eventfd: simplify eventfd_signal()

Ever since the eventfd type was introduced back in 2007 in commit
e1ad7468c77d ("signal/timer/event: eventfd core") the eventfd_signal()
function only ever passed 1 as a value for @n. There's no point in
keeping that additional argument.

Link: https://lore.kernel.org/r/20231122-vfs-eventfd-signal-v2-2-bd549b14ce0c@kernel.org
Acked-by: Xu Yilun <yilun.xu@intel.com>
Acked-by: Andrew Donnellan <ajd@linux.ibm.com> # ocxl
Acked-by: Eric Farman <farman@linux.ibm.com> # s390
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

virt: acrn: Introduce ioeventfd

ioeventfd is a mechanism to register PIO/MMIO regions to trigger an
eventfd signal when written to by a User VM. ACRN userspace can register
any arbitrary I/O address with a corresponding eventfd and then pass the
eventfd to a specific end-point of interest for handling.

Vhost is a kernel-level virtio server which uses eventfd for signalling.
To support vhost on ACRN, ioeventfd is introduced in HSM.

A new I/O client dedicated to ioeventfd is associated with a User VM
during VM creation. HSM provides ioctls to associate an I/O region with
a eventfd. The I/O client signals a eventfd once its corresponding I/O
region is matched with an I/O request.

Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Yu Wang <yu1.wang@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210207031040.49576-16-shuo.a.liu@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>