JDK源码分析 NIO实现

总列表：http://hg.openjdk.java.net/

小版本：http://hg.openjdk.java.net/jdk8u

jdk:http://hg.openjdk.java.net/jdk8u/jdk8u60/file/d8f4022fe0cd

hotspot:http://hg.openjdk.java.net/jdk8u/jdk8u60/hotspot/file/37240c1019fd

调用本地native方法

package sun.nio.ch;
public class IOUtil {
...
public static native void configureBlocking(FileDescriptor var0, boolean var1) throws IOException;

对应jdk文件位置：

https://blog.csdn.net/wangyangzhizhou/article/details/42613273

https://www.cnblogs.com/binarylei/p/11142083.html

EPoll.c

JNIEXPORT jint JNICALL
Java_sun_nio_ch_EPoll_epollWait(JNIEnv *env, jclass c,jint epfd, jlong address, jint numfds)
{struct epoll_event *events = jlong_to_ptr(address);int res;RESTARTABLE(epoll_wait(epfd, events, numfds, -1), res);if (res < 0) {JNU_ThrowIOExceptionWithLastError(env, "epoll_wait failed");}return res;
}

这种情况在同一层可以省略EPoll，否则是找不到的

package sun.nio.ch
class EPollArrayWrapper{private native int epollCreate();private native void epollCtl(int epfd, int opcode, int fd, int events);private native int epollWait(long pollAddress, int numfds, long timeout,int epfd) throws IOException;private static native int sizeofEPollEvent();private static native int offsetofData();private static native void interrupt(int fd);private static native void init();}

void initInterrupt(int fd0, int fd1) {outgoingInterruptFD = fd1;incomingInterruptFD = fd0;epollCtl(epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);}int poll(long timeout) throws IOException {updateRegistrations();updated = epollWait(pollArrayAddress, NUM_EPOLLEVENTS, timeout, epfd);for (int i=0; i<updated; i++) {if (getDescriptor(i) == incomingInterruptFD) {interruptedIndex = i;interrupted = true;break;}}return updated;}

调用方

  package sun.nio.ch;
class EPollSelectorImpl{/*** Package private constructor called by factory method in* the abstract superclass Selector.*/EPollSelectorImpl(SelectorProvider sp) throws IOException {super(sp);long pipeFds = IOUtil.makePipe(false);fd0 = (int) (pipeFds >>> 32);fd1 = (int) pipeFds;pollWrapper = new EPollArrayWrapper();pollWrapper.initInterrupt(fd0, fd1);fdToKey = new HashMap<>();}protected int doSelect(long timeout) throws IOException {if (closed)throw new ClosedSelectorException();processDeregisterQueue();try {begin();pollWrapper.poll(timeout);} finally {end();}processDeregisterQueue();int numKeysUpdated = updateSelectedKeys();if (pollWrapper.interrupted()) {// Clear the wakeup pipepollWrapper.putEventOps(pollWrapper.interruptedIndex(), 0);synchronized (interruptLock) {pollWrapper.clearInterrupted();IOUtil.drain(fd0);interruptTriggered = false;}}return numKeysUpdated;}
}

https://www.cnblogs.com/Jack-Blog/p/12394487.html

注意：epoll_wait在 \glibc-2.31\sysdeps\unix\sysv\linux\sys\epoll.h

glibc是gnu发布的libc库，也即c运行库。glibc是linux 系统中最底层的api（应用程序开发接口），几乎其它任何的运行库都会倚赖于glibc。

/* Copyright (C) 2002-2020 Free Software Foundation, Inc.This file is part of the GNU C Library.The GNU C Library is free software; you can redistribute it and/ormodify it under the terms of the GNU Lesser General PublicLicense as published by the Free Software Foundation; eitherversion 2.1 of the License, or (at your option) any later version.The GNU C Library is distributed in the hope that it will be useful,but WITHOUT ANY WARRANTY; without even the implied warranty ofMERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNULesser General Public License for more details.You should have received a copy of the GNU Lesser General PublicLicense along with the GNU C Library; if not, see<https://www.gnu.org/licenses/>.  */#ifndef	_SYS_EPOLL_H
#define	_SYS_EPOLL_H	1#include <stdint.h>
#include <sys/types.h>#include <bits/types/sigset_t.h>/* Get the platform-dependent flags.  */
#include <bits/epoll.h>#ifndef __EPOLL_PACKED
# define __EPOLL_PACKED
#endifenum EPOLL_EVENTS{EPOLLIN = 0x001,
#define EPOLLIN EPOLLINEPOLLPRI = 0x002,
#define EPOLLPRI EPOLLPRIEPOLLOUT = 0x004,
#define EPOLLOUT EPOLLOUTEPOLLRDNORM = 0x040,
#define EPOLLRDNORM EPOLLRDNORMEPOLLRDBAND = 0x080,
#define EPOLLRDBAND EPOLLRDBANDEPOLLWRNORM = 0x100,
#define EPOLLWRNORM EPOLLWRNORMEPOLLWRBAND = 0x200,
#define EPOLLWRBAND EPOLLWRBANDEPOLLMSG = 0x400,
#define EPOLLMSG EPOLLMSGEPOLLERR = 0x008,
#define EPOLLERR EPOLLERREPOLLHUP = 0x010,
#define EPOLLHUP EPOLLHUPEPOLLRDHUP = 0x2000,
#define EPOLLRDHUP EPOLLRDHUPEPOLLEXCLUSIVE = 1u << 28,
#define EPOLLEXCLUSIVE EPOLLEXCLUSIVEEPOLLWAKEUP = 1u << 29,
#define EPOLLWAKEUP EPOLLWAKEUPEPOLLONESHOT = 1u << 30,
#define EPOLLONESHOT EPOLLONESHOTEPOLLET = 1u << 31
#define EPOLLET EPOLLET};/* Valid opcodes ( "op" parameter ) to issue to epoll_ctl().  */
#define EPOLL_CTL_ADD 1	/* Add a file descriptor to the interface.  */
#define EPOLL_CTL_DEL 2	/* Remove a file descriptor from the interface.  */
#define EPOLL_CTL_MOD 3	/* Change file descriptor epoll_event structure.  */typedef union epoll_data
{void *ptr;int fd;uint32_t u32;uint64_t u64;
} epoll_data_t;struct epoll_event
{uint32_t events;	/* Epoll events */epoll_data_t data;	/* User data variable */
} __EPOLL_PACKED;__BEGIN_DECLS/* Creates an epoll instance.  Returns an fd for the new instance.The "size" parameter is a hint specifying the number of filedescriptors to be associated with the new instance.  The fdreturned by epoll_create() should be closed with close().  */
extern int epoll_create (int __size) __THROW;/* Same as epoll_create but with an FLAGS parameter.  The unused SIZEparameter has been dropped.  */
extern int epoll_create1 (int __flags) __THROW;/* Manipulate an epoll instance "epfd". Returns 0 in case of success,-1 in case of error ( the "errno" variable will contain thespecific error code ) The "op" parameter is one of the EPOLL_CTL_*constants defined above. The "fd" parameter is the target of theoperation. The "event" parameter describes which events the calleris interested in and any associated user data.  */
extern int epoll_ctl (int __epfd, int __op, int __fd,struct epoll_event *__event) __THROW;/* Wait for events on an epoll instance "epfd". Returns the number oftriggered events returned in "events" buffer. Or -1 in case oferror with the "errno" variable set to the specific error code. The"events" parameter is a buffer that will contain triggeredevents. The "maxevents" is the maximum number of events to bereturned ( usually size of "events" ). The "timeout" parameterspecifies the maximum wait time in milliseconds (-1 == infinite).This function is a cancellation point and therefore not marked with__THROW.  */
extern int epoll_wait (int __epfd, struct epoll_event *__events,int __maxevents, int __timeout);/* Same as epoll_wait, but the thread's signal mask is temporarilyand atomically replaced with the one provided as parameter.This function is a cancellation point and therefore not marked with__THROW.  */
extern int epoll_pwait (int __epfd, struct epoll_event *__events,int __maxevents, int __timeout,const __sigset_t *__ss);__END_DECLS#endif /* sys/epoll.h */

Epoll实现机制：

epoll fd有一个私有的struct eventpoll，它记录哪一个fd注册到了epfd上。

eventpoll 同样有一个等待队列，记录所有等待的线程。还有一个预备好的fd列表，这些fd可以进行读或写。

相关内核实现代码在fs/eventpoll.c

https://github.com/torvalds/linux/blob/master/fs/eventpoll.c

判断是否tcp有激活事件：net/ipv4/tcp.c:tcp_poll函数

/**  fs/eventpoll.c (Efficient event retrieval implementation)*  Copyright (C) 2001,...,2009	 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/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/string.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/spinlock.h>
#include <linux/syscalls.h>
#include <linux/rbtree.h>
#include <linux/wait.h>
#include <linux/eventpoll.h>
#include <linux/mount.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/anon_inodes.h>
#include <linux/device.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/mman.h>
#include <linux/atomic.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/compat.h>/** LOCKING:* There are three level of locking required by epoll :** 1) epmutex (mutex)* 2) ep->mtx (mutex)* 3) ep->lock (spinlock)** 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* mutex (ep->mtx). It is acquired during the event transfer loop,* during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().* Then we also need a global mutex to serialize eventpoll_release_file()* and ep_free().* This mutex 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 to epoll_ctl(EPOLL_CTL_DEL).* It is also acquired when inserting an epoll fd onto another epoll* fd. We do this so that we walk the epoll tree and ensure that this* insertion does not create a cycle of epoll file descriptors, which* could lead to deadlock. We need a global mutex to prevent two* simultaneous inserts (A into B and B into A) from racing and* constructing a cycle without either insert observing that it is* going to.* It is necessary to acquire multiple "ep->mtx"es at once in the* case when one epoll fd is added to another. In this case, we* always acquire the locks in the order of nesting (i.e. after* epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired* before e2->mtx). Since we disallow cycles of epoll file* descriptors, this ensures that the mutexes are well-ordered. In* order to communicate this nesting to lockdep, when walking a tree* of epoll file descriptors, we use the current recursion depth as* the lockdep subkey.* It is possible to drop the "ep->mtx" and to use the global* mutex "epmutex" (together with "ep->lock") to have it working,* but having "ep->mtx" will make the interface more scalable.* Events that require holding "epmutex" are very rare, while for* normal operations the epoll private "ep->mtx" will guarantee* a better scalability.*//* Epoll private bits inside the event mask */
#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET)/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))#define EP_UNACTIVE_PTR ((void *) -1L)#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))struct epoll_filefd {struct file *file;int fd;
} __packed;/** Structure used to track possible nested calls, for too deep recursions* and loop cycles.*/
struct nested_call_node {struct list_head llink;void *cookie;void *ctx;
};/** This structure is used as collector for nested calls, to check for* maximum recursion dept and loop cycles.*/
struct nested_calls {struct list_head tasks_call_list;spinlock_t lock;
};/** Each file descriptor added to the eventpoll interface will* have an entry of this type linked to the "rbr" RB tree.* Avoid increasing the size of this struct, there can be many thousands* of these on a server and we do not want this to take another cache line.*/
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;/** Works together "struct eventpoll"->ovflist in keeping the* single linked chain of items.*/struct epitem *next;/* 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;/* List header used to link this item to the "struct file" items list */struct list_head fllink;/* wakeup_source used when EPOLLWAKEUP is set */struct wakeup_source __rcu *ws;/* The structure that describe the interested events and the source fd */struct epoll_event event;
};/** This structure is stored inside the "private_data" member of the file* structure and represents the main data structure for the eventpoll* interface.*/
struct eventpoll {/* Protect the access to this structure */spinlock_t lock;/** This mutex is used to ensure that files are not removed* while epoll is using them. This is held during the event* collection loop, the file cleanup path, the epoll file exit* code and the ctl operations.*/struct mutex mtx;/* 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;/** This is a single linked list that chains all the "struct epitem" that* happened while transferring ready events to userspace w/out* holding ->lock.*/struct epitem *ovflist;/* wakeup_source used when ep_scan_ready_list is running */struct wakeup_source *ws;/* The user that created the eventpoll descriptor */struct user_struct *user;struct file *file;/* used to optimize loop detection check */int visited;struct list_head visited_list_link;
};/* 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" */struct epitem *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;
};/* Wrapper struct used by poll queueing */
struct ep_pqueue {poll_table pt;struct epitem *epi;
};/* Used by the ep_send_events() function as callback private data */
struct ep_send_events_data {int maxevents;struct epoll_event __user *events;
};/** Configuration options available inside /proc/sys/fs/epoll/*/
/* Maximum number of epoll watched descriptors, per user */
static long max_user_watches __read_mostly;/** This mutex is used to serialize ep_free() and eventpoll_release_file().*/
static DEFINE_MUTEX(epmutex);/* Used to check for epoll file descriptor inclusion loops */
static struct nested_calls poll_loop_ncalls;/* Used for safe wake up implementation */
static struct nested_calls poll_safewake_ncalls;/* Used to call file's f_op->poll() under the nested calls boundaries */
static struct nested_calls poll_readywalk_ncalls;/* Slab cache used to allocate "struct epitem" */
static struct kmem_cache *epi_cache __read_mostly;/* Slab cache used to allocate "struct eppoll_entry" */
static struct kmem_cache *pwq_cache __read_mostly;/* Visited nodes during ep_loop_check(), so we can unset them when we finish */
static LIST_HEAD(visited_list);/** List of files with newly added links, where we may need to limit the number* of emanating paths. Protected by the epmutex.*/
static LIST_HEAD(tfile_check_list);#ifdef CONFIG_SYSCTL#include <linux/sysctl.h>static long zero;
static long long_max = LONG_MAX;ctl_table epoll_table[] = {{.procname	= "max_user_watches",.data		= &max_user_watches,.maxlen		= sizeof(max_user_watches),.mode		= 0644,.proc_handler	= proc_doulongvec_minmax,.extra1		= &zero,.extra2		= &long_max,},{ }
};
#endif /* CONFIG_SYSCTL */static const struct file_operations eventpoll_fops;static inline int is_file_epoll(struct file *f)
{return f->f_op == &eventpoll_fops;
}/* Setup the structure that is used as key for the RB tree */
static inline void ep_set_ffd(struct epoll_filefd *ffd,struct file *file, int fd)
{ffd->file = file;ffd->fd = fd;
}/* Compare RB tree keys */
static inline int ep_cmp_ffd(struct epoll_filefd *p1,struct epoll_filefd *p2)
{return (p1->file > p2->file ? +1:(p1->file < p2->file ? -1 : p1->fd - p2->fd));
}/* Tells us if the item is currently linked */
static inline int ep_is_linked(struct list_head *p)
{return !list_empty(p);
}static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p)
{return container_of(p, struct eppoll_entry, wait);
}/* Get the "struct epitem" from a wait queue pointer */
static inline struct epitem *ep_item_from_wait(wait_queue_t *p)
{return container_of(p, struct eppoll_entry, wait)->base;
}/* Get the "struct epitem" from an epoll queue wrapper */
static inline struct epitem *ep_item_from_epqueue(poll_table *p)
{return container_of(p, struct ep_pqueue, pt)->epi;
}/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
static inline int ep_op_has_event(int op)
{return op != EPOLL_CTL_DEL;
}/* Initialize the poll safe wake up structure */
static void ep_nested_calls_init(struct nested_calls *ncalls)
{INIT_LIST_HEAD(&ncalls->tasks_call_list);spin_lock_init(&ncalls->lock);
}/*** ep_events_available - Checks if ready events might be available.** @ep: Pointer to the eventpoll context.** Returns: Returns a value different than zero if ready events are available,*          or zero otherwise.*/
static inline int ep_events_available(struct eventpoll *ep)
{return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
}/*** ep_call_nested - Perform a bound (possibly) nested call, by checking*                  that the recursion limit is not exceeded, and that*                  the same nested call (by the meaning of same cookie) is*                  no re-entered.** @ncalls: Pointer to the nested_calls structure to be used for this call.* @max_nests: Maximum number of allowed nesting calls.* @nproc: Nested call core function pointer.* @priv: Opaque data to be passed to the @nproc callback.* @cookie: Cookie to be used to identify this nested call.* @ctx: This instance context.** Returns: Returns the code returned by the @nproc callback, or -1 if*          the maximum recursion limit has been exceeded.*/
static int ep_call_nested(struct nested_calls *ncalls, int max_nests,int (*nproc)(void *, void *, int), void *priv,void *cookie, void *ctx)
{int error, call_nests = 0;unsigned long flags;struct list_head *lsthead = &ncalls->tasks_call_list;struct nested_call_node *tncur;struct nested_call_node tnode;spin_lock_irqsave(&ncalls->lock, flags);/** Try to see if the current task is already inside this wakeup call.* We use a list here, since the population inside this set is always* very much limited.*/list_for_each_entry(tncur, lsthead, llink) {if (tncur->ctx == ctx &&(tncur->cookie == cookie || ++call_nests > max_nests)) {/** Ops ... loop detected or maximum nest level reached.* We abort this wake by breaking the cycle itself.*/error = -1;goto out_unlock;}}/* Add the current task and cookie to the list */tnode.ctx = ctx;tnode.cookie = cookie;list_add(&tnode.llink, lsthead);spin_unlock_irqrestore(&ncalls->lock, flags);/* Call the nested function */error = (*nproc)(priv, cookie, call_nests);/* Remove the current task from the list */spin_lock_irqsave(&ncalls->lock, flags);list_del(&tnode.llink);
out_unlock:spin_unlock_irqrestore(&ncalls->lock, flags);return error;
}/** As described in commit 0ccf831cb lockdep: annotate epoll* the use of wait queues used by epoll is done in a very controlled* manner. Wake ups can nest inside each other, but are never done* with the same locking. For example:**   dfd = socket(...);*   efd1 = epoll_create();*   efd2 = epoll_create();*   epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);*   epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);** When a packet arrives to the device underneath "dfd", the net code will* issue a wake_up() on its poll wake list. Epoll (efd1) has installed a* callback wakeup entry on that queue, and the wake_up() performed by the* "dfd" net code will end up in ep_poll_callback(). At this point epoll* (efd1) notices that it may have some event ready, so it needs to wake up* the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()* that ends up in another wake_up(), after having checked about the* recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to* avoid stack blasting.** When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle* this special case of epoll.*/
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,unsigned long events, int subclass)
{unsigned long flags;spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);wake_up_locked_poll(wqueue, events);spin_unlock_irqrestore(&wqueue->lock, flags);
}
#else
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,unsigned long events, int subclass)
{wake_up_poll(wqueue, events);
}
#endifstatic int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
{ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN,1 + call_nests);return 0;
}/** 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_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_NESTS deep.*/
static void ep_poll_safewake(wait_queue_head_t *wq)
{int this_cpu = get_cpu();ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);put_cpu();
}static void ep_remove_wait_queue(struct eppoll_entry *pwq)
{wait_queue_head_t *whead;rcu_read_lock();/* If it is cleared by POLLFREE, it should be rcu-safe */whead = rcu_dereference(pwq->whead);if (whead)remove_wait_queue(whead, &pwq->wait);rcu_read_unlock();
}/** This function unregisters poll callbacks from the associated file* descriptor.  Must be called with "mtx" held (or "epmutex" if called from* ep_free).*/
static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
{struct list_head *lsthead = &epi->pwqlist;struct eppoll_entry *pwq;while (!list_empty(lsthead)) {pwq = list_first_entry(lsthead, struct eppoll_entry, llink);list_del(&pwq->llink);ep_remove_wait_queue(pwq);kmem_cache_free(pwq_cache, pwq);}
}/* call only when ep->mtx is held */
static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
{return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
}/* call only when ep->mtx is held */
static inline void ep_pm_stay_awake(struct epitem *epi)
{struct wakeup_source *ws = ep_wakeup_source(epi);if (ws)__pm_stay_awake(ws);
}static inline bool ep_has_wakeup_source(struct epitem *epi)
{return rcu_access_pointer(epi->ws) ? true : false;
}/* call when ep->mtx cannot be held (ep_poll_callback) */
static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
{struct wakeup_source *ws;rcu_read_lock();ws = rcu_dereference(epi->ws);if (ws)__pm_stay_awake(ws);rcu_read_unlock();
}/*** ep_scan_ready_list - Scans the ready list in a way that makes possible for*                      the scan code, to call f_op->poll(). Also allows for*                      O(NumReady) performance.** @ep: Pointer to the epoll private data structure.* @sproc: Pointer to the scan callback.* @priv: Private opaque data passed to the @sproc callback.* @depth: The current depth of recursive f_op->poll calls.** Returns: The same integer error code returned by the @sproc callback.*/
static int ep_scan_ready_list(struct eventpoll *ep,int (*sproc)(struct eventpoll *,struct list_head *, void *),void *priv,int depth)
{int error, pwake = 0;unsigned long flags;struct epitem *epi, *nepi;LIST_HEAD(txlist);/** We need to lock this because we could be hit by* eventpoll_release_file() and epoll_ctl().*/mutex_lock_nested(&ep->mtx, depth);/** Steal the ready list, and re-init the original one to the* empty list. Also, set ep->ovflist to NULL so that events* happening while looping w/out locks, are not lost. We cannot* have the poll callback to queue directly on ep->rdllist,* because we want the "sproc" callback to be able to do it* in a lockless way.*/spin_lock_irqsave(&ep->lock, flags);list_splice_init(&ep->rdllist, &txlist);ep->ovflist = NULL;spin_unlock_irqrestore(&ep->lock, flags);/** Now call the callback function.*/error = (*sproc)(ep, &txlist, priv);spin_lock_irqsave(&ep->lock, flags);/** During the time we spent inside the "sproc" callback, some* other events might have been queued by the poll callback.* We re-insert them inside the main ready-list here.*/for (nepi = ep->ovflist; (epi = nepi) != NULL;nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {/** We need to check if the item is already in the list.* During the "sproc" callback execution time, items are* queued into ->ovflist but the "txlist" might already* contain them, and the list_splice() below takes care of them.*/if (!ep_is_linked(&epi->rdllink)) {list_add_tail(&epi->rdllink, &ep->rdllist);ep_pm_stay_awake(epi);}}/** We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after* releasing the lock, events will be queued in the normal way inside* ep->rdllist.*/ep->ovflist = EP_UNACTIVE_PTR;/** Quickly re-inject items left on "txlist".*/list_splice(&txlist, &ep->rdllist);__pm_relax(ep->ws);if (!list_empty(&ep->rdllist)) {/** Wake up (if active) both the eventpoll wait list and* the ->poll() wait list (delayed after we release the lock).*/if (waitqueue_active(&ep->wq))wake_up_locked(&ep->wq);if (waitqueue_active(&ep->poll_wait))pwake++;}spin_unlock_irqrestore(&ep->lock, flags);mutex_unlock(&ep->mtx);/* We have to call this outside the lock */if (pwake)ep_poll_safewake(&ep->poll_wait);return error;
}/** Removes a "struct epitem" from the eventpoll RB tree and deallocates* all the associated resources. Must be called with "mtx" held.*/
static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{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_lock);if (ep_is_linked(&epi->fllink))list_del_init(&epi->fllink);spin_unlock(&file->f_lock);rb_erase(&epi->rbn, &ep->rbr);spin_lock_irqsave(&ep->lock, flags);if (ep_is_linked(&epi->rdllink))list_del_init(&epi->rdllink);spin_unlock_irqrestore(&ep->lock, flags);wakeup_source_unregister(ep_wakeup_source(epi));/* At this point it is safe to free the eventpoll item */kmem_cache_free(epi_cache, epi);atomic_long_dec(&ep->user->epoll_watches);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(&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->mtx" here because the epoll file* is on the way to be removed and no one has references to it* anymore. The only hit might come from eventpoll_release_file() but* holding "epmutex" is sufficient here.*/mutex_lock(&epmutex);/** Walks through the whole tree by unregistering poll callbacks.*/for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {epi = rb_entry(rbp, struct epitem, rbn);ep_unregister_pollwait(ep, epi);}/** Walks through the whole tree by freeing each "struct epitem". At this* point we are sure no poll callbacks will be lingering around, and also by* holding "epmutex" we can be sure that no file cleanup code will hit* us during this operation. So we can avoid the lock on "ep->lock".* We do not need to lock ep->mtx, either, we only do it to prevent* a lockdep warning.*/mutex_lock(&ep->mtx);while ((rbp = rb_first(&ep->rbr)) != NULL) {epi = rb_entry(rbp, struct epitem, rbn);ep_remove(ep, epi);}mutex_unlock(&ep->mtx);mutex_unlock(&epmutex);mutex_destroy(&ep->mtx);free_uid(ep->user);wakeup_source_unregister(ep->ws);kfree(ep);
}static int ep_eventpoll_release(struct inode *inode, struct file *file)
{struct eventpoll *ep = file->private_data;if (ep)ep_free(ep);return 0;
}static inline unsigned int ep_item_poll(struct epitem *epi, poll_table *pt)
{pt->_key = epi->event.events;return epi->ffd.file->f_op->poll(epi->ffd.file, pt) & epi->event.events;
}static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,void *priv)
{struct epitem *epi, *tmp;poll_table pt;init_poll_funcptr(&pt, NULL);list_for_each_entry_safe(epi, tmp, head, rdllink) {if (ep_item_poll(epi, &pt))return POLLIN | POLLRDNORM;else {/** Item has been dropped into the ready list by the poll* callback, but it's not actually ready, as far as* caller requested events goes. We can remove it here.*/__pm_relax(ep_wakeup_source(epi));list_del_init(&epi->rdllink);}}return 0;
}static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
{return ep_scan_ready_list(priv, ep_read_events_proc, NULL, call_nests + 1);
}static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
{int pollflags;struct eventpoll *ep = file->private_data;/* Insert inside our poll wait queue */poll_wait(file, &ep->poll_wait, wait);/** Proceed to find out if wanted events are really available inside* the ready list. This need to be done under ep_call_nested()* supervision, since the call to f_op->poll() done on listed files* could re-enter here.*/pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,ep_poll_readyevents_proc, ep, ep, current);return pollflags != -1 ? pollflags : 0;
}#ifdef CONFIG_PROC_FS
static int ep_show_fdinfo(struct seq_file *m, struct file *f)
{struct eventpoll *ep = f->private_data;struct rb_node *rbp;int ret = 0;mutex_lock(&ep->mtx);for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {struct epitem *epi = rb_entry(rbp, struct epitem, rbn);ret = seq_printf(m, "tfd: %8d events: %8x data: %16llx\n",epi->ffd.fd, epi->event.events,(long long)epi->event.data);if (ret)break;}mutex_unlock(&ep->mtx);return ret;
}
#endif/* File callbacks that implement the eventpoll file behaviour */
static const struct file_operations eventpoll_fops = {
#ifdef CONFIG_PROC_FS.show_fdinfo	= ep_show_fdinfo,
#endif.release	= ep_eventpoll_release,.poll		= ep_eventpoll_poll,.llseek		= noop_llseek,
};/** 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_lock" because it is not* necessary. It is not necessary because we're in the "struct file"* cleanup path, and this means that no one is using this file anymore.* So, for example, epoll_ctl() cannot hit here since if we reach this* point, the file counter already went to zero and fget() would fail.* The only hit might come from ep_free() but by holding the mutex* will correctly serialize the operation. We do need to acquire* "ep->mtx" after "epmutex" because ep_remove() requires it when called* from anywhere but ep_free().** Besides, ep_remove() acquires the lock, so we can't hold it here.*/mutex_lock(&epmutex);while (!list_empty(lsthead)) {epi = list_first_entry(lsthead, struct epitem, fllink);ep = epi->ep;list_del_init(&epi->fllink);mutex_lock_nested(&ep->mtx, 0);ep_remove(ep, epi);mutex_unlock(&ep->mtx);}mutex_unlock(&epmutex);
}static int ep_alloc(struct eventpoll **pep)
{int error;struct user_struct *user;struct eventpoll *ep;user = get_current_user();error = -ENOMEM;ep = kzalloc(sizeof(*ep), GFP_KERNEL);if (unlikely(!ep))goto free_uid;spin_lock_init(&ep->lock);mutex_init(&ep->mtx);init_waitqueue_head(&ep->wq);init_waitqueue_head(&ep->poll_wait);INIT_LIST_HEAD(&ep->rdllist);ep->rbr = RB_ROOT;ep->ovflist = EP_UNACTIVE_PTR;ep->user = user;*pep = ep;return 0;free_uid:free_uid(user);return error;
}/** Search the file inside the eventpoll tree. The RB tree operations* are protected by the "mtx" mutex, and ep_find() must be called with* "mtx" held.*/
static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
{int kcmp;struct rb_node *rbp;struct epitem *epi, *epir = NULL;struct epoll_filefd ffd;ep_set_ffd(&ffd, file, fd);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 {epir = epi;break;}}return epir;
}/** This is the callback that is passed to the wait queue wakeup* mechanism. 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;if ((unsigned long)key & POLLFREE) {ep_pwq_from_wait(wait)->whead = NULL;/** whead = NULL above can race with ep_remove_wait_queue()* which can do another remove_wait_queue() after us, so we* can't use __remove_wait_queue(). whead->lock is held by* the caller.*/list_del_init(&wait->task_list);}spin_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 out_unlock;/** Check the events coming with the callback. At this stage, not* every device reports the events in the "key" parameter of the* callback. We need to be able to handle both cases here, hence the* test for "key" != NULL before the event match test.*/if (key && !((unsigned long) key & epi->event.events))goto out_unlock;/** If we are transferring events to userspace, we can hold no locks* (because we're accessing user memory, and because of linux f_op->poll()* semantics). All the events that happen during that period of time are* chained in ep->ovflist and requeued later on.*/if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {if (epi->next == EP_UNACTIVE_PTR) {epi->next = ep->ovflist;ep->ovflist = epi;if (epi->ws) {/** Activate ep->ws since epi->ws may get* deactivated at any time.*/__pm_stay_awake(ep->ws);}}goto out_unlock;}/* If this file is already in the ready list we exit soon */if (!ep_is_linked(&epi->rdllink)) {list_add_tail(&epi->rdllink, &ep->rdllist);ep_pm_stay_awake_rcu(epi);}/** Wake up ( if active ) both the eventpoll wait list and the ->poll()* wait list.*/if (waitqueue_active(&ep->wq))wake_up_locked(&ep->wq);if (waitqueue_active(&ep->poll_wait))pwake++;out_unlock:spin_unlock_irqrestore(&ep->lock, flags);/* We have to call this outside the lock */if (pwake)ep_poll_safewake(&ep->poll_wait);return 1;
}/** This is the callback that is used to add our wait queue to the* target file wakeup lists.*/
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,poll_table *pt)
{struct epitem *epi = ep_item_from_epqueue(pt);struct eppoll_entry *pwq;if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);pwq->whead = whead;pwq->base = epi;add_wait_queue(whead, &pwq->wait);list_add_tail(&pwq->llink, &epi->pwqlist);epi->nwait++;} else {/* We have to signal that an error occurred */epi->nwait = -1;}
}static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
{int kcmp;struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;struct epitem *epic;while (*p) {parent = *p;epic = rb_entry(parent, struct epitem, rbn);kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);if (kcmp > 0)p = &parent->rb_right;elsep = &parent->rb_left;}rb_link_node(&epi->rbn, parent, p);rb_insert_color(&epi->rbn, &ep->rbr);
}#define PATH_ARR_SIZE 5
/** These are the number paths of length 1 to 5, that we are allowing to emanate* from a single file of interest. For example, we allow 1000 paths of length* 1, to emanate from each file of interest. This essentially represents the* potential wakeup paths, which need to be limited in order to avoid massive* uncontrolled wakeup storms. The common use case should be a single ep which* is connected to n file sources. In this case each file source has 1 path* of length 1. Thus, the numbers below should be more than sufficient. These* path limits are enforced during an EPOLL_CTL_ADD operation, since a modify* and delete can't add additional paths. Protected by the epmutex.*/
static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
static int path_count[PATH_ARR_SIZE];static int path_count_inc(int nests)
{/* Allow an arbitrary number of depth 1 paths */if (nests == 0)return 0;if (++path_count[nests] > path_limits[nests])return -1;return 0;
}static void path_count_init(void)
{int i;for (i = 0; i < PATH_ARR_SIZE; i++)path_count[i] = 0;
}static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
{int error = 0;struct file *file = priv;struct file *child_file;struct epitem *epi;list_for_each_entry(epi, &file->f_ep_links, fllink) {child_file = epi->ep->file;if (is_file_epoll(child_file)) {if (list_empty(&child_file->f_ep_links)) {if (path_count_inc(call_nests)) {error = -1;break;}} else {error = ep_call_nested(&poll_loop_ncalls,EP_MAX_NESTS,reverse_path_check_proc,child_file, child_file,current);}if (error != 0)break;} else {printk(KERN_ERR "reverse_path_check_proc: ""file is not an ep!\n");}}return error;
}/*** reverse_path_check - The tfile_check_list is list of file *, which have*                      links that are proposed to be newly added. We need to*                      make sure that those added links don't add too many*                      paths such that we will spend all our time waking up*                      eventpoll objects.** Returns: Returns zero if the proposed links don't create too many paths,*	    -1 otherwise.*/
static int reverse_path_check(void)
{int error = 0;struct file *current_file;/* let's call this for all tfiles */list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {path_count_init();error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,reverse_path_check_proc, current_file,current_file, current);if (error)break;}return error;
}static int ep_create_wakeup_source(struct epitem *epi)
{const char *name;struct wakeup_source *ws;if (!epi->ep->ws) {epi->ep->ws = wakeup_source_register("eventpoll");if (!epi->ep->ws)return -ENOMEM;}name = epi->ffd.file->f_path.dentry->d_name.name;ws = wakeup_source_register(name);if (!ws)return -ENOMEM;rcu_assign_pointer(epi->ws, ws);return 0;
}/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
static noinline void ep_destroy_wakeup_source(struct epitem *epi)
{struct wakeup_source *ws = ep_wakeup_source(epi);RCU_INIT_POINTER(epi->ws, NULL);/** wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is* used internally by wakeup_source_remove, too (called by* wakeup_source_unregister), so we cannot use call_rcu*/synchronize_rcu();wakeup_source_unregister(ws);
}/** Must be called with "mtx" held.*/
static int ep_insert(struct eventpoll *ep, struct epoll_event *event,struct file *tfile, int fd)
{int error, revents, pwake = 0;unsigned long flags;long user_watches;struct epitem *epi;struct ep_pqueue epq;user_watches = atomic_long_read(&ep->user->epoll_watches);if (unlikely(user_watches >= max_user_watches))return -ENOSPC;if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))return -ENOMEM;/* Item initialization follow here ... */INIT_LIST_HEAD(&epi->rdllink);INIT_LIST_HEAD(&epi->fllink);INIT_LIST_HEAD(&epi->pwqlist);epi->ep = ep;ep_set_ffd(&epi->ffd, tfile, fd);epi->event = *event;epi->nwait = 0;epi->next = EP_UNACTIVE_PTR;if (epi->event.events & EPOLLWAKEUP) {error = ep_create_wakeup_source(epi);if (error)goto error_create_wakeup_source;} else {RCU_INIT_POINTER(epi->ws, NULL);}/* 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. Note that after* this operation completes, the poll callback can start hitting* the new item.*/revents = ep_item_poll(epi, &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.*/error = -ENOMEM;if (epi->nwait < 0)goto error_unregister;/* Add the current item to the list of active epoll hook for this file */spin_lock(&tfile->f_lock);list_add_tail(&epi->fllink, &tfile->f_ep_links);spin_unlock(&tfile->f_lock);/** Add the current item to the RB tree. All RB tree operations are* protected by "mtx", and ep_insert() is called with "mtx" held.*/ep_rbtree_insert(ep, epi);/* now check if we've created too many backpaths */error = -EINVAL;if (reverse_path_check())goto error_remove_epi;/* We have to drop the new item inside our item list to keep track of it */spin_lock_irqsave(&ep->lock, flags);/* 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);ep_pm_stay_awake(epi);/* Notify waiting tasks that events are available */if (waitqueue_active(&ep->wq))wake_up_locked(&ep->wq);if (waitqueue_active(&ep->poll_wait))pwake++;}spin_unlock_irqrestore(&ep->lock, flags);atomic_long_inc(&ep->user->epoll_watches);/* We have to call this outside the lock */if (pwake)ep_poll_safewake(&ep->poll_wait);return 0;error_remove_epi:spin_lock(&tfile->f_lock);if (ep_is_linked(&epi->fllink))list_del_init(&epi->fllink);spin_unlock(&tfile->f_lock);rb_erase(&epi->rbn, &ep->rbr);error_unregister:ep_unregister_pollwait(ep, epi);/** We need to do this because an event could have been arrived on some* allocated wait queue. Note that we don't care about the ep->ovflist* list, since that is used/cleaned only inside a section bound by "mtx".* And ep_insert() is called with "mtx" held.*/spin_lock_irqsave(&ep->lock, flags);if (ep_is_linked(&epi->rdllink))list_del_init(&epi->rdllink);spin_unlock_irqrestore(&ep->lock, flags);wakeup_source_unregister(ep_wakeup_source(epi));error_create_wakeup_source:kmem_cache_free(epi_cache, epi);return error;
}/** Modify the interest event mask by dropping an event if the new mask* has a match in the current file status. Must be called with "mtx" held.*/
static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
{int pwake = 0;unsigned int revents;poll_table pt;init_poll_funcptr(&pt, NULL);/** Set the new event interest mask before calling f_op->poll();* otherwise we might miss an event that happens between the* f_op->poll() call and the new event set registering.*/epi->event.events = event->events; /* need barrier below */epi->event.data = event->data; /* protected by mtx */if (epi->event.events & EPOLLWAKEUP) {if (!ep_has_wakeup_source(epi))ep_create_wakeup_source(epi);} else if (ep_has_wakeup_source(epi)) {ep_destroy_wakeup_source(epi);}/** The following barrier has two effects:** 1) Flush epi changes above to other CPUs.  This ensures*    we do not miss events from ep_poll_callback if an*    event occurs immediately after we call f_op->poll().*    We need this because we did not take ep->lock while*    changing epi above (but ep_poll_callback does take*    ep->lock).** 2) We also need to ensure we do not miss _past_ events*    when calling f_op->poll().  This barrier also*    pairs with the barrier in wq_has_sleeper (see*    comments for wq_has_sleeper).** This barrier will now guarantee ep_poll_callback or f_op->poll* (or both) will notice the readiness of an item.*/smp_mb();/** 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 = ep_item_poll(epi, &pt);/** If the item is "hot" and it is not registered inside the ready* list, push it inside.*/if (revents & event->events) {spin_lock_irq(&ep->lock);if (!ep_is_linked(&epi->rdllink)) {list_add_tail(&epi->rdllink, &ep->rdllist);ep_pm_stay_awake(epi);/* Notify waiting tasks that events are available */if (waitqueue_active(&ep->wq))wake_up_locked(&ep->wq);if (waitqueue_active(&ep->poll_wait))pwake++;}spin_unlock_irq(&ep->lock);}/* We have to call this outside the lock */if (pwake)ep_poll_safewake(&ep->poll_wait);return 0;
}static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,void *priv)
{struct ep_send_events_data *esed = priv;int eventcnt;unsigned int revents;struct epitem *epi;struct epoll_event __user *uevent;struct wakeup_source *ws;poll_table pt;init_poll_funcptr(&pt, NULL);/** We can loop without lock because we are passed a task private list.* Items cannot vanish during the loop because ep_scan_ready_list() is* holding "mtx" during this call.*/for (eventcnt = 0, uevent = esed->events;!list_empty(head) && eventcnt < esed->maxevents;) {epi = list_first_entry(head, struct epitem, rdllink);/** Activate ep->ws before deactivating epi->ws to prevent* triggering auto-suspend here (in case we reactive epi->ws* below).** This could be rearranged to delay the deactivation of epi->ws* instead, but then epi->ws would temporarily be out of sync* with ep_is_linked().*/ws = ep_wakeup_source(epi);if (ws) {if (ws->active)__pm_stay_awake(ep->ws);__pm_relax(ws);}list_del_init(&epi->rdllink);revents = ep_item_poll(epi, &pt);/** If the event mask intersect the caller-requested one,* deliver the event to userspace. Again, ep_scan_ready_list()* is holding "mtx", so no operations coming from userspace* can change the item.*/if (revents) {if (__put_user(revents, &uevent->events) ||__put_user(epi->event.data, &uevent->data)) {list_add(&epi->rdllink, head);ep_pm_stay_awake(epi);return eventcnt ? eventcnt : -EFAULT;}eventcnt++;uevent++;if (epi->event.events & EPOLLONESHOT)epi->event.events &= EP_PRIVATE_BITS;else if (!(epi->event.events & EPOLLET)) {/** If this file has been added with Level* Trigger mode, we need to insert back inside* the ready list, so that the next call to* epoll_wait() will check again the events* availability. At this point, no one can insert* into ep->rdllist besides us. The epoll_ctl()* callers are locked out by* ep_scan_ready_list() holding "mtx" and the* poll callback will queue them in ep->ovflist.*/list_add_tail(&epi->rdllink, &ep->rdllist);ep_pm_stay_awake(epi);}}}return eventcnt;
}static int ep_send_events(struct eventpoll *ep,struct epoll_event __user *events, int maxevents)
{struct ep_send_events_data esed;esed.maxevents = maxevents;esed.events = events;return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0);
}static inline struct timespec ep_set_mstimeout(long ms)
{struct timespec now, ts = {.tv_sec = ms / MSEC_PER_SEC,.tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),};ktime_get_ts(&now);return timespec_add_safe(now, ts);
}/*** ep_poll - Retrieves ready events, and delivers them to the caller supplied*           event buffer.** @ep: Pointer to the eventpoll context.* @events: Pointer to the userspace buffer where the ready events should be*          stored.* @maxevents: Size (in terms of number of events) of the caller event buffer.* @timeout: Maximum timeout for the ready events fetch operation, in*           milliseconds. If the @timeout is zero, the function will not block,*           while if the @timeout is less than zero, the function will block*           until at least one event has been retrieved (or an error*           occurred).** Returns: Returns the number of ready events which have been fetched, or an*          error code, in case of error.*/
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,int maxevents, long timeout)
{int res = 0, eavail, timed_out = 0;unsigned long flags;long slack = 0;wait_queue_t wait;ktime_t expires, *to = NULL;if (timeout > 0) {struct timespec end_time = ep_set_mstimeout(timeout);slack = select_estimate_accuracy(&end_time);to = &expires;*to = timespec_to_ktime(end_time);} else if (timeout == 0) {/** Avoid the unnecessary trip to the wait queue loop, if the* caller specified a non blocking operation.*/timed_out = 1;spin_lock_irqsave(&ep->lock, flags);goto check_events;}fetch_events:spin_lock_irqsave(&ep->lock, flags);if (!ep_events_available(ep)) {/** 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_exclusive(&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 (ep_events_available(ep) || timed_out)break;if (signal_pending(current)) {res = -EINTR;break;}spin_unlock_irqrestore(&ep->lock, flags);if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))timed_out = 1;spin_lock_irqsave(&ep->lock, flags);}__remove_wait_queue(&ep->wq, &wait);set_current_state(TASK_RUNNING);}
check_events:/* Is it worth to try to dig for events ? */eavail = ep_events_available(ep);spin_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_send_events(ep, events, maxevents)) && !timed_out)goto fetch_events;return res;
}/*** ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()*                      API, to verify that adding an epoll file inside another*                      epoll structure, does not violate the constraints, in*                      terms of closed loops, or too deep chains (which can*                      result in excessive stack usage).** @priv: Pointer to the epoll file to be currently checked.* @cookie: Original cookie for this call. This is the top-of-the-chain epoll*          data structure pointer.* @call_nests: Current dept of the @ep_call_nested() call stack.** Returns: Returns zero if adding the epoll @file inside current epoll*          structure @ep does not violate the constraints, or -1 otherwise.*/
static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
{int error = 0;struct file *file = priv;struct eventpoll *ep = file->private_data;struct eventpoll *ep_tovisit;struct rb_node *rbp;struct epitem *epi;mutex_lock_nested(&ep->mtx, call_nests + 1);ep->visited = 1;list_add(&ep->visited_list_link, &visited_list);for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {epi = rb_entry(rbp, struct epitem, rbn);if (unlikely(is_file_epoll(epi->ffd.file))) {ep_tovisit = epi->ffd.file->private_data;if (ep_tovisit->visited)continue;error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,ep_loop_check_proc, epi->ffd.file,ep_tovisit, current);if (error != 0)break;} else {/** If we've reached a file that is not associated with* an ep, then we need to check if the newly added* links are going to add too many wakeup paths. We do* this by adding it to the tfile_check_list, if it's* not already there, and calling reverse_path_check()* during ep_insert().*/if (list_empty(&epi->ffd.file->f_tfile_llink))list_add(&epi->ffd.file->f_tfile_llink,&tfile_check_list);}}mutex_unlock(&ep->mtx);return error;
}/*** ep_loop_check - Performs a check to verify that adding an epoll file (@file)*                 another epoll file (represented by @ep) does not create*                 closed loops or too deep chains.** @ep: Pointer to the epoll private data structure.* @file: Pointer to the epoll file to be checked.** Returns: Returns zero if adding the epoll @file inside current epoll*          structure @ep does not violate the constraints, or -1 otherwise.*/
static int ep_loop_check(struct eventpoll *ep, struct file *file)
{int ret;struct eventpoll *ep_cur, *ep_next;ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,ep_loop_check_proc, file, ep, current);/* clear visited list */list_for_each_entry_safe(ep_cur, ep_next, &visited_list,visited_list_link) {ep_cur->visited = 0;list_del(&ep_cur->visited_list_link);}return ret;
}static void clear_tfile_check_list(void)
{struct file *file;/* first clear the tfile_check_list */while (!list_empty(&tfile_check_list)) {file = list_first_entry(&tfile_check_list, struct file,f_tfile_llink);list_del_init(&file->f_tfile_llink);}INIT_LIST_HEAD(&tfile_check_list);
}/** Open an eventpoll file descriptor.*/
SYSCALL_DEFINE1(epoll_create1, int, flags)
{int error, fd;struct eventpoll *ep = NULL;struct file *file;/* Check the EPOLL_* constant for consistency.  */BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);if (flags & ~EPOLL_CLOEXEC)return -EINVAL;/** Create the internal data structure ("struct eventpoll").*/error = ep_alloc(&ep);if (error < 0)return error;/** Creates all the items needed to setup an eventpoll file. That is,* a file structure and a free file descriptor.*/fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));if (fd < 0) {error = fd;goto out_free_ep;}file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,O_RDWR | (flags & O_CLOEXEC));if (IS_ERR(file)) {error = PTR_ERR(file);goto out_free_fd;}ep->file = file;fd_install(fd, file);return fd;out_free_fd:put_unused_fd(fd);
out_free_ep:ep_free(ep);return error;
}SYSCALL_DEFINE1(epoll_create, int, size)
{if (size <= 0)return -EINVAL;return sys_epoll_create1(0);
}/** The following function implements the controller interface for* the eventpoll file that enables the insertion/removal/change of* file descriptors inside the interest set.*/
SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,struct epoll_event __user *, event)
{int error;int did_lock_epmutex = 0;struct file *file, *tfile;struct eventpoll *ep;struct epitem *epi;struct epoll_event epds;error = -EFAULT;if (ep_op_has_event(op) &&copy_from_user(&epds, event, sizeof(struct epoll_event)))goto error_return;/* Get the "struct file *" for the eventpoll file */error = -EBADF;file = fget(epfd);if (!file)goto error_return;/* Get the "struct file *" for the target file */tfile = fget(fd);if (!tfile)goto error_fput;/* The target file descriptor must support poll */error = -EPERM;if (!tfile->f_op || !tfile->f_op->poll)goto error_tgt_fput;/* Check if EPOLLWAKEUP is allowed */if ((epds.events & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND))epds.events &= ~EPOLLWAKEUP;/** 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 error_tgt_fput;/** At this point it is safe to assume that the "private_data" contains* our own data structure.*/ep = file->private_data;/** When we insert an epoll file descriptor, inside another epoll file* descriptor, there is the change of creating closed loops, which are* better be handled here, than in more critical paths. While we are* checking for loops we also determine the list of files reachable* and hang them on the tfile_check_list, so we can check that we* haven't created too many possible wakeup paths.** We need to hold the epmutex across both ep_insert and ep_remove* b/c we want to make sure we are looking at a coherent view of* epoll network.*/if (op == EPOLL_CTL_ADD || op == EPOLL_CTL_DEL) {mutex_lock(&epmutex);did_lock_epmutex = 1;}if (op == EPOLL_CTL_ADD) {if (is_file_epoll(tfile)) {error = -ELOOP;if (ep_loop_check(ep, tfile) != 0) {clear_tfile_check_list();goto error_tgt_fput;}} elselist_add(&tfile->f_tfile_llink, &tfile_check_list);}mutex_lock_nested(&ep->mtx, 0);/** Try to lookup the file inside our RB tree, Since we grabbed "mtx"* above, we can be sure to be able to use the item looked up by* ep_find() till we release the mutex.*/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);} elseerror = -EEXIST;clear_tfile_check_list();break;case EPOLL_CTL_DEL:if (epi)error = ep_remove(ep, epi);elseerror = -ENOENT;break;case EPOLL_CTL_MOD:if (epi) {epds.events |= POLLERR | POLLHUP;error = ep_modify(ep, epi, &epds);} elseerror = -ENOENT;break;}mutex_unlock(&ep->mtx);error_tgt_fput:if (did_lock_epmutex)mutex_unlock(&epmutex);fput(tfile);
error_fput:fput(file);
error_return:return error;
}/** Implement the event wait interface for the eventpoll file. It is the kernel* part of the user space epoll_wait(2).*/
SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,int, maxevents, int, timeout)
{int error;struct fd f;struct eventpoll *ep;/* The maximum number of event must be greater than zero */if (maxevents <= 0 || maxevents > EP_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)))return -EFAULT;/* Get the "struct file *" for the eventpoll file */f = fdget(epfd);if (!f.file)return -EBADF;/** 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(f.file))goto error_fput;/** At this point it is safe to assume that the "private_data" contains* our own data structure.*/ep = f.file->private_data;/* Time to fish for events ... */error = ep_poll(ep, events, maxevents, timeout);error_fput:fdput(f);return error;
}/** Implement the event wait interface for the eventpoll file. It is the kernel* part of the user space epoll_pwait(2).*/
SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,int, maxevents, int, timeout, const sigset_t __user *, sigmask,size_t, sigsetsize)
{int error;sigset_t ksigmask, sigsaved;/** If the caller wants a certain signal mask to be set during the wait,* we apply it here.*/if (sigmask) {if (sigsetsize != sizeof(sigset_t))return -EINVAL;if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))return -EFAULT;sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);}error = sys_epoll_wait(epfd, events, maxevents, timeout);/** If we changed the signal mask, we need to restore the original one.* In case we've got a signal while waiting, we do not restore the* signal mask yet, and we allow do_signal() to deliver the signal on* the way back to userspace, before the signal mask is restored.*/if (sigmask) {if (error == -EINTR) {memcpy(&current->saved_sigmask, &sigsaved,sizeof(sigsaved));set_restore_sigmask();} elsesigprocmask(SIG_SETMASK, &sigsaved, NULL);}return error;
}#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,struct epoll_event __user *, events,int, maxevents, int, timeout,const compat_sigset_t __user *, sigmask,compat_size_t, sigsetsize)
{long err;compat_sigset_t csigmask;sigset_t ksigmask, sigsaved;/** If the caller wants a certain signal mask to be set during the wait,* we apply it here.*/if (sigmask) {if (sigsetsize != sizeof(compat_sigset_t))return -EINVAL;if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))return -EFAULT;sigset_from_compat(&ksigmask, &csigmask);sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);}err = sys_epoll_wait(epfd, events, maxevents, timeout);/** If we changed the signal mask, we need to restore the original one.* In case we've got a signal while waiting, we do not restore the* signal mask yet, and we allow do_signal() to deliver the signal on* the way back to userspace, before the signal mask is restored.*/if (sigmask) {if (err == -EINTR) {memcpy(&current->saved_sigmask, &sigsaved,sizeof(sigsaved));set_restore_sigmask();} elsesigprocmask(SIG_SETMASK, &sigsaved, NULL);}return err;
}
#endifstatic int __init eventpoll_init(void)
{struct sysinfo si;si_meminfo(&si);/** Allows top 4% of lomem to be allocated for epoll watches (per user).*/max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /EP_ITEM_COST;BUG_ON(max_user_watches < 0);/** Initialize the structure used to perform epoll file descriptor* inclusion loops checks.*/ep_nested_calls_init(&poll_loop_ncalls);/* Initialize the structure used to perform safe poll wait head wake ups */ep_nested_calls_init(&poll_safewake_ncalls);/* Initialize the structure used to perform file's f_op->poll() calls */ep_nested_calls_init(&poll_readywalk_ncalls);/** We can have many thousands of epitems, so prevent this from* using an extra cache line on 64-bit (and smaller) CPUs*/BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);/* Allocates slab cache used to allocate "struct epitem" items */epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);/* Allocates slab cache used to allocate "struct eppoll_entry" */pwq_cache = kmem_cache_create("eventpoll_pwq",sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL);return 0;
}
fs_initcall(eventpoll_init);

https://linux.die.net/man/2/epoll_wait

http://www.man7.org/linux/man-pages/man2/epoll_wait.2.html

扩展阅读：NIO 源码分析(02-1) BIO 源码分析

NIO-EPollSelectorIpml源码分析

epoll源码实现分析[整理]

epoll内核源码详解+自己总结的流程   这个是比较完整的注释。

epoll内核源码分析

一文看懂DPDK

内核是导致瓶颈的原因所在，要解决问题需要绕过内核。所以主流解决方案都是旁路网卡IO，绕过内核直接在用户态收发包来解决内核的瓶颈。

图片引自Jingjing Wu的文档《Flow Bifurcation on Intel® Ethernet Controller X710/XL710》

左边是原来的方式数据从 网卡 -> 驱动 -> 协议栈 -> Socket接口 -> 业务

右边是DPDK的方式，基于UIO（Userspace I/O）旁路数据。数据从 网卡 -> DPDK轮询模式-> DPDK基础库 -> 业务

用户态的好处是易用开发和维护，灵活性好。并且Crash也不影响内核运行，鲁棒性强。