Re: [PATCH v14 19/20] vfio: initialize the virqfd workqueue in VFIO generic code

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 2015-03-17 at 16:29 -0600, Alex Williamson wrote:
> On Mon, 2015-03-02 at 17:59 +0100, Baptiste Reynal wrote:
> > From: Antonios Motakis <a.motakis@virtualopensystems.com>
> > 
> > Now we have finally completely decoupled virqfd from VFIO_PCI. We can
> > initialize it from the VFIO generic code, in order to safely use it from
> > multiple independent VFIO bus drivers.
> > 
> > Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
> > Signed-off-by: Baptiste Reynal <b.reynal@virtualopensystems.com>
> > ---
> >  drivers/vfio/Makefile       | 4 +++-
> >  drivers/vfio/pci/Makefile   | 3 +--
> >  drivers/vfio/pci/vfio_pci.c | 8 --------
> >  drivers/vfio/vfio.c         | 8 ++++++++
> >  4 files changed, 12 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
> > index dadf0ca..d798b09 100644
> > --- a/drivers/vfio/Makefile
> > +++ b/drivers/vfio/Makefile
> > @@ -1,4 +1,6 @@
> > -obj-$(CONFIG_VFIO) += vfio.o
> > +vfio_core-y := vfio.o virqfd.o
> > +
> > +obj-$(CONFIG_VFIO) += vfio_core.o
> >  obj-$(CONFIG_VFIO_IOMMU_TYPE1) += vfio_iommu_type1.o
> >  obj-$(CONFIG_VFIO_IOMMU_SPAPR_TCE) += vfio_iommu_spapr_tce.o
> >  obj-$(CONFIG_VFIO_SPAPR_EEH) += vfio_spapr_eeh.o
> 
> This inadvertently (I assume) renames the main vfio module to vfio_core.
> That potentially breaks numerous userspace scripts that might try to
> load the "vfio" module.  I don't think that's acceptable.  A brute force
> way to fix this would be to rename vfio.c to vfio_core.c and change the
> Makefile to:
> 
> vfio-y := vfio_core.o virqfd.o
> obj-$(CONFIG_VFIO) += vfio.o
> 
> Is there any other trickery available to us that could include virqfd.o
> in vfio.o w/o source file renaming?  Thanks,

Maybe a better option, we could let virqfd be it's own support module
for bus drivers that need it.  Then we keep it out of vfio "core".
Something like this:

commit f4d91ec4b72ce11e9dba861d6bf2dba93b72f0ba
Author: Alex Williamson <alex.williamson@redhat.com>
Date:   Tue Mar 17 08:33:38 2015 -0600

    vfio: Split virqfd into a separate module for vfio bus drivers
    
    An unintended consequence of splittng virqfd support to be shared
    by bus drivers is renaming the core vfio module to vfio_core.  This
    is not very friendly to user scripts that may try to load the vfio
    module.  To resolve that and to make it clear that virqfd is a bus
    driver service and not a dependency of vfio core, move this to a
    separate module on which the bus drivers will depend.
    
    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
index d5322a4..7d092dd 100644
--- a/drivers/vfio/Kconfig
+++ b/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
diff --git a/drivers/vfio/Makefile b/drivers/vfio/Makefile
index d798b09..7b8a31f 100644
--- a/drivers/vfio/Makefile
+++ b/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
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index c6bb5da..579d83b 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/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.
diff --git a/drivers/vfio/platform/Kconfig b/drivers/vfio/platform/Kconfig
index c0a3bff..4ec14af 100644
--- a/drivers/vfio/platform/Kconfig
+++ b/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
@@ -11,6 +12,7 @@ config VFIO_PLATFORM
 config VFIO_AMBA
 	tristate "VFIO support for AMBA devices"
 	depends on VFIO_PLATFORM && ARM_AMBA
+	select VFIO_VIRQFD
 	help
 	  Support for ARM AMBA devices with VFIO. This is required to make
 	  use of ARM AMBA devices present on the system using the VFIO
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 86aac7e..0d33662 100644
--- a/drivers/vfio/vfio.c
+++ b/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);
diff --git a/drivers/vfio/virqfd.c b/drivers/vfio/virqfd.c
index 3d19aaf..ede0ca1 100644
--- a/drivers/vfio/virqfd.c
+++ b/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     "VFIO virqfd"
+
 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);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 683b514..cbed15f 100644
--- a/include/linux/vfio.h
+++ b/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 *),