先看下面這段英文說明：（include/linux/init.h)
/* These macros are used to mark some functions or
* initialized data (doesn't apply to uninitialized data)
* as `initialization' functions. The kernel can take this
* as hint that the function is used only during the initialization
* phase and free up used memory resources after
*
* Usage:
* For functions:
*
* You should add __init immediately before the function name, like:
*
* static void __init initme(int x, int y)
* {
* extern int z; z = x * y;
* }
*
* If the function has a prototype somewhere, you can also add
* __init between closing brace of the prototype and semicolon:
*
* extern int initialize_foobar_device(int, int, int) __init;
*
* For initialized data:
* You should insert __initdata between the variable name and equal
* sign followed by value, e.g.:
*
* static int init_variable __initdata = 0;
* static const char linux_logo[] __initconst = { 0x32, 0x36, ... };
*
* Don't forget to initialize data not at file scope, i.e. within a function,
* as gcc otherwise puts the data into the bss section and not into the init
* section.
*
* Also note, that this data cannot be "const".
*/
/* These are for everybody (although not all archs will actually
discard it in modules) */
#define __init __section(.init.text) __cold notrace
#define __initdata __section(.init.data)
#define __initconst __section(.init.rodata)
#define __exitdata __section(.exit.data)
#define __exit_call __used __section(.exitcall.exit)
/*
* modpost check for section mismatches during the kernel build.
* A section mismatch happens when there are references from a
* code or data section to an init section (both code or data).
* The init sections are (for most archs) discarded by the kernel
* when early init has completed so all such references are potential bugs.
* For exit sections the same issue exists.
*
* The following markers are used for the cases where the reference to
* the *init / *exit section (code or data) is valid and will teach
* modpost not to issue a warning. Intended semantics is that a code or
* data tagged __ref* can reference code or data from init section without
* producing a warning (of course, no warning does not mean code is
* correct, so optimally document why the __ref is needed and why it's OK).
*
* The markers follow same syntax rules as __init / __initdata.
*/
#define __ref __section(.ref.text) noinline
#define __refdata __section(.ref.data)
#define __refconst __section(.ref.rodata)
/* compatibility defines */
#define __init_refok __ref
#define __initdata_refok __refdata
#define __exit_refok __ref
#ifdef MODULE
#define __exitused
#else
#define __exitused __used
#endif
#define __exit __section(.exit.text) __exitused __cold notrace
是不是很清楚了？"__init"僅告訴kernel，此函數僅在初始化階段使用，使用後所佔用的內存資源會釋放
常用實例：
module_init(hello_init);
static int __init hello_init(void)
{
printk(KERN_ALERT "Hello, world!/n");
return 0;
}
關於module_init可參考 下面的解釋：（include/linux/init.h)
/**
* 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);關於__initcall(x) 可繼續參考此文件：(include/linux/init.h)
#define __initcall(fn) device_initcall(fn)
#define device_initcall(fn) __define_initcall("6",fn,6)關於宏__define_initcall 可結合上一篇
LINUX內核中的xx_initcall初始化標號
得到進一步理解
*******Done*******