Use wl_container_of() instead of casts

This slightly improves type safety.

The culprits were found with:

    git grep -E '\([a-z0-9_ ]+ \*\)\W?[a-z]'

3 files changed, 14 insertions, 9 deletions

diff --git a/render/allocator/drm_dumb.c b/render/allocator/drm_dumb.c
index 684ba2e3..03ff8e3f 100644
--- a/render/allocator/drm_dumb.c
+++ b/render/allocator/drm_dumb.c
@@ -25,7 +25,8 @@ static const struct wlr_buffer_impl buffer_impl;
 static struct wlr_drm_dumb_buffer *drm_dumb_buffer_from_buffer(
 		struct wlr_buffer *wlr_buf) {
 	assert(wlr_buf->impl == &buffer_impl);
-	return (struct wlr_drm_dumb_buffer *)wlr_buf;
+	struct wlr_drm_dumb_buffer *buf = wl_container_of(wlr_buf, buf, base);
+	return buf;
 }
 
 static struct wlr_drm_dumb_buffer *create_buffer(
@@ -163,7 +164,8 @@ static const struct wlr_allocator_interface allocator_impl;
 static struct wlr_drm_dumb_allocator *drm_dumb_alloc_from_alloc(
 		struct wlr_allocator *wlr_alloc) {
 	assert(wlr_alloc->impl == &allocator_impl);
-	return (struct wlr_drm_dumb_allocator *)wlr_alloc;
+	struct wlr_drm_dumb_allocator *alloc = wl_container_of(wlr_alloc, alloc, base);
+	return alloc;
 }
 
 static struct wlr_buffer *allocator_create_buffer(
diff --git a/render/allocator/gbm.c b/render/allocator/gbm.c
index 149ff6b9..32636d30 100644
--- a/render/allocator/gbm.c
+++ b/render/allocator/gbm.c
@@ -17,9 +17,10 @@
 static const struct wlr_buffer_impl buffer_impl;
 
 static struct wlr_gbm_buffer *get_gbm_buffer_from_buffer(
-		struct wlr_buffer *buffer) {
-	assert(buffer->impl == &buffer_impl);
-	return (struct wlr_gbm_buffer *)buffer;
+		struct wlr_buffer *wlr_buffer) {
+	assert(wlr_buffer->impl == &buffer_impl);
+	struct wlr_gbm_buffer *buffer = wl_container_of(wlr_buffer, buffer, base);
+	return buffer;
 }
 
 static bool export_gbm_bo(struct gbm_bo *bo,
@@ -179,9 +180,10 @@ static const struct wlr_buffer_impl buffer_impl = {
 static const struct wlr_allocator_interface allocator_impl;
 
 static struct wlr_gbm_allocator *get_gbm_alloc_from_alloc(
-		struct wlr_allocator *alloc) {
-	assert(alloc->impl == &allocator_impl);
-	return (struct wlr_gbm_allocator *)alloc;
+		struct wlr_allocator *wlr_alloc) {
+	assert(wlr_alloc->impl == &allocator_impl);
+	struct wlr_gbm_allocator *alloc = wl_container_of(wlr_alloc, alloc, base);
+	return alloc;
 }
 
 struct wlr_allocator *wlr_gbm_allocator_create(int fd) {
diff --git a/render/allocator/shm.c b/render/allocator/shm.c
index 55a8fab2..b6d3138c 100644
--- a/render/allocator/shm.c
+++ b/render/allocator/shm.c
@@ -17,7 +17,8 @@ static const struct wlr_buffer_impl buffer_impl;
 static struct wlr_shm_buffer *shm_buffer_from_buffer(
 		struct wlr_buffer *wlr_buffer) {
 	assert(wlr_buffer->impl == &buffer_impl);
-	return (struct wlr_shm_buffer *)wlr_buffer;
+	struct wlr_shm_buffer *buffer = wl_container_of(wlr_buffer, buffer, base);
+	return buffer;
 }
 
 static void buffer_destroy(struct wlr_buffer *wlr_buffer) {