buffer: track asynchronous buffers and don't release them until unref

synchronous buffers are read instantly and we can release them, but asynchronous ones have to be locked until they are unref'd from .current to avoid reading from a buffer after .release()

src/protocols/types/Buffer.hpp

@@ -49,6 +49,7 @@ class IWLBuffer {
     virtual eBufferCapability                      caps()                        = 0;
     virtual eBufferType                            type()                        = 0;
     virtual void                                   update(const CRegion& damage) = 0;
+    virtual bool                                   isSynchronous()               = 0; // whether the updates to this buffer are synchronous, aka happen over cpu
     virtual SDMABUFAttrs                           dmabuf();
     virtual SSHMAttrs                              shm();
     virtual std::tuple<uint8_t*, uint32_t, size_t> beginDataPtr(uint32_t flags);

src/protocols/types/DMABuffer.cpp

@@ -43,6 +43,10 @@ void CDMABuffer::update(const CRegion& damage) {
     ;
 }
 
+bool CDMABuffer::isSynchronous() {
+    return false;
+}
+
 SDMABUFAttrs CDMABuffer::dmabuf() {
     return attrs;
 }

src/protocols/types/DMABuffer.hpp

@@ -9,6 +9,7 @@ class CDMABuffer : public IWLBuffer {
 
     virtual eBufferCapability                      caps();
     virtual eBufferType                            type();
+    virtual bool                                   isSynchronous();
     virtual void                                   update(const CRegion& damage);
     virtual SDMABUFAttrs                           dmabuf();
     virtual std::tuple<uint8_t*, uint32_t, size_t> beginDataPtr(uint32_t flags);