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

From: Wenchao Xia
Subject: Re: [Qemu-devel] [PATCH v10 5/8] module: implement module loading
Date: Tue, 17 Sep 2013 16:50:17 +0800
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv: Gecko/20110303 Thunderbird/3.1.9

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
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?


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