Linux Kernel中有意思的函数命名

在Linux Kernel中某些特定含义的函数命令有自己的规律，比如这里将简单的介绍一下函数名前双下划线__和devm_xxx函数的意思。

函数名称前的双下划线__

• 标记需要加锁：
  在内核中，有很多函数，有的是需要调用者自己加锁保护的，有些是不需要加锁保护的。对于这些场景，linux kernel采取了统一的策略：基本函数名字是一样的，只不过需要调用者自己加锁保护的那个函数需要增加__的前缀，例如内核有有下面两个函数：setup_irq()和__setup_irq()。
  两个函数在kernel/irq/manage.c中定义：

  /**
   *	setup_irq - setup an interrupt
   *	@irq: Interrupt line to setup
   *	@act: irqaction for the interrupt
   *
   * Used to statically setup interrupts in the early boot process.
   */
  int setup_irq(unsigned int irq, struct irqaction *act)
  {
  	int retval;
  	struct irq_desc *desc = irq_to_desc(irq);
  
  	if (WARN_ON(irq_settings_is_per_cpu_devid(desc)))
  		return -EINVAL;
  	chip_bus_lock(desc);
  	retval = __setup_irq(irq, desc, act);
  	chip_bus_sync_unlock(desc);
  
  	return retval;
  }
  EXPORT_SYMBOL_GPL(setup_irq);

• 标记更接近底层的调用
  一般双下划线也用于标记更接近底层的调用，如kernel/irq/manage.c中的__disable_irq_nosync():

  /** * disable_irq_nosync - disable an irq without waiting 
  * @irq: Interrupt to disable 
  * 
  * Disable the selected interrupt line. Disables and Enables are 
  * nested. 
  * Unlike disable_irq(), this function does not ensure existing 
  * instances of the IRQ handler have completed before returning. 
  * 
  * This function may be called from IRQ context. 
  */
  void disable_irq_nosync(unsignedint irq)
  {
  __disable_irq_nosync(irq);
  }
  EXPORT_SYMBOL(disable_irq_nosync);
  
  /** 
  * disable_irq - disable an irq and wait for completion 
  * @irq: Interrupt to disable 
  * 
  * Disable the selected interrupt line. Enables and Disables are 
  * nested. 
  * This function waits for any pending IRQ handlers for this interrupt 
  * to complete before returning. If you use this function while 
  * holding a resource the IRQ handler may need you will deadlock. 
  * 
  * This function may be called - with care - from IRQ context. 
  */
  void disable_irq(unsignedint irq)
  {
  if(!__disable_irq_nosync(irq)) synchronize_irq(irq);
  }
  EXPORT_SYMBOL(disable_irq);

---

devm_xxx 函数

下面列举一些常用的资源申请接口，它们由各个framework（如clock、regulator、gpio等等）基于device resource management实现。使用时，直接忽略devm_的前缀，后面剩下的部分，driver工程师都很熟悉。只需记住一点，driver可以只申请，不释放，设备模型会帮忙释放。不过如果为了严谨，在driver remove时，可以主动释放（也有相应的接口，这里没有列出）。

externvoid*devm_kzalloc(struct device *dev,size_t size, gfp_t gfp);

void __iomem *devm_ioremap_resource(struct device *dev,struct resource *res);

void __iomem *devm_ioremap(struct device *dev, resource_size_t offset,unsignedlong size);

struct clk *devm_clk_get(struct device *dev,constchar*id);

int devm_gpio_request(struct device *dev,unsigned gpio,constchar*label);

static inline struct pinctrl * devm_pinctrl_get_select(struct device *dev,constchar*name)

static inline struct pwm_device *devm_pwm_get(struct device *dev,constchar*consumer);

struct regulator *devm_regulator_get(struct device *dev,constchar*id);
static inline int devm_request_irq(struct device *dev,unsignedint irq, irq_handler_t handler,
                                   unsignedlong irqflags,constchar*devname,void*dev_id);

struct reset_control *devm_reset_control_get(struct device *dev,constchar*id);