Re: [dpdk-dev] Issue with rte_compat versioning macros

["Gajdzica, MaciejX T" <maciejx.t.gajdzica@intel.com>]

Hi Neil

> -----Original Message-----
> From: Neil Horman [mailto:nhorman@tuxdriver.com]
> Sent: Friday, June 19, 2015 5:32 PM
> To: Gajdzica, MaciejX T
> Cc: Thomas Monjalon; dev@dpdk.org
> Subject: Re: [dpdk-dev] Issue with rte_compat versioning macros
> 
> On Fri, Jun 19, 2015 at 03:04:17PM +0000, Gajdzica, MaciejX T wrote:
> > > -----Original Message-----
> > > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > Sent: Friday, June 19, 2015 4:48 PM
> > > To: Gajdzica, MaciejX T
> > > Cc: dev@dpdk.org; nhorman@tuxdriver.com
> > > Subject: Re: [dpdk-dev] Issue with rte_compat versioning macros
> > >
> > > 2015-06-19 14:38, Gajdzica, MaciejX T:
> > > > There is an issue with macros in rte_compat.h. For shared library
> > > > case, macro BIND_DEFAULT_SYMBOL takes three arguments and for
> > > > other case it takes only two arguments. Also letters for macro
> > > > variable names are
> > > not consistent in these two cases.
> > >
> > > Yes, and your patch fix it:
> > > 	http://dpdk.org/dev/patchwork/patch/5475/
> > > But it is part of a series which is not accepted yet.
> > >
> > > It would be faster merged if you send it as a standalone patch.
> > > Thanks
> >
> > But simple solution with adding third argument to static library case doesn't
> work. Comment in rte_compat.h file describes steps needed to add new version
> of the function and it says:
> >
> > * 2) rename the existing function int foo(char *string) to
> > * 	int __vsym foo_v20(char *string)
> > *
> > * 3) Add this macro immediately below the function
> > * 	VERSION_SYMBOL(foo, _v20, 2.0);
> > *
> > * 4) Implement a new version of foo.
> > * 	char foo(int value, int otherval) { ...}
> > *
> > * 5) Mark the newest version as the default version
> > * 	BIND_DEFAULT_SYMBOL(foo, 2.1);
> >
> > So probably BIND_DEFAULT_SYMBOL macro for shared library case needs to
> be modified to have two arguments.
> > I'm not familiar with that symver syntax so I need some help. It would be
> better when original author say how it should look like.
> >
> > Best Regards
> > Maciek
> >
> >
> 
> No adding the third parameter will work just fine.  The documentation needs to
> be updated as well to reflect the 3rd argument:
> * 5) Mark the newest version as the default version
> *      BIND_DEFAULT_SYMBOL(foo, foo, 2.1);
> 
> 
> Neil
> 

For me versioning still don't work, even though I try to do it as you say. I had function:

int
rte_cfgfile_section_entries(struct rte_cfgfile *cfg,
	const char *sectionname,
	struct rte_cfgfile_entry *entries,
	int max_entries)
{
[...]
}

And I wanted to add new version of it. So I marked it as _v20, added version macro,
added new implementation and default symbol macro:

int __vsym
rte_cfgfile_section_entries_v20(struct rte_cfgfile *cfg,
	const char *sectionname,
	struct rte_cfgfile_entry *entries,
	int max_entries)
{
[...]
}
VERSION_SYMBOL(rte_cfgfile_section_entries, _v20, 2.0);

int __vsym
rte_cfgfile_section_entries(struct rte_cfgfile *cfg,
		const char *sectionname, struct rte_cfgfile_entry2 **entries,
		int max_entries)
{
[...]
}
BIND_DEFAULT_SYMBOL(rte_cfgfile_section_entries, rte_cfgfile_section_entries, 2.1);

I edited map file so it looks like this:

DPDK_2.0 {
	global:

[...]
	rte_cfgfile_section_entries;
[...]

	local: *;
};

DPDK_2.1 {
	global:

	rte_cfgfile_section_entries;

	local: *;
};

Then I try to build dpdk and qos_sched example which uses this function. When I build dpdk
as static library, everything works fine. When I build dpdk as shared library, compilation of example
returns error, that it doesn't see rte_cfgfile_section_entries function.

Maybe I do something wrong, but it's obvious that better documentation is needed. In current
dpdk master code, versioning is not used. There are only 2 patchsets that tries to use it. This one and:
http://dpdk.org/ml/archives/dev/2015-May/018169.html
That second one probably uses it wrong, because second argument of BIND_DEFAULT_SYMBOL is _v21.
And you said, it should be the same as function name. I don't need versioning for now as we decided
That rte_cfgfile modifications should be done in next release. But knowing that versioning macros
are well documented and work properly could encourage more people to use it.

Best Regards
Maciek