btrfs: simplify + bugfix

src/lxc/bdev/bdev.c

@@ -392,7 +392,7 @@ struct bdev *bdev_copy(struct lxc_container *c0, const char *cname,
 		*needs_rdep = 1;
 	}
 
-	if (strcmp(oldpath, lxcpath) && !bdevtype)
+	if (strcmp(oldpath, lxcpath) && !bdevtype && !snap)
 		bdevtype = "dir";
 	else if (!bdevtype)
 		bdevtype = orig->type;
@@ -403,6 +403,7 @@ struct bdev *bdev_copy(struct lxc_container *c0, const char *cname,
 		bdev_put(orig);
 		return NULL;
 	}
+	TRACE("Detected \"%s\" storage driver", new->type);
 
 	if (new->ops->clone_paths(orig, new, oldname, cname, oldpath, lxcpath,
 				  snap, newsize, c0->lxc_conf) < 0) {

src/lxc/bdev/lxcbtrfs.c

@@ -32,6 +32,7 @@
 #include <unistd.h>
 #include <sys/ioctl.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 #include <sys/types.h>
 #include <sys/vfs.h>
 
@@ -39,14 +40,10 @@
 #include "log.h"
 #include "lxcbtrfs.h"
 #include "lxcrsync.h"
-#include "utils.h"
+#include "../utils.h"
 
 lxc_log_define(lxcbtrfs, lxc);
 
-/* defined in lxccontainer.c: needs to become common helper */
-extern char *dir_new_path(char *src, const char *oldname, const char *name,
-			  const char *oldpath, const char *lxcpath);
-
 /*
  * Return the full path of objid under dirid.  Let's say dirid is
  * /lxc/c1/rootfs, and objid is /lxc/c1/rootfs/a/b/c.  Then we will
@@ -377,30 +374,20 @@ int btrfs_clonepaths(struct bdev *orig, struct bdev *new, const char *oldname,
 	if (!orig->dest || !orig->src)
 		return -1;
 
-	if (strcmp(orig->type, "btrfs")) {
-		int len, ret;
-		if (snap) {
+	if (strcmp(orig->type, "btrfs") && snap) {
 		ERROR("btrfs snapshot from %s backing store is not supported",
 		      orig->type);
 		return -1;
 	}
 
-		len = strlen(lxcpath) + strlen(cname) + strlen("rootfs") + 6 + 3;
-		new->src = malloc(len);
+	new->src = lxc_string_join(
+	    "/",
+	    (const char *[]){"btrfs:", *lxcpath != '/' ? lxcpath : ++lxcpath,
+			     cname, "rootfs", NULL},
+	    false);
 	if (!new->src)
 		return -1;
 
-		ret = snprintf(new->src, len, "btrfs:%s/%s/rootfs", lxcpath, cname);
-		if (ret < 0 || ret >= len)
-			return -1;
-	} else {
-		/* In case rootfs is in custom path, reuse it. */
-		new->src = dir_new_path(orig->src, oldname, cname, oldpath, lxcpath);
-		if (!new->src)
-			return -1;
-
-	}
-
 	src = lxc_storage_get_path(new->src, "btrfs");
 	new->dest = strdup(src);
 	if (!new->dest)