Messages in this thread | | | Date | Thu, 18 Oct 2007 09:49:56 -0700 | From | Randy Dunlap <> | Subject | Re: post_coreinitcall and module_init() in tty_io.c linux kernel 2.6.10 |
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On Thu, 18 Oct 2007 16:41:06 +0630 Deepak Gaur wrote:
> Hi all, > > I am novice in field of linux device drivers. I have a small question regarding module > _init() call in file drivers/char/tty_io.c. In this file there are two init calls mentioned > > (a) postcore_initcall(tty_class_init); > (b) module_init(tty_init); > > The postcore_initcall is defined in include/linux/init.h as > ----------------------------------------------------------------------- > /** > * module_init() - driver initialization entry point > * @x: function to be run at kernel boot time or module insertion > * > * module_init() will either be called during do_initcalls (if > * builtin) or at module insertion time (if a module). There can only > * be one per module. > */ > #define module_init(x) __initcall(x); > > /** > * module_exit() - driver exit entry point > * @x: function to be run when driver is removed > * > * module_exit() will wrap the driver clean-up code > * with cleanup_module() when used with rmmod when > * the driver is a module. If the driver is statically > * compiled into the kernel, module_exit() has no effect. > * There can only be one per module. > */ > #define module_exit(x) __exitcall(x); > > #else /* MODULE */ > > /* Don't use these in modules, but some people do... */ > #define core_initcall(fn) module_init(fn) > #define postcore_initcall(fn) module_init(fn) > #define arch_initcall(fn) module_init(fn) > #define subsys_initcall(fn) module_init(fn) > #define fs_initcall(fn) module_init(fn) > #define device_initcall(fn) module_init(fn) > #define late_initcall(fn) module_init(fn) > > --------------------------------------------------------- > > It's written in quoted text that "There can only be one per module". But in tty_io.c > there are two; postcore_initcall also maps to module_init. Each call is using different > init functions and both functions seems to be required to be executed for proper > functioning of module.
First, note that tty_io.c cannot be built as a loadable module; it is always built into the kernel build image (see drivers/char/Makefile).
The quoted text really means "There can only be one module_init() per loadable module." It does not apply to code that is built into the kernel image proper. In fact, I count 105 source files that contain >= 2 initcalls.
> So my query is > > (1) Which one of the two (postcore_initcall/module_init) get executed and when?
For code that is built into the kernel (i.e., not loadable modules), the order of initcalls in defined in include/linux/init.h:
* This only exists for built-in code, not for modules. */ #define pure_initcall(fn) __define_initcall("0",fn,0)
#define core_initcall(fn) __define_initcall("1",fn,1) #define core_initcall_sync(fn) __define_initcall("1s",fn,1s) #define postcore_initcall(fn) __define_initcall("2",fn,2) #define postcore_initcall_sync(fn) __define_initcall("2s",fn,2s) #define arch_initcall(fn) __define_initcall("3",fn,3) #define arch_initcall_sync(fn) __define_initcall("3s",fn,3s) #define subsys_initcall(fn) __define_initcall("4",fn,4) #define subsys_initcall_sync(fn) __define_initcall("4s",fn,4s) #define fs_initcall(fn) __define_initcall("5",fn,5) #define fs_initcall_sync(fn) __define_initcall("5s",fn,5s) #define rootfs_initcall(fn) __define_initcall("rootfs",fn,rootfs) #define device_initcall(fn) __define_initcall("6",fn,6) #define device_initcall_sync(fn) __define_initcall("6s",fn,6s) #define late_initcall(fn) __define_initcall("7",fn,7) #define late_initcall_sync(fn) __define_initcall("7s",fn,7s)
> (2) If both get executed does it not break the rule that a kernel module should have > only one module_init() and one module_exit()?
That rule applies to loadable modules only. They can have only one entry/init point (and zero or one exit point :).
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