Message-ID: <CAGsizzLFoXdUQrA-WtdRq4FDdnDNnevyK6HCRmrT2joUV=ZRXg@mail.gmail.com>
Date:	Mon, 6 Feb 2012 09:53:28 +0100
From:	Štefan Gula <steweg@...t.sk>
To:	"Rose, Gregory V" <gregory.v.rose@...el.com>
Cc:	David Miller <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [patch v1, kernel version 3.2.1] rtnetlink workaround around the
 skb buff size issue

2012/2/6 Rose, Gregory V <gregory.v.rose@...el.com>:
>
> The patch below is what I've got so far.  Right now the bit mask array is global so if you enable display of VF (n) on one interface it will enable display of the same VF on other interfaces.  I intend to move the bit mask array into the net_device structure so we can set the display mask for each interface independently.
>
> The command to set the filter mask is "set only", I see no reason to add it to the info dump.  If other folks see it differently then I can do that too.
>
> Anyway, it will allow the user to control which VFs are getting displayed during the info dump.  They all default to off so initially no VF info gets displayed.
>
> I've also whipped up a patch for the iproute2 ip command.  It'll work like this:
>
> 'ip link set <dev> vf (n) filter [on|off]'
>
> So if you have 128 VFs on the device you could enable info dumps for arbitrary VFs, e.g. VFs 3, 9, 16, 21, and 31.  Only the info for those VFs would display.  This method has the advantage of not breaking scripts which parse the current VF info display.  Of course, one could also script up something to sequentially enable the display of a single VF, dump the info for it, and then move on to the next.
As this patch will allow one to filter some information and possible
lower the need on skb buffer size, the general idea is ok. On the
other hand it will not eliminate the problem. e.g.:
- assume that one didn't know the limits behind it and put all options enabled
- it also doesn't fix the need to fill relevant info by interface
bigger than buffer size, e.g. my macvlan interface mac address list.
If I try to request for it, it will eventually fail with a lot of
records even with filtering...

So I would rather see a proper general method for requesting some
information in cycles inside the single interface like sending request
to kernel per VF for particular device or per MAC address from macvlan
associated lists. This approach is I believe slightly more scalable as
it can be potentially reused on other types of network devices as
well.

My original idea was to have these methods:
1st kernel method will return some info about the absolute number of
cycles needed per given interface - this can be done in standard
GETLINK operation with some associated IFLA_* value.
2nd user-space method will based on that number sends netlink request
per records or reasonable page of records (e.g. 10) and parse the
output in the user-space.
 - this is needed to overcome another issue when kernel generates so
many netlink messages with NLM_F_MULTI that netlink socket will not be
able to hold and further write/read code will fail.
3rd kernel method, which will allocated, fill, and send required info
per record -> this one can be done by ops/command netlink association
(in my proposal it is DEVDUMP)

To sum up, I believe that both approaches (using cycles and filtering)
should be allowed to coexists in kernel, but they should be considered
separately as they are doing different jobs.

I can provide whole example of code (not just rtnetlink part), if the
list is interested to see live example.
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