netdev - Re: [net PATCH 1/2] ipv4: Restore fib_trie_flush_external function and fix call ordering

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Date:   Tue, 15 Nov 2016 21:01:03 +0000
From:   "Duyck, Alexander H" <alexander.h.duyck@...el.com>
To:     "jiri@...nulli.us" <jiri@...nulli.us>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jiri@...lanox.com" <jiri@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>
Subject: Re: [net PATCH 1/2] ipv4: Restore fib_trie_flush_external function
 and fix call ordering

On Tue, 2016-11-15 at 21:52 +0100, Jiri Pirko wrote:
> Tue, Nov 15, 2016 at 09:49:02PM CET, alexander.h.duyck@...el.com wrote:
> > 
> > On Tue, 2016-11-15 at 21:31 +0100, Jiri Pirko wrote:
> > > 
> > > Tue, Nov 15, 2016 at 09:29:09PM CET, alexander.h.duyck@...el.com wrote:
> > > > 
> > > > 
> > > > On Tue, 2016-11-15 at 20:51 +0100, Jiri Pirko wrote:
> > > > > 
> > > > > 
> > > > > Tue, Nov 15, 2016 at 11:46:06AM CET, alexander.h.duyck@...el.com wrote:
> > > > > > 
> > > > > > 
> > > > > > 
> > > > > > The patch that removed the FIB offload infrastructure was a bit too
> > > > > > aggressive and also removed code needed to clean up us splitting the table
> > > > > > if additional rules were added.  Specifically the function
> > > > > > fib_trie_flush_external was called at the end of a new rule being added to
> > > > > > flush the foreign trie entries from the main trie.
> > > > > > 
> > > > > > I updated the code so that we only call fib_trie_flush_external on the main
> > > > > > table so that we flush the entries for local from main.  This way we don't
> > > > > > call it for every rule change which is what was happening previously.
> > > > > 
> > > > > Well, the function was introduced by:
> > > > > 
> > > > > commit 104616e74e0b464d449fdd2ee2f547d2fad71610
> > > > > Author: Scott Feldman <sfeldma@...il.com>
> > > > > Date:   Thu Mar 5 21:21:16 2015 -0800
> > > > > 
> > > > >     switchdev: don't support custom ip rules, for now
> > > > >     
> > > > >     Keep switchdev FIB offload model simple for now and don't allow custom ip
> > > > >     rules.
> > > > > 
> > > > > Why this was not needed before? What changed in between:
> > > > > 104616e74e0b464d449fdd2ee2f547d2fad71610 ("switchdev: don't support custom ip rules, for now")
> > > > > and
> > > > > 347e3b28c1ba2 ("switchdev: remove FIB offload infrastructure")
> > > > 
> > > > We collapsed the two tables into one in commit 0ddcf43d5d4a ("ipv4: FIB
> > > > Local/MAIN table collapse") which was submitted the next day.  Scott
> > > > and I were working on things at the same time and the
> > > > fib_table_flush_external function was something we had worked out that
> > > > would allow him to take care of his use case and me to take care of
> > > > cleaning up the tables after unmerging.
> > > 
> > > Okay. But please name the fuction differently, as it does not flush
> > > external. Thanks!
> > 
> > You and I have different meanings for "external".
> > 
> > In my case I am flushing entries that belong to a foreign "external"
> > table from the table specified. So by "external" I am referring to
> > entries that don't actually live in main, but actually reside in local.
> > If you take a look at fib_table_flush that gets rid of all entries,
> > fib_table_flush_external simply clears the foreign ones.
> > 
> > Also I'd rather maintain naming since it makes it easier if we need to
> > backport fixes.
> > 
> > Finally, the flag RTNH_F_EXTERNAL was renamed over a year ago in commit
> > 36583eb54d46c ("rename RTNH_F_EXTERNAL to RTNH_F_OFFLOAD") so there
> > isn't too much likelihood of this being confused for something that
> > handles offloaded entries.  If you take a look in net/ipv4/* after your
> > patch there isn't actually anything that references the word external
> > so the likelihood for any confusion is extremely low.
> 
> Okay. But if you can, please put a comment to this function in order to
> prevent future confusion. Thanks!

I'm not sure there is much left to confuse at this point.  The function
has gone from multi-purpose to single purpose so anyone that is messing
with this should only be doing so if they are messing with the unmerge
functionality.

If anything it would be more confusing to refer to functionality that
this function doesn't support in the comments.  All this function does
is flush foreign/external objects from the tree.

I'm willing to review a patch if you have a suggestion for a comment
that would work.  I just want to avoid confusing people by referring to
code and functionality that is no longer relevent.

- Alex