floppy: remove floppy-specific O_EXCL handling

Block layer now handles O_EXCL in a generic way for block devices.

The semantics is however different for floppy and all other block devices,
as floppy driver contains its own O_EXCL handling.

The semantics for all-but-floppy bdevs is "there can be at most one O_EXCL
open of this file", while for floppy bdev the semantics is "if someone has
the bdev open with O_EXCL, noone else can open it".

There is actual userspace-observable change in behavior because of this
since commit e525fd89d380c ("block: make blkdev_get/put() handle exclusive
access") -- on kernels containing this commit, mount of /dev/fd0 causes
the fd0 block device be claimed with _EXCL, preventing subsequent
open(/dev/fd0).

Bring things back into shape, i.e.  make it possible, analogically to
other block devices, to mount the floppy and open() it afterwards --
remove the floppy-specific handling and let the generic bdev code O_EXCL
handling take over.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: NeilBrown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/block/floppy.c

@@ -3607,9 +3607,7 @@ static int floppy_release(struct gendisk *disk, fmode_t mode)
 
 	mutex_lock(&floppy_mutex);
 	mutex_lock(&open_lock);
-	if (UDRS->fd_ref < 0)
-		UDRS->fd_ref = 0;
-	else if (!UDRS->fd_ref--) {
+	if (!UDRS->fd_ref--) {
 		DPRINT("floppy_release with fd_ref == 0");
 		UDRS->fd_ref = 0;
 	}
@@ -3645,13 +3643,7 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
 		set_bit(FD_VERIFY_BIT, &UDRS->flags);
 	}
 
-	if (UDRS->fd_ref == -1 || (UDRS->fd_ref && (mode & FMODE_EXCL)))
-		goto out2;
-
-	if (mode & FMODE_EXCL)
-		UDRS->fd_ref = -1;
-	else
-		UDRS->fd_ref++;
+	UDRS->fd_ref++;
 
 	opened_bdev[drive] = bdev;
 
@@ -3714,10 +3706,8 @@ static int floppy_open(struct block_device *bdev, fmode_t mode)
 	mutex_unlock(&floppy_mutex);
 	return 0;
 out:
-	if (UDRS->fd_ref < 0)
-		UDRS->fd_ref = 0;
-	else
-		UDRS->fd_ref--;
+	UDRS->fd_ref--;
+
 	if (!UDRS->fd_ref)
 		opened_bdev[drive] = NULL;
 out2: