From: Thomas Monjalon <thomas.monjalon@6wind.com>
To: Neil Horman <nhorman@tuxdriver.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCHv2 2/2] ABI: Add some documentation
Date: Thu, 25 Jun 2015 15:22:41 +0200 [thread overview]
Message-ID: <2292015.PuzxyQTVl3@xps13> (raw)
In-Reply-To: <20150625113533.GA17026@hmsreliant.think-freely.org>
2015-06-25 07:35, Neil Horman:
> On Wed, Jun 24, 2015 at 11:09:29PM +0200, Thomas Monjalon wrote:
> > 2015-06-24 14:34, Neil Horman:
> > > +Some ABI changes may be too significant to reasonably maintain multiple
> > > +versions. In those cases ABI's may be updated without backward compatibility
> > > +being provided. The requirements for doing so are:
> > > +
> > > +#. At least 3 acknowledgments of the need to do so must be made on the
> > > + dpdk.org mailing list.
> > > +
> > > +#. A full deprecation cycle, as explained above, must be made to offer
> > > + downstream consumers sufficient warning of the change.
> > > +
> > > +#. The ``LIBABIVER`` variable in the makefile(s) where the ABI changes are
> > > + incorporated must be incremented in parallel with the ABI changes
> > > + themselves.
> >
> > The proposal was to provide the old and the new ABI in the same source code
> > during the deprecation cycle. The old ABI would be the default and people
> > can build the new one by enabling the NEXT_ABI config option.
> > So the migration to the new ABI is smoother.
>
> Yes....I'm not sure what you're saying here. The ABI doesn't 'Change' until the
> old ABI is removed (i.e. old applications are forced to adopt a new ABI), and so
> LIBABIVER has to be updated in parallel with that removal
I'm referring to previous threads suggesting a NEXT_ABI build option to be able
to build the old (default) ABI or the next one.
So the LIBABIVER and .map file would depend of enabling NEXT_ABI or not:
http://dpdk.org/ml/archives/dev/2015-June/019147.html
http://dpdk.org/ml/archives/dev/2015-June/019784.html
http://dpdk.org/ml/archives/dev/2015-June/019810.html
> > [...]
> > > +The macros exported are:
> > > +
> > > +* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
> > > + unversioned symbol ``b`` to the internal function ``b_e``.
> >
> > The definition is the same as BASE_SYMBOL.
> >
> No, they're different. VERSION_SYMBOL is defined as:
> VERSION_SYMBOL(b, e, n) __asm__(".symver " RTE_STR(b) RTE_STR(e) ", " RTE_STR(b) "@DPDK_" RTE_STR(n))
>
> while BASE_SYMBOL is
> #define BASE_SYMBOL(b, e) __asm__(".symver " RTE_STR(b) RTE_STR(e) ", " RTE_STR(b)"@")
Yes. I mean the comments are the same, so don't reflect the difference.
> > [...]
> > > + DPDK_2.0 {
> > > + global:
> > > +
> > > + rte_acl_add_rules;
> > > + rte_acl_build;
> > > + rte_acl_classify;
> > > + rte_acl_classify_alg;
> > > + rte_acl_classify_scalar;
> > > + rte_acl_create;
> >
> > So it's declared twice, right?
> > I think it should be explicit.
> >
> Yes, its listed once for each version node, so 2 delcarations. I thought that
> was made explicit by the use of the code block. What else would you like to
> see?
I think you should say it explicitly in the comment below the block.
> > > + rte_acl_dump;
> > > + rte_acl_find_existing;
> > > + rte_acl_free;
> > > + rte_acl_ipv4vlan_add_rules;
> > > + rte_acl_ipv4vlan_build;
> > > + rte_acl_list_dump;
> > > + rte_acl_reset;
> > > + rte_acl_reset_rules;
> > > + rte_acl_set_ctx_classify;
> > > +
> > > + local: *;
> > > + };
> > > +
> > > + DPDK_2.1 {
> > > + global:
> > > + rte_acl_create;
> > > +
> > > + } DPDK_2.0;
> > [...]
> > > +the macros used for versioning symbols. That is our next step, mapping this new
> > > +symbol name to the initial symbol name at version node 2.0. Immediately after
> > > +the function, we add this line of code
> > > +
> > > +.. code-block:: c
> > > +
> > > + VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> >
> > Can it be declared before the function?
> >
> Strictly speaking yes, though its a bit odd from a sylistic point to declare
> versioned aliases for a symbol prior to defining the symbol itself (its like a
> forward declaration)
It allows to declare it near the function header.
> > When do we need to use BASE_SYMBOL?
> >
> For our purposes you currently don't, because there are no unversioned symbols
> in DPDK (since we use a map file). I've just included it here for completeness
> in the header file should it ever be needed in the future.
If it can be useful, please integrate a note to explain when it should be used.
> > [...]
> > > +This code serves as our new API call. Its the same as our old call, but adds
> > > +the new parameter in place. Next we need to map this function to the symbol
> > > +``rte_acl_create@DPDK_2.1``. To do this, we modify the public prototype of the call
> > > +in the header file, adding the macro there to inform all including applications,
> > > +that on re-link, the default rte_acl_create symbol should point to this
> > > +function. Note that we could do this by simply naming the function above
> > > +rte_acl_create, and the linker would chose the most recent version tag to apply
> > > +in the version script, but we can also do this in the header file
> > > +
> > > +.. code-block:: c
> > > +
> > > + struct rte_acl_ctx *
> > > + -rte_acl_create(const struct rte_acl_param *param);
> > > + +rte_acl_create(const struct rte_acl_param *param, int debug);
> > > + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> >
> > Will it work with static library?
> >
> hmm, this example in particular? No, I didn't think of that. To work with a
> static build, you still need to define the unversioned symbol. Thats easy
> enough to do though, by either defining rte_acl_create as a public api and
> calling the appropriate versioned function, or by creating a macro to point to
> the right version via an alias. I can fix that easily enough.
Yes please, static libraries are really important in DPDK.
next prev parent reply other threads:[~2015-06-25 13:25 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-23 19:33 [dpdk-dev] [PATCH 1/2] rte_compat.h : Clean up some typos Neil Horman
2015-06-23 19:33 ` [dpdk-dev] [PATCH 2/2] ABI: Add some documentation Neil Horman
2015-06-24 11:21 ` Mcnamara, John
2015-06-24 11:23 ` [dpdk-dev] [PATCH 1/2] rte_compat.h : Clean up some typos Mcnamara, John
2015-06-24 18:06 ` Neil Horman
2015-06-24 18:34 ` [dpdk-dev] [PATCHv2 " Neil Horman
2015-06-24 18:34 ` [dpdk-dev] [PATCHv2 2/2] ABI: Add some documentation Neil Horman
2015-06-24 21:09 ` Thomas Monjalon
2015-06-25 11:35 ` Neil Horman
2015-06-25 13:22 ` Thomas Monjalon [this message]
2015-06-25 7:19 ` Zhang, Helin
2015-06-25 7:42 ` Gonzalez Monroy, Sergio
2015-06-25 8:00 ` Gonzalez Monroy, Sergio
2015-06-25 12:25 ` Neil Horman
2015-06-29 16:35 ` [dpdk-dev] [PATCH] lib: remove redundant definition of local symbols Thomas Monjalon
2015-06-30 15:50 ` Thomas Monjalon
2015-06-24 19:41 ` [dpdk-dev] [PATCHv2 1/2] rte_compat.h : Clean up some typos Thomas Monjalon
2015-06-24 20:15 ` Neil Horman
2015-06-24 20:49 ` Thomas Monjalon
2015-06-25 7:37 ` [dpdk-dev] [PATCH " Gajdzica, MaciejX T
2015-06-25 12:28 ` Neil Horman
2015-06-25 14:35 ` [dpdk-dev] [PATCHv3 1/3] " Neil Horman
2015-06-25 14:35 ` [dpdk-dev] [PATCHv3 2/3] rte_compat: Add MAP_STATIC_SYMBOL macro Neil Horman
2015-06-26 10:13 ` Gajdzica, MaciejX T
2015-06-26 12:52 ` Thomas Monjalon
2015-06-26 14:30 ` Neil Horman
2015-06-28 20:13 ` Thomas Monjalon
2015-06-29 13:44 ` Neil Horman
2015-06-25 14:35 ` [dpdk-dev] [PATCHv3 3/3] ABI: Add some documentation Neil Horman
2015-06-26 13:00 ` Thomas Monjalon
2015-06-26 14:54 ` Neil Horman
2015-06-28 20:24 ` Thomas Monjalon
2015-06-29 13:53 ` Neil Horman
2015-06-26 12:45 ` [dpdk-dev] [PATCHv3 1/3] rte_compat.h : Clean up some typos Thomas Monjalon
2015-06-29 13:59 ` [dpdk-dev] [PATCHv4 1/4] " Neil Horman
2015-06-29 13:59 ` [dpdk-dev] [PATCHv4 2/4] rte_compat: Add MAP_STATIC_SYMBOL macro Neil Horman
2015-06-29 13:59 ` [dpdk-dev] [PATCHv4 3/4] rte_compat: remove BASE_SYMBOL Neil Horman
2015-06-29 13:59 ` [dpdk-dev] [PATCHv4 4/4] ABI: Add some documentation Neil Horman
2015-06-29 15:07 ` Thomas Monjalon
2015-07-08 9:52 ` [dpdk-dev] [PATCHv4 1/4] rte_compat.h : Clean up some typos Thomas Monjalon
2015-07-08 11:04 ` Neil Horman
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