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

From: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
To: Damien Le Moal <Damien.LeMoal@wdc.com>,
	"dm-devel@redhat.com" <dm-devel@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	Christoph Hellwig <hch@lst.de>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
	David Sterba <dsterba@suse.com>,
	Josef Bacik <josef@toxicpanda.com>
Cc: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>,
	Naohiro Aota <Naohiro.Aota@wdc.com>
Subject: Re: [PATCH 2/4] dm crypt: Fix zoned block device support
Date: Fri, 16 Apr 2021 09:10:12 +0000	[thread overview]
Message-ID: <PH0PR04MB7416D55514E54F67BD8D92A89B4C9@PH0PR04MB7416.namprd04.prod.outlook.com> (raw)
In-Reply-To: BL0PR04MB6514908FACBF6A34D8A085C9E74C9@BL0PR04MB6514.namprd04.prod.outlook.com

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

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.