[PATCH 4/7] sync_file: add support for sem_file

[Dave Airlie]

From: Dave Airlie <airlied at redhat.com>

This adds support for a file that has semaphore semantics
(for Vulkan shared semaphores).

These objects are persistent objects that can have a
fence that changes. When the object is signaled, a fence
is attached to it, and when an object is waited on, the
fence is removed. All interactions with these objects
should be via command submission routines in the drm
drivers. The sem_file is just for passing the sems between
processes.

Signed-off-by: Dave Airlie <airlied at redhat.com>
---
 drivers/dma-buf/sync_file.c | 101 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/sync_file.h   |  16 +++++++
 2 files changed, 117 insertions(+)

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 2342d8b..a88d786 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -468,3 +468,104 @@ static const struct file_operations sync_file_fops = {
 	.unlocked_ioctl = sync_file_ioctl,
 	.compat_ioctl = sync_file_ioctl,
 };
+
+static int sem_file_release(struct inode *inode, struct file *file)
+{
+	struct sem_file *sem_file = file->private_data;
+	struct dma_fence *fence;
+
+	fence = rcu_dereference_protected(sem_file->base.fence, 1);
+	dma_fence_put(fence);
+	kfree(sem_file);
+
+	return 0;
+}
+
+static const struct file_operations sem_file_fops = {
+	.release = sem_file_release,
+};
+
+struct sem_file *sem_file_alloc(void)
+{
+	struct sem_file *sem_file;
+	int ret;
+
+	sem_file = kzalloc(sizeof(*sem_file), GFP_KERNEL);
+	if (!sem_file)
+		return NULL;
+
+	ret = fence_file_init(&sem_file->base,
+			      &sem_file_fops);
+	if (ret)
+		goto err;
+
+	RCU_INIT_POINTER(sem_file->base.fence, NULL);
+	mutex_init(&sem_file->lock);
+
+	return sem_file;
+
+err:
+	kfree(sem_file);
+	return NULL;
+}
+EXPORT_SYMBOL(sem_file_alloc);
+
+struct sem_file *sem_file_fdget(int fd)
+{
+	struct file *file = fget(fd);
+
+	if (!file)
+		return NULL;
+
+	if (file->f_op != &sem_file_fops)
+		goto err;
+
+	return file->private_data;
+
+err:
+	fput(file);
+	return NULL;
+}
+EXPORT_SYMBOL(sem_file_fdget);
+
+#define sem_file_held(obj) lockdep_is_held(&(obj)->lock)
+
+struct dma_fence *sem_file_get_fence(struct sem_file *sem_file)
+{
+	struct dma_fence *fence;
+
+	if (!rcu_access_pointer(sem_file->base.fence)) {
+		return NULL;
+	}
+
+	rcu_read_lock();
+	fence = dma_fence_get_rcu_safe(&sem_file->base.fence);
+	rcu_read_unlock();
+	return fence;
+}
+EXPORT_SYMBOL(sem_file_get_fence);
+
+static inline struct dma_fence *
+sem_file_get_fence_locked(struct sem_file *sem_file)
+{
+	return rcu_dereference_protected(sem_file->base.fence,
+					 sem_file_held(sem_file));
+}
+
+int sem_file_replace_fence(struct sem_file *sem_file,
+			   struct dma_fence *fence,
+			   struct dma_fence **old_fence)
+{
+	struct dma_fence *ret_fence = NULL;
+
+	if (fence)
+		dma_fence_get(fence);
+
+	mutex_lock(&sem_file->lock);
+	ret_fence = sem_file_get_fence_locked(sem_file);
+	RCU_INIT_POINTER(sem_file->base.fence, fence);
+	mutex_unlock(&sem_file->lock);
+	*old_fence = ret_fence;
+	return 0;
+}
+EXPORT_SYMBOL(sem_file_replace_fence);
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
index b0ae1cf..49735c8 100644
--- a/include/linux/sync_file.h
+++ b/include/linux/sync_file.h
@@ -54,4 +54,20 @@ struct sync_file {
 struct sync_file *sync_file_create(struct dma_fence *fence);
 struct dma_fence *sync_file_get_fence(int fd);
 
+
+/**
+ * struct sem_file - shared semaphore file for userspace.
+ * @base: base fence file.
+ * @lock: mutex to lock the fence_file fence ptr.
+ */
+struct sem_file {
+	struct fence_file base;
+	struct mutex lock;
+};
+struct sem_file *sem_file_create(void);
+struct sem_file *sem_file_fdget(int fd);
+struct dma_fence *sem_file_get_fence(struct sem_file *sem_file);
+int sem_file_replace_fence(struct sem_file *sem_file,
+			   struct dma_fence *fence,
+			   struct dma_fence **old_fence);
 #endif /* _LINUX_SYNC_H */
-- 
2.9.3