Re: [PATCH 2/4] dm crypt: Fix zoned block device support

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2021/04/16 16:13, Johannes Thumshirn wrote:
> On 16/04/2021 05:05, Damien Le Moal wrote:
> 
> [...]
> 
>> +	CRYPT_IV_NO_SECTORS,		/* IV calculation does not use sectors */
> 
> [...]
> 
>> -	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)
> 
> [...]
> 
>> +		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.

> 
> 	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.


> 
> 


-- 
Damien Le Moal
Western Digital Research