flex_array.h

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#ifndef _FLEX_ARRAY_H
#define _FLEX_ARRAY_H

#include <linux/types.h>
#include <asm/page.h>

#define FLEX_ARRAY_PART_SIZE PAGE_SIZE
#define FLEX_ARRAY_BASE_SIZE PAGE_SIZE

struct flex_array_part;

/*
 * This is meant to replace cases where an array-like
 * structure has gotten too big to fit into kmalloc()
 * and the developer is getting tempted to use
 * vmalloc().
 */

struct flex_array {
    union {
        struct {
            int element_size;
            int total_nr_elements;
            int elems_per_part;
            u32 reciprocal_elems;
            struct flex_array_part *parts[];
        };
        /*
         * This little trick makes sure that
         * sizeof(flex_array) == PAGE_SIZE
         */
        char padding[FLEX_ARRAY_BASE_SIZE];
    };
};

/* Number of bytes left in base struct flex_array, excluding metadata */
#define FLEX_ARRAY_BASE_BYTES_LEFT                  \
    (FLEX_ARRAY_BASE_SIZE - offsetof(struct flex_array, parts))

/* Number of pointers in base to struct flex_array_part pages */
#define FLEX_ARRAY_NR_BASE_PTRS                     \
    (FLEX_ARRAY_BASE_BYTES_LEFT / sizeof(struct flex_array_part *))

/* Number of elements of size that fit in struct flex_array_part */
#define FLEX_ARRAY_ELEMENTS_PER_PART(size)              \
    (FLEX_ARRAY_PART_SIZE / size)

/*
 * Defines a statically allocated flex array and ensures its parameters are
 * valid.
 */
#define DEFINE_FLEX_ARRAY(__arrayname, __element_size, __total)     \
    struct flex_array __arrayname = { { {               \
        .element_size = (__element_size),           \
        .total_nr_elements = (__total),             \
    } } };                              \
    static inline void __arrayname##_invalid_parameter(void)    \
    {                               \
        BUILD_BUG_ON((__total) > FLEX_ARRAY_NR_BASE_PTRS *  \
            FLEX_ARRAY_ELEMENTS_PER_PART(__element_size));  \
    }

struct flex_array *flex_array_alloc(int element_size, unsigned int total,
        gfp_t flags);
int flex_array_prealloc(struct flex_array *fa, unsigned int start,
        unsigned int nr_elements, gfp_t flags);
void flex_array_free(struct flex_array *fa);
void flex_array_free_parts(struct flex_array *fa);
int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
        gfp_t flags);
int flex_array_clear(struct flex_array *fa, unsigned int element_nr);
void *flex_array_get(struct flex_array *fa, unsigned int element_nr);
int flex_array_shrink(struct flex_array *fa);

#define flex_array_put_ptr(fa, nr, src, gfp) \
    flex_array_put(fa, nr, (void *)&(src), gfp)

void *flex_array_get_ptr(struct flex_array *fa, unsigned int element_nr);

#endif /* _FLEX_ARRAY_H */