzzy rezrov &&
+	test -h myconfig &&
+	test -f notyet &&
+	test "z$(GIT_CONFIG=notyet git config test.frotz)" = znitfol &&
+	test "z$(GIT_CONFIG=notyet git config test.xyzzy)" = zrezrov
+
+'
+
 test_done