vfio: Split virqfd into a separate module for vfio bus drivers

An unintended consequence of commit 42ac9bd18d4f ("vfio: initialize
the virqfd workqueue in VFIO generic code") is that the vfio module
is renamed to vfio_core so that it can include both vfio and virqfd.
That's a user visible change that may break module loading scritps
and it imposes eventfd support as a dependency on the core vfio code,
which it's really not.  virqfd is intended to be provided as a service
to vfio bus drivers, so instead of wrapping it into vfio.ko, we can
make it a stand-alone module toggled by vfio bus drivers.  This has
the additional benefit of removing initialization and exit from the
core vfio code.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/Kconfig

@@ -13,6 +13,11 @@ config VFIO_SPAPR_EEH
 	depends on EEH && VFIO_IOMMU_SPAPR_TCE
 	default n
 
+config VFIO_VIRQFD
+	tristate
+	depends on VFIO && EVENTFD
+	default n
+
 menuconfig VFIO
 	tristate "VFIO Non-Privileged userspace driver framework"
 	depends on IOMMU_API

drivers/vfio/Makefile

@@ -1,6 +1,7 @@
-vfio_core-y := vfio.o virqfd.o
+vfio_virqfd-y := virqfd.o
 
-obj-$(CONFIG_VFIO) += vfio_core.o
+obj-$(CONFIG_VFIO) += vfio.o
+obj-$(CONFIG_VFIO_VIRQFD) += vfio_virqfd.o
 obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
 obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
 obj-$(CONFIG_VFIO_SPAPR_EEH) += vfio_spapr_eeh.o

drivers/vfio/pci/Kconfig

@@ -1,6 +1,7 @@
 config VFIO_PCI
 	tristate "VFIO support for PCI devices"
 	depends on VFIO && PCI && EVENTFD
+	select VFIO_VIRQFD
 	help
 	  Support for the PCI VFIO bus driver.  This is required to make
 	  use of PCI drivers using the VFIO framework.

drivers/vfio/platform/Kconfig

@@ -1,6 +1,7 @@
 config VFIO_PLATFORM
 	tristate "VFIO support for platform devices"
 	depends on VFIO && EVENTFD && ARM
+	select VFIO_VIRQFD
 	help
 	  Support for platform devices with VFIO. This is required to make
 	  use of platform devices present on the system using the VFIO

drivers/vfio/vfio.c

@@ -1552,11 +1552,6 @@ static int __init vfio_init(void)
 	if (ret)
 		goto err_cdev_add;
 
-	/* Start the virqfd cleanup handler used by some VFIO bus drivers */
-	ret = vfio_virqfd_init();
-	if (ret)
-		goto err_virqfd;
-
 	pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
 
 	/*
@@ -1569,8 +1564,6 @@ static int __init vfio_init(void)
 
 	return 0;
 
-err_virqfd:
-	cdev_del(&vfio.group_cdev);
 err_cdev_add:
 	unregister_chrdev_region(vfio.group_devt, MINORMASK);
 err_alloc_chrdev:
@@ -1585,7 +1578,6 @@ static void __exit vfio_cleanup(void)
 {
 	WARN_ON(!list_empty(&vfio.group_list));
 
-	vfio_virqfd_exit();
 	idr_destroy(&vfio.group_idr);
 	cdev_del(&vfio.group_cdev);
 	unregister_chrdev_region(vfio.group_devt, MINORMASK);

drivers/vfio/virqfd.c

@@ -13,12 +13,17 @@
 #include <linux/vfio.h>
 #include <linux/eventfd.h>
 #include <linux/file.h>
+#include <linux/module.h>
 #include <linux/slab.h>
 
+#define DRIVER_VERSION  "0.1"
+#define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@redhat.com>"
+#define DRIVER_DESC     "IRQFD support for VFIO bus drivers"
+
 static struct workqueue_struct *vfio_irqfd_cleanup_wq;
 static DEFINE_SPINLOCK(virqfd_lock);
 
-int __init vfio_virqfd_init(void)
+static int __init vfio_virqfd_init(void)
 {
 	vfio_irqfd_cleanup_wq =
 		create_singlethread_workqueue("vfio-irqfd-cleanup");
@@ -28,7 +33,7 @@ int __init vfio_virqfd_init(void)
 	return 0;
 }
 
-void vfio_virqfd_exit(void)
+static void __exit vfio_virqfd_exit(void)
 {
 	destroy_workqueue(vfio_irqfd_cleanup_wq);
 }
@@ -211,3 +216,11 @@ void vfio_virqfd_disable(struct virqfd **pvirqfd)
 	flush_workqueue(vfio_irqfd_cleanup_wq);
 }
 EXPORT_SYMBOL_GPL(vfio_virqfd_disable);
+
+module_init(vfio_virqfd_init);
+module_exit(vfio_virqfd_exit);
+
+MODULE_VERSION(DRIVER_VERSION);
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);

include/linux/vfio.h

@@ -142,8 +142,6 @@ struct virqfd {
 	struct virqfd		**pvirqfd;
 };
 
-extern int vfio_virqfd_init(void);
-extern void vfio_virqfd_exit(void);
 extern int vfio_virqfd_enable(void *opaque,
 			      int (*handler)(void *, void *),
 			      void (*thread)(void *, void *),