linux-kernel - Re: [PATCH net-next v5 08/22] ethtool: support for netlink notifications

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Date:   Wed, 27 Mar 2019 11:43:19 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 08/22] ethtool: support for netlink
 notifications

Wed, Mar 27, 2019 at 10:59:50AM CET, mkubecek@...e.cz wrote:
>On Wed, Mar 27, 2019 at 10:38:43AM +0100, Jiri Pirko wrote:
>> Tue, Mar 26, 2019 at 07:17:20PM CET, mkubecek@...e.cz wrote:
>> >On Tue, Mar 26, 2019 at 05:34:00PM +0100, Jiri Pirko wrote:
>> >> Mon, Mar 25, 2019 at 06:08:18PM CET, mkubecek@...e.cz wrote:
>> >> >+void ethtool_notify(struct net_device *dev, struct netlink_ext_ack *extack,
>> >> >+		    unsigned int cmd, u32 req_mask, const void *data)
>> >> >+{
>> >> >+	if (unlikely(!ethnl_ok))
>> >> 
>> >> Why do you need this?
>> >
>> >If genetlink family registration fails, ethtool_notify() can be still
>> >called from other code (e.g. the ethtool ioctl interface). In such case,
>> >better bail out right away than fail somewhere later (probably after
>> >preparing the message which can't be sent anyway).
>> 
>> Again, haven't seen this in any other gen netlink implementation. Why do
>> they not need it?
>
>Do they have notifications triggered from other code by directly calling
>a function (i.e. not through e.g. a netdev notifier)?

Okay, got it.


>
>An alternative to a flag would be using a RCU pointer for this function
>(initialized to null and set once the family is registered) which is
>what e.g. netfilter is doing with its hooks but that would mean that
>each external notification would use an indirect call.

It's slow path, I don't think this kind of overhead is of any issue.
Sounds good.


>
>> >> >diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
>> >> >index b8a6cd3dc3e3..5f2299548915 100644
>> >> >--- a/net/ethtool/netlink.h
>> >> >+++ b/net/ethtool/netlink.h
>> >> >@@ -11,6 +11,8 @@
>> >> > #define ETHNL_SET_ERRMSG(info, msg) \
>> >> > 	do { if (info) GENL_SET_ERR_MSG(info, msg); } while (0)
>> >> > 
>> >> >+extern u32 ethnl_bcast_seq;
>> >> 
>> >> Why do you need to have this in header? Second, it is not used by
>> >> anything. Please don't introduce variables that are not used. Introduce
>> >> them only in patch where you use it.
>> >
>> >It's the same as with ethtool_genl_family. I'll make it static as well
>> >until it's used in some other file.
>> 
>> Not only static. You should remove it as you are not using it in this
>> patch at all.
>
>OK
>
>Michal