RE: [PATCH net-next v4 3/6] devlink: support default values for param-get and param-set

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Cc: netdev@vger.kernel.org; linux-doc@vger.kernel.org; linux-
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Subject: [PATCH net-next v4 3/6] devlink: support default values for
param-get and param-set

Support querying and resetting to default param values.

Introduce two new devlink netlink attrs:
DEVLINK_ATTR_PARAM_VALUE_DEFAULT and
DEVLINK_ATTR_PARAM_RESET_DEFAULT. The former is used to contain an
optional parameter value inside of the param_value nested attribute.
The latter is used in param-set requests from userspace to indicate
that the driver should reset the param to its default value.

To implement this, two new functions are added to the devlink driver
api: devlink_param::get_default() and
devlink_param::reset_default(). These callbacks allow drivers to
implement default param actions for runtime and permanent cmodes. For
driverinit params, the core latches the last value set by a driver via
devl_param_driverinit_value_set(), and uses that as the default value
for a param.

Because default parameter values are optional, it would be impossible
to discern whether or not a param of type bool has default value of
false or not provided if the default value is encoded using a netlink
flag type. For this reason, when a DEVLINK_PARAM_TYPE_BOOL has an
associated default value, the default value is encoded using a u8
type.

Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
---
 Documentation/netlink/specs/devlink.yaml      |   9 ++
 .../networking/devlink/devlink-params.rst     |  10 ++
 include/net/devlink.h                         |  42 +++++++
 include/uapi/linux/devlink.h                  |   3 +
 net/devlink/netlink_gen.c                     |   5 +-
 net/devlink/param.c                           | 105 ++++++++++++++++-
-
 6 files changed, 160 insertions(+), 14 deletions(-)

diff --git a/Documentation/netlink/specs/devlink.yaml

b/Documentation/netlink/specs/devlink.yaml
index 426d5aa7d955..837112da6738 100644

--- a/Documentation/netlink/specs/devlink.yaml
+++ b/Documentation/netlink/specs/devlink.yaml

@@ -859,6 +859,14 @@ attribute-sets:
         name: health-reporter-burst-period
         type: u64
         doc: Time (in msec) for recoveries before starting the grace

period.
+

diff --git a/include/uapi/linux/devlink.h

b/include/uapi/linux/devlink.h index 157f11d3fb72..e7d6b6d13470 100644

--- a/include/uapi/linux/devlink.h
+++ b/include/uapi/linux/devlink.h

@@ -639,6 +639,9 @@ enum devlink_attr {

 	DEVLINK_ATTR_HEALTH_REPORTER_BURST_PERIOD,	/* u64 */

+	DEVLINK_ATTR_PARAM_VALUE_DEFAULT,	/* dynamic */
+	DEVLINK_ATTR_PARAM_RESET_DEFAULT,	/* flag */
+