77 	kstat_named_t	polllistmiss;	/* failed to find a cached poll list */
102 /* Contention lock & list for preventing deadlocks in recursive /dev/poll. */
118  * The per-thread poll state consists of
129  *	poll when a cached fd is closed. This is protected by uf_lock.
148  * Whenever possible the design relies on the fact that the poll cache state
149  * is per thread thus for both poll and exit it is self-synchronizing.
154  * The two key locks in poll proper is ps_lock and pc_lock.
156  * The ps_lock is used for synchronization between poll, (lwp_)exit and close
158  * This lock is held through most of poll() except where poll sleeps
160  * of poll.
162  * structures (which are accessed by poll, pollwakeup, and polltime)
165  * Those exceptions occur in poll when first allocating the per-thread state,
166  * when poll grows the number of polldat (never shrinks), and when
168  * pollheads or fpollinfo to the threads poll state.
170  * Poll(2) system call is the only path which ps_lock and pc_lock are both
175  * that poll acquires these locks in the order of pc_lock and then PHLOCK
179  * from exiting and freeing all of the poll related state. Thus is done
186  * issues. Poll holds ps_lock and/or pc_lock across calls to getf/releasef
187  * which acquire uf_lock. The poll cleanup in close needs to hold uf_lock
188  * to prevent poll or exit from doing a delfpollinfo after which the thread
190  * the poll cache state. The solution is to use pc_busy and do the close
193  *	This prevents the per-thread poll related state from being freed.
198  *	poll has been woken up and checked getf() again).
200  * When removing a polled fd from poll cache, the fd is always removed
230  * (which hold poll locks on entry to xx_poll(), then acquire foo)
231  * and pollwakeup() threads (which hold foo, then acquire poll locks).
233  * pollunlock(*cookie) releases whatever poll locks the current thread holds,
236  * pollrelock(cookie) reacquires previously dropped poll locks;
242  * /dev/poll is in progress and pollcache locks cannot be dropped.  Callers
255 	 * of a recursive /dev/poll operation.  in pollunlock()
264 	 * t_pollcache is set by /dev/poll and event ports (port_fd.c).  in pollunlock()
265 	 * If the pollrelock/pollunlock is called as a result of poll(2),  in pollunlock()
301 	 * t_pollcache is set by /dev/poll and event ports (port_fd.c).  in pollrelock()
302 	 * If the pollrelock/pollunlock is called as a result of poll(2),  in pollrelock()
382 	 * Check to see if this one just wants to use poll() as a timeout.  in poll_common()
422 	 * NOTE: for performance, buffers are saved across poll() calls.  in poll_common()
423 	 * The theory is that if a process polls heavily, it tends to poll  in poll_common()
448 		 * poll lists are keyed by the address of the passed-in fds  in poll_common()
450 		 * poll cache list entry.  As such, we elect not to support  in poll_common()
451 		 * NULL as a valid (user) memory address and fail the poll()  in poll_common()
459 	 * If this thread polls for the first time, allocate ALL poll  in poll_common()
460 	 * cache data structures and cache the poll fd list. This  in poll_common()
462 	 * (i.e. using poll as timeout()) don't need this memory.  in poll_common()
470 		 * poll and cache this poll fd list in ps_pcacheset[0].  in poll_common()
481 		 * Not first time polling. Select a cached poll list by  in poll_common()
494 				 * difference of the current poll  in poll_common()
498 				 * of cached poll list and cache content.  in poll_common()
519 				 * this poll list.  in poll_common()
532 			 * We failed to find a matching cached poll fd list.  in poll_common()
555 	 * the pcache before updating poll bitmap.  in poll_common()
578 		 * If you get here, the poll of fds was unsuccessful.  in poll_common()
601 		 * Continue around and poll fds again.  in poll_common()
660  * This is the system call trap that poll(),
706  * Clean up any state left around by poll(2). Called when a thread exits.
718 	 * free up all cached poll fds  in pollcleanup()
721 		/* this pollstate is used by /dev/poll */  in pollcleanup()
760  * pollwakeup() - poke threads waiting in poll() for some event
860 				 *	   and is trying to get out of poll().  in pollwakeup()
903 	 * thread attempting to poll this port are blocked. There can be  in pollwakeup()
1030  * walk through the poll fd lists to see if they are identical. This is an
1031  * expensive operation and should not be done more than once for each poll()
1036  * Zeroing out the revents field of each entry in current poll list is
1037  * required by poll man page.
1039  * Since the events field of cached list has illegal poll events filtered
1058 			 * Filter out invalid poll events while we are in  in pcacheset_cmp()
1081  * This routine returns a pointer to a cached poll fd entry, or NULL if it
1249 	 * we come here because an earlier close() on this cached poll fd.  in pcacheset_invalidate()
1290  * Insert poll fd into the pollcache, and add poll registration.
1309 	 * The poll caching uses the existing VOP_POLL interface. If there  in pcache_insert()
1311 	 * one is sleeping in poll" flag. When the polled events happen  in pcache_insert()
1341 	 * If this entry was used to cache a poll fd which was closed, and  in pcache_insert()
1373 	 * by different threads. Unless this is a new first poll(), pd_events  in pcache_insert()
1375 	 * is no way to cancel that event. In that case, poll degrade to its  in pcache_insert()
1376 	 * old form -- polling on this fd every time poll() is called. The  in pcache_insert()
1385 	 * appearance in poll list. If this is called from pcacheset_cache_list,  in pcache_insert()
1398 		 * xf_position records the fd's first appearance in poll list  in pcache_insert()
1578  * resolve the difference between the current poll list and a cached one.
1610 		 * the length of poll list has changed. allocate a new  in pcacheset_resolve()
1619 	 * The comparison is done on the current poll list and the  in pcacheset_resolve()
1621 	 * cached list for next poll.  in pcacheset_resolve()
1675 					 * poll list. Find the next one on the  in pcacheset_resolve()
1724 					 * after we updated cache poll list  in pcacheset_resolve()
1732 						 * entry in cached poll list  in pcacheset_resolve()
1739 						 * effect on next poll().  in pcacheset_resolve()
1854 	 *    will be called on this fd in next poll.  in pcacheset_resolve()
1860 	 * make sure cross reference between cached poll lists and cached  in pcacheset_resolve()
1861 	 * poll fds are correct.  in pcacheset_resolve()
1898  * read the bitmap and poll on fds corresponding to the '1' bits. The ps_lock
1928 		 * only poll fds which may have events  in pcache_poll()
1943 			 * A bitmap caches poll state information of  in pcache_poll()
1944 			 * multiple poll lists. Call VOP_POLL only if  in pcache_poll()
1945 			 * the bit corresponds to an fd in this poll  in pcache_poll()
1961 			 * blocked in poll. This ensures that we don't  in pcache_poll()
1972 					 * in the poll list. Find all of them.  in pcache_poll()
1996 					 * in the poll list. Find all of them.  in pcache_poll()
2011 			 * Since we no longer hold poll head lock across  in pcache_poll()
2018 			 * flag when it sees the poll may block. Pollwakeup()  in pcache_poll()
2025 			 * the pd_events is union of all cached poll events  in pcache_poll()
2027 			 * how the polled device sets the "poll pending"  in pcache_poll()
2035 			 * poll entry. To prevent close() coming in to clear  in pcache_poll()
2067 					 * in the poll list. This is rare but  in pcache_poll()
2106 					 * wakeup on this device. Re-poll once.  in pcache_poll()
2115 					 * in the poll list. This is rare but  in pcache_poll()
2144  * Going through the poll list without much locking. Poll all fds and
2164 	 * cache the new poll list in pollcachset.  in pcacheset_cache_list()
2173 	 * We have saved a copy of current poll fd list in one pollcacheset.  in pcacheset_cache_list()
2181 		 * We also filter out the illegal poll events in the event  in pcacheset_cache_list()
2182 		 * field for the cached poll list/set.  in pcacheset_cache_list()
2195 			 * invalidate this cache entry in the cached poll list  in pcacheset_cache_list()
2210 			 * poll list. Undo every thing.  in pcacheset_cache_list()
2249 	 * set the event in cached poll lists to POLLCLOSED. This invalidate  in pcache_clean_entry()
2250 	 * the cached poll fd entry in that poll list, which will force a  in pcache_clean_entry()
2251 	 * removal of this cached entry in next poll(). The cleanup is done  in pcache_clean_entry()
2425 			 * to calculate a final depth for the local /dev/poll  in pollstate_contend()
2492 		 * called on a recursion-enabled /dev/poll handle from outside  in pollstate_enter()
2493 		 * the poll() or /dev/poll codepaths.  in pollstate_enter()
2556  * Complete phase 2 of cached poll fd cleanup. Call pcache_clean_entry to mark
2557  * the pcacheset events field POLLCLOSED to force the next poll() to remove
2559  * lwp block in poll() needs the info to return. Wakeup anyone blocked in
2560  * poll and let exiting lwp go. No lock is help upon entry. So it's OK for
2613  * this routine implements poll cache list replacement policy.
2645  * (2) /dev/poll.
2646  * When a polled fd is cached in /dev/poll, its polldat will remain on the
2670 			 * to synchronize this lwp with any other /dev/poll  in pollhead_clean()
2788  * for resolved set poll list, the xref info in the pcache should be
2789  * consistent with this poll list.
2900  * current poll list should be 0.
2954 	 * allocate enough bits for the poll fd list  in pcache_create()
3034  * Check each duplicated poll fd in the poll list. It may be necessary to
3035  * VOP_POLL the same fd again using different poll events. getf() has been
3037  * entire poll fd list. It returns -1 if underlying vnode has changed during