fs: add new vfs_poll and file_can_poll helpers

These abstract out calls to the poll method in preparation for changes
in how we poll.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 602ca42..67db22f 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -884,8 +884,7 @@
 
 	pt->_key = epi->event.events;
 	if (!is_file_epoll(epi->ffd.file))
-		return epi->ffd.file->f_op->poll(epi->ffd.file, pt) &
-		       epi->event.events;
+		return vfs_poll(epi->ffd.file, pt) & epi->event.events;
 
 	ep = epi->ffd.file->private_data;
 	poll_wait(epi->ffd.file, &ep->poll_wait, pt);
@@ -2025,7 +2024,7 @@
 
 	/* The target file descriptor must support poll */
 	error = -EPERM;
-	if (!tf.file->f_op->poll)
+	if (!file_can_poll(tf.file))
 		goto error_tgt_fput;
 
 	/* Check if EPOLLWAKEUP is allowed */
diff --git a/fs/select.c b/fs/select.c
index 25da262..e30def6 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -502,14 +502,10 @@
 					continue;
 				f = fdget(i);
 				if (f.file) {
-					const struct file_operations *f_op;
-					f_op = f.file->f_op;
-					mask = DEFAULT_POLLMASK;
-					if (f_op->poll) {
-						wait_key_set(wait, in, out,
-							     bit, busy_flag);
-						mask = (*f_op->poll)(f.file, wait);
-					}
+					wait_key_set(wait, in, out, bit,
+						     busy_flag);
+					mask = vfs_poll(f.file, wait);
+
 					fdput(f);
 					if ((mask & POLLIN_SET) && (in & bit)) {
 						res_in |= bit;
@@ -825,13 +821,10 @@
 
 	/* userland u16 ->events contains POLL... bitmap */
 	filter = demangle_poll(pollfd->events) | EPOLLERR | EPOLLHUP;
-	mask = DEFAULT_POLLMASK;
-	if (f.file->f_op->poll) {
-		pwait->_key = filter | busy_flag;
-		mask = f.file->f_op->poll(f.file, pwait);
-		if (mask & busy_flag)
-			*can_busy_poll = true;
-	}
+	pwait->_key = filter | busy_flag;
+	mask = vfs_poll(f.file, pwait);
+	if (mask & busy_flag)
+		*can_busy_poll = true;
 	mask &= filter;		/* Mask out unneeded events. */
 	fdput(f);