linux-kernel - Re: [PATCH net-next v6 07/15] ethtool: support for netlink notifications

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Date:   Wed, 3 Jul 2019 16:16:14 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Jiri Pirko <jiri@...nulli.us>, David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Linville <linville@...driver.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Johannes Berg <johannes@...solutions.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 07/15] ethtool: support for netlink
 notifications

On Wed, Jul 03, 2019 at 03:33:52PM +0200, Jiri Pirko wrote:
> >+/* notifications */
> >+
> >+typedef void (*ethnl_notify_handler_t)(struct net_device *dev,
> >+				       struct netlink_ext_ack *extack,
> >+				       unsigned int cmd, u32 req_mask,
> >+				       const void *data);
> >+
> >+static const ethnl_notify_handler_t ethnl_notify_handlers[] = {
> >+};
> >+
> >+void ethtool_notify(struct net_device *dev, struct netlink_ext_ack *extack,
> >+		    unsigned int cmd, u32 req_mask, const void *data)
> 
> What's "req_mask" ?

It's infomask to interpret the same way as if it came from request
header (the notification triggered by a SET request or its ioctl
equivalent uses the same format as corresponding GET_REPLY message and
is created by the same code). But it could be called infomask, I have no
strong opinion about that.

> >+{
> >+	if (unlikely(!ethnl_ok))
> >+		return;
> >+	ASSERT_RTNL();
> >+
> >+	if (likely(cmd < ARRAY_SIZE(ethnl_notify_handlers) &&
> >+		   ethnl_notify_handlers[cmd]))
> 
> How it could be null?

Notification message types share the enum with other kernel messages:

/* message types - kernel to userspace */
enum {
	ETHTOOL_MSG_KERNEL_NONE,
	ETHTOOL_MSG_STRSET_GET_REPLY,
	ETHTOOL_MSG_SETTINGS_GET_REPLY,
	ETHTOOL_MSG_SETTINGS_NTF,
	ETHTOOL_MSG_SETTINGS_SET_REPLY,
	ETHTOOL_MSG_INFO_GET_REPLY,
	ETHTOOL_MSG_PARAMS_GET_REPLY,
	ETHTOOL_MSG_PARAMS_NTF,
	ETHTOOL_MSG_NWAYRST_NTF,
	ETHTOOL_MSG_PHYSID_NTF,
	ETHTOOL_MSG_RESET_NTF,
	ETHTOOL_MSG_RESET_ACT_REPLY,
	ETHTOOL_MSG_RXFLOW_GET_REPLY,
	ETHTOOL_MSG_RXFLOW_NTF,
	ETHTOOL_MSG_RXFLOW_SET_REPLY,

	/* add new constants above here */
	__ETHTOOL_MSG_KERNEL_CNT,
	ETHTOOL_MSG_KERNEL_MAX = (__ETHTOOL_MSG_KERNEL_CNT - 1)
};

Only entries for *_NTF types are non-null in ethnl_notify_handlers[]:

static const ethnl_notify_handler_t ethnl_notify_handlers[] = {
	[ETHTOOL_MSG_SETTINGS_NTF]	= ethnl_std_notify,
	[ETHTOOL_MSG_PARAMS_NTF]	= ethnl_std_notify,
	[ETHTOOL_MSG_NWAYRST_NTF]	= ethnl_nwayrst_notify,
	[ETHTOOL_MSG_PHYSID_NTF]	= ethnl_physid_notify,
	[ETHTOOL_MSG_RESET_NTF]		= ethnl_reset_notify,
	[ETHTOOL_MSG_RXFLOW_NTF]	= ethnl_rxflow_notify,
};

If the check above fails, it means that kernel code tried to send
a notification with type which does not exist or is not a notification,
i.e. a bug in kernel; that's why the WARN_ONCE.

Michal

> >+		ethnl_notify_handlers[cmd](dev, extack, cmd, req_mask, data);
> >+	else
> >+		WARN_ONCE(1, "notification %u not implemented (dev=%s, req_mask=0x%x)\n",
> >+			  cmd, netdev_name(dev), req_mask);
> >+}
> >+EXPORT_SYMBOL(ethtool_notify);