netdev - Re: [PATCH net-next 1/2] rtnetlink: Add new RTM_GETEECSTATE message to get SyncE status

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Message-ID: <20210903151425.0bea0ce7@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 3 Sep 2021 15:14:25 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Maciej Machnikowski <maciej.machnikowski@...el.com>
Cc:     netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        richardcochran@...il.com, abyagowi@...com,
        anthony.l.nguyen@...el.com, davem@...emloft.net,
        linux-kselftest@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Michal Kubecek <mkubecek@...e.cz>
Subject: Re: [PATCH net-next 1/2] rtnetlink: Add new RTM_GETEECSTATE message
 to get SyncE status

On Fri,  3 Sep 2021 17:14:35 +0200 Maciej Machnikowski wrote:
> This patch series introduces basic interface for reading the Ethernet
> Equipment Clock (EEC) state on a SyncE capable device. This state gives
> information about the state of EEC. This interface is required to
> implement Synchronization Status Messaging on upper layers.
> 
> Initial implementation returns SyncE EEC state and flags attributes.
> The only flag currently implemented is the EEC_SRC_PORT. When it's set
> the EEC is synchronized to the recovered clock recovered from the
> current port.
> 
> SyncE EEC state read needs to be implemented as a ndo_get_eec_state
> function.
> 
> Signed-off-by: Maciej Machnikowski <maciej.machnikowski@...el.com>

Since we're talking SyncE-only now my intuition would be to put this 
op in ethtool. Was there a reason ethtool was not chosen? If not what
do others think / if yes can the reason be included in the commit
message?


> +/* SyncE section */
> +
> +enum if_eec_state {
> +	IF_EEC_STATE_INVALID = 0,
> +	IF_EEC_STATE_FREERUN,
> +	IF_EEC_STATE_LOCKACQ,
> +	IF_EEC_STATE_LOCKREC,
> +	IF_EEC_STATE_LOCKED,
> +	IF_EEC_STATE_HOLDOVER,
> +	IF_EEC_STATE_OPEN_LOOP,
> +	__IF_EEC_STATE_MAX,
> +};
> +
> +#define IF_EEC_STATE_MAX	(__IF_EEC_STATE_MAX - 1)

You don't need MAC for an output-only enum, MAX define in netlink is
usually for attributes to know how to size attribute arrays.

> +#define EEC_SRC_PORT		(1 << 0) /* recovered clock from the port is
> +					  * currently the source for the EEC
> +					  */

Why include it then? Just leave the value out and if the attr is not
present user space should assume the source is port.

> +struct if_eec_state_msg {
> +	__u32 ifindex;
> +};
> +
> +enum {
> +	IFLA_EEC_UNSPEC,
> +	IFLA_EEC_STATE,
> +	IFLA_EEC_FLAGS,

With "SRC_PORT" gone there's no reason for flags at this point.

> +	__IFLA_EEC_MAX,
> +};
> +
> +#define IFLA_EEC_MAX (__IFLA_EEC_MAX - 1)

> +static int rtnl_fill_eec_state(struct sk_buff *skb, struct net_device *dev,
> +			       u32 portid, u32 seq, struct netlink_callback *cb,
> +			       int flags, struct netlink_ext_ack *extack)
> +{
> +	const struct net_device_ops *ops = dev->netdev_ops;
> +	struct if_eec_state_msg *state_msg;
> +	enum if_eec_state state;
> +	struct nlmsghdr *nlh;
> +	u32 eec_flags;
> +	int err;
> +
> +	ASSERT_RTNL();
> +
> +	if (!ops->ndo_get_eec_state)
> +		return -EOPNOTSUPP;
> +
> +	err = ops->ndo_get_eec_state(dev, &state, &eec_flags, extack);
> +	if (err)
> +		return err;
> +
> +	nlh = nlmsg_put(skb, portid, seq, RTM_GETEECSTATE, sizeof(*state_msg),
> +			flags);
> +	if (!nlh)
> +		return -EMSGSIZE;
> +
> +	state_msg = nlmsg_data(nlh);
> +	state_msg->ifindex = dev->ifindex;
> +
> +	if (nla_put(skb, IFLA_EEC_STATE, sizeof(state), &state) ||

This should be a u32.

> +	    nla_put_u32(skb, IFLA_EEC_FLAGS, eec_flags))
> +		return -EMSGSIZE;
> +
> +	nlmsg_end(skb, nlh);
> +	return 0;
> +}
> +
> +static int rtnl_eec_state_get(struct sk_buff *skb, struct nlmsghdr *nlh,
> +			      struct netlink_ext_ack *extack)
> +{
> +	struct net *net = sock_net(skb->sk);
> +	struct if_eec_state_msg *state;
> +	struct net_device *dev;
> +	struct sk_buff *nskb;
> +	int err;
> +
> +	state = nlmsg_data(nlh);
> +	if (state->ifindex > 0)
> +		dev = __dev_get_by_index(net, state->ifindex);
> +	else
> +		return -EINVAL;
> +
> +	if (!dev)
> +		return -ENODEV;

I think I pointed this out already, this is more natural without the
else branch:

if (ifindex <= 0)
	return -EINVAL;

dev = ...
if (!dev)
	return -ENOENT;

or don't check the ifindex at all and let dev_get_by.. fail.


Thanks for pushing this API forward!