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

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013/9/16 19:29, Fam Zheng 写道:
> On Mon, 09/16 12:30, Paolo Bonzini wrote:
>> 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$$$RANDOM)
>>>>>>>> Does this work for a module that calls module_init multiple times?
>>>>>>> Why should a module calls module_init, instead of the main function?
>>>>>> I think you mean "why should a module calls register_module_init", and I
>>>>>> agree that with this patch a module will not call register_module_init.
>>>>>>
>>>>>> But a module is still using the module_init macro.
>>>>>>
>>>>>> With this patch, a module will not be able to use the module_init macro
>>>>>> twice.  I am not sure this is an acceptable limitation, especially if we
>>>>>> do not have a dependency system within modules and/or load them with
>>>>>> G_MODULE_LOCAL/RTLD_LOCAL.
>>>>> Why would a module ever want to use the module_init macro twice ?
>>>> Because our coding standard is to have each source file do its own
>>>> one-time initialization, using static functions and an invocation of
>>>> module_init per source file.
>>> Is there ever a case where two source files, each using module_init
>>> will be compiled into the same .so loadable module. Looking at the
>>> uses of block_init(), I don't see any obvious candidates for trouble,
>>> all uses look like they'd be going into separate .so files.
>> Without inter-module exports, all of SPICE probably would have to be in
>> a single .so file.  This includes spice-qemu-char.c and
>> hw/display/qxl.c, both of which use type_init.
>>
>> If we use G_MODULE_GLOBAL as a primitive system for intermodule exports,
>> then indeed this is a much smaller problem, but then we need a
>> dependency system.  But I'm almost sure that Windows and maybe Darwin
>> lack support for the equivalent of G_MODULE_GLOBAL.
>>
> An idea for single .so file:
>      - before loads a .so, an empty initializer list is created.
>      - module_init adds a __attribute__((constructor)) function, which appends
>        its real initializer to the initializer list. So this function is
>        automatically called after dlopen().
>      - make init_$(date +%s$$$RANDOM) a dummy symbol.
>      - module_load first checks the presense of the symbol, if yes, call the
>        functions in the initializer list. Else clean up and unload .so.
>
> Does this enable multiple calls of module_init()?
>
I like this way since it keeps the old init behavior which delayed the 
work with a list.

> OTOH. As for multiple spice modules, is it possible to solve it by having a
> spice-common.o and link all spice modules to it, to share code?
>
> Fam
>