floppy: fix open(O_ACCMODE) for ioctl-only open

Commit 09954bad ("floppy: refactor open() flags handling"), as a
side-effect, causes open(/dev/fdX, O_ACCMODE) to fail. It turns out that
this is being used setfdprm userspace for ioctl-only open().

Reintroduce back the original behavior wrt !(FMODE_READ|FMODE_WRITE)
modes, while still keeping the original O_NDELAY bug fixed.

Cc: stable@vger.kernel.org # v4.5+
Reported-by: NWim Osterholt <wim@djo.tudelft.nl>
Tested-by: NWim Osterholt <wim@djo.tudelft.nl>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>
Signed-off-by: NJens Axboe <axboe@fb.com>

drivers/block/floppy.c

@@ -3663,11 +3663,6 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
 
 	opened_bdev[drive] = bdev;
 
-	if (!(mode & (FMODE_READ|FMODE_WRITE))) {
-		res = -EINVAL;
-		goto out;
-	}
-
 	res = -ENXIO;
 
 	if (!floppy_track_buffer) {
@@ -3711,6 +3706,7 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
 	if (UFDCS->rawcmd == 1)
 		UFDCS->rawcmd = 2;
 
+	if (mode & (FMODE_READ|FMODE_WRITE)) {
 		UDRS->last_checked = 0;
 		clear_bit(FD_OPEN_SHOULD_FAIL_BIT, &UDRS->flags);
 		check_disk_change(bdev);
@@ -3718,6 +3714,7 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
 			goto out;
 		if (test_bit(FD_OPEN_SHOULD_FAIL_BIT, &UDRS->flags))
 			goto out;
+	}
 
 	res = -EROFS;