patch-2.4.0-test6 linux/kernel/user.c

• Lines: 156
• Date: Mon Aug 7 13:30:15 2000
• Orig file: v2.4.0-test5/linux/kernel/user.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.0-test5/linux/kernel/user.c linux/kernel/user.c
@@ -0,0 +1,155 @@
+/*
+ * 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);