netdev - Re: [RFC PATCH 1/4] rtnetlink: new flag NLM_F_HW_OFFLOAD to indicate kernel object offload to hardware

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Date:	Sat, 22 Nov 2014 12:29:36 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:	jiri@...nulli.us, sfeldma@...il.com, jhs@...atatu.com,
	bcrl@...ck.org, john.fastabend@...il.com,
	stephen@...workplumber.org, linville@...driver.com,
	nhorman@...driver.com, nicolas.dichtel@...nd.com,
	vyasevic@...hat.com, f.fainelli@...il.com, buytenh@...tstofly.org,
	aviadr@...lanox.com, netdev@...r.kernel.org, davem@...emloft.net,
	Shrijeet Mukherjee <shm@...ulusnetworks.com>,
	gospo@...ulusnetworks.com
Subject: Re: [RFC PATCH 1/4] rtnetlink: new flag NLM_F_HW_OFFLOAD to indicate
 kernel object offload to hardware

On 11/21/14 at 04:10pm, Roopa Prabhu wrote:
> On 11/21/14, 3:12 PM, Thomas Graf wrote:
> >On 11/21/14 at 02:49pm, roopa@...ulusnetworks.com wrote:
> >>diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
> >>index 1a85940..f78522d 100644
> >>--- a/include/uapi/linux/netlink.h
> >>+++ b/include/uapi/linux/netlink.h
> >>@@ -54,6 +54,8 @@ struct nlmsghdr {
> >>  #define NLM_F_ACK		4	/* Reply with ack, with zero or error code */
> >>  #define NLM_F_ECHO		8	/* Echo this request 		*/
> >>  #define NLM_F_DUMP_INTR		16	/* Dump was inconsistent due to sequence change */
> >>++#define NLM_F_KERNEL       32      /* This msg is only for the kernel */
> >>+#define NLM_F_HW_OFFLOAD	64	/* offload this msg to hw */
> >>  /* Modifiers to GET request */
> >>  #define NLM_F_ROOT	0x100	/* specify tree	root	*/
> >The NLM_F_ flag space applies to all Netlink messages including non
> >networking bits and is reserved for flags vital to the functioning
> >of the Netlink protocol itself. I suggest you move this to a
> >RTNETLINK specific flags space.
> 
> I did try to add it at a layer lower than the netlink header. But, nothing
> else fits so well as this :).
> I did not find a place where i could make it a global flag for just
> networking objects. As I mention in my patch description,
> If not here it will be a per subsystem flag/attribute. I can post a patch
> showing that approach as well.

Global variables have their appeal ;-) The issue I see with this
besides polluting a wide namespace is that it is not extendable.
We get a single bit and if a single bit is not enough we'll start
adding things in lower layers anyway (as you already do).

I think this should really be an IFF_ flag for net_device so its
state is exposed to user space as well.
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