netdev - RE: [RFC PATCH] netlink: Increase netlink dump skb message size

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Date:	Wed, 27 Apr 2011 20:05:40 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Rose, Gregory V" <gregory.v.rose@...el.com>
Cc:	Steve Hodgson <shodgson@...arflare.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"bhutchings@...arflare.com" <bhutchings@...arflare.com>
Subject: RE: [RFC PATCH] netlink: Increase netlink dump skb message size

Le mercredi 27 avril 2011 à 10:39 -0700, Rose, Gregory V a écrit :

> Right, but when I look in rtnetlink I see the routine to calculate the
> amount of buffer needed for VF info dump is the number of device
> parent (PF) VFs * the sizeof various IFLA_VF_INFO items.  The more the
> VFs the bigger this gets, especially if you want to add more stuff to
> IFLA_VF_INFO.  So when the kernel dumps this all out it can get bigger
> than the NLMSG_GOODSIZE (or DUMPSIZE) pretty quickly.
> 
> > 
> > BTW "ip" uses a 16384 bytes buffer, not a 8192 bytes one.
> 
> I know, that's why I suffered some confusion about which size to use.
> The ip command uses 16K but the NLMSG_GOODSIZE can be as small as 3712
> bytes (depending on page size).  Despite the user buffer being 16k if
> the size calculated by if_nlmsg_size() in rtnetlink.c is bigger than
> NLMSG_GOODSIZE then you don't see the info for more than 40 or so VFs.
> More VFs than that and nothing gets displayed.
> 

One solution is to change rtnl_dump_ifinfo() to call rtnl_fill_ifinfo()
once time per device (RTM_NEWLINK like now but no more VFINFO inside),
then call another function to provide vf/vlan informations (RTM_NEWVF),
using cb->args[2] as an index into VF space, so that we can stop if
current skb is filled, and next recvmsg() starts at previous saved
index.

Or implement a new "ip vf ..." dumper and only dumps RTM_NEWVF messages.



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