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SubjectRe: [patch 3/5] Add MMC password protection (lock/unlock) support V3
On Mon, Jan 09, 2006 at 06:16:02PM -0400, Anderson Briglia wrote:
> + dev = bus_find_device(&mmc_bus_type, NULL, NULL, mmc_match_lockable);
> + if (!dev)
> + goto error;
> + card = dev_to_mmc_card(dev);
> +
> + if (operation == KEY_OP_INSTANTIATE) { /* KEY_OP_INSTANTIATE */
> + if (mmc_card_locked(card)) {
> + ret = mmc_lock_unlock(card, key, MMC_LOCK_MODE_UNLOCK);
> + mmc_remove_card(card);
> + mmc_register_card(card);
> + }
> + else
> + ret = mmc_lock_unlock(card, key, MMC_LOCK_MODE_SET_PWD);

I really don't like this - if the MMC card is not locked, we set a
password on it. If it's locked, we unlock it.

That's a potential race condition if you're trying to unlock a card
and the card is changed beneath you while you slept waiting for
memory - you end up setting that password on the new card.

It's far better to have separate "unlock this card" and "set a
password on this card" commands rather than trying to combine the
two operations.

Also, removing and re-registering a card is an offence. These
things are ref-counted, and mmc_remove_card() will drop the last
reference - so the memory associated with it will be freed. Then
you re-register it. Whoops.

If you merely want to try to attach a driver, use device_attach()
instead.

Also, what if you have multiple MMC cards? I have a board here
with two MMC slots. I'd rather not have it try to set the same
password on both devices.


--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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