Review Board 1.7.16


optional_api: Fix linking problems between modules that export global symbols

Review Request #2797 - Created Aug. 27, 2013 and submitted

David Lee
/team/dlee/ASTERISK-22296
ASTERISK-22296
Reviewers
asterisk-dev
Asterisk
With the new work in Asterisk 12, there are some uses of the
optional_api that are prone to failure. The details are rather involved,
and captured on [the wiki][1].

This patch addresses the issue by removing almost all of the magic from
the optional API implementation. Instead of relying on weak symbol
resolution, a new optional_api.c module was added to Asterisk core.

For modules providing an optional API, the pointer to the implementation
function is registered with the core. For modules that use an optional
API, a pointer to a stub function, along with a optional_ref function
pointer are registered with the core. The optional_ref function pointers
is set to the implementation function when it's provided, or the stub
function when it's now.

Since the implementation no longer relies on magic, it is now supported
on all platforms. In the spirit of choice, an OPTIONAL_API flag was
added, so we can disable the optional_api if needed (maybe it's buggy on
some bizarre platform I haven't tested on)

The AST_OPTIONAL_API*() macros themselves remained unchanged, so
existing code could remain unchanged. But to help with debugging the
optional_api, the patch limits the #include of optional API's to just
the modules using the API. This also reduces resource waste maintaining
optional_ref pointers that aren't used.

Other changes made as a part of this patch:
 * The stubs for http_websocket that wrap system calls set errno to
   ENOSYS.

 * res_http_websocket now properly increments module use count.

 * In loader.c, the while() wrappers around dlclose() were removed. The
   while(!dlclose()) is actually an anti-pattern, which can lead to
   infinite loops if the module you're attempting to unload exports a
   symbol that was directly linked to.

 * The special handling of nonoptreq on systems without weak symbol
   support was removed, since we no longer rely on weak symbols for
   optional_api.

 [1]: https://wiki.asterisk.org/wiki/x/wACUAQ
New optional_api tests pass.

The config below consistently fails when attempting to connect to the
ARI WebSocket without this patch; consistently passes with this patch.

modules.conf:
    [modules]
    load => res_stasis.so
    load => res_ari.so
    load => res_ari_model.so
    load => res_ari_events.so
    load => res_http_websocket.so

http.conf:
    [general]
    enabled=yes
    bindaddr=127.0.0.1

ari.conf:
    [general]
    enabled = yes

    [ari]
    type = user
    password = ari
Review request changed
Updated (Aug. 30, 2013, 9:21 a.m.)
  • changed from pending to submitted
Committed in revision 397999

https://reviewboard.asterisk.org/ runs on a server provided by Digium, Inc. and uses bandwidth donated to the open source Asterisk community by API Digital Communications in Huntsville, AL USA.
Please report problems with this site to asteriskteam@digium.com.