[RFC,v2,1/2] media: Add a function removing all links of a media entity

Commit Message

Sylwester Nawrocki June 9, 2013, 7:41 p.m. UTC

This function allows to remove all media entity's links to other
entities, leaving no references to a media entity's links array
at its remote entities.

Currently, when a driver of some entity is removed it will free its
media entities links[] array, leaving dangling pointers at other
entities that are part of same media graph. This is troublesome when
drivers of a media device entities are in separate kernel modules,
removing only some modules will leave others in an incorrect state.

This function is intended to be used when an entity is being
unregistered from a media device.

With an assumption that normally the media links should be created
between media entities registered to a media device and with the
graph mutex held.

Signed-off-by: Sylwester Nawrocki <[e-mail]>
Reviewed-by: Andrzej Hajda <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>
---

Changes since v1:
 - couple code improvements like variable localization, type change, etc.
 - removed WARN_ON_ONCE() to avoid warnings when the media_entity_remove_links()
   function is called from within remove() callback of a driver of subdev
   which has not yet been registered to the media device, e.g. due to
   deferred probing, with a call stack like
      -> remove()
         -> v4l2_device_unregister_subdev()
            -> media_entity_remove_links()
---
 drivers/media/media-entity.c |   48 ++++++++++++++++++++++++++++++++++++++++++
 include/media/media-entity.h |    3 ++
 2 files changed, 51 insertions(+), 0 deletions(-)

Patch

diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
index e1cd132..f5ea82e 100644
--- a/drivers/media/media-entity.c
+++ b/drivers/media/media-entity.c
@@ -429,6 +429,54 @@  media_entity_create_link(struct media_entity *source, u16 source_pad,
 }
 EXPORT_SYMBOL_GPL(media_entity_create_link);
 
+void __media_entity_remove_links(struct media_entity *entity)
+{
+	unsigned int i;
+
+	for (i = 0; i < entity->num_links; i++) {
+		struct media_link *link = &entity->links[i];
+		struct media_entity *remote;
+		unsigned int r, num_links;
+
+		if (link->source->entity == entity)
+			remote = link->sink->entity;
+		else
+			remote = link->source->entity;
+
+		num_links = remote->num_links;
+
+		for (r = 0; r < num_links; r++) {
+			if (remote->links[r] != link->reverse)
+				continue;
+
+			if (link->source->entity == entity)
+				remote->num_backlinks--;
+
+			if (--remote->num_links == 0)
+				break;
+
+			/* Insert last entry in place of the dropped link. */
+			remote->links[r--] = remote->links[remote->num_links];
+		}
+	}
+
+	entity->num_links = 0;
+	entity->num_backlinks = 0;
+}
+EXPORT_SYMBOL_GPL(__media_entity_remove_links);
+
+void media_entity_remove_links(struct media_entity *entity)
+{
+	/* Do nothing if the entity is not registered. */
+	if (entity->parent == NULL)
+		return;
+
+	mutex_lock(&entity->parent->graph_mutex);
+	__media_entity_remove_links(entity);
+	mutex_lock(&entity->parent->graph_mutex);
+}
+EXPORT_SYMBOL_GPL(media_entity_remove_links);
+
 static int __media_entity_setup_link_notify(struct media_link *link, u32 flags)
 {
 	int ret;
diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 0c16f51..0d941d2 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -128,6 +128,9 @@  void media_entity_cleanup(struct media_entity *entity);
 
 int media_entity_create_link(struct media_entity *source, u16 source_pad,
 		struct media_entity *sink, u16 sink_pad, u32 flags);
+void __media_entity_remove_links(struct media_entity *entity);
+void media_entity_remove_links(struct media_entity *entity);
+
 int __media_entity_setup_link(struct media_link *link, u32 flags);
 int media_entity_setup_link(struct media_link *link, u32 flags);
 struct media_link *media_entity_find_link(struct media_pad *source,