Btrfs-progs: try other mirrors on read failure

If we hit a bad disk and the read doesn't work, try other mirrors in case we
have other disks with good copies.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

Author: Josef Bacik

restore.c

@@ -244,9 +244,16 @@ static int copy_one_extent(struct btrfs_root *root, int fd,
 
 	done = pread(dev_fd, inbuf+count, length, dev_bytenr);
 	if (done < length) {
-		ret = -1;
-		fprintf(stderr, "Short read %d\n", errno);
-		goto out;
+		num_copies = btrfs_num_copies(&root->fs_info->mapping_tree,
+					      bytenr, length);
+		mirror_num++;
+		if (mirror_num >= num_copies) {
+			ret = -1;
+			fprintf(stderr, "Exhausted mirrors trying to read\n");
+			goto out;
+		}
+		fprintf(stderr, "Trying another mirror\n");
+		goto again;
 	}
 
 	count += length;