netdev - Re: Expose bond_xmit

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Date:   Wed, 15 Jan 2020 11:12:54 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        Leon Romanovsky <leonro@...lanox.com>,
        Maor Gottlieb <maorg@...lanox.com>,
        "vfalico@...il.com" <vfalico@...il.com>,
        "andy@...yhouse.net" <andy@...yhouse.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Alex Rosenbaum <alexr@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Mark Zhang <markz@...lanox.com>,
        Parav Pandit <parav@...lanox.com>
Subject: Re: Expose bond_xmit_hash function

On 1/15/20 11:04 AM, Jay Vosburgh wrote:
> 
>> Something similar is needed for xdp and not necessarily tied to a
>> specific bond mode. Some time back I was using this as a prototype:
>>
>> https://github.com/dsahern/linux/commit/2714abc1e629613e3485b7aa860fa3096e273cb2
>>
>> It is incomplete, but shows the intent - exporting bond_egress_slave for
>> use by other code to take a bond device and return an egress leg.
> 
> 	This seems much less awful, but would it make bonding a
> dependency on pretty much everything?
> 

The intent is to hide the bond details beyond the general "a bond has
multiple egress paths and we need to pick one". ie., all of the logic
and data structures are still private.

Exporting the function for use by modules is the easy part.

Making it accessible to core code (XDP) means ??? Obviously not a
concern when bond is built in but the usual case is a module. One
solution is to repeat the IPv6 stub format; not great from an indirect
call perspective. I have not followed the work on INDIRECT_CALL to know
if that mitigates the concern about the stub when bond is a module.