Re: [PATCH v3 3/3] blk-crypto: show crypto capabilities in sysfs

On Thu, Dec 09, 2021 at 03:40:46PM -0800, Eric Biggers wrote:

On Thu, Dec 09, 2021 at 02:51:59PM -0800, Bart Van Assche wrote:

quoted

On 12/7/21 5:35 PM, Eric Biggers wrote:

quoted

+What:		/sys/block/<disk>/queue/crypto/modes/<mode>
+Date:		December 2021
+Contact:	linux-block@vger.kernel.org
+Description:
+		[RO] For each crypto mode (i.e., encryption/decryption
+		algorithm) the device supports with inline encryption, a file
+		will exist at this location.  It will contain a hexadecimal
+		number that is a bitmask of the supported data unit sizes, in
+		bytes, for that crypto mode.
+
+		Currently, the crypto modes that may be supported are:
+
+		   * AES-256-XTS
+		   * AES-128-CBC-ESSIV
+		   * Adiantum
+
+		For example, if a device supports AES-256-XTS inline encryption
+		with data unit sizes of 512 and 4096 bytes, the file
+		/sys/block/<disk>/queue/crypto/modes/AES-256-XTS will exist and
+		will contain "0x1200".

So a bitmask is used to combine multiple values into a single number?

You could think of it that way, yes.

quoted

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.

No multi-line outputs in sysfs please.  If you have to do a "selection
from an array", that is not how to do it.

Look at the output of /sys/power/pm_test/ as one way you can do it if
you have to choose one option from a list:
$ cat /sys/power/pm_test
[none] core processors platform devices freezer

But I don't think that applies here, right?

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.

Greg already reviewed this patch, but maybe he wasn't looking at this part.

Greg, any opinion on the best way to report a set of power-of-2 values via
sysfs?

A single hex value makes sense to me.

thanks,

greg k-h