Date: Mon, 04 Aug 2014 23:51:20 +0400 From: "Alexander V. Chernikov" <melifaro@FreeBSD.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: freebsd-ipfw <freebsd-ipfw@freebsd.org>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: ipfw named objejcts, table values and syntax change Message-ID: <53DFE438.5050209@FreeBSD.org> In-Reply-To: <20140804115817.GA13814@onelab2.iet.unipi.it> References: <53DC01DE.3000000@FreeBSD.org> <CA%2BhQ2%2BgNjA0rucTYAaPYQKtEMt9GZLC6RCi%2BOgPVRpuDC5Ei7Q@mail.gmail.com> <53DCA25C.1000108@FreeBSD.org> <53DF55FA.8010303@FreeBSD.org> <20140804115817.GA13814@onelab2.iet.unipi.it>
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On 04.08.2014 15:58, Luigi Rizzo wrote:
> On Mon, Aug 04, 2014 at 01:44:26PM +0400, Alexander V. Chernikov wrote:=
>> On 02.08.2014 12:33, Alexander V. Chernikov wrote:
>>> On 02.08.2014 10:33, Luigi Rizzo wrote:
>>>>
>>>>
>>>> On Fri, Aug 1, 2014 at 11:08 PM, Alexander V. Chernikov
>>>> <melifaro@freebsd.org <mailto:melifaro@freebsd.org>> wrote:
>>>>
>>>> Hello all.
>>>>
>>>> I'm currently working on to enhance ipfw in some areas.
>>>> The most notable (and user-visible) change is named table suppo=
rt.
>>>> The other one is support for different lookup algorithms for di=
fferent
>>>> key types.
>>>>
>>>> For example, new ipfw permits writing this:
>>>>
>>>> ipfw table tb1 create type cidr
>>>> ipfw add allow ip from table(tl1) to any
>>>> ipfw add allow ip from any lookup dst-ip tb1
>>>>
>>>> ipfw table if1 create type iface
>>>> ipfw add skipto tablearg ip from any to any via table(if1)
>>>>
>>>> or even this:
>>>> ipfw table fl1 create type flow:src-ip,proto,dst-ip,dst-port
>>>> ipfw table fl1 add 10.0.0.5,tcp,10.0.0.6,80 4444
>>>> ipfw add allow ip from any to any flow table(fl1)
>>>>
>>>> all these changes fully preserve backward compatibility.
>>>> (actually tables needs now to be created before use and their t=
ype needs
>>>> to match with opcode used, but new ipfw(8) performs auto-creati=
on
>>>> for cidr tables).
>>>>
>>>> There is another thing I'm going to change and I'm not sure I c=
an keep
>>>> the same compatibility level.
>>>>
>>>> Table values, from one point of view, can be classified to the =
following
>>>> types:
>>>>
>>>> - skipto argument
>>>> - fwd argument (*)
>>>> - link to another object (nat, pipe, queue)
>>>> - plain u32 (not bound to any object)
>>>> (divert/tee,netgraph,tag/utag,limit)
>>>>
>>>> There are the following reasons why I think it is necessary to =
implement
>>>> explicit table values typing (like tables):
>>>> - Implementing fwd tablearg for IPv6 hosts requires indirection=
table
>>>> - Converting nat/pipe instance ids to names renders values unus=
able
>>>> - retiring old hack with storing saved pointer of found object/=
rule
>>>> inside rule w/o proper locking
>>>> - making faster skipto
>>>>
>>>>
>>>> ??????i don't buy the idea that you need typed arguments
>>>> for all the cases above. Maybe the case that
>>>> may make sense is the fwd argument (and in the future
>>>> something else).
>>>> We already discussed, i think, the fact that now it
>>>> is legal to have references to non existing things
>>>> (skipto, pipes etc.) implemented as u32.
>>>> Removing that would break configurations.
>>> It depends on actual implementation. This can be preserved by
>>> auto-creating necessary objects in kernel and/or in userspace, so
>>> we can (and should) avoid breaking in this particular way.
>> Can you please explain your vision on values another time?
>> As far as I understand, you're not against it in general, but the=20
>> details matter:
>> * IP address can be one of the types (it won't break much, and we can =
>> simply skip that one for MFC)
>> * what about typing for nat/pipes ? we're not going to convert their i=
ds=20
>> to names? (or maybe you can suggest other non-disruptive way?)
>> * everything else is type "u32"
>=20
> Correct, I am mostly concerned about the details, not on the general co=
ncept.
>=20
> To summarize the discussion Alexander and I had about converting
> identifiers from numbers to arbitrary strings (this is partly related
> to the values stored in tables, but I think we should have a coherent
> behaviour)
>=20
> 1. CURRENTLY ipfw uses numeric identifiers in a small range (16 bits or=
less)
> for rules, pipes, queues, tables, probably nat instances.
>=20
> 2. CURRENTLY, in all the above contexts, it is legal to reference a
> non existing object (rule, pipe, table names, etc.),
> and the kernel will do something reasonable, namely jump to the
> next rule, drop traffic for non existing pipes, and so on.
>=20
> 3. of course we want to preserve backward compatibility both for
> the ioctl interface, and for user configurations.
>=20
> 4. The in-kernel representation of identifiers is not visible to users,=
> so we can use a numeric representation in the kernel for identifiers=
=2E
> Strings like "12345" are converted with atoi() or the like,
> whereas for other identifiers or numbers outside of the 2^16 range
> the kernel manages a translation table, allocating new numeric
> identifiers if a new string appears.
> This permits backward compatibility for old rulesets, and does not
> impact performance because the translation table is only
> used during rules additions or deletion.
Yes. However this requires either holding either (1) 2 pointers (old&new
arrays), or (2) 65k+ index array, or (3) chained hash table.
(1) would require additional pointers for each subsystem (and some
additional management),
(2) will definitely upset embedded guys and
(3) is worse in terms of performance
>=20
> With this in mind, i think we should follow a similar approach for
> objects stored in tables, hence
>=20
> if an u32 value was available in the past, it must be
> available also in the new implementation.
>=20
> The issue with tables is that some convoluted configuration could
> use the same table to reference pipes _and_ rules _and_ perhaps
> other things represented as numbers (the former is not too strange,
> if i have a large configuration i might place sections at rules
> 12000, 13000, 14000... and associate pipes with the same numberic
> identifier to each block of rules).
>=20
> Typed table values would clearly disturb backward compatibility
> in the above configurations. However it should not be difficult
> to accept arbitrary strings as the values stored in tables, and
> then store multiple representations as appropriate, including:
Well, I've thought about thas one. It may be an option, but the details
are not so promising (below)
> - the string representation, unconditionally
> - for names that can be resolved by DNS, the ipv6 and ipv4 address(es)
> associated with them. ipfw already translates hostnames in rules
> so this is POLA
I'm not happy what ipfw(8) is doing instead of translation. The proper
way would be not simply using first AF_INET answer but saving ALL
IPv4+IPv6 records inside rule (and some more tracking should be done
afterwards, but that's totally different story). Additionally, I'm
unsure if we really need next-hop value expressed as hostname (how can
we deal with multiple addresses and diffrent AFs?). We may store strings
(and I think we should do it) but I'm unsure about this particular
option of interpreting them.
> - for other strings, a u32 from the translation table as previously
> indicated
> - and for numeric values, the u32 representation (truncated if needed,
> according to whatever is the existing behaviour)
> - <add other representations if needed>
> If we cannot generate an u32 we will put some value (e.g. 0)
> that hopefully will not cause confusion.
As far as I understand, we accept some string "s" as table value inside
the kernel, than, we have some logic that says:
oh, dummynet pipe has the same name "s"s, oh, nat entity with name "s"
has just been created, let's save indices.
That would require additional indirection table like:
index | [ skipto idx | nat idx | pipe idx | queue idx | fwd index ]
( so we will have 2-level indirection table for fwd if we do IPv6)
We can optimize this if we use "same name -> same kidx" approach
regardless of kernel object we're refering to. That might require some
more memory, but that's OK from my point of view.
So we end up with
int [ skipto idx | fwd idx | obj idx ]
idx "0" is special value which means the same as 2.CURRENT
That looks better, but still way to complex.
I do care about compatibility, but it's hard to improve things without
changing.
I'd like to propose the following:
* Split values into 3 types ("ip|nexthop", "number", "object")
* Do not insist on object existence, use value "0" to mimic 2.CURRENT
behavior.
* Retain full compatibility by introducing special value type "legacy"
which matches any type and is backed by given indirection table.
* Issue warning in ipfw(8) binary on all auto-created tables that
auto-creation is legacy and this behavior will be dropped in next major
release (e.g. 11.0)
* Save this behavior in MFC but drop "legacy" tables in head after a
month after actual MFC.
That do you think?
>=20
> If we do it this way, we should be able to preserve backward
> compatibility _and_ add features that people may need.
>=20
> cheers
> luigi
>=20
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