/* * fs/eventpoll.c ( Efficent event polling implementation ) * Copyright (C) 2001,...,2003 Davide Libenzi * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * Davide Libenzi <davidel@xmailserver.org> * */ #include <linux/module.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/sched.h> #include <linux/fs.h> #include <linux/file.h> #include <linux/signal.h> #include <linux/errno.h> #include <linux/mm.h> #include <linux/slab.h> #include <linux/poll.h> #include <linux/smp_lock.h> #include <linux/string.h> #include <linux/list.h> #include <linux/hash.h> #include <linux/spinlock.h> #include <linux/syscalls.h> #include <linux/rwsem.h> #include <linux/rbtree.h> #include <linux/wait.h> #include <linux/eventpoll.h> #include <linux/mount.h> #include <linux/bitops.h> #include <linux/mutex.h> #include <asm/uaccess.h> #include <asm/system.h> #include <asm/io.h> #include <asm/mman.h> #include <asm/atomic.h> #include <asm/semaphore.h> /* * LOCKING: * There are three level of locking required by epoll : * * 1) epmutex (mutex) * 2) ep->sem (rw_semaphore) * 3) ep->lock (rw_lock) * * The acquire order is the one listed above, from 1 to 3. * We need a spinlock (ep->lock) because we manipulate objects * from inside the poll callback, that might be triggered from * a wake_up() that in turn might be called from IRQ context. * So we can't sleep inside the poll callback and hence we need * a spinlock. During the event transfer loop (from kernel to * user space) we could end up sleeping due a copy_to_user(), so * we need a lock that will allow us to sleep. This lock is a * read-write semaphore (ep->sem). It is acquired on read during * the event transfer loop and in write during epoll_ctl(EPOLL_CTL_DEL) * and during eventpoll_release_file(). Then we also need a global * semaphore to serialize eventpoll_release_file() and ep_free(). * This semaphore is acquired by ep_free() during the epoll file * cleanup path and it is also acquired by eventpoll_release_file() * if a file has been pushed inside an epoll set and it is then * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL). * It is possible to drop the "ep->sem" and to use the global * semaphore "epmutex" (together with "ep->lock") to have it working, * but having "ep->sem" will make the interface more scalable. * Events that require holding "epmutex" are very rare, while for * normal operations the epoll private "ep->sem" will guarantee * a greater scalability. */ #define EVENTPOLLFS_MAGIC 0x03111965 /* My birthday should work for this :) */ #define DEBUG_EPOLL 0 #if DEBUG_EPOLL > 0 #define DPRINTK(x) printk x #define DNPRINTK(n, x) do { if ((n) <= DEBUG_EPOLL) printk x; } while (0) #else /* #if DEBUG_EPOLL > 0 */ #define DPRINTK(x) (void) 0 #define DNPRINTK(n, x) (void) 0 #endif /* #if DEBUG_EPOLL > 0 */ #define DEBUG_EPI 0 #if DEBUG_EPI != 0 #define EPI_SLAB_DEBUG (SLAB_DEBUG_FREE | SLAB_RED_ZONE /* | SLAB_POISON */) #else /* #if DEBUG_EPI != 0 */ #define EPI_SLAB_DEBUG 0 #endif /* #if DEBUG_EPI != 0 */ /* Epoll private bits inside the event mask */ #define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET) /* Maximum number of poll wake up nests we are allowing */ #define EP_MAX_POLLWAKE_NESTS 4 /* Maximum msec timeout value storeable in a long int */ #define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ) struct epoll_filefd { struct file *file; int fd; }; /* * Node that is linked into the "wake_task_list" member of the "struct poll_safewake". * It is used to keep track on all tasks that are currently inside the wake_up() code * to 1) short-circuit the one coming from the same task and same wait queue head * ( loop ) 2) allow a maximum number of epoll descriptors inclusion nesting * 3) let go the ones coming from other tasks. */ struct wake_task_node { struct list_head llink; task_t *task; wait_queue_head_t *wq; }; /* * This is used to implement the safe poll wake up avoiding to reenter * the poll callback from inside wake_up(). */ struct poll_safewake { struct list_head wake_task_list; spinlock_t lock; }; /* * This structure is stored inside the "private_data" member of the file * structure and rapresent the main data sructure for the eventpoll * interface. */ struct eventpoll { /* Protect the this structure access */ rwlock_t lock; /* * This semaphore is used to ensure that files are not removed * while epoll is using them. This is read-held during the event * collection loop and it is write-held during the file cleanup * path, the epoll file exit code and the ctl operations. */ struct rw_semaphore sem; /* Wait queue used by sys_epoll_wait() */ wait_queue_head_t wq; /* Wait queue used by file->poll() */ wait_queue_head_t poll_wait; /* List of ready file descriptors */ struct list_head rdllist; /* RB-Tree root used to store monitored fd structs */ struct rb_root rbr; }; /* Wait structure used by the poll hooks */ struct eppoll_entry { /* List header used to link this structure to the "struct epitem" */ struct list_head llink; /* The "base" pointer is set to the container "struct epitem" */ void *base; /* * Wait queue item that will be linked to the target file wait * queue head. */ wait_queue_t wait; /* The wait queue head that linked the "wait" wait queue item */ wait_queue_head_t *whead; }; /* * Each file descriptor added to the eventpoll interface will * have an entry of this type linked to the hash. */ struct epitem { /* RB-Tree node used to link this structure to the eventpoll rb-tree */ struct rb_node rbn; /* List header used to link this structure to the eventpoll ready list */ struct list_head rdllink; /* The file descriptor information this item refers to */ struct epoll_filefd ffd; /* Number of active wait queue attached to poll operations */ int nwait; /* List containing poll wait queues */ struct list_head pwqlist; /* The "container" of this item */ struct eventpoll *ep; /* The structure that describe the interested events and the source fd */ struct epoll_event event; /* * Used to keep track of the usage count of the structure. This avoids * that the structure will desappear from underneath our processing. */ atomic_t usecnt; /* List header used to link this item to the "struct file" items list */ struct list_head fllink; /* List header used to link the item to the transfer list */ struct list_head txlink; /* * This is used during the collection/transfer of events to userspace * to pin items empty events set. */ unsigned int revents; }; /* Wrapper struct used by poll queueing */ struct ep_pqueue { poll_table pt; struct epitem *epi; }; static void ep_poll_safewake_init(struct poll_safewake *psw); static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq); static int ep_getfd(int *efd, struct inode **einode, struct file **efile, struct eventpoll *ep); static int ep_alloc(struct eventpoll **pep); static void ep_free(struct eventpoll *ep); static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd); static void ep_use_epitem(struct epitem *epi); static void ep_release_epitem(struct epitem *epi); static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, poll_table *pt); static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi); static int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile, int fd); static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event); static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi); static int ep_unlink(struct eventpoll *ep, struct epitem *epi); static int ep_remove(struct eventpoll *ep, struct epitem *epi); static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key); static int ep_eventpoll_close(struct inode *inode, struct file *file); static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait); static int ep_collect_ready_items(struct eventpoll *ep, struct list_head *txlist, int maxevents); static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, struct epoll_event __user *events); static void ep_reinject_items(struct eventpoll *ep, struct list_head *txlist); static int ep_events_transfer(struct eventpoll *ep, struct epoll_event __user *events, int maxevents); static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, long timeout); static int eventpollfs_delete_dentry(struct dentry *dentry); static struct inode *ep_eventpoll_inode(void); static struct super_block *eventpollfs_get_sb(struct file_system_type *fs_type, int flags, const char *dev_name, void *data); /* * This semaphore is used to serialize ep_free() and eventpoll_release_file(). */ static struct mutex epmutex; /* Safe wake up implementation */ static struct poll_safewake psw; /* Slab cache used to allocate "struct epitem" */ static kmem_cache_t *epi_cache __read_mostly; /* Slab cache used to allocate "struct eppoll_entry" */ static kmem_cache_t *pwq_cache __read_mostly; /* Virtual fs used to allocate inodes for eventpoll files */ static struct vfsmount *eventpoll_mnt __read_mostly; /* File callbacks that implement the eventpoll file behaviour */ static struct file_operations eventpoll_fops = { .release = ep_eventpoll_close, .poll = ep_eventpoll_poll }; /* * This is used to register the virtual file system from where * eventpoll inodes are allocated. */ static struct file_system_type eventpoll_fs_type = { .name = "eventpollfs", .get_sb = eventpollfs_get_sb, .kill_sb = kill_anon_super, }; /* Very basic directory entry operations for the eventpoll virtual file system */ static struct dentry_operations eventpollfs_dentry_operations = { .d_delete = eventpollfs_delete_dentry, }; /* Fast test to see if the file is an evenpoll file */ static inline int is_file_epoll(struct file *f) { return f->f_op == &eventpoll_fops; } /* Setup the structure that is used as key for the rb-tree */ static inline void ep_set_ffd(struct epoll_filefd *ffd, struct file *file, int fd) { ffd->file = file; ffd->fd = fd; } /* Compare rb-tree keys */ static inline int ep_cmp_ffd(struct epoll_filefd *p1, struct epoll_filefd *p2) { return (p1->file > p2->file ? +1: (p1->file < p2->file ? -1 : p1->fd - p2->fd)); } /* Special initialization for the rb-tree node to detect linkage */ static inline void ep_rb_initnode(struct rb_node *n) { n->rb_parent = n; } /* Removes a node from the rb-tree and marks it for a fast is-linked check */ static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r) { rb_erase(n, r); n->rb_parent = n; } /* Fast check to verify that the item is linked to the main rb-tree */ static inline int ep_rb_linked(struct rb_node *n) { return n->rb_parent != n; } /* * Remove the item from the list and perform its initialization. * This is useful for us because we can test if the item is linked * using "ep_is_linked(p)". */ static inline void ep_list_del(struct list_head *p) { list_del(p); INIT_LIST_HEAD(p); } /* Tells us if the item is currently linked */ static inline int ep_is_linked(struct list_head *p) { return !list_empty(p); } /* Get the "struct epitem" from a wait queue pointer */ static inline struct epitem * ep_item_from_wait(wait_queue_t *p) { return container_of(p, struct eppoll_entry, wait)->base; } /* Get the "struct epitem" from an epoll queue wrapper */ static inline struct epitem * ep_item_from_epqueue(poll_table *p) { return container_of(p, struct ep_pqueue, pt)->epi; } /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */ static inline int ep_op_hash_event(int op) { return op != EPOLL_CTL_DEL; } /* Initialize the poll safe wake up structure */ static void ep_poll_safewake_init(struct poll_safewake *psw) { INIT_LIST_HEAD(&psw->wake_task_list); spin_lock_init(&psw->lock); } /* * Perform a safe wake up of the poll wait list. The problem is that * with the new callback'd wake up system, it is possible that the * poll callback is reentered from inside the call to wake_up() done * on the poll wait queue head. The rule is that we cannot reenter the * wake up code from the same task more than EP_MAX_POLLWAKE_NESTS times, * and we cannot reenter the same wait queue head at all. This will * enable to have a hierarchy of epoll file descriptor of no more than * EP_MAX_POLLWAKE_NESTS deep. We need the irq version of the spin lock * because this one gets called by the poll callback, that in turn is called * from inside a wake_up(), that might be called from irq context. */ static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq) { int wake_nests = 0; unsigned long flags; task_t *this_task = current; struct list_head *lsthead = &psw->wake_task_list, *lnk; struct wake_task_node *tncur; struct wake_task_node tnode; spin_lock_irqsave(&psw->lock, flags); /* Try to see if the current task is already inside this wakeup call */ list_for_each(lnk, lsthead) { tncur = list_entry(lnk, struct wake_task_node, llink); if (tncur->wq == wq || (tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_NESTS)) { /* * Ops ... loop detected or maximum nest level reached. * We abort this wake by breaking the cycle itself. */ spin_unlock_irqrestore(&psw->lock, flags); return; } } /* Add the current task to the list */ tnode.task = this_task; tnode.wq = wq; list_add(&tnode.llink, lsthead); spin_unlock_irqrestore(&psw->lock, flags); /* Do really wake up now */ wake_up(wq); /* Remove the current task from the list */ spin_lock_irqsave(&psw->lock, flags); list_del(&tnode.llink); spin_unlock_irqrestore(&psw->lock, flags); } /* * This is called from eventpoll_release() to unlink files from the eventpoll * interface. We need to have this facility to cleanup correctly files that are * closed without being removed from the eventpoll interface. */ void eventpoll_release_file(struct file *file) { struct list_head *lsthead = &file->f_ep_links; struct eventpoll *ep; struct epitem *epi; /* * We don't want to get "file->f_ep_lock" because it is not * necessary. It is not necessary because we're in the "struct file" * cleanup path, and this means that noone is using this file anymore. * The only hit might come from ep_free() but by holding the semaphore * will correctly serialize the operation. We do need to acquire * "ep->sem" after "epmutex" because ep_remove() requires it when called * from anywhere but ep_free(). */ mutex_lock(&epmutex); while (!list_empty(lsthead)) { epi = list_entry(lsthead->next, struct epitem, fllink); ep = epi->ep; ep_list_del(&epi->fllink); down_write(&ep->sem); ep_remove(ep, epi); up_write(&ep->sem); } mutex_unlock(&epmutex); } /* * It opens an eventpoll file descriptor by suggesting a storage of "size" * file descriptors. The size parameter is just an hint about how to size * data structures. It won't prevent the user to store more than "size" * file descriptors inside the epoll interface. It is the kernel part of * the userspace epoll_create(2). */ asmlinkage long sys_epoll_create(int size) { int error, fd; struct eventpoll *ep; struct inode *inode; struct file *file; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n", current, size)); /* * Sanity check on the size parameter, and create the internal data * structure ( "struct eventpoll" ). */ error = -EINVAL; if (size <= 0 || (error = ep_alloc(&ep)) != 0) goto eexit_1; /* * Creates all the items needed to setup an eventpoll file. That is, * a file structure, and inode and a free file descriptor. */ error = ep_getfd(&fd, &inode, &file, ep); if (error) goto eexit_2; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n", current, size, fd)); return fd; eexit_2: ep_free(ep); kfree(ep); eexit_1: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n", current, size, error)); return error; } /* * The following function implements the controller interface for * the eventpoll file that enables the insertion/removal/change of * file descriptors inside the interest set. It represents * the kernel part of the user space epoll_ctl(2). */ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd, struct epoll_event __user *event) { int error; struct file *file, *tfile; struct eventpoll *ep; struct epitem *epi; struct epoll_event epds; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p)\n", current, epfd, op, fd, event)); error = -EFAULT; if (ep_op_hash_event(op) && copy_from_user(&epds, event, sizeof(struct epoll_event))) goto eexit_1; /* Get the "struct file *" for the eventpoll file */ error = -EBADF; file = fget(epfd); if (!file) goto eexit_1; /* Get the "struct file *" for the target file */ tfile = fget(fd); if (!tfile) goto eexit_2; /* The target file descriptor must support poll */ error = -EPERM; if (!tfile->f_op || !tfile->f_op->poll) goto eexit_3; /* * We have to check that the file structure underneath the file descriptor * the user passed to us _is_ an eventpoll file. And also we do not permit * adding an epoll file descriptor inside itself. */ error = -EINVAL; if (file == tfile || !is_file_epoll(file)) goto eexit_3; /* * At this point it is safe to assume that the "private_data" contains * our own data structure. */ ep = file->private_data; down_write(&ep->sem); /* Try to lookup the file inside our hash table */ epi = ep_find(ep, tfile, fd); error = -EINVAL; switch (op) { case EPOLL_CTL_ADD: if (!epi) { epds.events |= POLLERR | POLLHUP | POLLRDHUP; error = ep_insert(ep, &epds, tfile, fd); } else error = -EEXIST; break; case EPOLL_CTL_DEL: if (epi) error = ep_remove(ep, epi); else error = -ENOENT; break; case EPOLL_CTL_MOD: if (epi) { epds.events |= POLLERR | POLLHUP | POLLRDHUP; error = ep_modify(ep, epi, &epds); } else error = -ENOENT; break; } /* * The function ep_find() increments the usage count of the structure * so, if this is not NULL, we need to release it. */ if (epi) ep_release_epitem(epi); up_write(&ep->sem); eexit_3: fput(tfile); eexit_2: fput(file); eexit_1: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p) = %d\n", current, epfd, op, fd, event, error)); return error; } #define MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) /* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_wait(2). */ asmlinkage long sys_epoll_wait(int epfd, struct epoll_event __user *events, int maxevents, int timeout) { int error; struct file *file; struct eventpoll *ep; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d)\n", current, epfd, events, maxevents, timeout)); /* The maximum number of event must be greater than zero */ if (maxevents <= 0 || maxevents > MAX_EVENTS) return -EINVAL; /* Verify that the area passed by the user is writeable */ if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) { error = -EFAULT; goto eexit_1; } /* Get the "struct file *" for the eventpoll file */ error = -EBADF; file = fget(epfd); if (!file) goto eexit_1; /* * We have to check that the file structure underneath the fd * the user passed to us _is_ an eventpoll file. */ error = -EINVAL; if (!is_file_epoll(file)) goto eexit_2; /* * At this point it is safe to assume that the "private_data" contains * our own data structure. */ ep = file->private_data; /* Time to fish for events ... */ error = ep_poll(ep, events, maxevents, timeout); eexit_2: fput(file); eexit_1: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d) = %d\n", current, epfd, events, maxevents, timeout, error)); return error; } /* * Creates the file descriptor to be used by the epoll interface. */ static int ep_getfd(int *efd, struct inode **einode, struct file **efile, struct eventpoll *ep) { struct qstr this; char name[32]; struct dentry *dentry; struct inode *inode; struct file *file; int error, fd; /* Get an ready to use file */ error = -ENFILE; file = get_empty_filp(); if (!file) goto eexit_1; /* Allocates an inode from the eventpoll file system */ inode = ep_eventpoll_inode(); error = PTR_ERR(inode); if (IS_ERR(inode)) goto eexit_2; /* Allocates a free descriptor to plug the file onto */ error = get_unused_fd(); if (error < 0) goto eexit_3; fd = error; /* * Link the inode to a directory entry by creating a unique name * using the inode number. */ error = -ENOMEM; sprintf(name, "[%lu]", inode->i_ino); this.name = name; this.len = strlen(name); this.hash = inode->i_ino; dentry = d_alloc(eventpoll_mnt->mnt_sb->s_root, &this); if (!dentry) goto eexit_4; dentry->d_op = &eventpollfs_dentry_operations; d_add(dentry, inode); file->f_vfsmnt = mntget(eventpoll_mnt); file->f_dentry = dentry; file->f_mapping = inode->i_mapping; file->f_pos = 0; file->f_flags = O_RDONLY; file->f_op = &eventpoll_fops; file->f_mode = FMODE_READ; file->f_version = 0; file->private_data = ep; /* Install the new setup file into the allocated fd. */ fd_install(fd, file); *efd = fd; *einode = inode; *efile = file; return 0; eexit_4: put_unused_fd(fd); eexit_3: iput(inode); eexit_2: put_filp(file); eexit_1: return error; } static int ep_alloc(struct eventpoll **pep) { struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL); if (!ep) return -ENOMEM; rwlock_init(&ep->lock); init_rwsem(&ep->sem); init_waitqueue_head(&ep->wq); init_waitqueue_head(&ep->poll_wait); INIT_LIST_HEAD(&ep->rdllist); ep->rbr = RB_ROOT; *pep = ep; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_alloc() ep=%p\n", current, ep)); return 0; } static void ep_free(struct eventpoll *ep) { struct rb_node *rbp; struct epitem *epi; /* We need to release all tasks waiting for these file */ if (waitqueue_active(&ep->poll_wait)) ep_poll_safewake(&psw, &ep->poll_wait); /* * We need to lock this because we could be hit by * eventpoll_release_file() while we're freeing the "struct eventpoll". * We do not need to hold "ep->sem" here because the epoll file * is on the way to be removed and no one has references to it * anymore. The only hit might come from eventpoll_release_file() but * holding "epmutex" is sufficent here. */ mutex_lock(&epmutex); /* * Walks through the whole tree by unregistering poll callbacks. */ for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { epi = rb_entry(rbp, struct epitem, rbn); ep_unregister_pollwait(ep, epi); } /* * Walks through the whole hash by freeing each "struct epitem". At this * point we are sure no poll callbacks will be lingering around, and also by * write-holding "sem" we can be sure that no file cleanup code will hit * us during this operation. So we can avoid the lock on "ep->lock". */ while ((rbp = rb_first(&ep->rbr)) != 0) { epi = rb_entry(rbp, struct epitem, rbn); ep_remove(ep, epi); } mutex_unlock(&epmutex); } /* * Search the file inside the eventpoll hash. It add usage count to * the returned item, so the caller must call ep_release_epitem() * after finished using the "struct epitem". */ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) { int kcmp; unsigned long flags; struct rb_node *rbp; struct epitem *epi, *epir = NULL; struct epoll_filefd ffd; ep_set_ffd(&ffd, file, fd); read_lock_irqsave(&ep->lock, flags); for (rbp = ep->rbr.rb_node; rbp; ) { epi = rb_entry(rbp, struct epitem, rbn); kcmp = ep_cmp_ffd(&ffd, &epi->ffd); if (kcmp > 0) rbp = rbp->rb_right; else if (kcmp < 0) rbp = rbp->rb_left; else { ep_use_epitem(epi); epir = epi; break; } } read_unlock_irqrestore(&ep->lock, flags); DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n", current, file, epir)); return epir; } /* * Increment the usage count of the "struct epitem" making it sure * that the user will have a valid pointer to reference. */ static void ep_use_epitem(struct epitem *epi) { atomic_inc(&epi->usecnt); } /* * Decrement ( release ) the usage count by signaling that the user * has finished using the structure. It might lead to freeing the * structure itself if the count goes to zero. */ static void ep_release_epitem(struct epitem *epi) { if (atomic_dec_and_test(&epi->usecnt)) kmem_cache_free(epi_cache, epi); } /* * This is the callback that is used to add our wait queue to the * target file wakeup lists. */ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, poll_table *pt) { struct epitem *epi = ep_item_from_epqueue(pt); struct eppoll_entry *pwq; if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, SLAB_KERNEL))) { init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); pwq->whead = whead; pwq->base = epi; add_wait_queue(whead, &pwq->wait); list_add_tail(&pwq->llink, &epi->pwqlist); epi->nwait++; } else { /* We have to signal that an error occurred */ epi->nwait = -1; } } static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) { int kcmp; struct rb_node **p = &ep->rbr.rb_node, *parent = NULL; struct epitem *epic; while (*p) { parent = *p; epic = rb_entry(parent, struct epitem, rbn); kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); if (kcmp > 0) p = &parent->rb_right; else p = &parent->rb_left; } rb_link_node(&epi->rbn, parent, p); rb_insert_color(&epi->rbn, &ep->rbr); } static int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile, int fd) { int error, revents, pwake = 0; unsigned long flags; struct epitem *epi; struct ep_pqueue epq; error = -ENOMEM; if (!(epi = kmem_cache_alloc(epi_cache, SLAB_KERNEL))) goto eexit_1; /* Item initialization follow here ... */ ep_rb_initnode(&epi->rbn); INIT_LIST_HEAD(&epi->rdllink); INIT_LIST_HEAD(&epi->fllink); INIT_LIST_HEAD(&epi->txlink); INIT_LIST_HEAD(&epi->pwqlist); epi->ep = ep; ep_set_ffd(&epi->ffd, tfile, fd); epi->event = *event; atomic_set(&epi->usecnt, 1); epi->nwait = 0; /* Initialize the poll table using the queue callback */ epq.epi = epi; init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); /* * Attach the item to the poll hooks and get current event bits. * We can safely use the file* here because its usage count has * been increased by the caller of this function. */ revents = tfile->f_op->poll(tfile, &epq.pt); /* * We have to check if something went wrong during the poll wait queue * install process. Namely an allocation for a wait queue failed due * high memory pressure. */ if (epi->nwait < 0) goto eexit_2; /* Add the current item to the list of active epoll hook for this file */ spin_lock(&tfile->f_ep_lock); list_add_tail(&epi->fllink, &tfile->f_ep_links); spin_unlock(&tfile->f_ep_lock); /* We have to drop the new item inside our item list to keep track of it */ write_lock_irqsave(&ep->lock, flags); /* Add the current item to the rb-tree */ ep_rbtree_insert(ep, epi); /* If the file is already "ready" we drop it inside the ready list */ if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) { list_add_tail(&epi->rdllink, &ep->rdllist); /* Notify waiting tasks that events are available */ if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } write_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n", current, ep, tfile, fd)); return 0; eexit_2: ep_unregister_pollwait(ep, epi); /* * We need to do this because an event could have been arrived on some * allocated wait queue. */ write_lock_irqsave(&ep->lock, flags); if (ep_is_linked(&epi->rdllink)) ep_list_del(&epi->rdllink); write_unlock_irqrestore(&ep->lock, flags); kmem_cache_free(epi_cache, epi); eexit_1: return error; } /* * Modify the interest event mask by dropping an event if the new mask * has a match in the current file status. */ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event) { int pwake = 0; unsigned int revents; unsigned long flags; /* * Set the new event interest mask before calling f_op->poll(), otherwise * a potential race might occur. In fact if we do this operation inside * the lock, an event might happen between the f_op->poll() call and the * new event set registering. */ epi->event.events = event->events; /* * Get current event bits. We can safely use the file* here because * its usage count has been increased by the caller of this function. */ revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL); write_lock_irqsave(&ep->lock, flags); /* Copy the data member from inside the lock */ epi->event.data = event->data; /* * If the item is not linked to the hash it means that it's on its * way toward the removal. Do nothing in this case. */ if (ep_rb_linked(&epi->rbn)) { /* * If the item is "hot" and it is not registered inside the ready * list, push it inside. If the item is not "hot" and it is currently * registered inside the ready list, unlink it. */ if (revents & event->events) { if (!ep_is_linked(&epi->rdllink)) { list_add_tail(&epi->rdllink, &ep->rdllist); /* Notify waiting tasks that events are available */ if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } } } write_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); return 0; } /* * This function unregister poll callbacks from the associated file descriptor. * Since this must be called without holding "ep->lock" the atomic exchange trick * will protect us from multiple unregister. */ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) { int nwait; struct list_head *lsthead = &epi->pwqlist; struct eppoll_entry *pwq; /* This is called without locks, so we need the atomic exchange */ nwait = xchg(&epi->nwait, 0); if (nwait) { while (!list_empty(lsthead)) { pwq = list_entry(lsthead->next, struct eppoll_entry, llink); ep_list_del(&pwq->llink); remove_wait_queue(pwq->whead, &pwq->wait); kmem_cache_free(pwq_cache, pwq); } } } /* * Unlink the "struct epitem" from all places it might have been hooked up. * This function must be called with write IRQ lock on "ep->lock". */ static int ep_unlink(struct eventpoll *ep, struct epitem *epi) { int error; /* * It can happen that this one is called for an item already unlinked. * The check protect us from doing a double unlink ( crash ). */ error = -ENOENT; if (!ep_rb_linked(&epi->rbn)) goto eexit_1; /* * Clear the event mask for the unlinked item. This will avoid item * notifications to be sent after the unlink operation from inside * the kernel->userspace event transfer loop. */ epi->event.events = 0; /* * At this point is safe to do the job, unlink the item from our rb-tree. * This operation togheter with the above check closes the door to * double unlinks. */ ep_rb_erase(&epi->rbn, &ep->rbr); /* * If the item we are going to remove is inside the ready file descriptors * we want to remove it from this list to avoid stale events. */ if (ep_is_linked(&epi->rdllink)) ep_list_del(&epi->rdllink); error = 0; eexit_1: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_unlink(%p, %p) = %d\n", current, ep, epi->file, error)); return error; } /* * Removes a "struct epitem" from the eventpoll hash and deallocates * all the associated resources. */ static int ep_remove(struct eventpoll *ep, struct epitem *epi) { int error; unsigned long flags; struct file *file = epi->ffd.file; /* * Removes poll wait queue hooks. We _have_ to do this without holding * the "ep->lock" otherwise a deadlock might occur. This because of the * sequence of the lock acquisition. Here we do "ep->lock" then the wait * queue head lock when unregistering the wait queue. The wakeup callback * will run by holding the wait queue head lock and will call our callback * that will try to get "ep->lock". */ ep_unregister_pollwait(ep, epi); /* Remove the current item from the list of epoll hooks */ spin_lock(&file->f_ep_lock); if (ep_is_linked(&epi->fllink)) ep_list_del(&epi->fllink); spin_unlock(&file->f_ep_lock); /* We need to acquire the write IRQ lock before calling ep_unlink() */ write_lock_irqsave(&ep->lock, flags); /* Really unlink the item from the hash */ error = ep_unlink(ep, epi); write_unlock_irqrestore(&ep->lock, flags); if (error) goto eexit_1; /* At this point it is safe to free the eventpoll item */ ep_release_epitem(epi); error = 0; eexit_1: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p) = %d\n", current, ep, file, error)); return error; } /* * This is the callback that is passed to the wait queue wakeup * machanism. It is called by the stored file descriptors when they * have events to report. */ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key) { int pwake = 0; unsigned long flags; struct epitem *epi = ep_item_from_wait(wait); struct eventpoll *ep = epi->ep; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: poll_callback(%p) epi=%p ep=%p\n", current, epi->file, epi, ep)); write_lock_irqsave(&ep->lock, flags); /* * If the event mask does not contain any poll(2) event, we consider the * descriptor to be disabled. This condition is likely the effect of the * EPOLLONESHOT bit that disables the descriptor when an event is received, * until the next EPOLL_CTL_MOD will be issued. */ if (!(epi->event.events & ~EP_PRIVATE_BITS)) goto is_disabled; /* If this file is already in the ready list we exit soon */ if (ep_is_linked(&epi->rdllink)) goto is_linked; list_add_tail(&epi->rdllink, &ep->rdllist); is_linked: /* * Wake up ( if active ) both the eventpoll wait list and the ->poll() * wait list. */ if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; is_disabled: write_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); return 1; } static int ep_eventpoll_close(struct inode *inode, struct file *file) { struct eventpoll *ep = file->private_data; if (ep) { ep_free(ep); kfree(ep); } DNPRINTK(3, (KERN_INFO "[%p] eventpoll: close() ep=%p\n", current, ep)); return 0; } static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait) { unsigned int pollflags = 0; unsigned long flags; struct eventpoll *ep = file->private_data; /* Insert inside our poll wait queue */ poll_wait(file, &ep->poll_wait, wait); /* Check our condition */ read_lock_irqsave(&ep->lock, flags); if (!list_empty(&ep->rdllist)) pollflags = POLLIN | POLLRDNORM; read_unlock_irqrestore(&ep->lock, flags); return pollflags; } /* * Since we have to release the lock during the __copy_to_user() operation and * during the f_op->poll() call, we try to collect the maximum number of items * by reducing the irqlock/irqunlock switching rate. */ static int ep_collect_ready_items(struct eventpoll *ep, struct list_head *txlist, int maxevents) { int nepi; unsigned long flags; struct list_head *lsthead = &ep->rdllist, *lnk; struct epitem *epi; write_lock_irqsave(&ep->lock, flags); for (nepi = 0, lnk = lsthead->next; lnk != lsthead && nepi < maxevents;) { epi = list_entry(lnk, struct epitem, rdllink); lnk = lnk->next; /* If this file is already in the ready list we exit soon */ if (!ep_is_linked(&epi->txlink)) { /* * This is initialized in this way so that the default * behaviour of the reinjecting code will be to push back * the item inside the ready list. */ epi->revents = epi->event.events; /* Link the ready item into the transfer list */ list_add(&epi->txlink, txlist); nepi++; /* * Unlink the item from the ready list. */ ep_list_del(&epi->rdllink); } } write_unlock_irqrestore(&ep->lock, flags); return nepi; } /* * This function is called without holding the "ep->lock" since the call to * __copy_to_user() might sleep, and also f_op->poll() might reenable the IRQ * because of the way poll() is traditionally implemented in Linux. */ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, struct epoll_event __user *events) { int eventcnt = 0; unsigned int revents; struct list_head *lnk; struct epitem *epi; /* * We can loop without lock because this is a task private list. * The test done during the collection loop will guarantee us that * another task will not try to collect this file. Also, items * cannot vanish during the loop because we are holding "sem". */ list_for_each(lnk, txlist) { epi = list_entry(lnk, struct epitem, txlink); /* * Get the ready file event set. We can safely use the file * because we are holding the "sem" in read and this will * guarantee that both the file and the item will not vanish. */ revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL); /* * Set the return event set for the current file descriptor. * Note that only the task task was successfully able to link * the item to its "txlist" will write this field. */ epi->revents = revents & epi->event.events; if (epi->revents) { if (__put_user(epi->revents, &events[eventcnt].events) || __put_user(epi->event.data, &events[eventcnt].data)) return -EFAULT; if (epi->event.events & EPOLLONESHOT) epi->event.events &= EP_PRIVATE_BITS; eventcnt++; } } return eventcnt; } /* * Walk through the transfer list we collected with ep_collect_ready_items() * and, if 1) the item is still "alive" 2) its event set is not empty 3) it's * not already linked, links it to the ready list. Same as above, we are holding * "sem" so items cannot vanish underneath our nose. */ static void ep_reinject_items(struct eventpoll *ep, struct list_head *txlist) { int ricnt = 0, pwake = 0; unsigned long flags; struct epitem *epi; write_lock_irqsave(&ep->lock, flags); while (!list_empty(txlist)) { epi = list_entry(txlist->next, struct epitem, txlink); /* Unlink the current item from the transfer list */ ep_list_del(&epi->txlink); /* * If the item is no more linked to the interest set, we don't * have to push it inside the ready list because the following * ep_release_epitem() is going to drop it. Also, if the current * item is set to have an Edge Triggered behaviour, we don't have * to push it back either. */ if (ep_rb_linked(&epi->rbn) && !(epi->event.events & EPOLLET) && (epi->revents & epi->event.events) && !ep_is_linked(&epi->rdllink)) { list_add_tail(&epi->rdllink, &ep->rdllist); ricnt++; } } if (ricnt) { /* * Wake up ( if active ) both the eventpoll wait list and the ->poll() * wait list. */ if (waitqueue_active(&ep->wq)) wake_up(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } write_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); } /* * Perform the transfer of events to user space. */ static int ep_events_transfer(struct eventpoll *ep, struct epoll_event __user *events, int maxevents) { int eventcnt = 0; struct list_head txlist; INIT_LIST_HEAD(&txlist); /* * We need to lock this because we could be hit by * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL). */ down_read(&ep->sem); /* Collect/extract ready items */ if (ep_collect_ready_items(ep, &txlist, maxevents) > 0) { /* Build result set in userspace */ eventcnt = ep_send_events(ep, &txlist, events); /* Reinject ready items into the ready list */ ep_reinject_items(ep, &txlist); } up_read(&ep->sem); return eventcnt; } static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, long timeout) { int res, eavail; unsigned long flags; long jtimeout; wait_queue_t wait; /* * Calculate the timeout by checking for the "infinite" value ( -1 ) * and the overflow condition. The passed timeout is in milliseconds, * that why (t * HZ) / 1000. */ jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ? MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000; retry: write_lock_irqsave(&ep->lock, flags); res = 0; if (list_empty(&ep->rdllist)) { /* * We don't have any available event to return to the caller. * We need to sleep here, and we will be wake up by * ep_poll_callback() when events will become available. */ init_waitqueue_entry(&wait, current); add_wait_queue(&ep->wq, &wait); for (;;) { /* * We don't want to sleep if the ep_poll_callback() sends us * a wakeup in between. That's why we set the task state * to TASK_INTERRUPTIBLE before doing the checks. */ set_current_state(TASK_INTERRUPTIBLE); if (!list_empty(&ep->rdllist) || !jtimeout) break; if (signal_pending(current)) { res = -EINTR; break; } write_unlock_irqrestore(&ep->lock, flags); jtimeout = schedule_timeout(jtimeout); write_lock_irqsave(&ep->lock, flags); } remove_wait_queue(&ep->wq, &wait); set_current_state(TASK_RUNNING); } /* Is it worth to try to dig for events ? */ eavail = !list_empty(&ep->rdllist); write_unlock_irqrestore(&ep->lock, flags); /* * Try to transfer events to user space. In case we get 0 events and * there's still timeout left over, we go trying again in search of * more luck. */ if (!res && eavail && !(res = ep_events_transfer(ep, events, maxevents)) && jtimeout) goto retry; return res; } static int eventpollfs_delete_dentry(struct dentry *dentry) { return 1; } static struct inode *ep_eventpoll_inode(void) { int error = -ENOMEM; struct inode *inode = new_inode(eventpoll_mnt->mnt_sb); if (!inode) goto eexit_1; inode->i_fop = &eventpoll_fops; /* * Mark the inode dirty from the very beginning, * that way it will never be moved to the dirty * list because mark_inode_dirty() will think * that it already _is_ on the dirty list. */ inode->i_state = I_DIRTY; inode->i_mode = S_IRUSR | S_IWUSR; inode->i_uid = current->fsuid; inode->i_gid = current->fsgid; inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; inode->i_blksize = PAGE_SIZE; return inode; eexit_1: return ERR_PTR(error); } static struct super_block * eventpollfs_get_sb(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { return get_sb_pseudo(fs_type, "eventpoll:", NULL, EVENTPOLLFS_MAGIC); } static int __init eventpoll_init(void) { int error; mutex_init(&epmutex); /* Initialize the structure used to perform safe poll wait head wake ups */ ep_poll_safewake_init(&psw); /* Allocates slab cache used to allocate "struct epitem" items */ epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), 0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL); /* Allocates slab cache used to allocate "struct eppoll_entry" */ pwq_cache = kmem_cache_create("eventpoll_pwq", sizeof(struct eppoll_entry), 0, EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL); /* * Register the virtual file system that will be the source of inodes * for the eventpoll files */ error = register_filesystem(&eventpoll_fs_type); if (error) goto epanic; /* Mount the above commented virtual file system */ eventpoll_mnt = kern_mount(&eventpoll_fs_type); error = PTR_ERR(eventpoll_mnt); if (IS_ERR(eventpoll_mnt)) goto epanic; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: successfully initialized.\n", current)); return 0; epanic: panic("eventpoll_init() failed\n"); } static void __exit eventpoll_exit(void) { /* Undo all operations done inside eventpoll_init() */ unregister_filesystem(&eventpoll_fs_type); mntput(eventpoll_mnt); kmem_cache_destroy(pwq_cache); kmem_cache_destroy(epi_cache); } module_init(eventpoll_init); module_exit(eventpoll_exit); MODULE_LICENSE("GPL");