[PATCH v4 1/4] epoll: convert internal api to timespec64

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

From: Willem de Bruijn <willemb@google.com>

Make epoll more consistent with select/poll: pass along the timeout as
timespec64 pointer.

In anticipation of additional changes affecting all three polling
mechanisms:

- add epoll_pwait2 syscall with timespec semantics,
  and share poll_select_set_timeout implementation.
- compute slack before conversion to absolute time,
  to save one ktime_get_ts64 call.

Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 fs/eventpoll.c | 57 ++++++++++++++++++++++++++++++++------------------
 1 file changed, 37 insertions(+), 20 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 297aeb0ee9d1..7082dfbc3166 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1714,15 +1714,25 @@ static int ep_send_events(struct eventpoll *ep,
 	return res;
 }
 
-static inline struct timespec64 ep_set_mstimeout(long ms)
+static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms)
 {
-	struct timespec64 now, ts = {
-		.tv_sec = ms / MSEC_PER_SEC,
-		.tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
-	};
+	struct timespec64 now;
+
+	if (ms < 0)
+		return NULL;
+
+	if (!ms) {
+		to->tv_sec = 0;
+		to->tv_nsec = 0;
+		return to;
+	}
+
+	to->tv_sec = ms / MSEC_PER_SEC;
+	to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC);
 
 	ktime_get_ts64(&now);
-	return timespec64_add_safe(now, ts);
+	*to = timespec64_add_safe(now, *to);
+	return to;
 }
 
 /**
@@ -1734,8 +1744,8 @@ static inline struct timespec64 ep_set_mstimeout(long ms)
  *          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
+ *           timespec. If the timeout is zero, the function will not block,
+ *           while if the @timeout ptr is NULL, the function will block
  *           until at least one event has been retrieved (or an error
  *           occurred).
  *
@@ -1743,7 +1753,7 @@ static inline struct timespec64 ep_set_mstimeout(long ms)
  *          error code, in case of error.
  */
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
-		   int maxevents, long timeout)
+		   int maxevents, struct timespec64 *timeout)
 {
 	int res, eavail, timed_out = 0;
 	u64 slack = 0;
@@ -1752,13 +1762,11 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
 
 	lockdep_assert_irqs_enabled();
 
-	if (timeout > 0) {
-		struct timespec64 end_time = ep_set_mstimeout(timeout);
-
-		slack = select_estimate_accuracy(&end_time);
+	if (timeout && (timeout->tv_sec | timeout->tv_nsec)) {
+		slack = select_estimate_accuracy(timeout);
 		to = &expires;
-		*to = timespec64_to_ktime(end_time);
-	} else if (timeout == 0) {
+		*to = timespec64_to_ktime(*timeout);
+	} else if (timeout) {
 		/*
 		 * Avoid the unnecessary trip to the wait queue loop, if the
 		 * caller specified a non blocking operation.
@@ -2177,7 +2185,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
  * part of the user space epoll_wait(2).
  */
 static int do_epoll_wait(int epfd, struct epoll_event __user *events,
-			 int maxevents, int timeout)
+			 int maxevents, struct timespec64 *to)
 {
 	int error;
 	struct fd f;
@@ -2211,7 +2219,7 @@ static int do_epoll_wait(int epfd, struct epoll_event __user *events,
 	ep = f.file->private_data;
 
 	/* Time to fish for events ... */
-	error = ep_poll(ep, events, maxevents, timeout);
+	error = ep_poll(ep, events, maxevents, to);
 
 error_fput:
 	fdput(f);
@@ -2221,7 +2229,10 @@ static int do_epoll_wait(int epfd, struct epoll_event __user *events,
 SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
 		int, maxevents, int, timeout)
 {
-	return do_epoll_wait(epfd, events, maxevents, timeout);
+	struct timespec64 to;
+
+	return do_epoll_wait(epfd, events, maxevents,
+			     ep_timeout_to_timespec(&to, timeout));
 }
 
 /*
@@ -2232,6 +2243,7 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
 		int, maxevents, int, timeout, const sigset_t __user *, sigmask,
 		size_t, sigsetsize)
 {
+	struct timespec64 to;
 	int error;
 
 	/*
@@ -2242,7 +2254,9 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
 	if (error)
 		return error;
 
-	error = do_epoll_wait(epfd, events, maxevents, timeout);
+	error = do_epoll_wait(epfd, events, maxevents,
+			      ep_timeout_to_timespec(&to, timeout));
+
 	restore_saved_sigmask_unless(error == -EINTR);
 
 	return error;
@@ -2255,6 +2269,7 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
 			const compat_sigset_t __user *, sigmask,
 			compat_size_t, sigsetsize)
 {
+	struct timespec64 to;
 	long err;
 
 	/*
@@ -2265,7 +2280,9 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
 	if (err)
 		return err;
 
-	err = do_epoll_wait(epfd, events, maxevents, timeout);
+	err = do_epoll_wait(epfd, events, maxevents,
+			    ep_timeout_to_timespec(&to, timeout));
+
 	restore_saved_sigmask_unless(err == -EINTR);
 
 	return err;
-- 
2.29.2.454.gaff20da3a2-goog