Re: [RFC PATCH 0/4] IPVS: Backup Adding Ipv6 and Persistence support

To: Simon Horman <horms@xxxxxxxxxxxx>
Subject: Re: [RFC PATCH 0/4] IPVS: Backup Adding Ipv6 and Persistence support
Cc: Hans Schillstrom <hans.schillstrom@xxxxxxxxxxxx>, "wensong@xxxxxxxxxxxx" <wensong@xxxxxxxxxxxx>, "lvs-devel@xxxxxxxxxxxxxxx" <lvs-devel@xxxxxxxxxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxx>
From: Julian Anastasov <ja@xxxxxx>
Date: Fri, 29 Oct 2010 00:07:30 +0300 (EEST)


On Thu, 28 Oct 2010, Simon Horman wrote:

As it stands a little more than 256 bytes may be needed for
pe_data (+ pe_name_length + pe_name). This could be resolved by
shortening the maximum pe_data length. Or perhaps we could use 16 bytes for
Option length, which should ensure its never too small.

The 256 byte limit that I made for pe_data was arbitrarily chosen.

        Yes, this is a problem.

We can have a better fine tuning of options in this way.

        Yes, that is exactly my idea. I more like the name
"Parameter" instead of "Option", i.e. we have additional
parameters that can be mandatory (usually) but also can be
optional. For now I don't have idea for any optional
parameters but allocating 1 bit for this does not look

I'm not sure I understand the motivation for optional parameters.
I think its important to allow for backwards compatibility. But
I don't see that there will be multiple independent implementations
of the synchronisation daemon in the near future. So the use-case
isn't clear to me.

        If we want to support optional parameters they
must have some known length field, 16 bits if needed.
But if we don't want such optional parameters then
we can just use single octet for parameter type
which can imply the length of the following data. Types that have data with variable length should provide
1 or 2 octets after the parameter type for their length.
So, the parsing should be per-type. If one day
we need optional parameters we can just add 1 octet for
type and 2 for length before data.

        For example, ip_vs_sync_conn_options if implemented
as parameter can be coded with 1 octet for type and the
following data structure. OTOH, PE params can use 1 octet
for type, 2 for length (read with get_unaligned_be16) and
then data.

That said, I agree that allocating 1 bit isn't a show-stopper.


Julian Anastasov <ja@xxxxxx>
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