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    SubjectRe: [PATCH] sys_epoll for 2.4
    Date
    > 
    > > Thanks for finding this. fs/ncpfs/sock.c is likewise broken.
    > np :)
    >
    > > The following patch compiles, but I haven't tested it.
    > also works :-)
    >
    > Thnx alot.
    >
    > ciao, Marc
    >

    Thanks for the feedback. Here's a refresh of the sys_epoll patch
    which includes the sock.c updates and a minor correction to timod.c:

    --- linux-2.4.20/arch/i386/kernel/entry.S Thu Nov 28 15:53:09 2002
    +++ sys_epoll/arch/i386/kernel/entry.S Mon Dec 16 16:24:04 2002
    @@ -657,6 +657,10 @@
    .long SYMBOL_NAME(sys_ni_syscall) /* 250 sys_alloc_hugepages */
    .long SYMBOL_NAME(sys_ni_syscall) /* sys_free_hugepages */
    .long SYMBOL_NAME(sys_ni_syscall) /* sys_exit_group */
    + .long SYMBOL_NAME(sys_ni_syscall) /* reserved for sys_lookup_dcookie */
    + .long SYMBOL_NAME(sys_epoll_create)
    + .long SYMBOL_NAME(sys_epoll_ctl) /* 255 sys_epoll_ctl */
    + .long SYMBOL_NAME(sys_epoll_wait)

    .rept NR_syscalls-(.-sys_call_table)/4
    .long SYMBOL_NAME(sys_ni_syscall)
    --- linux-2.4.20/arch/sparc64/solaris/timod.c Fri Aug 2 17:39:43 2002
    +++ sys_epoll/arch/sparc64/solaris/timod.c Mon Dec 16 16:26:08 2002
    @@ -651,10 +651,11 @@
    SOLD("LISTEN done");
    }
    if (!(filp->f_flags & O_NONBLOCK)) {
    - poll_table wait_table, *wait;
    + struct poll_wqueues wait_table;
    + poll_table *wait;

    poll_initwait(&wait_table);
    - wait = &wait_table;
    + wait = &wait_table.pt;
    for(;;) {
    SOLD("loop");
    set_current_state(TASK_INTERRUPTIBLE);
    --- linux-2.4.20/fs/Makefile Thu Nov 28 15:53:15 2002
    +++ sys_epoll/fs/Makefile Mon Dec 16 16:24:04 2002
    @@ -14,7 +14,7 @@
    super.o block_dev.o char_dev.o stat.o exec.o pipe.o namei.o \
    fcntl.o ioctl.o readdir.o select.o fifo.o locks.o \
    dcache.o inode.o attr.o bad_inode.o file.o iobuf.o dnotify.o \
    - filesystems.o namespace.o seq_file.o xattr.o
    + filesystems.o namespace.o seq_file.o xattr.o eventpoll.o

    ifeq ($(CONFIG_QUOTA),y)
    obj-y += dquot.o
    --- linux-2.4.20/fs/eventpoll.c Wed Dec 31 16:00:00 1969
    +++ sys_epoll/fs/eventpoll.c Mon Dec 16 16:24:04 2002
    @@ -0,0 +1,1624 @@
    +/*
    + * fs/eventpoll.c ( Efficent event polling implementation )
    + * Copyright (C) 2001,...,2002 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>
    + *
    + * 11 December 2002
    + * Ported from 2.5.51 - janetinc@us.ibm.com
    + *
    + */
    +
    +#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/rwsem.h>
    +#include <linux/wait.h>
    +#include <linux/eventpoll.h>
    +#include <linux/mount.h>
    +#include <asm/bitops.h>
    +#include <asm/uaccess.h>
    +#include <asm/system.h>
    +#include <asm/io.h>
    +#include <asm/mman.h>
    +#include <asm/atomic.h>
    +
    +
    +
    +#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 */
    +
    +
    +/* Maximum number of poll wake up nests we are allowing */
    +#define EP_MAX_POLLWAKE_NESTS 4
    +
    +/* Maximum size of the hash in bits ( 2^N ) */
    +#define EP_MAX_HASH_BITS 17
    +
    +/* Minimum size of the hash in bits ( 2^N ) */
    +#define EP_MIN_HASH_BITS 9
    +
    +/* Number of hash entries ( "struct list_head" ) inside a page */
    +#define EP_HENTRY_X_PAGE (PAGE_SIZE / sizeof(struct list_head))
    +
    +/* Maximum size of the hash in pages */
    +#define EP_MAX_HPAGES ((1 << EP_MAX_HASH_BITS) / EP_HENTRY_X_PAGE + 1)
    +
    +/* Number of pages allocated for an "hbits" sized hash table */
    +#define EP_HASH_PAGES(hbits) ((int) ((1 << (hbits)) / EP_HENTRY_X_PAGE + \
    + ((1 << (hbits)) % EP_HENTRY_X_PAGE ? 1: 0)))
    +
    +/* 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)
    +
    +/*
    + * Remove the item from the list and perform its initialization.
    + * This is usefull 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)
    +
    +/*
    + * This is used to optimize the event transfer to userspace. Since this
    + * is kept on stack, it should be pretty small.
    + */
    +#define EP_MAX_BUF_EVENTS 32
    +
    +/*
    + * Used to optimize ready items collection by reducing the irqlock/irqunlock
    + * switching rate. This is kept in stack too, so do not go wild with this number.
    + */
    +#define EP_MAX_COLLECT_ITEMS 64
    +
    +
    +/*
    + * 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;
    +
    + /* 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;
    +
    + /* Size of the hash */
    + unsigned int hashbits;
    +
    + /* Pages for the "struct epitem" hash */
    + char *hpages[EP_MAX_HPAGES];
    +};
    +
    +/* 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 {
    + /* List header used to link this structure to the eventpoll hash */
    + struct list_head llink;
    +
    + /* List header used to link this structure to the eventpoll ready list */
    + struct list_head rdllink;
    +
    + /* 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 file this item refers to */
    + struct file *file;
    +
    + /* 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;
    +};
    +
    +/* 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 unsigned int ep_get_hash_bits(unsigned int hintsize);
    +static int ep_getfd(int *efd, struct inode **einode, struct file **efile);
    +static int ep_alloc_pages(char **pages, int numpages);
    +static int ep_free_pages(char **pages, int numpages);
    +static int ep_file_init(struct file *file, unsigned int hashbits);
    +static unsigned int ep_hash_index(struct eventpoll *ep, struct file *file);
    +static struct list_head *ep_hash_entry(struct eventpoll *ep, unsigned int index);
    +static int ep_init(struct eventpoll *ep, unsigned int hashbits);
    +static void ep_free(struct eventpoll *ep);
    +static struct epitem *ep_find(struct eventpoll *ep, struct file *file);
    +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 int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile);
    +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);
    +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 epitem **aepi, int maxepi);
    +static int ep_send_events(struct eventpoll *ep, struct epitem **aepi, int nepi,
    + struct epoll_event *events);
    +static int ep_events_transfer(struct eventpoll *ep, struct epoll_event *events, int maxevents);
    +static int ep_poll(struct eventpoll *ep, struct epoll_event *events, int maxevents,
    + int timeout);
    +static int eventpollfs_delete_dentry(struct dentry *dentry);
    +static struct inode *ep_eventpoll_inode(void);
    +
    +
    +/* Safe wake up implementation */
    +static struct poll_safewake psw;
    +
    +/*
    + * This semaphore is used to ensure that files are not removed
    + * while epoll is using them. Namely the f_op->poll(), since
    + * it has to be called from outside the lock, must be protected.
    + * This is read-held during the event transfer loop to userspace
    + * and it is write-held during the file cleanup path and the epoll
    + * file exit code.
    + */
    +static struct rw_semaphore epsem;
    +
    +/* 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
    +};
    +
    +static int eventpollfs_statfs(struct super_block *sb, struct statfs *buf)
    +{
    + buf->f_type = EVENTPOLLFS_MAGIC;
    + buf->f_bsize = 1024;
    + buf->f_namelen = 255;
    + return 0;
    +}
    +
    +static struct super_operations eventpollfs_ops = {
    + statfs: eventpollfs_statfs,
    +};
    +
    +static struct super_block * eventpollfs_read_super(struct super_block *sb, void *data, int silent)
    +{
    + struct inode *root = new_inode(sb);
    + if (!root)
    + return NULL;
    + root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
    + root->i_uid = root->i_gid = 0;
    + root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
    + sb->s_blocksize = 1024;
    + sb->s_blocksize_bits = 10;
    + sb->s_magic = EVENTPOLLFS_MAGIC;
    + sb->s_op = &eventpollfs_ops;
    + sb->s_root = d_alloc(NULL, &(const struct qstr) {"eventpoll:", 10, 0 });
    + if (!sb->s_root) {
    + iput(root);
    + return NULL;
    + }
    + sb->s_root->d_sb = sb;
    + sb->s_root->d_parent = sb->s_root;
    + d_instantiate(sb->s_root, root);
    + return sb;
    +}
    +
    +static DECLARE_FSTYPE(eventpoll_fs_type, "eventpollfs", eventpollfs_read_super, FS_NOMOUNT);
    +
    +
    +/* 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 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) {
    + struct wake_task_node *tncur = list_entry(lnk, struct wake_task_node, llink);
    +
    + if (tncur->task == this_task) {
    + if (tncur->wq == wq || ++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);
    +}
    +
    +
    +/*
    + * Calculate the size of the hash in bits. The returned size will be
    + * bounded between EP_MIN_HASH_BITS and EP_MAX_HASH_BITS.
    + */
    +static unsigned int ep_get_hash_bits(unsigned int hintsize)
    +{
    + unsigned int i, val;
    +
    + for (i = 0, val = 1; val < hintsize && i < EP_MAX_HASH_BITS; i++, val <<= 1);
    + return i < EP_MIN_HASH_BITS ? EP_MIN_HASH_BITS: i;
    +}
    +
    +
    +/* 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 inside fs/file_table.c:__fput() 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(struct file *file)
    +{
    + struct list_head *lsthead = &file->f_ep_links;
    + struct epitem *epi;
    +
    + /*
    + * Fast check to avoid the get/release of the semaphore. Since
    + * we're doing this outside the semaphore lock, it might return
    + * false negatives, but we don't care. It'll help in 99.99% of cases
    + * to avoid the semaphore lock. False positives simply cannot happen
    + * because the file in on the way to be removed and nobody ( but
    + * eventpoll ) has still a reference to this file.
    + */
    + if (list_empty(lsthead))
    + return;
    +
    + /*
    + * 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.
    + */
    + down_write(&epsem);
    + while (!list_empty(lsthead)) {
    + epi = list_entry(lsthead->next, struct epitem, fllink);
    +
    + EP_LIST_DEL(&epi->fllink);
    + ep_remove(epi->ep, epi);
    + }
    + up_write(&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 int sys_epoll_create(int size)
    +{
    + int error, fd;
    + unsigned int hashbits;
    + struct inode *inode;
    + struct file *file;
    +
    + DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
    + current, size));
    +
    + /* Correctly size the hash */
    + hashbits = ep_get_hash_bits((unsigned int) size);
    +
    + /*
    + * 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, hashbits);
    + 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 implement the controller interface for the eventpoll
    + * file that enable the insertion/removal/change of file descriptors inside
    + * the interest set. It rapresents the kernel part of the user spcae epoll_ctl(2).
    + */
    +asmlinkage int sys_epoll_ctl(int epfd, int op, int fd, struct epoll_event *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, %u)\n",
    + current, epfd, op, fd, event->events));
    +
    + error = -EFAULT;
    + if (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;
    +
    + /*
    + * Try to lookup the file inside our hash table. When an item is found
    + * ep_find() increases the usage count of the item so that it won't
    + * desappear underneath us. The only thing that might happen, if someone
    + * tries very hard, is a double insertion of the same file descriptor.
    + * This does not rapresent a problem though and we don't really want
    + * to put an extra syncronization object to deal with this harmless condition.
    + */
    + epi = ep_find(ep, tfile);
    +
    + error = -EINVAL;
    + switch (op) {
    + case EPOLL_CTL_ADD:
    + if (!epi) {
    + epds.events |= POLLERR | POLLHUP;
    +
    + error = ep_insert(ep, &epds, tfile);
    + } 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);
    +
    +eexit_3:
    + fput(tfile);
    +eexit_2:
    + fput(file);
    +eexit_1:
    + DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %u) = %d\n",
    + current, epfd, op, fd, event->events, error));
    +
    + return error;
    +}
    +
    +
    +/*
    + * Implement the event wait interface for the eventpoll file. It is the kernel
    + * part of the user space epoll_wait(2).
    + */
    +asmlinkage int sys_epoll_wait(int epfd, struct epoll_event *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)
    + return -EINVAL;
    +
    + /* Verify that the area passed by the user is writeable */
    + if ((error = verify_area(VERIFY_WRITE, events, maxevents * 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;
    +
    + /*
    + * We have to check that the file structure underneath the file descriptor
    + * 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 = dget(dentry);
    +
    + /*
    + * Initialize the file as read/write because it could be used
    + * with write() to add/remove/change interest sets.
    + */
    + 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_alloc_pages(char **pages, int numpages)
    +{
    + int i;
    +
    + for (i = 0; i < numpages; i++) {
    + pages[i] = (char *) __get_free_pages(GFP_KERNEL, 0);
    + if (!pages[i]) {
    + for (--i; i >= 0; i--) {
    + ClearPageReserved(virt_to_page(pages[i]));
    + free_pages((unsigned long) pages[i], 0);
    + }
    + return -ENOMEM;
    + }
    + SetPageReserved(virt_to_page(pages[i]));
    + }
    + return 0;
    +}
    +
    +
    +static int ep_free_pages(char **pages, int numpages)
    +{
    + int i;
    +
    + for (i = 0; i < numpages; i++) {
    + ClearPageReserved(virt_to_page(pages[i]));
    + free_pages((unsigned long) pages[i], 0);
    + }
    + return 0;
    +}
    +
    +
    +static int ep_file_init(struct file *file, unsigned int hashbits)
    +{
    + int error;
    + struct eventpoll *ep;
    +
    + if (!(ep = kmalloc(sizeof(struct eventpoll), GFP_KERNEL)))
    + return -ENOMEM;
    +
    + memset(ep, 0, sizeof(*ep));
    +
    + error = ep_init(ep, hashbits);
    + if (error) {
    + kfree(ep);
    + return error;
    + }
    +
    + file->private_data = ep;
    +
    + DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_file_init() ep=%p\n",
    + current, ep));
    + return 0;
    +}
    +
    +
    +/*
    + * Calculate the index of the hash relative to "file".
    + */
    +static unsigned int ep_hash_index(struct eventpoll *ep, struct file *file)
    +{
    +
    + return (unsigned int) hash_ptr(file, ep->hashbits);
    +}
    +
    +
    +/*
    + * Returns the hash entry ( struct list_head * ) of the passed index.
    + */
    +static struct list_head *ep_hash_entry(struct eventpoll *ep, unsigned int index)
    +{
    +
    + return (struct list_head *) (ep->hpages[index / EP_HENTRY_X_PAGE] +
    + (index % EP_HENTRY_X_PAGE) * sizeof(struct list_head));
    +}
    +
    +
    +static int ep_init(struct eventpoll *ep, unsigned int hashbits)
    +{
    + int error;
    + unsigned int i, hsize;
    +
    + rwlock_init(&ep->lock);
    + init_waitqueue_head(&ep->wq);
    + init_waitqueue_head(&ep->poll_wait);
    + INIT_LIST_HEAD(&ep->rdllist);
    +
    + /* Hash allocation and setup */
    + ep->hashbits = hashbits;
    + error = ep_alloc_pages(ep->hpages, EP_HASH_PAGES(ep->hashbits));
    + if (error)
    + goto eexit_1;
    +
    + /* Initialize hash buckets */
    + for (i = 0, hsize = 1 << hashbits; i < hsize; i++)
    + INIT_LIST_HEAD(ep_hash_entry(ep, i));
    +
    + return 0;
    +eexit_1:
    + return error;
    +}
    +
    +
    +static void ep_free(struct eventpoll *ep)
    +{
    + unsigned int i, hsize;
    + struct list_head *lsthead, *lnk;
    +
    + /*
    + * We need to lock this because we could be hit by
    + * eventpoll_release() while we're freeing the "struct eventpoll".
    + */
    + down_write(&epsem);
    +
    + /*
    + * Walks through the whole hash by unregistering poll callbacks.
    + */
    + for (i = 0, hsize = 1 << ep->hashbits; i < hsize; i++) {
    + lsthead = ep_hash_entry(ep, i);
    +
    + list_for_each(lnk, lsthead) {
    + struct epitem *epi = list_entry(lnk, struct epitem, llink);
    +
    + 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 "epsem" we can be sure that no file cleanup code will hit
    + * us during this operation. So we can avoid the lock on "ep->lock".
    + */
    + for (i = 0, hsize = 1 << ep->hashbits; i < hsize; i++) {
    + lsthead = ep_hash_entry(ep, i);
    +
    + while (!list_empty(lsthead)) {
    + struct epitem *epi = list_entry(lsthead->next, struct epitem, llink);
    +
    + ep_remove(ep, epi);
    + }
    + }
    +
    + up_write(&epsem);
    +
    + /* Free hash pages */
    + ep_free_pages(ep->hpages, EP_HASH_PAGES(ep->hashbits));
    +}
    +
    +
    +/*
    + * 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)
    +{
    + unsigned long flags;
    + struct list_head *lsthead, *lnk;
    + struct epitem *epi = NULL;
    +
    + read_lock_irqsave(&ep->lock, flags);
    +
    + lsthead = ep_hash_entry(ep, ep_hash_index(ep, file));
    + list_for_each(lnk, lsthead) {
    + epi = list_entry(lnk, struct epitem, llink);
    +
    + if (epi->file == file) {
    + ep_use_epitem(epi);
    + break;
    + }
    + epi = NULL;
    + }
    +
    + read_unlock_irqrestore(&ep->lock, flags);
    +
    + DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n",
    + current, file, epi));
    +
    + return epi;
    +}
    +
    +
    +/*
    + * 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 occured */
    + epi->nwait = -1;
    + }
    +}
    +
    +
    +static int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile)
    +{
    + 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 ... */
    + INIT_LIST_HEAD(&epi->llink);
    + INIT_LIST_HEAD(&epi->rdllink);
    + INIT_LIST_HEAD(&epi->fllink);
    + INIT_LIST_HEAD(&epi->pwqlist);
    + epi->ep = ep;
    + epi->file = tfile;
    + 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 hash table */
    + list_add(&epi->llink, ep_hash_entry(ep, ep_hash_index(ep, tfile)));
    +
    + /* 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)\n",
    + current, ep, tfile));
    +
    + 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->file->f_op->poll(epi->file, NULL);
    +
    + write_lock_irqsave(&ep->lock, flags);
    +
    + /* Copy the data member from inside the lock */
    + epi->event.data = event->data;
    +
    + /* If the file is already "ready" we drop it inside the ready list */
    + if ((revents & event->events) && EP_IS_LINKED(&epi->llink) &&
    + !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_IS_LINKED(&epi->llink))
    + goto eexit_1;
    +
    + /*
    + * At this point is safe to do the job, unlink the item from our list.
    + * This operation togheter with the above check closes the door to
    + * double unlinks.
    + */
    + EP_LIST_DEL(&epi->llink);
    +
    + /*
    + * 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;
    +
    + /*
    + * 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(&epi->file->f_ep_lock);
    + if (EP_IS_LINKED(&epi->fllink))
    + EP_LIST_DEL(&epi->fllink);
    + spin_unlock(&epi->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, epi->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)
    +{
    + 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 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++;
    +
    + 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 epitem **aepi, int maxepi)
    +{
    + int nepi;
    + unsigned long flags;
    + struct list_head *lsthead = &ep->rdllist;
    +
    + write_lock_irqsave(&ep->lock, flags);
    +
    + for (nepi = 0; nepi < maxepi && !list_empty(lsthead);) {
    + struct epitem *epi = list_entry(lsthead->next, struct epitem, rdllink);
    +
    + /* Remove the item from the ready list */
    + EP_LIST_DEL(&epi->rdllink);
    +
    + /*
    + * We need to increase the usage count of the "struct epitem" because
    + * another thread might call EPOLL_CTL_DEL on this target and make the
    + * object to vanish underneath our nose.
    + */
    + ep_use_epitem(epi);
    +
    + aepi[nepi++] = epi;
    + }
    +
    + 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 epitem **aepi, int nepi,
    + struct epoll_event *events)
    +{
    + int i, eventcnt, eventbuf, revents;
    + struct epitem *epi;
    + struct epoll_event event[EP_MAX_BUF_EVENTS];
    +
    + for (i = 0, eventcnt = 0, eventbuf = 0; i < nepi; i++, aepi++) {
    + epi = *aepi;
    +
    + /* Get the ready file event set */
    + revents = epi->file->f_op->poll(epi->file, NULL);
    +
    + if (revents & epi->event.events) {
    + event[eventbuf] = epi->event;
    + event[eventbuf].events &= revents;
    + eventbuf++;
    + if (eventbuf == EP_MAX_BUF_EVENTS) {
    + if (__copy_to_user(&events[eventcnt], event,
    + eventbuf * sizeof(struct epoll_event))) {
    + for (; i < nepi; i++, aepi++)
    + ep_release_epitem(*aepi);
    + return -EFAULT;
    + }
    + eventcnt += eventbuf;
    + eventbuf = 0;
    + }
    + }
    +
    + ep_release_epitem(epi);
    + }
    +
    + if (eventbuf) {
    + if (__copy_to_user(&events[eventcnt], event,
    + eventbuf * sizeof(struct epoll_event)))
    + return -EFAULT;
    + eventcnt += eventbuf;
    + }
    +
    + return eventcnt;
    +}
    +
    +
    +/*
    + * Perform the transfer of events to user space.
    + */
    +static int ep_events_transfer(struct eventpoll *ep, struct epoll_event *events, int maxevents)
    +{
    + int eventcnt, nepi, sepi, maxepi;
    + struct epitem *aepi[EP_MAX_COLLECT_ITEMS];
    +
    + /*
    + * We need to lock this because we could be hit by
    + * eventpoll_release() while we're transfering
    + * events to userspace. Read-holding "epsem" will lock
    + * out eventpoll_release() during the whole
    + * transfer loop and this will garantie us that the
    + * file will not vanish underneath our nose when
    + * we will call f_op->poll() from ep_send_events().
    + */
    + down_read(&epsem);
    +
    + for (eventcnt = 0; eventcnt < maxevents;) {
    + /* Maximum items we can extract this time */
    + maxepi = min(EP_MAX_COLLECT_ITEMS, maxevents - eventcnt);
    +
    + /* Collect/extract ready items */
    + nepi = ep_collect_ready_items(ep, aepi, maxepi);
    +
    + if (nepi) {
    + /* Send events to userspace */
    + sepi = ep_send_events(ep, aepi, nepi, &events[eventcnt]);
    + if (sepi < 0) {
    + up_read(&epsem);
    + return sepi;
    + }
    + eventcnt += sepi;
    + }
    +
    + if (nepi < maxepi)
    + break;
    + }
    +
    + up_read(&epsem);
    +
    + return eventcnt;
    +}
    +
    +
    +static int ep_poll(struct eventpoll *ep, struct epoll_event *events, int maxevents,
    + int timeout)
    +{
    + int res, eavail;
    + unsigned long flags;
    + long jtimeout;
    + wait_queue_t wait;
    +
    + /*
    + * Calculate the timeout by checking for the "infinite" value ( -1 ).
    + * The passed timeout is in milliseconds, that why (t * HZ) / 1000.
    + */
    + jtimeout = timeout == -1 ? MAX_SCHEDULE_TIMEOUT: (timeout * HZ) / 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 int __init eventpoll_init(void)
    +{
    + int error;
    +
    + /* Initialize the semaphore used to syncronize the file cleanup code */
    + init_rwsem(&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 */
    + error = -ENOMEM;
    + epi_cache = kmem_cache_create("eventpoll epi",
    + sizeof(struct epitem),
    + 0,
    + SLAB_HWCACHE_ALIGN | EPI_SLAB_DEBUG, NULL, NULL);
    + if (!epi_cache)
    + goto eexit_1;
    +
    + /* Allocates slab cache used to allocate "struct eppoll_entry" */
    + error = -ENOMEM;
    + pwq_cache = kmem_cache_create("eventpoll pwq",
    + sizeof(struct eppoll_entry),
    + 0,
    + EPI_SLAB_DEBUG, NULL, NULL);
    + if (!pwq_cache)
    + goto eexit_2;
    +
    + /*
    + * 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 eexit_3;
    +
    + /* 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 eexit_4;
    +
    + return 0;
    +
    +eexit_4:
    + unregister_filesystem(&eventpoll_fs_type);
    +eexit_3:
    + kmem_cache_destroy(pwq_cache);
    +eexit_2:
    + kmem_cache_destroy(epi_cache);
    +eexit_1:
    +
    + return error;
    +}
    +
    +
    +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");
    +
    --- linux-2.4.20/fs/file_table.c Thu Nov 28 15:53:15 2002
    +++ sys_epoll/fs/file_table.c Mon Dec 16 16:24:04 2002
    @@ -12,6 +12,7 @@
    #include <linux/module.h>
    #include <linux/smp_lock.h>
    #include <linux/iobuf.h>
    +#include <linux/eventpoll.h>

    /* sysctl tunables... */
    struct files_stat_struct files_stat = {0, 0, NR_FILE};
    @@ -42,6 +43,7 @@
    files_stat.nr_free_files--;
    new_one:
    memset(f, 0, sizeof(*f));
    + eventpoll_init_file(f);
    atomic_set(&f->f_count,1);
    f->f_version = ++event;
    f->f_uid = current->fsuid;
    @@ -85,6 +87,7 @@
    int init_private_file(struct file *filp, struct dentry *dentry, int mode)
    {
    memset(filp, 0, sizeof(*filp));
    + eventpoll_init_file(filp);
    filp->f_mode = mode;
    atomic_set(&filp->f_count, 1);
    filp->f_dentry = dentry;
    @@ -104,6 +107,11 @@
    struct inode * inode = dentry->d_inode;

    if (atomic_dec_and_test(&file->f_count)) {
    + /*
    + * The function eventpoll_release() should be the
    + * first called in the file cleanup chain.
    + */
    + eventpoll_release(file);
    locks_remove_flock(file);

    if (file->f_iobuf)
    --- linux-2.4.20/fs/select.c Mon Sep 10 13:04:33 2001
    +++ sys_epoll/fs/select.c Mon Dec 16 16:24:04 2002
    @@ -19,6 +19,7 @@
    #include <linux/poll.h>
    #include <linux/personality.h> /* for STICKY_TIMEOUTS */
    #include <linux/file.h>
    +#include <linux/fs.h>

    #include <asm/uaccess.h>

    @@ -52,10 +53,18 @@
    * as all select/poll functions have to call it to add an entry to the
    * poll table.
    */
    +void __pollwait(struct file *filp, wait_queue_head_t *wait_address, poll_table *p);

    -void poll_freewait(poll_table* pt)
    +void poll_initwait(struct poll_wqueues *pwq)
    {
    - struct poll_table_page * p = pt->table;
    + init_poll_funcptr(&pwq->pt, __pollwait);
    + pwq->error = 0;
    + pwq->table = NULL;
    +}
    +
    +void poll_freewait(struct poll_wqueues *pwq)
    +{
    + struct poll_table_page * p = pwq->table;
    while (p) {
    struct poll_table_entry * entry;
    struct poll_table_page *old;
    @@ -72,8 +81,9 @@
    }
    }

    -void __pollwait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
    +void __pollwait(struct file *filp, wait_queue_head_t *wait_address, poll_table *_p)
    {
    + struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
    struct poll_table_page *table = p->table;

    if (!table || POLL_TABLE_FULL(table)) {
    @@ -103,6 +113,7 @@
    }
    }

    +
    #define __IN(fds, n) (fds->in + n)
    #define __OUT(fds, n) (fds->out + n)
    #define __EX(fds, n) (fds->ex + n)
    @@ -163,7 +174,8 @@

    int do_select(int n, fd_set_bits *fds, long *timeout)
    {
    - poll_table table, *wait;
    + struct poll_wqueues table;
    + poll_table *wait;
    int retval, i, off;
    long __timeout = *timeout;

    @@ -176,7 +188,7 @@
    n = retval;

    poll_initwait(&table);
    - wait = &table;
    + wait = &table.pt;
    if (!__timeout)
    wait = NULL;
    retval = 0;
    @@ -383,10 +395,10 @@
    }

    static int do_poll(unsigned int nfds, unsigned int nchunks, unsigned int nleft,
    - struct pollfd *fds[], poll_table *wait, long timeout)
    + struct pollfd *fds[], struct poll_wqueues *wait, long timeout)
    {
    int count;
    - poll_table* pt = wait;
    + poll_table* pt = &wait->pt;

    for (;;) {
    unsigned int i;
    @@ -413,7 +425,7 @@
    {
    int i, j, fdcount, err;
    struct pollfd **fds;
    - poll_table table, *wait;
    + struct poll_wqueues table, *wait;
    int nchunks, nleft;

    /* Do a sanity check on nfds ... */
    --- linux-2.4.20/include/asm-i386/unistd.h Thu Nov 28 15:53:15 2002
    +++ sys_epoll/include/asm-i386/unistd.h Mon Dec 16 16:24:04 2002
    @@ -257,6 +257,10 @@
    #define __NR_alloc_hugepages 250
    #define __NR_free_hugepages 251
    #define __NR_exit_group 252
    +#define __NR_epoll_create 254
    +#define __NR_epoll_ctl 255
    +#define __NR_epoll_wait 256
    +

    /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */

    --- linux-2.4.20/include/asm-ppc/unistd.h Thu Nov 28 15:53:15 2002
    +++ sys_epoll/include/asm-ppc/unistd.h Mon Dec 16 16:24:04 2002
    @@ -241,6 +241,9 @@
    #define __NR_io_submit 230
    #define __NR_io_cancel 231
    #endif
    +#define __NR_epoll_create 254
    +#define __NR_epoll_ctl 255
    +#define __NR_epoll_wait 256

    #define __NR(n) #n

    --- linux-2.4.20/include/linux/eventpoll.h Wed Dec 31 16:00:00 1969
    +++ sys_epoll/include/linux/eventpoll.h Mon Dec 16 16:24:04 2002
    @@ -0,0 +1,49 @@
    +/*
    + * include/linux/eventpoll.h ( Efficent event polling implementation )
    + * Copyright (C) 2001,...,2002 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>
    + *
    + */
    +
    +#ifndef _LINUX_EVENTPOLL_H
    +#define _LINUX_EVENTPOLL_H
    +
    +
    +/* Valid opcodes to issue to sys_epoll_ctl() */
    +#define EPOLL_CTL_ADD 1
    +#define EPOLL_CTL_DEL 2
    +#define EPOLL_CTL_MOD 3
    +
    +struct epoll_event {
    + __u32 events;
    + __u64 data;
    +};
    +
    +#ifdef __KERNEL__
    +
    +/* Forward declarations to avoid compiler errors */
    +struct file;
    +
    +
    +/* Kernel space functions implementing the user space "epoll" API */
    +asmlinkage int sys_epoll_create(int size);
    +asmlinkage int sys_epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
    +asmlinkage int sys_epoll_wait(int epfd, struct epoll_event *events, int maxevents,
    + int timeout);
    +
    +/* Used to initialize the epoll bits inside the "struct file" */
    +void eventpoll_init_file(struct file *file);
    +
    +/* Used in fs/file_table.c:__fput() to unlink files from the eventpoll interface */
    +void eventpoll_release(struct file *file);
    +
    +#endif /* #ifdef __KERNEL__ */
    +
    +#endif /* #ifndef _LINUX_EVENTPOLL_H */
    +
    --- linux-2.4.20/include/linux/fs.h Thu Nov 28 15:53:15 2002
    +++ sys_epoll/include/linux/fs.h Mon Dec 16 16:24:04 2002
    @@ -542,6 +542,8 @@
    /* preallocated helper kiobuf to speedup O_DIRECT */
    struct kiobuf *f_iobuf;
    long f_iobuf_lock;
    + struct list_head f_ep_links;
    + spinlock_t f_ep_lock;
    };
    extern spinlock_t files_lock;
    #define file_list_lock() spin_lock(&files_lock);
    --- linux-2.4.20/include/linux/hash.h Wed Dec 31 16:00:00 1969
    +++ sys_epoll/include/linux/hash.h Mon Dec 16 16:24:04 2002
    @@ -0,0 +1,58 @@
    +#ifndef _LINUX_HASH_H
    +#define _LINUX_HASH_H
    +/* Fast hashing routine for a long.
    + (C) 2002 William Lee Irwin III, IBM */
    +
    +/*
    + * Knuth recommends primes in approximately golden ratio to the maximum
    + * integer representable by a machine word for multiplicative hashing.
    + * Chuck Lever verified the effectiveness of this technique:
    + * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
    + *
    + * These primes are chosen to be bit-sparse, that is operations on
    + * them can use shifts and additions instead of multiplications for
    + * machines where multiplications are slow.
    + */
    +#if BITS_PER_LONG == 32
    +/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
    +#define GOLDEN_RATIO_PRIME 0x9e370001UL
    +#elif BITS_PER_LONG == 64
    +/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
    +#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
    +#else
    +#error Define GOLDEN_RATIO_PRIME for your wordsize.
    +#endif
    +
    +static inline unsigned long hash_long(unsigned long val, unsigned int bits)
    +{
    + unsigned long hash = val;
    +
    +#if BITS_PER_LONG == 64
    + /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
    + unsigned long n = hash;
    + n <<= 18;
    + hash -= n;
    + n <<= 33;
    + hash -= n;
    + n <<= 3;
    + hash += n;
    + n <<= 3;
    + hash -= n;
    + n <<= 4;
    + hash += n;
    + n <<= 2;
    + hash += n;
    +#else
    + /* On some cpus multiply is faster, on others gcc will do shifts */
    + hash *= GOLDEN_RATIO_PRIME;
    +#endif
    +
    + /* High bits are more random, so use them. */
    + return hash >> (BITS_PER_LONG - bits);
    +}
    +
    +static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
    +{
    + return hash_long((unsigned long)ptr, bits);
    +}
    +#endif /* _LINUX_HASH_H */
    --- linux-2.4.20/include/linux/kernel.h Thu Nov 28 15:53:15 2002
    +++ sys_epoll/include/linux/kernel.h Mon Dec 16 16:24:04 2002
    @@ -174,6 +174,18 @@
    extern void __out_of_line_bug(int line) ATTRIB_NORET;
    #define out_of_line_bug() __out_of_line_bug(__LINE__)

    +/**
    + * container_of - cast a member of a structure out to the containing structure
    + *
    + * @ptr: the pointer to the member.
    + * @type: the type of the container struct this is embedded in.
    + * @member: the name of the member within the struct.
    + *
    + */
    +#define container_of(ptr, type, member) ({ \
    + const typeof( ((type *)0)->member ) *__mptr = (ptr); \
    + (type *)( (char *)__mptr - offsetof(type,member) );})
    +
    #endif /* __KERNEL__ */

    #define SI_LOAD_SHIFT 16
    --- linux-2.4.20/include/linux/poll.h Thu Nov 22 11:46:26 2001
    +++ sys_epoll/include/linux/poll.h Mon Dec 16 16:24:04 2002
    @@ -10,28 +10,39 @@
    #include <linux/mm.h>
    #include <asm/uaccess.h>

    -struct poll_table_page;
    +struct poll_table_struct;
    +
    +/*
    + * structures and helpers for f_op->poll implementations
    + */
    +typedef void (*poll_queue_proc)(struct file *, wait_queue_head_t *, struct poll_table_struct *);

    typedef struct poll_table_struct {
    - int error;
    - struct poll_table_page * table;
    + poll_queue_proc qproc;
    } poll_table;

    -extern void __pollwait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p);
    -
    static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
    {
    if (p && wait_address)
    - __pollwait(filp, wait_address, p);
    + p->qproc(filp, wait_address, p);
    }

    -static inline void poll_initwait(poll_table* pt)
    +static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc)
    {
    - pt->error = 0;
    - pt->table = NULL;
    + pt->qproc = qproc;
    }
    -extern void poll_freewait(poll_table* pt);

    +/*
    + * Structures and helpers for sys_poll/sys_poll
    + */
    +struct poll_wqueues {
    + poll_table pt;
    + struct poll_table_page * table;
    + int error;
    +};
    +
    +extern void poll_initwait(struct poll_wqueues *pwq);
    +extern void poll_freewait(struct poll_wqueues *pwq);

    /*
    * Scaleable version of the fd_set.
    --- linux-2.4.20/include/linux/sched.h Thu Nov 28 15:53:15 2002
    +++ sys_epoll/include/linux/sched.h Mon Dec 16 16:24:04 2002
    @@ -145,6 +145,8 @@
    extern spinlock_t runqueue_lock;
    extern spinlock_t mmlist_lock;

    +typedef struct task_struct task_t;
    +
    extern void sched_init(void);
    extern void init_idle(void);
    extern void show_state(void);
    --- linux-2.4.20/include/linux/sys.h Sun Dec 10 20:56:37 1995
    +++ sys_epoll/include/linux/sys.h Mon Dec 16 16:24:04 2002
    @@ -4,7 +4,7 @@
    /*
    * system call entry points ... but not all are defined
    */
    -#define NR_syscalls 256
    +#define NR_syscalls 260

    /*
    * These are system calls that will be removed at some time
    --- linux-2.4.20/include/linux/wait.h Thu Nov 22 11:46:19 2001
    +++ sys_epoll/include/linux/wait.h Mon Dec 16 16:24:04 2002
    @@ -19,6 +19,9 @@
    #include <asm/page.h>
    #include <asm/processor.h>

    +typedef struct __wait_queue wait_queue_t;
    +typedef void (*wait_queue_func_t)(wait_queue_t *wait);
    +
    /*
    * Debug control. Slow but useful.
    */
    @@ -32,13 +35,13 @@
    unsigned int flags;
    #define WQ_FLAG_EXCLUSIVE 0x01
    struct task_struct * task;
    + wait_queue_func_t func;
    struct list_head task_list;
    #if WAITQUEUE_DEBUG
    long __magic;
    long __waker;
    #endif
    };
    -typedef struct __wait_queue wait_queue_t;

    /*
    * 'dual' spinlock architecture. Can be switched between spinlock_t and
    @@ -138,6 +141,7 @@

    #define __WAITQUEUE_INITIALIZER(name, tsk) { \
    task: tsk, \
    + func: NULL, \
    task_list: { NULL, NULL }, \
    __WAITQUEUE_DEBUG_INIT(name)}

    @@ -174,10 +178,18 @@
    #endif
    q->flags = 0;
    q->task = p;
    + q->func = NULL;
    #if WAITQUEUE_DEBUG
    q->__magic = (long)&q->__magic;
    #endif
    }
    +static inline void init_waitqueue_func_entry(wait_queue_t *q,
    + wait_queue_func_t func)
    +{
    + q->flags = 0;
    + q->task = NULL;
    + q->func = func;
    +}

    static inline int waitqueue_active(wait_queue_head_t *q)
    {
    @@ -189,6 +201,22 @@

    return !list_empty(&q->task_list);
    }
    +#define add_wait_queue_cond(q, wait, cond) \
    + ({ \
    + unsigned long flags; \
    + int _raced = 0; \
    + wq_write_lock_irqsave(&(q)->lock, flags); \
    + (wait)->flags = 0; \
    + __add_wait_queue((q), (wait)); \
    + rmb(); \
    + if (!(cond)) { \
    + _raced = 1; \
    + __remove_wait_queue((q), (wait)); \
    + } \
    + wq_write_unlock_irqrestore(&(q)->lock, flags); \
    + _raced; \
    + })
    +

    static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new)
    {
    --- linux-2.4.20/kernel/ksyms.c Thu Nov 28 15:53:15 2002
    +++ sys_epoll/kernel/ksyms.c Mon Dec 16 16:24:04 2002
    @@ -257,7 +257,7 @@
    EXPORT_SYMBOL(generic_read_dir);
    EXPORT_SYMBOL(generic_file_llseek);
    EXPORT_SYMBOL(no_llseek);
    -EXPORT_SYMBOL(__pollwait);
    +EXPORT_SYMBOL(poll_initwait);
    EXPORT_SYMBOL(poll_freewait);
    EXPORT_SYMBOL(ROOT_DEV);
    EXPORT_SYMBOL(__find_get_page);
    --- linux-2.4.20/kernel/sched.c Thu Nov 28 15:53:15 2002
    +++ sys_epoll/kernel/sched.c Mon Dec 16 16:24:04 2002
    @@ -714,16 +714,24 @@
    static inline void __wake_up_common (wait_queue_head_t *q, unsigned int mode,
    int nr_exclusive, const int sync)
    {
    - struct list_head *tmp;
    + struct list_head *tmp, *next;
    struct task_struct *p;

    CHECK_MAGIC_WQHEAD(q);
    WQ_CHECK_LIST_HEAD(&q->task_list);

    - list_for_each(tmp,&q->task_list) {
    + list_for_each_safe(tmp, next, &q->task_list) {
    unsigned int state;
    + wait_queue_func_t func;
    wait_queue_t *curr = list_entry(tmp, wait_queue_t, task_list);
    -
    + func = curr->func;
    + if (func) {
    + unsigned flags = curr->flags;
    + func(curr);
    + if ((flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
    + break;
    + continue;
    + }
    CHECK_MAGIC(curr->__magic);
    p = curr->task;
    state = p->state;
    --- linux-2.4.20/fs/smbfs/sock.c Thu Nov 28 15:53:15 2002
    +++ sys_epoll/fs/smbfs/sock.c Mon Dec 16 16:24:29 2002
    @@ -314,16 +314,18 @@
    smb_receive_poll(struct smb_sb_info *server)
    {
    struct file *file = server->sock_file;
    - poll_table wait_table;
    + struct poll_wqueues wait_table;
    + poll_table *wait;
    int result = 0;
    int timeout = server->mnt->timeo * HZ;
    int mask;

    for (;;) {
    poll_initwait(&wait_table);
    + wait = &wait_table.pt;
    set_current_state(TASK_INTERRUPTIBLE);

    - mask = file->f_op->poll(file, &wait_table);
    + mask = file->f_op->poll(file, wait);
    if (mask & POLLIN) {
    poll_freewait(&wait_table);
    current->state = TASK_RUNNING;
    --- linux-2.4.20/fs/ncpfs/sock.c Sat Jan 20 08:51:51 2001
    +++ sys_epoll/fs/ncpfs/sock.c Mon Dec 16 16:24:29 2002
    @@ -86,7 +86,8 @@
    struct socket *sock;
    int result;
    char *start = server->packet;
    - poll_table wait_table;
    + struct poll_wqueues wait_table;
    + poll_table *wait;
    int init_timeout, max_timeout;
    int timeout;
    int retrans;
    @@ -136,11 +137,12 @@
    }
    re_select:
    poll_initwait(&wait_table);
    + wait = &wait_table.pt;
    /* mb() is not necessary because ->poll() will serialize
    instructions adding the wait_table waitqueues in the
    waitqueue-head before going to calculate the mask-retval. */
    __set_current_state(TASK_INTERRUPTIBLE);
    - if (!(sock->ops->poll(file, sock, &wait_table) & POLLIN)) {
    + if (!(sock->ops->poll(file, sock, wait) & POLLIN)) {
    int timed_out;
    if (timeout > max_timeout) {
    /* JEJB/JSP 2/7/94
    @@ -261,7 +263,8 @@
    }

    static int do_tcp_rcv(struct ncp_server *server, void *buffer, size_t len) {
    - poll_table wait_table;
    + struct poll_wqueues wait_table;
    + poll_table *wait;
    struct file *file;
    struct socket *sock;
    int init_timeout;
    @@ -281,11 +284,12 @@

    while (len) {
    poll_initwait(&wait_table);
    + wait = &wait_table.pt;
    /* mb() is not necessary because ->poll() will serialize
    instructions adding the wait_table waitqueues in the
    waitqueue-head before going to calculate the mask-retval. */
    __set_current_state(TASK_INTERRUPTIBLE);
    - if (!(sock->ops->poll(file, sock, &wait_table) & POLLIN)) {
    + if (!(sock->ops->poll(file, sock, wait) & POLLIN)) {
    init_timeout = schedule_timeout(init_timeout);
    poll_freewait(&wait_table);
    current->state = TASK_RUNNING;
    -
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