On 16/04/2021 09:30, Damien Le Moal wrote:

On 2021/04/16 16:13, Johannes Thumshirn wrote:

quoted

On 16/04/2021 05:05, Damien Le Moal wrote:

[...]

quoted

+	CRYPT_IV_NO_SECTORS,		/* IV calculation does not use sectors */

[...]

quoted

-	if (ivmode == NULL)
+	if (ivmode == NULL) {
 		cc->iv_gen_ops = NULL;
-	else if (strcmp(ivmode, "plain") == 0)
+		set_bit(CRYPT_IV_NO_SECTORS, &cc->cipher_flags);
+	} else if (strcmp(ivmode, "plain") == 0)

[...]

quoted

+		if (!test_bit(CRYPT_IV_NO_SECTORS, &cc->cipher_flags)) {
+			DMWARN("Zone append is not supported with sector-based IV cyphers");
+			ti->zone_append_not_supported = true;
+		}

I think this negation is hard to follow, at least I had a hard time
reviewing it.

Wouldn't it make more sense to use CRYPT_IV_USE_SECTORS, set the bit
for algorithms that use sectors as IV (like plain64) and then do a 
normal

There are only 2 IV modes that do not use sectors. null and random. All others
do. Hence the "NO_SECTORS" choice. That is the exception rather than the norm,
the flag indicates that.

quoted

	if (test_bit(CRYPT_IV_USE_SECTORS, &cc->cipher_flags)) {
		DMWARN("Zone append is not supported with sector-based IV cyphers");
		ti->zone_append_not_supported = true;
	}

i.e. without the double negation?

Yes. I agree, it is more readable. But adds more lines for the same result. I
could add a small boolean helper to make the "!test_bit(CRYPT_IV_NO_SECTORS,
&cc->cipher_flags)" easier to understand.

Yes I guessed this was the reason for the choice.
Maybe 

set_bit(CRYPT_IV_USE_SECTORS, &cc->cipher_flags);

if (!strcmp(ivmode, "plain") || !strcmp(ivmode, "random"))
	clear_bit(CRYPT_IV_USE_SECTORS, &cc->cipher_flags);

if (test_bit(CRYPT_IV_USE_SECTORS, &cc->cipher_flags)) {
	DMWARN("Zone append is not supported with sector-based IV cyphers");
	ti->zone_append_not_supported = true;
}


Ultimately it's your and Mikes's call, but I /think/ this makes the code easier
to understand.