Calling btrfsctl results in this message when module btrfs.ko is not loaded:

root@asus:/root# btrfsctl -A /dev/sda
ioctl:: Bad file descriptor

An strace shows that actually opening of /dev/btrfs-control failed.

open("/dev/btrfs-control", O_RDWR)      = -1 ENOENT (No such file or 
directory)
ioctl(4294967295, 0x50009404, 0x7fff11fb76b0) = -1 EBADF (Bad file 
descriptor)

The attached patch (against btrfsctl 0.18) terminates btrfsctl if 
/dev/btrfs-control cannot be opened.

The output with applied patch:

root@asus:/root# btrfsctl -A /dev/sda
failed to open /dev/btrfs-control

Regards, Peter.