netdev - Sending big Netlink messages to userspace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <f4845fc0806240938h36d275ect109fd5f5414cba37@mail.gmail.com>
Date:	Tue, 24 Jun 2008 18:38:07 +0200
From:	"Julius Volz" <juliusv@...gle.com>
To:	netdev@...r.kernel.org
Cc:	"Patrick McHardy" <kaber@...sh.net>,
	"Vince Busam" <vbusam@...gle.com>, "Thomas Graf" <tgraf@...g.ch>
Subject: Sending big Netlink messages to userspace

Hi,

While adding a Netlink interface to IPVS, I've been wondering how to
properly send very big messages to userspace and found these posts:

http://lists.openwall.net/netdev/2007/03/06/214
http://lists.openwall.net/netdev/2007/03/07/2

Herbert writes in the second one, "Dumps should be done using 4K
(NLMSG_GOODSIZE) skb's, where is the problem?" How is that meant?
Should one manually split up dumps into several NLMSG_GOODSIZE
messages or is there some mechanism for that?

I need to send arbitrarily long lists to userspace and I'm already
choosing a big enough size for nlmsg_new(), so I get no put failures
while constructing the message. However, when receiving the data in
userspace (with libnl), the receive callback is never called. An
strace shows that MSG_TRUNC is set in the oversized message, so the
data is never fully received.

I just call nl_recvmsgs_default(sock) once (which does not return an
error). Am I handling libnl incorrectly or do I need to do this
differently on the kernel side?

Thanks,
Julius

-- 
Google Switzerland GmbH
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html