1. 1.
    +1
    struct group_info init_groups = { .usage = ATOMIC_INIT(2) };

    struct group_info *groups_alloc(int gidsetsize){

    struct group_info *group_info;

    int nblocks;

    int i;

    nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;

    /* Make sure we always allocate at least one indirect block pointer */

    nblocks = nblocks ? : 1;

    group_info = kmalloc(sizeof(*group_info) + nblocks*sizeof(gid_t *), GFP_USER);

    if (!group_info)

    return NULL;

    group_info->ngroups = gidsetsize;

    group_info->nblocks = nblocks;

    atomic_set(&group_info->usage, 1);

    if (gidsetsize <= NGROUPS_SMALL)

    group_info->blocks[0] = group_info->small_block;

    else {

    for (i = 0; i < nblocks; i++) {

    gid_t *b;

    b = (void *)__get_free_page(GFP_USER);

    if (!b)

    goto out_undo_partial_alloc;

    group_info->blocks[i] = b;

    }

    }

    return group_info;

    out_undo_partial_alloc:

    while (--i >= 0) {

    free_page((unsigned long)group_info->blocks[i]);

    }

    kfree(group_info);

    return NULL;

    }

    EXPORT_SYMBOL(groups_alloc);

    void groups_free(struct group_info *group_info)

    {

    if (group_info->blocks[0] != group_info->small_block) {

    int i;

    for (i = 0; i < group_info->nblocks; i++)

    free_page((unsigned long)group_info->blocks[i]);

    }

    kfree(group_info);

    }

    EXPORT_SYMBOL(groups_free);

    /* export the group_info to a user-space array */

    static int groups_to_user(gid_t __user *grouplist,

    const struct group_info *group_info)

    {

    int i;

    unsigned int count = group_info->ngroups;

    for (i = 0; i < group_info->nblocks; i++) {
    ···
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