Re: [PATCH v4 0/3] Split logging functionality out of EAL

[David Marchand <david.marchand@redhat.com>]

On Mon, Jan 23, 2023 at 3:24 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
>
> On Sun, Jan 22, 2023 at 03:56:12PM +0100, David Marchand wrote:
> > Hi Bruce,
> >
> > On Fri, Jan 20, 2023 at 7:22 PM Bruce Richardson
> > <bruce.richardson@intel.com> wrote:
> > >
> > > There is a general desire to reduce the size and scope of EAL. To this
> > > end, this patchset makes a (very) small step in that direction by taking
> > > the logging functionality out of EAL and putting it into its own library
> > > that can be built and maintained separately.
> > >
> > > As with the first RFC for this, the main obstacle is the "fnmatch"
> > > function which is needed by both EAL and the new log function when
> > > building on windows. While the function cannot stay in EAL - or we would
> > > have a circular dependency, moving it to a new library or just putting
> > > it in the log library have the disadvantages that it then "leaks" into
> > > the public namespace without an rte_prefix, which could cause issues.
> > > Since only a single function is involved, subsequent versions take a
> > > different approach to v1, and just moves the offending function to be a
> > > static function in a header file. This allows use by multiple libs
> > > without conflicting names or making it public.
> > >
> > > The other complication, as explained in v1 RFC was that of multiple
> > > implementations for different OS's. This is solved here in the same
> > > way as v1, by including the OS in the name and having meson pick the
> > > correct file for each build. Since only one file is involved, there
> > > seemed little need for replicating EAL's separate subdirectories
> > > per-OS.
> >
> > There is another complication.
> >
> > The ABI check is not handling properly the case where symbols are
> > moved to the new log library (even though the dependency to librte_log
> > is explicit in librte_eal elf).
> > For now, I don't have a good way to handle this.
> >
> > A workaround to pass the check is to suppress those symbols wrt the eal dump:
> > [suppress_function]
> >         symbol_name_regexp = rte_log
> > [suppress_function]
> >         symbol_name = rte_openlog_stream
> > [suppress_function]
> >         symbol_name = rte_vlog
> >
> > But this is not a good solution because we would be losing checks on
> > them for the rest of the v23 ABI life.
> >
> Right, I got error messages from the CI job for this too, but I also have
> no idea how to work around this. Perhaps we only get to move content
> between libraries when we do an ABI bump? Seems a bit restrictive, though.

Moving symbols as you did does not seem an ABI breakage.
An application that links to eal would see the dt_needed entry for the
new log library, load it accordingly and gets the right symbols.


-- 
David Marchand