bonefish+mmu_man: fix cbuf_user_memcpy_from_chain() returning an error when the source buffer was NULL despite being asked for 0 bytes, while the counterpart was actually not creating a buffer for 0 bytes to send... Also don't bother calling it from receive_data() in that case anyway.

This fixes a deadlock in SoundPlay that made it freeze when trying to play the 2nd sound.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@28179 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/thread.cpp

@@ -743,7 +743,7 @@ receive_data_etc(thread_id *_sender, void *buffer, size_t bufferSize,
 		return status;
 	}
 
-	if (buffer != NULL && bufferSize != 0) {
+	if (buffer != NULL && bufferSize != 0 && thread->msg.buffer != NULL) {
 		size = min_c(bufferSize, thread->msg.size);
 		status = cbuf_user_memcpy_from_chain(buffer, thread->msg.buffer,
 			0, size);

src/system/kernel/util/cbuf.c

@@ -529,6 +529,8 @@ cbuf_user_memcpy_from_chain(void *_dest, cbuf *chain, size_t offset, size_t leng
 	int bufferOffset;
 	int err;
 
+	if (length == 0)
+		return B_OK;
 	if (chain == NULL)
 		return B_BAD_VALUE;