[PATCH wayland] shm: add a note about shm pool base address changing

Pekka Paalanen ppaalanen at gmail.com
Fri Feb 5 13:25:03 UTC 2016

From: Pekka Paalanen <pekka.paalanen at collabora.co.uk>

Since shm_pool_resize() uses mremap(MREMAP_MAYMOVE), the pool's base
address may change at that point.

If a compositor stores the pointer and a client enlarges the pool, the
compositor will have a stale pointer.

Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
 src/wayland-shm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/wayland-shm.c b/src/wayland-shm.c
index a4343a4..7e42dcb 100644
--- a/src/wayland-shm.c
+++ b/src/wayland-shm.c
@@ -348,6 +348,10 @@ wl_shm_buffer_get_stride(struct wl_shm_buffer *buffer)
  * to crash you should call wl_shm_buffer_begin_access and
  * wl_shm_buffer_end_access around code that reads from the memory.
+ * @note The return value of this function must not be stored across
+ * dispatching client requests. If a client resizes the underlying shm pool,
+ * the resize request handler will remap, and the pool base address may change.
+ *
  * \memberof wl_shm_buffer
 WL_EXPORT void *

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