can: netlink: report the CAN controller mode supported flags

Currently, the CAN netlink interface provides no easy ways to check
the capabilities of a given controller. The only method from the
command line is to try each CAN_CTRLMODE_* individually to check
whether the netlink interface returns an -EOPNOTSUPP error or not
(alternatively, one may find it easier to directly check the source
code of the driver instead...)

This patch introduces a method for the user to check both the
supported and the static capabilities. The proposed method introduces
a new IFLA nest: IFLA_CAN_CTRLMODE_EXT which extends the current
IFLA_CAN_CTRLMODE. This is done to guaranty a full forward and
backward compatibility between the kernel and the user land
applications.

The IFLA_CAN_CTRLMODE_EXT nest contains one single entry:
IFLA_CAN_CTRLMODE_SUPPORTED. Because this entry is only used in one
direction: kernel to userland, no new struct nla_policy are
introduced.

Below table explains how IFLA_CAN_CTRLMODE_SUPPORTED (hereafter:
"supported") and can_ctrlmode::flags (hereafter: "flags") allow us to
identify both the supported and the static capabilities, when masked
with any of the CAN_CTRLMODE_* bit flags:

 supported &	flags &		Controller capabilities
 CAN_CTRLMODE_*	CAN_CTRLMODE_*
 -----------------------------------------------------------------------
 false		false		Feature not supported (always disabled)
 false		true		Static feature (always enabled)
 true		false		Feature supported but disabled
 true		true		Feature supported and enabled

Link: https://lore.kernel.org/all/20211213160226.56219-5-mailhol.vincent@wanadoo.fr
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 26c3368..7633d98 100644 (file)
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -21,6 +21,7 @@ static const struct nla_policy can_policy[IFLA_CAN_MAX + 1] = {
        [IFLA_CAN_DATA_BITTIMING_CONST] = { .len = sizeof(struct can_bittiming_const) },
        [IFLA_CAN_TERMINATION] = { .type = NLA_U16 },
        [IFLA_CAN_TDC] = { .type = NLA_NESTED },
+       [IFLA_CAN_CTRLMODE_EXT] = { .type = NLA_NESTED },
 };
 
 static const struct nla_policy can_tdc_policy[IFLA_CAN_TDC_MAX + 1] = {
@@ -383,6 +384,12 @@ static size_t can_tdc_get_size(const struct net_device *dev)
        return size;
 }
 
+static size_t can_ctrlmode_ext_get_size(void)
+{
+       return nla_total_size(0) +              /* nest IFLA_CAN_CTRLMODE_EXT */
+               nla_total_size(sizeof(u32));    /* IFLA_CAN_CTRLMODE_SUPPORTED */
+}
+
 static size_t can_get_size(const struct net_device *dev)
 {
        struct can_priv *priv = netdev_priv(dev);
@@ -415,6 +422,7 @@ static size_t can_get_size(const struct net_device *dev)
                                       priv->data_bitrate_const_cnt);
        size += sizeof(priv->bitrate_max);                      /* IFLA_CAN_BITRATE_MAX */
        size += can_tdc_get_size(dev);                          /* IFLA_CAN_TDC */
+       size += can_ctrlmode_ext_get_size();                    /* IFLA_CAN_CTRLMODE_EXT */
 
        return size;
 }
@@ -472,6 +480,25 @@ err_cancel:
        return -EMSGSIZE;
 }
 
+static int can_ctrlmode_ext_fill_info(struct sk_buff *skb,
+                                     const struct can_priv *priv)
+{
+       struct nlattr *nest;
+
+       nest = nla_nest_start(skb, IFLA_CAN_CTRLMODE_EXT);
+       if (!nest)
+               return -EMSGSIZE;
+
+       if (nla_put_u32(skb, IFLA_CAN_CTRLMODE_SUPPORTED,
+                       priv->ctrlmode_supported)) {
+               nla_nest_cancel(skb, nest);
+               return -EMSGSIZE;
+       }
+
+       nla_nest_end(skb, nest);
+       return 0;
+}
+
 static int can_fill_info(struct sk_buff *skb, const struct net_device *dev)
 {
        struct can_priv *priv = netdev_priv(dev);
@@ -531,7 +558,9 @@ static int can_fill_info(struct sk_buff *skb, const struct net_device *dev)
                     sizeof(priv->bitrate_max),
                     &priv->bitrate_max)) ||
 
-           (can_tdc_fill_info(skb, dev))
+           can_tdc_fill_info(skb, dev) ||
+
+           can_ctrlmode_ext_fill_info(skb, priv)
            )
 
                return -EMSGSIZE;

diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
index 75b85c6..02ec32d 100644 (file)
--- a/include/uapi/linux/can/netlink.h
+++ b/include/uapi/linux/can/netlink.h
@@ -137,6 +137,7 @@ enum {
        IFLA_CAN_DATA_BITRATE_CONST,
        IFLA_CAN_BITRATE_MAX,
        IFLA_CAN_TDC,
+       IFLA_CAN_CTRLMODE_EXT,
 
        /* add new constants above here */
        __IFLA_CAN_MAX,
@@ -166,6 +167,18 @@ enum {
        IFLA_CAN_TDC_MAX = __IFLA_CAN_TDC - 1
 };
 
+/*
+ * IFLA_CAN_CTRLMODE_EXT nest: controller mode extended parameters
+ */
+enum {
+       IFLA_CAN_CTRLMODE_UNSPEC,
+       IFLA_CAN_CTRLMODE_SUPPORTED,    /* u32 */
+
+       /* add new constants above here */
+       __IFLA_CAN_CTRLMODE,
+       IFLA_CAN_CTRLMODE_MAX = __IFLA_CAN_CTRLMODE - 1
+};
+
 /* u16 termination range: 1..65535 Ohms */
 #define CAN_TERMINATION_DISABLED 0