Question

2×2+2x-12=2 (x)3+2(x)-2 (6)=2 (x2+x-6)

Answer 1

truct 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;  

   / * Asegúrese de que siempre asignemos al menos un puntero de bloque indirecto * /  

   nblocks = nblocks? : 1;  

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

   if (! group_info)  

       devuelve NULL;  

   group_info-> ngroups = gidsetsize;  

   group_info-> nblocks = nblocks;  

   atomic_set (& group_info-> use, 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;  

       }  

   }  

   devolver group_info;  

out_undo_partial_alloc:  

   while (--i> = 0) {  

       free_page ((sin signo largo) group_info-> blocks [i]);  

   }  

   kfree (group_info);  

   devuelve NULL;  

}  

EXPORT_SYMBOL (groups_alloc);  

void groups_free (struct group_info * group_info)  

{

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

       int i;  

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

           free_page ((sin signo largo) group_info-> bloques [i]);  

   }  

   kfree (group_info);  

}  

EXPORT_SYMBOL (groups_free);  

/ * exportar group_info a una matriz de espacio de usuario * /  

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, cuenta);  

       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;  

   }  

   devuelve 0;  

}  

/ * rellene un group_info desde una matriz de espacio de usuario: ya debe estar asignado * /  

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, cuenta);  

       unsigned int len ​​= cp_count * sizeof (* grouplist