Teach "fsck" and "read-tree" about recursive tree-nodes.

This is totally untested, since we can't actually _write_ things that
way yet, but I'll get to that next, I hope. That should fix the
huge wasted space for kernel-sized tree objects.

fsck-cache.c

@@ -24,11 +24,12 @@ static int fsck_tree(unsigned char *sha1, void *data, unsigned long size)
 		int len = 1+strlen(data);
 		unsigned char *file_sha1 = data + len;
 		char *path = strchr(data, ' ');
-		if (size < len + 20 || !path)
+		unsigned int mode;
+		if (size < len + 20 || !path || sscanf(data, "%o", &mode) != 1)
 			return -1;
 		data += len + 20;
 		size -= len + 20;
-		mark_needs_sha1(sha1, "blob", file_sha1);
+		mark_needs_sha1(sha1, S_ISDIR(mode) ? "tree" : "blob", file_sha1);
 	}
 	return 0;
 }

read-tree.c

@@ -5,22 +5,23 @@
  */
 #include "cache.h"
 
-static int read_one_entry(unsigned char *sha1, const char *pathname, unsigned mode)
+static int read_one_entry(unsigned char *sha1, const char *base, int baselen, const char *pathname, unsigned mode)
 {
 	int len = strlen(pathname);
-	unsigned int size = cache_entry_size(len);
+	unsigned int size = cache_entry_size(baselen + len);
 	struct cache_entry *ce = malloc(size);
 
 	memset(ce, 0, size);
 
 	ce->st_mode = mode;
-	ce->namelen = len;
-	memcpy(ce->name, pathname, len+1);
+	ce->namelen = baselen + len;
+	memcpy(ce->name, base, baselen);
+	memcpy(ce->name + baselen, pathname, len+1);
 	memcpy(ce->sha1, sha1, 20);
 	return add_cache_entry(ce);
 }
 
-static int read_tree(unsigned char *sha1)
+static int read_tree(unsigned char *sha1, const char *base, int baselen)
 {
 	void *buffer;
 	unsigned long size;
@@ -43,7 +44,20 @@ static int read_tree(unsigned char *sha1)
 		buffer = sha1 + 20;
 		size -= len + 20;
 
-		if (read_one_entry(sha1, path, mode) < 0)
+		if (S_ISDIR(mode)) {
+			int retval;
+			int pathlen = strlen(path);
+			char *newbase = malloc(baselen + 1 + pathlen);
+			memcpy(newbase, base, baselen);
+			memcpy(newbase + baselen, path, pathlen);
+			newbase[baselen + pathlen] = '/';
+			retval = read_tree(sha1, newbase, baselen + pathlen + 1);
+			free(newbase);
+			if (retval)
+				return -1;
+			continue;
+		}
+		if (read_one_entry(sha1, base, baselen, path, mode) < 0)
 			return -1;
 	}
 	return 0;
@@ -77,7 +91,7 @@ int main(int argc, char **argv)
 			fprintf(stderr, "read-tree [-m] <sha1>\n");
 			goto out;
 		}
-		if (read_tree(sha1) < 0) {
+		if (read_tree(sha1, "", 0) < 0) {
 			fprintf(stderr, "failed to unpack tree object %s\n", arg);
 			goto out;
 		}