/* * 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/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_BITS		8#define UIDHASH_SZ		(1 << UIDHASH_BITS)#define UIDHASH_MASK		(UIDHASH_SZ - 1)#define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) ^ uid) & UIDHASH_MASK)#define uidhashentry(uid)	(uidhash_table + __uidhashfn(uid))static kmem_cache_t *uid_cachep;static struct user_struct *uidhash_table[UIDHASH_SZ];static spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;struct user_struct root_user = {	__count:	ATOMIC_INIT(1),	processes:	ATOMIC_INIT(1),	files:		ATOMIC_INIT(0)};/* * These routines must be called with the uidhash spinlock held! */static inline void uid_hash_insert(struct user_struct *up, struct user_struct **hashent){	struct user_struct *next = *hashent;	up->next = next;	if (next)		next->pprev = &up->next;	up->pprev = hashent;	*hashent = up;}static inline void uid_hash_remove(struct user_struct *up){	struct user_struct *next = up->next;	struct user_struct **pprev = up->pprev;	if (next)		next->pprev = pprev;	*pprev = next;}static inline struct user_struct *uid_hash_find(uid_t uid, struct user_struct **hashent){	struct user_struct *next;	next = *hashent;	for (;;) {		struct user_struct *up = next;		if (next) {			next = up->next;			if (up->uid != uid)				continue;			atomic_inc(&up->__count);		}		return up;	}}void free_uid(struct user_struct *up){	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {		uid_hash_remove(up);		kmem_cache_free(uid_cachep, up);		spin_unlock(&uidhash_lock);	}}struct user_struct * alloc_uid(uid_t uid){	struct user_struct **hashent = uidhashentry(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){	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");	/* Insert the root user immediately - init already runs with this */	uid_hash_insert(&root_user, uidhashentry(0));	return 0;}module_init(uid_cache_init);