The register/unregister gralloc calls were avoiding
mmapping/munmapping the shared memory region if the buffer was created
by the current process. This is left over from the pmem-based
implementation, where trying to map the same region twice in the same
process would fail, or would reuse a single mapping without
refcounting.
This causes problems if a buffer is
- allocated in process A,
- transferred from A to process B and registered there
- unregistered/freed in A
- transferred back from B to A and re-registered
Process A then has a new handle to the buffer, but since it originally
created the buffer it will not be mmapped, so trying to read or write
the buffer will crash.
With ashmem, mmaping a region twice in the same process creates two
distinct mappings which can be used and munmapped independently. So
we no longer need to avoid mmapping again in the allocating process.
Bug: 8468756
Change-Id: I167bec5ca07e5534c5e2115630fe8386e481388e
this gralloc module is only used on the emulator or without a h/w
renderer. therefore there is no synchronization to do in lock/unlock
and pmem buffers are not relevant.
hopefully this will remove some of the confusion about how gralloc
should be implemented and make it more obvious that this implementation
is not intended to be used by h/w renderers.
- make sure to return an error if a buffer is locked twice or unlocked while not locked.
- added registerBuffer() and unregisterBuffer() to the gralloc module so that we can do some cleanup when a buffer is no longer needed. this became necessary after we removed map/unmap so we have a place to unmap buffers without the need of a kernel module.
- change the constants for GRALLOC_USAGE_SW_{READ|WRITE}_NEVER to 0, so that NOT specifying them means "NEVER".
