Re: dump to cgdNb device

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Wed, 15 Jun 2016 23:49:55 +0100
   From: Alexander Nasonov <alnsn%yandex.ru@localhost>

   I setup an encrypted disk cgd1 (aes-cbc 256 on top of wd0g, disklabel
   verification) with a dump device cgd1b but I can't dump to it (I enter
   ddb and type sync to dump). It prints "device bad".

   [...]

   Is it expected to work at all?

I have not witnessed it working.  But I would like it to work!

By a quick skim of cgddump and dk_dump, it looks likely that the
missing part is a definition for cgddkdriver.d_dumpblocks.  Here's a
candidate definition that you might try, attached.  (Not tested, not
even compile-tested, caveat lector, &c.)

static int
cgd_dumpblocks(device_t dev, void *va, daddr_t blkno, int nblk)
{
	struct cgd_softc *sc;
	struct dk_softc *dksc;
	struct disk_geom *dg;
	struct disklabel *lp;
	size_t nbytes;
	void *buf;
	int error;

	/* Try to get the cgd device state.  */
	sc = device_private(dev);
	if (sc == NULL)
		/* No cgd device: give up.  */
		return ENXIO;

	/* Extract the disk parameters: geometry, disklabel.  */
	dksc = &sc->sc_dksc;
	dg = &dksc->sc_dkdev.dk_geom;
	lp = dksc->sc_dkdev.dk_label;

	/*
	 * Compute the number of bytes in this request, which dk_dump
	 * has `helpfully' converted to a number of blocks for us.
	 */
	nbytes = nblk*lp->d_secsize;

	/* Try to acquire a buffer to store the ciphertext.  */
	buf = cgd_getdata(dksc, nbytes);
	if (buf == NULL)
		/* Out of memory: give up.  */
		return ENOMEM;

	/* Encrypt the caller's data into the temporary buffer.  */
	cgd_cipher(sc, buf, va, nbytes, blkno, dg->dg_secsize,
	    CGD_CIPHER_ENCRYPT);

	/* Pass it on to the underlying disk device.  */
	error = bdev_dump(sc->sc_tdev, blkno, buf, nbytes);

	/* Release the buffer.  */
	cgd_putdata(dksc, buf);

	/* Return any error from the underlying disk device.  */
	return error;
}