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![Robert Love](/assets/img/avatar_default.png)
inotify is intended to correct the deficiencies of dnotify, particularly its inability to scale and its terrible user interface: * dnotify requires the opening of one fd per each directory that you intend to watch. This quickly results in too many open files and pins removable media, preventing unmount. * dnotify is directory-based. You only learn about changes to directories. Sure, a change to a file in a directory affects the directory, but you are then forced to keep a cache of stat structures. * dnotify's interface to user-space is awful. Signals? inotify provides a more usable, simple, powerful solution to file change notification: * inotify's interface is a system call that returns a fd, not SIGIO. You get a single fd, which is select()-able. * inotify has an event that says "the filesystem that the item you were watching is on was unmounted." * inotify can watch directories or files. Inotify is currently used by Beagle (a desktop search infrastructure), Gamin (a FAM replacement), and other projects. See Documentation/filesystems/inotify.txt. Signed-off-by: Robert Love <rml@novell.com> Cc: John McCutchan <ttb@tentacle.dhs.org> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
193 lines
4.4 KiB
C
193 lines
4.4 KiB
C
/*
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* The "user cache".
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*
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* (C) Copyright 1991-2000 Linus Torvalds
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*
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* We have a per-user structure to keep track of how many
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* processes, files etc the user has claimed, in order to be
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* able to have per-user limits for system resources.
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*/
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#include <linux/init.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/bitops.h>
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#include <linux/key.h>
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/*
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* UID task count cache, to get fast user lookup in "alloc_uid"
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* when changing user ID's (ie setuid() and friends).
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*/
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#define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 8)
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#define UIDHASH_SZ (1 << UIDHASH_BITS)
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#define UIDHASH_MASK (UIDHASH_SZ - 1)
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#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
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#define uidhashentry(uid) (uidhash_table + __uidhashfn((uid)))
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static kmem_cache_t *uid_cachep;
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static struct list_head uidhash_table[UIDHASH_SZ];
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static DEFINE_SPINLOCK(uidhash_lock);
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struct user_struct root_user = {
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.__count = ATOMIC_INIT(1),
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.processes = ATOMIC_INIT(1),
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.files = ATOMIC_INIT(0),
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.sigpending = ATOMIC_INIT(0),
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.mq_bytes = 0,
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.locked_shm = 0,
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#ifdef CONFIG_KEYS
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.uid_keyring = &root_user_keyring,
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.session_keyring = &root_session_keyring,
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#endif
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};
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/*
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* These routines must be called with the uidhash spinlock held!
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*/
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static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
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{
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list_add(&up->uidhash_list, hashent);
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}
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static inline void uid_hash_remove(struct user_struct *up)
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{
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list_del(&up->uidhash_list);
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}
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static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
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{
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struct list_head *up;
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list_for_each(up, hashent) {
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struct user_struct *user;
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user = list_entry(up, struct user_struct, uidhash_list);
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if(user->uid == uid) {
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atomic_inc(&user->__count);
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return user;
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}
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}
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return NULL;
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}
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/*
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* Locate the user_struct for the passed UID. If found, take a ref on it. The
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* caller must undo that ref with free_uid().
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*
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* If the user_struct could not be found, return NULL.
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*/
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struct user_struct *find_user(uid_t uid)
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{
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struct user_struct *ret;
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spin_lock(&uidhash_lock);
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ret = uid_hash_find(uid, uidhashentry(uid));
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spin_unlock(&uidhash_lock);
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return ret;
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}
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void free_uid(struct user_struct *up)
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{
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if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
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uid_hash_remove(up);
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key_put(up->uid_keyring);
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key_put(up->session_keyring);
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kmem_cache_free(uid_cachep, up);
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spin_unlock(&uidhash_lock);
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}
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}
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struct user_struct * alloc_uid(uid_t uid)
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{
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struct list_head *hashent = uidhashentry(uid);
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struct user_struct *up;
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spin_lock(&uidhash_lock);
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up = uid_hash_find(uid, hashent);
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spin_unlock(&uidhash_lock);
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if (!up) {
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struct user_struct *new;
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new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
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if (!new)
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return NULL;
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new->uid = uid;
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atomic_set(&new->__count, 1);
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atomic_set(&new->processes, 0);
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atomic_set(&new->files, 0);
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atomic_set(&new->sigpending, 0);
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#ifdef CONFIG_INOTIFY
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atomic_set(&new->inotify_watches, 0);
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atomic_set(&new->inotify_devs, 0);
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#endif
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new->mq_bytes = 0;
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new->locked_shm = 0;
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if (alloc_uid_keyring(new) < 0) {
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kmem_cache_free(uid_cachep, new);
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return NULL;
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}
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/*
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* Before adding this, check whether we raced
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* on adding the same user already..
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*/
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spin_lock(&uidhash_lock);
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up = uid_hash_find(uid, hashent);
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if (up) {
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key_put(new->uid_keyring);
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key_put(new->session_keyring);
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kmem_cache_free(uid_cachep, new);
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} else {
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uid_hash_insert(new, hashent);
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up = new;
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}
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spin_unlock(&uidhash_lock);
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}
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return up;
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}
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void switch_uid(struct user_struct *new_user)
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{
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struct user_struct *old_user;
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/* What if a process setreuid()'s and this brings the
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* new uid over his NPROC rlimit? We can check this now
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* cheaply with the new uid cache, so if it matters
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* we should be checking for it. -DaveM
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*/
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old_user = current->user;
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atomic_inc(&new_user->processes);
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atomic_dec(&old_user->processes);
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switch_uid_keyring(new_user);
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current->user = new_user;
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free_uid(old_user);
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suid_keys(current);
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}
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static int __init uid_cache_init(void)
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{
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int n;
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uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
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0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
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for(n = 0; n < UIDHASH_SZ; ++n)
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INIT_LIST_HEAD(uidhash_table + n);
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/* Insert the root user immediately (init already runs as root) */
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spin_lock(&uidhash_lock);
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uid_hash_insert(&root_user, uidhashentry(0));
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spin_unlock(&uidhash_lock);
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return 0;
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}
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module_init(uid_cache_init);
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