add dir support

It used to be supported with the lxc-create.in script, and
the manpage says it's supported...  So let's just support it.

Now

sudo lxc-create -t download --dir /opt/ab -n ab

works, creating the container rootfs under /opt/ab.  This
generally isn't something I'd recommend, however telling users
to use a different lxc-path isn't as friendly as I'd like,
because each lxcpath requires separate lxc-ls and lxc-autostart
runs.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

src/lxc/bdev.c

@@ -477,7 +477,10 @@ static int dir_destroy(struct bdev *orig)
 static int dir_create(struct bdev *bdev, const char *dest, const char *n,
 			struct bdev_specs *specs)
 {
-	bdev->src = strdup(dest);
+	if (specs->dir)
+		bdev->src = strdup(specs->dir);
+	else
+		bdev->src = strdup(dest);
 	bdev->dest = strdup(dest);
 	if (!bdev->src || !bdev->dest) {
 		ERROR("Out of memory");

src/lxc/bdev.h

@@ -48,6 +48,7 @@ struct bdev_specs {
 		char *lv;
 		char *thinpool; // lvm thin pool to use, if any
 	} lvm;
+	char *dir;
 };
 
 struct bdev_ops {

src/lxc/lxc_create.c

@@ -256,8 +256,7 @@ int main(int argc, char *argv[])
 			spec.lvm.thinpool = my_args.thinpool;
 	}
 	if (my_args.dir) {
-		ERROR("--dir is not yet supported");
-		exit(1);
+		spec.dir = my_args.dir;
 	}
 
 	if (strcmp(my_args.bdevtype, "_unset") == 0)