On Mon, Nov 09, 2015 at 10:35:42PM +0200, Julian Anastasov wrote:
>
> Hello,
>
> On Sun, 8 Nov 2015, Neil Horman wrote:
>
> > On Sat, Nov 07, 2015 at 01:49:25AM +0200, Julian Anastasov wrote:
> > >
> > > flush can provide many parameters. As there is no
> > > any kind of indication in the netlink message that all addresses
> > > are removed, we can not avoid the promotion.
> > >
> > This is true, but seems irrellevant to me. A flush operation is a sequence
> > of
> > RTM_DELADDR operations in a one or more netlink packets. The way my patch
> > is
> > written, if a set of DELADDR requests is interspersed with other non DELADDR
> > requests, then we do a promotion check between each consecutive set of
> > DELADDR
> > requests. As such, all that happens is that the promotion check happens
> > possibly more often than needed. Its not optimal, but not harmful either.
>
> It is harmful, you miss promotion for some of the
> subnets, see below...
>
> > > > + * Only check for address promotion when this is the last
> > > > request
> > > > + * in this netlink transaction. It allows this operation to
> > > > complete
> > > > + * in O(n) time rather than O(n^2)
> > >
> > > It is not correct to assume that one promotion per
> > > transaction is enough. The promotion happens in every subnet,
> > > it was not once per device.
> > >
> >
> > I'm not sure I understand the relevance here. All I'm doing is, in effect
> > masking the promote_secondaries sysctl for an interface doing a flush
> > operation.
> > Its equivalent to doing this in user space:
> >
> > echo 0 > /proc/sys/net/ipv4/conf/<ifc>/promote_secondaries
> > A=`some arbitrary address in <ifc>`
> > ip addr del <every addressin in <ifc> except A>
> > echo 1 > /proc/sys/net/ipv4/conf/<ifc>/promote_secondaries
> > ip addr del A
> >
> > Can you please explain to me the use case in which delaying a promotion
> > operation until we think we're done ('done' being defined by the above
> > transition
> > from a DELADDR operation to a non-DELADDR operation in a netlink packet)
> > produces an outcome that differs from the expectation with this patch in
> > place?
>
> Here is how we can miss promotion...
>
> dev=eth1
> ifconfig $dev up
> ip addr add 1.2.3.4/24 dev $dev
> ip addr add 1.2.3.4/16 dev $dev
> ip addr add 1.2.3.44/24 dev $dev
> ip addr add 1.2.3.44/16 dev $dev
> echo 1 > /proc/sys/net/ipv4/conf/$dev/promote_secondaries
> ip addr flush dev $dev to 1.2.3.4/30
> ip -V
> ip utility, iproute2-ss010824
>
> What happens is a request to delete just primary addresses:
> 1.2.3.4/24 and 1.2.3.4/16. The /30 is chosen in such a way,
> so that any repeating attempts to flush the secondary
> addresses are avoided. As result, with your patch, only
> 1.2.3.44/16 is promoted (the last secondary), 1.2.3.44/24
> which is first in the list of the secondaries, is not
> promoted, it is removed. You can even use 1.2.3.4/24,
> 1.2.3.5/16, 1.2.3.44/24 and 1.2.3.55/16 in case the
> equal IPs are not a good example.
>
> The problem will be more visible if one builds netlink message
> by hand containing DEL for different primaries.
>
Ah, crap, Ok. I didn't consider the use case in which user space would build a
filter of addresses that were on a mix of subnets. That makes sense now, thanks
for the explination.
I suppose then the only optimization to be had here is to detect the case of a
complete flush of all addresses in user space and either manually or
automatically disable promotion during the flush operation
Neil
> Regards
>
> --
> Julian Anastasov <j...@ssi.bg>
>
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