resolve_symlink(): use a strbuf for internal scratch space

Aside from shortening and simplifying the code, this removes another
place where the path name length is arbitrarily limited.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

lockfile.c

@@ -126,44 +126,35 @@ static char *last_path_elm(char *p)
 static char *resolve_symlink(char *p, size_t s)
 {
 	int depth = MAXDEPTH;
+	static struct strbuf link = STRBUF_INIT;
 
 	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 (strbuf_readlink(&link, p, strlen(p)) < 0)
+			break;
 
-		if (is_absolute_path(link)) {
+		if (is_absolute_path(link.buf)) {
 			/* absolute path simply replaces p */
-			if (link_len < s)
-				strcpy(p, link);
+			if (link.len < s)
+				strcpy(p, link.buf);
 			else {
 				warning("%s: symlink too long", p);
-				return p;
+				break;
 			}
 		} else {
 			/*
-			 * link is a relative path, so I must replace the
+			 * link is a relative path, so replace the
 			 * last element of p with it.
 			 */
 			char *r = (char *)last_path_elm(p);
-			if (r - p + link_len < s)
-				strcpy(r, link);
+			if (r - p + link.len < s)
+				strcpy(r, link.buf);
 			else {
 				warning("%s: symlink too long", p);
-				return p;
+				break;
 			}
 		}
 	}
+	strbuf_reset(&link);
 	return p;
 }