Linux内核内存分配函数之kzalloc和kcalloc

本文介绍Linux内核内存分配函数：kzalloc()和kcalloc()。

一、kzalloc

文件：include/linux/slab.h，定义如下：

/**
 * kzalloc - allocate memory. The memory is set to zero.
 * @size: how many bytes of memory are required.
 * @flags: the type of memory to allocate (see kmalloc).
 */
static inline void *kzalloc(size_t size, gfp_t flags)
{
    return kmalloc(size, flags | __GFP_ZERO);
}

kzalloc()函数功能同kmalloc()。区别：内存分配成功后清零。

每次使用kzalloc()后，都要有对应的内存释放函数kfree()。
举例：

static int rockchip_drm_open(struct drm_device *dev, struct drm_file *file)
{
    ...
    file_priv = kzalloc(sizeof(*file_priv), GFP_KERNEL);
    ...
    kfree(file_priv);
    file_priv = NULL;
    ...
}

二、kcalloc

文件：include/linux/slab.h，定义如下：

/**
 * kmalloc_array - allocate memory for an array.
 * @n: number of elements.
 * @size: element size.
 * @flags: the type of memory to allocate (see kmalloc).
 */
static inline void *kmalloc_array(size_t n, size_t size, gfp_t flags)
{
    if (size != 0 && n > SIZE_MAX / size)
        return NULL;
    return __kmalloc(n * size, flags);
}

/**
 * kcalloc - allocate memory for an array. The memory is set to zero.
 * @n: number of elements.
 * @size: element size.
 * @flags: the type of memory to allocate (see kmalloc).
 */
static inline void *kcalloc(size_t n, size_t size, gfp_t flags)
{
    return kmalloc_array(n, size, flags | __GFP_ZERO);
}

kcalloc()函数为数组分配内存，大小n*size，并对分配的内存清零。该函数的最终实现类似kmalloc()函数。

每次使用kcalloc()后，都要有对应的内存释放函数kfree()。

举例：

struct drm_clip_rect {
    unsigned short x1;
    unsigned short y1;
    unsigned short x2;
    unsigned short y2;
};

int drm_mode_dirtyfb_ioctl(struct drm_device *dev,
               void *data, struct drm_file *file_priv)
{
    ...
    struct drm_clip_rect *clips = NULL;
    ...
    clips = kcalloc(num_clips, sizeof(*clips), GFP_KERNEL);
    ...
    kfree(clips);
    ...
}