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++) { unsigned int cp_count = min(NGROUPS_PER_BLOCK, count); unsigned int len = cp_count * sizeof(*grouplist); if (copy_to_user(grouplist, group_info->blocks[i], len)) return -EFAULT;

grouplist += NGROUPS_PER_BLOCK;
count -= cp_count; } return 0; } /* fill a group_info from a user-space array - it must be allocated already */ static int groups_from_user(struct group_info *group_info, gid_t __user *grouplist)
{
int i;
unsigned int count = group_info->ngroups;
for (i = 0; i < group_info->nblocks; i++) {
unsigned int cp_count = min(NGROUPS_PER_BLOCK, count);
unsigned int len = cp_count * sizeof(*grouplist);
if (copy_from_user(group_info->blocks[i], grouplist, len))
return -EFAULT;
grouplist += NGROUPS_PER_BLOCK; count -= cp_count; } return 0; } /* a simple Shell sort * static void groups_sort(struct group_info *group_info) {
int base, max, stride; int gidsetsize = group_info->ngroups; for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1)
; /* nothing */
stride /= 3;
while (stride) {
max = gidsetsize - stride;
for (base = 0; base < max; base++) {
int left = base;
int right = left + stride;
gid_t tmp = GROUP_AT(group_info, righ|
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