Re: [PATCH 01/15] netlink: specs: Introduce multi-message blobs for SPDM

["Dan Williams (nvidia)" <djbw@kernel.org>]

Donald Hunter wrote:
> Dan Williams <djbw@kernel.org> writes:
> 
> > The SPDM, Security Protocol and Data Model, underpins PCI device security
> > and other use cases. It defines objects that allow for verification of
> > device identity and configuration. These objects can be large in size 16MB.
> > Netlink is otherwise suitable to define the operations, with optional
> > parameters, and notifications for working with these objects. For example,
> > operations like "regenerate evidence with nonce", "mark evidence
> > validated", and "broadcast evidence / security state change events".
> >
> > A netlink 'blob' is introduced as a way to teach YNL that one instance of a
> > attribute may span multiple messages. It enables netlink to convey all the
> > data needed for verification and manipulation of SPDM transported evidence.
> >
> > The schema change to allows YNL to infer that an attribute may span
> 
> change to allows -> change allows

ack.

> > multiple messages and interrogate its length to preallocate an
> > appropriately sized receive buffer.
> >
> > The design direction to extend the netlink schema for a "multi-message
> > object receive" case was the result of this discussion [1].
> >
> > Cc: Alistair Francis <alistair.francis@wdc.com>
> > Cc: Lukas Wunner <lukas@wunner.de>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Donald Hunter <donald.hunter@gmail.com>
> > Link: http://lore.kernel.org/20260318170014.6650d2bf@kernel.org [1]
> > Signed-off-by: Dan Williams <djbw@kernel.org>
> > ---
> >  Documentation/netlink/genetlink-legacy.yaml | 6 ++++++
> >  Documentation/netlink/genetlink.yaml        | 7 +++++++
> >  Documentation/netlink/netlink-raw.yaml      | 7 +++++++
> 
> I suggest you drop the changes to genetlink-legacy and netlink-raw
> because I don't think we want to support the blob functionality for
> legacy families.

Done.

> Can you also update Documentation/userspace-api/netlink/specs.rst to
> describe the multi-attr / bloblen API behaviour.

Added:

@@ -239,6 +239,16 @@ Boolean property signifying that the attribute may be present multiple times.
 Allowing an attribute to repeat is the recommended way of implementing arrays
 (no extra nesting).
 
+bloblen (multi-message binary blob)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+String property specified on a ``type: binary`` ``multi-attr: true``
+attribute to indicate that this single byte array may span multiple
+messages. The string names an attribute that indicates the final size of
+the blob when all messages are received. This differs from other ``type:
+binary`` ``multi-attr: true`` instances without bloblen where each
+message is an attribute boundary.
+
 byte-order
 ~~~~~~~~~~