netdev - Re: [PATCH 2/7] net: dcbnl, add multicast group for DCB

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Date:	Sun, 19 Jun 2011 21:14:39 +0300
From:	"Shmulik Ravid" <shmulikr@...adcom.com>
To:	"John Fastabend" <john.r.fastabend@...el.com>
cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/7] net: dcbnl, add multicast group for DCB


On Fri, 2011-06-17 at 14:16 -0700, John Fastabend wrote:
> Now that dcbnl is being used in many cases by more
> than a single agent it is beneficial to be notified
> when some entity either driver or user space has
> changed the DCB attributes.
> 
> Today applications either end up polling the interface
> or relying on a user space database to maintain the DCB
> state and post events. Polling is a poor solution for
> obvious reasons. And relying on a user space database
> has its own downside. Namely it has created strange
> boot dependencies requiring the database be populated
> before any applications dependent on DCB attributes
> starts or the application goes into a polling loop.
> Populating the database requires negotiating link
> setting with the peer and can take anywhere from less
> than a second up to a few seconds depending on the switch
> implementation.
> 
> Perhaps more importantly if another application or an
> embedded agent sets a DCB link attribute the database
> has no way of knowing other than polling the kernel.
> This prevents applications from responding quickly to
> changes in link events which at least in the FCoE case
> and probably any other protocols expecting a lossless
> link may result in IO errors.
> 
> By adding a multicast group for DCB we have clean way
> to disseminate kernel DCB link attributes up to user
> space. Avoiding the need for user space to maintain
> a coherant database and disperse events that potentially
> do not reflect the current link state.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
> 
>  include/linux/rtnetlink.h |    2 
>  net/dcb/dcbnl.c           |  228 +++++++++++++++++++++++++++++----------------
>  2 files changed, 147 insertions(+), 83 deletions(-)
> 
[...]
> +static int dcbnl_notify(struct net_device *dev, int event, int cmd,
> +			u32 seq, u32 pid)
[...]
A driver supporting an embedded dcbx stack would want to directly invoke
the notification routine, therefore it should be exported. I'd like also
to add support for a CEE notification. Also when the driver invokes the
notification shouldn't it use a new event type something like
RTM_NEWDCB?
 


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