vfio/mdev: add mdev available instance checking to the core

Many of the mdev drivers use a simple counter for keeping track of the
available instances. Move this code to the core code and store the counter
in the mdev_parent. Implement it using correct locking, fixing mdpy.

Drivers just provide the value in the mdev_driver at registration time
and the core code takes care of maintaining it and exposing the value in
sysfs.

[hch: count instances per-parent instead of per-type, use an atomic_t
 to avoid taking mdev_list_lock in the show method]

Signed-off-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Reviewed-by: Kirti Wankhede <[email protected]>
Reviewed-by: Eric Farman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alex Williamson <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/mdev.h b/include/linux/mdev.h
index 33674cb5ed5d..139d05b26f82 100644
--- a/include/linux/mdev.h
+++ b/include/linux/mdev.h
@@ -45,6 +45,7 @@ struct mdev_parent {
 	struct rw_semaphore unreg_sem;
 	struct mdev_type **types;
 	unsigned int nr_types;
+	atomic_t available_instances;
 };
 
 static inline struct mdev_device *to_mdev_device(struct device *dev)
@@ -55,6 +56,7 @@ static inline struct mdev_device *to_mdev_device(struct device *dev)
 /**
  * struct mdev_driver - Mediated device driver
  * @device_api: string to return for the device_api sysfs
+ * @max_instances: maximum number of instances supported (optional)
  * @probe: called when new device created
  * @remove: called when device removed
  * @get_available: Return the max number of instances that can be created
@@ -63,6 +65,7 @@ static inline struct mdev_device *to_mdev_device(struct device *dev)
  **/
 struct mdev_driver {
 	const char *device_api;
+	unsigned int max_instances;
 	int (*probe)(struct mdev_device *dev);
 	void (*remove)(struct mdev_device *dev);
 	unsigned int (*get_available)(struct mdev_type *mtype);