驱动程序文件中__devexit_p的用途

Question

有人能告诉我驱动程序文件中__devexit_p部件的用途吗？

我发现__devexit_p通常在驱动程序代码中使用删除函数。

示例1

static struct i2c_driver lsm9ds0_driver = {
    .driver = {
        .owner = THIS_MODULE,
        .name = LSM9DS0_DEV_NAME,
    },
    .probe = lsm9ds0_probe,
    .remove = __devexit_p(lsm9ds0_remove),
    .id_table = lsm9ds0_id,
};

示例2:

static struct spi_driver light_driver = {
    .driver = {
        .name = "light",
        .owner = THIS_MODULE,
    },
    .probe = light_probe,
    .remove = __devexit_p(light_remove),
};

如果我从上面的例子中删除了__devexit_p，会有什么不同吗？当__devexit_p删除时，它会影响驱动程序的性能吗？

Answer 1

基于这个2.6.32中的LXR列表

/*
Functions marked as __devexit may be discarded at kernel link time,
depending on config options.  Newer versions of binutils detect references 
from retained sections to discarded sections and flag an error.  Pointers to 
__devexit functions must use __devexit_p(function_name), the wrapper will 
insert either the function_name or NULL, depending on the config options.
*/

#if defined(MODULE) || defined(CONFIG_HOTPLUG)
#define __devexit_p(x) x
#else
#define __devexit_p(x) NULL
#endif

它似乎被用于根据作为内核模块(MODULE)的一部分编译的代码和CONFIG_HOTPLUG内核选项，有条件地将其扩展到给定的参数或CONFIG_HOTPLUG。