Re: [PATCH v2 3/3] blk-crypto: show crypto capabilities in sysfs

Greg Kroah-Hartman
2021-11-30T07:13:46Z

On Mon, Nov 29, 2021 at 08:03:06PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> Add sysfs files that expose the inline encryption capabilities of
> request queues:
>
> /sys/class/block/$disk/queue/crypto/max_dun_bits
> /sys/class/block/$disk/queue/crypto/modes/$mode
> /sys/class/block/$disk/queue/crypto/num_keyslots
>
> Userspace can use these new files to decide what encryption settings to
> use, or whether to use inline encryption at all. This also brings the
> crypto capabilities in line with the other queue properties, which are
> already discoverable via the queue directory in sysfs.
>
> Design notes:
>
> - Place the new files in a new subdirectory "crypto" to group them
> together and to avoid complicating the main "queue" directory. This
> also makes it possible to replace "crypto" with a symlink later if
> we ever make the blk_crypto_profiles into real kobjects (see below).
>
> - It was necessary to define a new kobject that corresponds to the
> crypto subdirectory. For now, this kobject just contains a pointer
> to the blk_crypto_profile. Note that multiple queues (and hence
> multiple such kobjects) may refer to the same blk_crypto_profile.
>
> An alternative design would more closely match the current kernel
> data structures: the blk_crypto_profile could be a kobject itself,
> located directly under the host controller device's kobject, while
> /sys/class/block/$disk/queue/crypto would be a symlink to it.
>
> I decided not to do that for now because it would require a lot more
> changes, such as no longer embedding blk_crypto_profile in other
> structures, and also because I'm not sure we can rule out moving the
> crypto capabilities into 'struct queue_limits' in the future. (Even
> if multiple queues share the same crypto engine, maybe the supported
> data unit sizes could differ due to other queue properties.) It
> would also still be possible to switch to that design later without
> breaking userspace, by replacing the directory with a symlink.
>
> - Use "max_dun_bits" instead of "max_dun_bytes". Currently, the
> kernel internally stores this value in bytes, but that's an
> implementation detail. It probably makes more sense to talk about
> this value in bits, and choosing bits is more future-proof.
>
> - "modes" is a sub-subdirectory, since there may be multiple supported
> crypto modes, and sysfs is supposed to have one value per file.
>
> - Each mode had to be named. The crypto API names like "xts(aes)" are
> not appropriate because they don't specify the key size. Therefore,
> I assigned new names. The exact names chosen are arbitrary, but
> they happen to match the names used in log messages in fs/crypto/.
>
> - The "num_keyslots" file is a bit different from the others in that
> it is only useful to know for performance reasons. However, it's
> included as it can still be useful. For example, a user might not
> want to use inline encryption if there aren't very many keyslots.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
> Documentation/block/queue-sysfs.rst | 30 +++++

Same objection as before. Please add these to Documentation/ABI/
otherwise when running 'scripts/get_abi undefined' will show these new
sysfs files you are adding as having no documentation :(

thanks,

greg k-h