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epoll: fix compiler warning and optimize the non-blocking path 

Add a comment to ep_poll(), rename labels a bit clearly, fix a warning of
unused variable from gcc and optimize the non-blocking path a little.

Hinted-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>

hannes@cmpxchg.org:

: The non-blocking ep_poll path optimization introduced skipping over the
: return value setup.
:
: Initialize it properly, my userspace gets upset by epoll_wait() returning
: random things.
:
: In addition, remove the reinitialization at the fetch_events label, the
: return value is garuanteed to be zero when execution reaches there.

[hannes@cmpxchg.org: fix initialization]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Shawn Bohrer 2011-03-22 16:34:47 -07:00 committed by Linus Torvalds
parent 3fb0e584a6
commit f4d93ad74c
1 changed files with 28 additions and 5 deletions
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33
fs/eventpoll.c
View File

@ -1148,12 +1148,29 @@ static inline struct timespec ep_set_mstimeout(long ms)
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, eavail, timed_out = 0;
int res = 0, eavail, timed_out = 0;
unsigned long flags;
long slack;
long slack = 0;
wait_queue_t wait;
ktime_t expires, *to = NULL;
@ -1164,13 +1181,18 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
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;
}
retry:
fetch_events:
spin_lock_irqsave(&ep->lock, flags);
res = 0;
if (!ep_events_available(ep)) {
/*
* We don't have any available event to return to the caller.
@ -1204,6 +1226,7 @@ retry:
set_current_state(TASK_RUNNING);
}
check_events:
/* Is it worth to try to dig for events ? */
eavail = ep_events_available(ep);
@ -1216,7 +1239,7 @@ retry:
*/
if (!res && eavail &&
!(res = ep_send_events(ep, events, maxevents)) && !timed_out)
goto retry;
goto fetch_events;
return res;
}