3 files changed, 41 insertions, 0 deletions
diff --git a/mkfs.c b/mkfs.c
index 5631a62b..bb2c58ed 100644
--- a/mkfs.c
+++ b/mkfs.c
@@ -430,6 +430,14 @@ int main(int ac, char **av)
 			fprintf(stderr, "unable to open %s\n", file);
 			exit(1);
 		}
+		ret = btrfs_device_already_in_root(root, fd,
+						   BTRFS_SUPER_INFO_OFFSET);
+		if (ret) {
+			fprintf(stderr, "skipping duplicate device %s in FS\n",
+				file);
+			close(fd);
+			continue;
+		}
 		ret = btrfs_prepare_device(fd, file, zero_end,
 					   &dev_block_count);
 
diff --git a/utils.c b/utils.c
index ba9c7fbb..b9d85ac0 100644
--- a/utils.c
+++ b/utils.c
@@ -743,3 +743,34 @@ int btrfs_scan_for_fsid(struct btrfs_fs_devices *fs_devices, u64 total_devs,
 {
 	return btrfs_scan_one_dir("/dev", run_ioctls);
 }
+
+int btrfs_device_already_in_root(struct btrfs_root *root, int fd,
+				 int super_offset)
+{
+	struct btrfs_super_block *disk_super;
+	char *buf;
+	int ret = 0;
+
+	buf = malloc(BTRFS_SUPER_INFO_SIZE);
+	if (!buf) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	ret = pread(fd, buf, BTRFS_SUPER_INFO_SIZE, super_offset);
+	if (ret != BTRFS_SUPER_INFO_SIZE)
+		goto brelse;
+
+	ret = 0;
+	disk_super = (struct btrfs_super_block *)buf;
+	if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
+	    sizeof(disk_super->magic)))
+		goto brelse;
+
+	if (!memcmp(disk_super->fsid, root->fs_info->super_copy.fsid,
+		    BTRFS_FSID_SIZE))
+		ret = 1;
+brelse:
+	free(buf);
+out:
+	return ret;
+}
diff --git a/utils.h b/utils.h
index d03cd076..f93f8b30 100644
--- a/utils.h
+++ b/utils.h
@@ -37,4 +37,6 @@ int btrfs_scan_for_fsid(struct btrfs_fs_devices *fs_devices, u64 total_devs,
 int btrfs_register_one_device(char *fname);
 int btrfs_scan_one_dir(char *dirname, int run_ioctl);
 int check_mounted(char *devicename);
+int btrfs_device_already_in_root(struct btrfs_root *root, int fd,
+				 int super_offset);
 #endif