Re: [Qemu-devel] [PATCH v10 5/8] module: implement module loading

[Paolo Bonzini <pbonzini@redhat.com>]

Il 16/09/2013 12:21, Daniel P. Berrange ha scritto:
> On Mon, Sep 16, 2013 at 12:18:54PM +0200, Paolo Bonzini wrote:
>> Il 16/09/2013 12:14, Daniel P. Berrange ha scritto:
>>> On Mon, Sep 16, 2013 at 12:09:47PM +0200, Paolo Bonzini wrote:
>>>> Il 16/09/2013 11:51, Fam Zheng ha scritto:
>>>>> On Mon, 09/16 11:44, Paolo Bonzini wrote:
>>>>>> Il 16/09/2013 10:59, Daniel P. Berrange ha scritto:
>>>>>>>> The init function of dynamic module is no longer with
>>>>>>>> __attribute__((constructor)) as static linked version, and need to be
>>>>>>>> explicitly called once loaded. The function name is mangled with per
>>>>>>>> configure fingerprint as:
>>>>>>>>
>>>>>>>>     init_$(date +%s$$$RANDOM)
>>>>>>
>>>>>> Does this work for a module that calls module_init multiple times?
>>>>>
>>>>> Why should a module calls module_init, instead of the main function?
>>>>
>>>> I think you mean "why should a module calls register_module_init", and I
>>>> agree that with this patch a module will not call register_module_init.
>>>>
>>>> But a module is still using the module_init macro.
>>>>
>>>> With this patch, a module will not be able to use the module_init macro
>>>> twice.  I am not sure this is an acceptable limitation, especially if we
>>>> do not have a dependency system within modules and/or load them with
>>>> G_MODULE_LOCAL/RTLD_LOCAL.
>>>
>>> Why would a module ever want to use the module_init macro twice ?
>>
>> Because our coding standard is to have each source file do its own
>> one-time initialization, using static functions and an invocation of
>> module_init per source file.
> 
> Is there ever a case where two source files, each using module_init
> will be compiled into the same .so loadable module. Looking at the
> uses of block_init(), I don't see any obvious candidates for trouble,
> all uses look like they'd be going into separate .so files.

Without inter-module exports, all of SPICE probably would have to be in
a single .so file.  This includes spice-qemu-char.c and
hw/display/qxl.c, both of which use type_init.

If we use G_MODULE_GLOBAL as a primitive system for intermodule exports,
then indeed this is a much smaller problem, but then we need a
dependency system.  But I'm almost sure that Windows and maybe Darwin
lack support for the equivalent of G_MODULE_GLOBAL.

BTW, we need a buildbot for the static linking case, otherwise as
modules become more widespread, we'll have hard to detect bugs due to
duplicate symbols.

Paolo