Date:   Thu, 9 Dec 2021 16:12:18 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, linux-scsi@vger.kernel.org,
        linux-mmc@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH v3 3/3] blk-crypto: show crypto capabilities in sysfs
Message-ID: <YbKbYsFFW77AxYEO@sol.localdomain>
References: <20211208013534.136590-1-ebiggers@kernel.org>
 <20211208013534.136590-4-ebiggers@kernel.org>
 <6ff4d074-7508-4f4c-de06-f36899668168@acm.org>
 <YbKT/lcp6iZ+lD4n@sol.localdomain>
 <de725f08-2f98-56fc-8305-baf93f867af3@acm.org>
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On Thu, Dec 09, 2021 at 04:02:07PM -0800, Bart Van Assche wrote:
> On 12/9/21 3:40 PM, Eric Biggers wrote:
> > On Thu, Dec 09, 2021 at 02:51:59PM -0800, Bart Van Assche wrote:
> > > Has it been considered to report each value separately, e.g. 512\n4096\n
> > > instead of 0x1200\n?  I think the former approach is more friendly for shell
> > > scripts.
> > 
> > I don't think that would be acceptable to the sysfs folks, as they only allow
> > one value per file.  I suppose a bitmask could be viewed as unacceptable too,
> > but it seemed to make sense here, given that the data unit sizes are always
> > powers of 2, and the hardware reports them as bitmasks.
> 
> In case Greg wouldn't have the time to reply, I think the following quote from
> Documentation/filesystems/sysfs.txt is relevant in this context: "Attributes
> should be ASCII text files, preferably with only one value per file. It is
> noted that it may not be efficient to contain only one value per file, so it is
> socially acceptable to express an array of values of the same type."
> 
> Thanks,

It should be, but I thought that Greg had complained about people doing that
before, and required strictly one value per file.  So we would need his opinion.

Note that a bitmask isn't hard to handle in a shell script:

	mask=$(</sys/block/sda/queue/crypto/modes/AES-256-XTS)
	if (( mask & 4096 )); then
		echo "4096-byte data units supported"
	fi

But I could see how someone could prefer something like

	if grep -q '\<4096\>' /sys/block/sda/queue/crypto/modes/AES-256-XTS; then
		echo "4096-byte data units supported"
	fi

- Eric