Linux中的devm_kmalloc()是设备驱动程序用来向内核申请一块内存，当设备驱动程序被卸载时，内存会被自动释放。devm_kfree()用来释放由devm_kmalloc()分配的内存。

1、devm_kmalloc()

#define __malloc    __attribute__((__malloc__))

/* managed devm_k.alloc/kfree for device drivers */

extern void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) __malloc;

static inline void *devm_kzalloc(struct device *dev, size_t size, gfp_t gfp)

{/*向内核申请一块内存，当设备驱动程序被卸载时，内存会被自动释放*/

return devm_kmalloc(dev, size, gfp | __GFP_ZERO);

}

2、devm_kfree()

//检查addr，若addr位于“.rodata”中，则返回TRUE;

static inline bool is_kernel_rodata(unsigned long addr)

{

return addr >= (unsigned long)__start_rodata && addr < (unsigned long)__end_rodata;

}

#define likely(x) __builtin_expect(!!(x), 1)   /*如果x是1,则返回1*/

#define unlikely(x) __builtin_expect(!!(x), 0) /*如果x是0,则返回1*/

int devres_destroy(struct device *dev, dr_release_t release, dr_match_t match, void *match_data)

{

void *res;

res = devres_remove(dev, release, match, match_data);//找到一个设备资源并删除它

if (unlikely(!res)) return -ENOENT;

devres_free(res);//释放设备资源数据

return 0;

}

//释放由devm_kmalloc()分配的内存,p指向要释放的内存,这个内存属于dev设备

void devm_kfree(struct device *dev, const void *p)

{

int rc;

/* Special case: pointer to a string in .rodata returned by devm_kstrdup_const().*/

if (unlikely(is_kernel_rodata((unsigned long)p)))  return;

//检查p，若p位于“.rodata”中，则返回TRUE，unlikely(TRUE)不执行;

rc = devres_destroy(dev, devm_kmalloc_release,devm_kmalloc_match, (void *)p);

WARN_ON(rc);

}