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Re: [PATCH 2.6 NET] Device name changing via rtnetlink

To: Thomas Graf <tgraf@xxxxxxx>
Subject: Re: [PATCH 2.6 NET] Device name changing via rtnetlink
From: jamal <hadi@xxxxxxxxxx>
Date: 12 Sep 2004 13:27:29 -0400
Cc: jt@xxxxxxxxxx, "David S. Miller" <davem@xxxxxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <20040911220614.GF21181@xxxxxxxxxxxxxx>
Organization: jamalopolous
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On Sat, 2004-09-11 at 18:06, Thomas Graf wrote:
> * jamal <1094932793.2344.82.camel@xxxxxxxxxxxxxxxx> 2004-09-11 15:59
> > So my suggestion is making your code the exception.
> > i.e something along the lines of:
> > 
> > addrchg = 1;
> > 
> > if (mtu/weight/name related)
> >     addrchng = 0;
> > if (!err & addrchang)
> >     call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
> OK, however I'd prefer to invert the concept. See patch
> below. This would send out the following updates:

Guess it wont make difference in number of lines of code, so fine.

> ififlags - NETDEV_(UP|DOWN) if IFF_UP has changed
> IFLA_MAP - none
> IFLA_WEIGHT - none
> Only send NETDEV_CHANGEADDR notifies for address and broadcast changes.
> Notify is also sent out if only one of the 2 changes is successful.

This one is sort of grey area. 
Sigh. In any case, i think that this is ok for now. So patch should go
in - we can revisit the whole atomicity where applicable in kernel at
some later point.
Dave please go ahead and apply the patch.

> > Also note, the semantics of netlink are all-or-nothing transaction. i.e
> > if one of the things requested for fails then you undo the rest. We can
> > probably loosely say that unles the ATOMIC flag is set you dont need to
> > undo that .. something to think about (summary is you probably dont want
> > to send progress update to user space unless the transaction is
> > successful; you however want to report progress of where failure happens
> > - as we are discussing at the moment in the error code thread).
> Agreed, I think undo should happen from user space though. In the
> example of do_setlink, you can see that while it would be quite easy to
> do the sanity checks before actually doing something you can't catch
> all errors if you don't want to implement the name/mtu/addr change
> routines yourself. Keeping in mind that those sanity checks will
> probably only fail during the development of a application it doesn't
> really help. That's why I implemented it this way.

sure. The hard part i think is you cant force every one wanting to make
changes to link parameters to go via setlink. If you could then it
should be doable to not make changes until after the attributes are all
known (and therefore make it easy to undo).

> I'm experimenting with a commit/fallback netlink library which basically
> fetches the subject of change and stores the netlink message to be used
> in case of fallback. NLM_F_ATOMIC makes it even more useable but is
> quite expensive. A netlink change daemon would probably solve the
> problem better.

Daemon seems to be the only way to do it. Lets discuss this at some
later point.


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