[RFC PATCH v3 4/9] vfio/pci: macros to generate module_init and module_exit for vendor modules

Yan Zhao
2020-02-11T10:21:56Z

vendor modules call macro module_vfio_pci_register_vendor_handler to
generate module_init and module_exit.
It is necessary to ensure that vendor modules always call
vfio_pci_register_vendor_driver() on driver loading and
vfio_pci_unregister_vendor_driver on driver unloading,
because
(1) at compiling time, there's only a dependency of vendor modules on
vfio_pci.
(2) at runtime,
- vendor modules add refs of vfio_pci on a successful calling of
vfio_pci_register_vendor_driver() and deref of vfio_pci on a
successful calling of vfio_pci_unregister_vendor_driver().
- vfio_pci only adds refs of vendor module on a successful probe of vendor
driver.
vfio_pci derefs vendor module when unbinding from a device.

So, after vfio_pci is unbound from a device, the vendor module to that
device is free to get unloaded. However, if that vendor module does not
call vfio_pci_unregister_vendor_driver() in its module_exit, vfio_pci may
hold a stale pointer to vendor module.

That's how module_vfio_pci_register_vendor_handler helps.

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

Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
include/linux/vfio.h | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 43b2222da2bf..71a03471b208 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -222,4 +222,31 @@ extern int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma);
extern void vfio_pci_request(void *device_data, unsigned int count);
extern int vfio_pci_open(void *device_data);
extern void vfio_pci_release(void *device_data);
+
+#define vfio_pci_register_vendor_driver(__name, __probe, __remove, \
+ __device_ops) \
+static struct vfio_pci_vendor_driver_ops __ops ## _node = { \
+ .owner = THIS_MODULE, \
+ .name = __name, \
+ .probe = __probe, \
+ .remove = __remove, \
+ .device_ops = __device_ops, \
+}; \
+__vfio_pci_register_vendor_driver(&__ops ## _node)
+
+#define module_vfio_pci_register_vendor_handler(name, probe, remove, \
+ device_ops) \
+static int __init device_ops ## _module_init(void) \
+{ \
+ vfio_pci_register_vendor_driver(name, probe, remove, \
+ device_ops); \
+ return 0; \
+}; \
+static void __exit device_ops ## _module_exit(void) \
+{ \
+ vfio_pci_unregister_vendor_driver(device_ops); \
+}; \
+module_init(device_ops ## _module_init); \
+module_exit(device_ops ## _module_exit)
+
#endif /* VFIO_H */
--
2.17.1