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

[Dan Williams <djbw@kernel.org>]

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
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 +++++++
 3 files changed, 20 insertions(+)

diff --git a/Documentation/netlink/genetlink-legacy.yaml b/Documentation/netlink/genetlink-legacy.yaml
index f9c44747729a..fff9d7b76dbc 100644
--- a/Documentation/netlink/genetlink-legacy.yaml
+++ b/Documentation/netlink/genetlink-legacy.yaml
@@ -239,6 +239,12 @@ properties:
                 enum: [ little-endian, big-endian ]
               multi-attr:
                 type: boolean
+              bloblen:
+                description: |
+                  Marks this attribute as a variable-length blob that may be split across
+                  multiple messages. The value names a separate scalar attribute that carries
+                  the total blob length, and which is sent ahead of the blob data so a consumer
+                  can preallocate the full payload.
               nested-attributes:
                 description: Name of the space (sub-space) used inside the attribute.
                 type: string
diff --git a/Documentation/netlink/genetlink.yaml b/Documentation/netlink/genetlink.yaml
index d3f3f3399ddf..4caee7d55303 100644
--- a/Documentation/netlink/genetlink.yaml
+++ b/Documentation/netlink/genetlink.yaml
@@ -153,6 +153,13 @@ properties:
                 enum: [ little-endian, big-endian ]
               multi-attr:
                 type: boolean
+              bloblen:
+                description: |
+                  Marks this attribute as a variable-length blob that may be split across
+                  multiple messages. The value names a separate scalar attribute that carries
+                  the total blob length, and which is sent ahead of the blob data so a consumer
+                  can preallocate the full payload.
+                type: string
               nested-attributes:
                 description: Name of the space (sub-space) used inside the attribute.
                 type: string
diff --git a/Documentation/netlink/netlink-raw.yaml b/Documentation/netlink/netlink-raw.yaml
index 4c436b59a34b..dd85f0c56631 100644
--- a/Documentation/netlink/netlink-raw.yaml
+++ b/Documentation/netlink/netlink-raw.yaml
@@ -263,6 +263,13 @@ properties:
                 enum: [ little-endian, big-endian ]
               multi-attr:
                 type: boolean
+              bloblen:
+                description: |
+                  Marks this attribute as a variable-length blob that may be split across
+                  multiple messages. The value names a separate scalar attribute that carries
+                  the total blob length, and which is sent ahead of the blob data so a consumer
+                  can preallocate the full payload.
+                type: string
               nested-attributes:
                 description: Name of the space (sub-space) used inside the attribute.
                 type: string
-- 
2.54.0