Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1639 insertions, 0 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
new file mode 100644
index 000000000000..05b966cd6f76
--- /dev/null
+++ b/fs/eventpoll.c
@@ -0,0 +1,1639 @@
+/*
+ *  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 <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) epsem (semaphore)
+ * 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 "epsem" (together with "ep->lock") to have it working,
+ * but having "ep->sem" will make the interface more scalable.
+ * Events that require holding "epsem" 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
+
+/* Macro to allocate a "struct epitem" from the slab cache */
+#define EPI_MEM_ALLOC() (struct epitem *) kmem_cache_alloc(epi_cache, SLAB_KERNEL)
+
+/* Macro to free a "struct epitem" to the slab cache */
+#define EPI_MEM_FREE(p) kmem_cache_free(epi_cache, p)
+
+/* Macro to allocate a "struct eppoll_entry" from the slab cache */
+#define PWQ_MEM_ALLOC() (struct eppoll_entry *) kmem_cache_alloc(pwq_cache, SLAB_KERNEL)
+
+/* Macro to free a "struct eppoll_entry" to the slab cache */
+#define PWQ_MEM_FREE(p) kmem_cache_free(pwq_cache, p)
+
+/* Fast test to see if the file is an evenpoll file */
+#define IS_FILE_EPOLL(f) ((f)->f_op == &eventpoll_fops)
+
+/* Setup the structure that is used as key for the rb-tree */
+#define EP_SET_FFD(p, f, d) do { (p)->file = (f); (p)->fd = (d); } while (0)
+
+/* Compare rb-tree keys */
+#define EP_CMP_FFD(p1, p2) ((p1)->file > (p2)->file ? +1: \
+                            ((p1)->file < (p2)->file ? -1: (p1)->fd - (p2)->fd))
+
+/* Special initialization for the rb-tree node to detect linkage */
+#define EP_RB_INITNODE(n) (n)->rb_parent = (n)
+
+/* Removes a node from the rb-tree and marks it for a fast is-linked check */
+#define EP_RB_ERASE(n, r) do { rb_erase(n, r); (n)->rb_parent = (n); } while (0)
+
+/* Fast check to verify that the item is linked to the main rb-tree */
+#define EP_RB_LINKED(n) ((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)".
+ */
+#define EP_LIST_DEL(p) do { list_del(p); INIT_LIST_HEAD(p); } while (0)
+
+/* Tells us if the item is currently linked */
+#define EP_IS_LINKED(p) (!list_empty(p))
+
+/* Get the "struct epitem" from a wait queue pointer */
+#define EP_ITEM_FROM_WAIT(p) ((struct epitem *) container_of(p, struct eppoll_entry, wait)->base)
+
+/* Get the "struct epitem" from an epoll queue wrapper */
+#define EP_ITEM_FROM_EPQUEUE(p) (container_of(p, struct ep_pqueue, pt)->epi)
+
+/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
+#define EP_OP_HASH_EVENT(op) ((op) != EPOLL_CTL_DEL)
+
+
+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);
+static int ep_file_init(struct file *file);
+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().
+ */
+struct semaphore epsem;
+
+/* Safe wake up implementation */
+static struct poll_safewake psw;
+
+/* Slab cache used to allocate "struct epitem" */
+static kmem_cache_t *epi_cache;
+
+/* Slab cache used to allocate "struct eppoll_entry" */
+static kmem_cache_t *pwq_cache;
+
+/* Virtual fs used to allocate inodes for eventpoll files */
+static struct vfsmount *eventpoll_mnt;
+
+/* 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,
+};
+
+
+
+/* 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);
+}
+
+
+/* Used to initialize the epoll bits inside the "struct file" */
+void eventpoll_init_file(struct file *file)
+{
+
+        INIT_LIST_HEAD(&file->f_ep_links);
+        spin_lock_init(&file->f_ep_lock);
+}
+
+
+/*
+ * 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 "epsem" because ep_remove() requires it when called
+         * from anywhere but ep_free().
+         */
+        down(&epsem);
+
+        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);
+        }
+
+        up(&epsem);
+}
+
+
+/*
+ * 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 inode *inode;
+        struct file *file;
+
+        DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
+                     current, size));
+
+        /* Sanity check on the size parameter */
+        error = -EINVAL;
+        if (size <= 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);
+        if (error)
+                goto eexit_1;
+
+        /* Setup the file internal data structure ( "struct eventpoll" ) */
+        error = ep_file_init(file);
+        if (error)
+                goto eexit_2;
+
+
+        DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
+                     current, size, fd));
+
+        return fd;
+
+eexit_2:
+        sys_close(fd);
+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;
+
+                        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;
+                        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 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 = NULL;
+
+        /* 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_file_init(struct file *file)
+{
+        struct eventpoll *ep;
+
+        if (!(ep = kmalloc(sizeof(struct eventpoll), GFP_KERNEL)))
+                return -ENOMEM;
+
+        memset(ep, 0, sizeof(*ep));
+        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;
+
+        file->private_data = ep;
+
+        DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_file_init() 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 "epsem" is sufficent here.
+         */
+        down(&epsem);
+
+        /*
+         * 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);
+        }
+
+        up(&epsem);
+}
+
+
+/*
+ * 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))
+                EPI_MEM_FREE(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 = PWQ_MEM_ALLOC())) {
+                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 = EPI_MEM_ALLOC()))
+                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);
+
+        EPI_MEM_FREE(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);
+                        PWQ_MEM_FREE(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 == -1 || timeout > (MAX_SCHEDULE_TIMEOUT - 1000) / HZ ?
+                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;
+
+        init_MUTEX(&epsem);
+
+        /* 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");