[ovs-dev] [netlink v3 08/16] datapath: Change listing ports to use an iterator concept.

Ben Pfaff blp at nicira.com
Mon Jan 10 22:05:06 UTC 2011


On Mon, Jan 10, 2011 at 04:53:19PM -0500, Jesse Gross wrote:
> Since this is just an intermediate step, the more important question
> is what these two interfaces will look like when we actually start
> using Netlink.
> 
> Is it:
> * For the flows, we always start dumping at the beginning and report
> everything present at a given snapshot in time.
> * For the ports, do we do the same thing (all ports at a given point)?
>  Or do we still have userspace specify a point to start from (and
> quantity?)?

The apparently customary way for Netlink table dumping to work is for it
to always start at the beginning and report everything.  It can't always
generate an atomic snapshot, however, because the socket has a receive
buffer of limited size.  (The Netlink designers must have had some kind
of passing thought about atomic snapshots because there is an
NLM_F_ATOMIC in include/linux/netlink.h and a few words about it in
netlink(7), but that's the only reference to it anywhere in the Linux
tree.)

This keeps coming up, so it must be something you are worried about, but
actually I'm not sure why you are so concerned.  Can you explain?




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