On Wed, Aug 23, 2017 at 04:48:51PM -0700, Dan Williams wrote: > The mmap(2) syscall suffers from the ABI anti-pattern of not validating > unknown flags. However, proposals like MAP_SYNC and MAP_DIRECT need a > mechanism to define new behavior that is known to fail on older kernels > without the support. Define a new mmap3 syscall that checks for > unsupported flags at syscall entry and add a 'mmap_supported_mask' to > 'struct file_operations' so generic code can validate the ->mmap() > handler knows about the specified flags. This also arranges for the > flags to be passed to the handler so it can do further local validation > if the requested behavior can be fulfilled. What is the reason to not go with __MAP_VALID hack? Adding new syscalls is extremely painful, it will take forever to trickle this through all architectures (especially with the various 32-bit architectures having all kinds of different granularities for the offset) and then the various C libraries, never mind applications.
