netdev - Can netlink_recvmsg not truncate messages unless asked to?

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Message-ID: <1771.1176487470@redhat.com>
Date:	Fri, 13 Apr 2007 19:04:30 +0100
From:	David Howells <dhowells@...hat.com>
To:	netdev@...r.kernel.org
Subject: Can netlink_recvmsg not truncate messages unless asked to?

Would it be feasible to make netlink_recvmsg() _not_ truncate message unless
it is asked to by having MSG_TRUNC passed to it?

Unless netlink data packets are limited to PAGE_SIZE or less, it's entirely
possible that the kernel can be in a situation where it can't guarantee to get
a buffer large enough to receive a packet larger than that.

What I was trying to do was use recvmsg with MSG_PEEK to grab the nlmsghdr,
and then using that to predict the size of the buffer I need.  But that
doesn't work because a packet might contain multiple netlink messages.

David
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