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/*
* The "user cache".
*
* (C) Copyright 1991-2000 Linus Torvalds
*
* We have a per-user structure to keep track of how many
* processes, files etc the user has claimed, in order to be
* able to have per-user limits for system resources.
*/
#include <linux/config.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/slab.h>
/*
* UID task count cache, to get fast user lookup in "alloc_uid"
* when changing user ID's (ie setuid() and friends).
*/
#define UIDHASH_SZ (256)
static struct user_struct *uidhash[UIDHASH_SZ];
spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;
struct user_struct root_user = {
__count: ATOMIC_INIT(1),
processes: ATOMIC_INIT(1),
files: ATOMIC_INIT(0)
};
static kmem_cache_t *uid_cachep;
#define uidhashfn(uid) (((uid >> 8) ^ uid) & (UIDHASH_SZ - 1))
/*
* These routines must be called with the uidhash spinlock held!
*/
static inline void uid_hash_insert(struct user_struct *up, unsigned int hashent)
{
if((up->next = uidhash[hashent]) != NULL)
uidhash[hashent]->pprev = &up->next;
up->pprev = &uidhash[hashent];
uidhash[hashent] = up;
}
static inline void uid_hash_remove(struct user_struct *up)
{
if(up->next)
up->next->pprev = up->pprev;
*up->pprev = up->next;
}
static inline struct user_struct *uid_hash_find(unsigned short uid, unsigned int hashent)
{
struct user_struct *up, *next;
next = uidhash[hashent];
for (;;) {
up = next;
if (next) {
next = up->next;
if (up->uid != uid)
continue;
atomic_inc(&up->__count);
}
break;
}
return up;
}
/*
* For SMP, we need to re-test the user struct counter
* after having aquired the spinlock. This allows us to do
* the common case (not freeing anything) without having
* any locking.
*/
#ifdef CONFIG_SMP
#define uid_hash_free(up) (!atomic_read(&(up)->__count))
#else
#define uid_hash_free(up) (1)
#endif
void free_uid(struct user_struct *up)
{
if (up) {
if (atomic_dec_and_test(&up->__count)) {
spin_lock(&uidhash_lock);
if (uid_hash_free(up)) {
uid_hash_remove(up);
kmem_cache_free(uid_cachep, up);
}
spin_unlock(&uidhash_lock);
}
}
}
struct user_struct * alloc_uid(uid_t uid)
{
unsigned int hashent = uidhashfn(uid);
struct user_struct *up;
spin_lock(&uidhash_lock);
up = uid_hash_find(uid, hashent);
spin_unlock(&uidhash_lock);
if (!up) {
struct user_struct *new;
new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
if (!new)
return NULL;
new->uid = uid;
atomic_set(&new->__count, 1);
atomic_set(&new->processes, 0);
atomic_set(&new->files, 0);
/*
* Before adding this, check whether we raced
* on adding the same user already..
*/
spin_lock(&uidhash_lock);
up = uid_hash_find(uid, hashent);
if (up) {
kmem_cache_free(uid_cachep, new);
} else {
uid_hash_insert(new, hashent);
up = new;
}
spin_unlock(&uidhash_lock);
}
return up;
}
static int __init uid_cache_init(void)
{
int i;
uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
0,
SLAB_HWCACHE_ALIGN, NULL, NULL);
if(!uid_cachep)
panic("Cannot create uid taskcount SLAB cache\n");
for(i = 0; i < UIDHASH_SZ; i++)
uidhash[i] = 0;
/* Insert the root user immediately - init already runs with this */
uid_hash_insert(&root_user, uidhashfn(0));
return 0;
}
module_init(uid_cache_init);
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