-----Original Message-----
From: Eric Dumazet [mailto:eric.dumazet@gmail.com]
Sent: Wednesday, April 27, 2011 11:06 AM
To: Rose, Gregory V
Cc: Steve Hodgson; David Miller; netdev@vger.kernel.org;
bhutchings@solarflare.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 :

quoted

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.

quoted

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.

I'm a netlink newbie so maybe that is a more obvious solution that I missed.  Let me have a look at the code and see.

Thanks,

- Greg