mapping_kind.c

#define _DEFAULT_SOURCE
#include "mapping_kind.h"
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>

static
void *
create_mapping_portable(size_t len)
{
    int fd = open("/dev/zero", O_RDWR);
    if (fd < 0) {
        perror("open: /dev/zero");
        abort();
    }
    void *r = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    return r == MAP_FAILED ? NULL : r;
}

#ifdef __linux__
static
void *
create_mapping_ondemand(size_t len)
{
    void *r = mmap(
        NULL, len, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED | MAP_NORESERVE, -1, 0);
    return r == MAP_FAILED ? NULL : r;
}

static
int
punch_hole(void *addr, size_t len)
{
    return madvise(addr, len, MADV_REMOVE);
}
#endif

const MappingKind MAPPING_KIND_PORTABLE = {
    .default_len = 1024ull * 1024 * 16,
    .create = create_mapping_portable,
};

const MappingKind MAPPING_KIND_ONDEMAND = {
    .default_len = 1024ull * 1024 * 1024 * 16,
#ifdef __linux__
    .create = create_mapping_ondemand,
    .reclaim_pages = punch_hole,
#endif
};

#ifdef __linux__
const MappingKind *mapping_kind_pdefault = &MAPPING_KIND_ONDEMAND;
#else
const MappingKind *mapping_kind_pdefault = &MAPPING_KIND_PORTABLE;
#endif