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Re: [RFC] meta ematch

To: Patrick McHardy <kaber@xxxxxxxxx>
Subject: Re: [RFC] meta ematch
From: Thomas Graf <tgraf@xxxxxxx>
Date: Thu, 13 Jan 2005 20:20:47 +0100
Cc: jamal <hadi@xxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <41E6C3E5.2020908@trash.net>
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* Patrick McHardy <41E6C3E5.2020908@xxxxxxxxx> 2005-01-13 19:54

> Looks great. I have a few doubts about about the set of chosen values
> though. Things like nf_debug and nf_cache were never meant to be
> userspace-visible. What about backwards compatibility if we want to
> remove it, or some other more meaningful value where just returning 0
> wouldn't be the same ?

It is indeed problematic and they should be marked as "for debugging
purposes (unreliable)" but at least nf_debug and nfctinfo are
very useful for debugging.

> - var_dev sets dst->value to dev->name, meta_var_destroy will try to
>  free dev->name.

The `dst` meta_value is the l_value/r_lvalue from em_meta_match and
never gets destroyed. I reused meta_data to store address & length.
It might be a good idea to make a new struct for this to make it
more readable though.

> - meta_int_change only uses 32 bit, but dst->value is unsigned long
>  (64 bit on 64-bit arches). nfmark for example is unsigned long, so
>  you should also use *(unsigned long *).

Doesn't work when size of long differs between kernel and userspace.
I'm aware of this but it seems everyone is using int anyway for nfmark,
so yes this indeed limits the use of nfmark match to only 32 bits
on 64bit machines. The proper way is to introduce a new type
TCF_EM_TYPE_INT64 and access nfmark over it but I didn't want to
create a new type just because of this special case. We can always
add it later as addition to the 32bit version.

> - for the same reason meta_int_compare should return long not int

Agreed.

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