Add flags support to MmapAllocator

[kubiak-jpl]

F´ Version	4.1.0
Affected Component	Fw/TypesMmapAllocator

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Feature Description

Add optional constructor arguments to Fw::MmapAllocator to set the allocation flags used when allocating memory with the created object

Something like

class MmapAllocator : public MemAllocator {
  public:
  MmapAllocator(int prot = PROT_READ | PROT_WRITE, int flags = MAP_SHARED | MAP_ANONYMOUS);

  private:
  int m_prot;
  int m_flags;
}

void* MmapAllocator::allocate(const FwEnumStoreType identifier,
                              FwSizeType& size,
                              bool& recoverable,
                              FwSizeType alignment) {
    void* addr = mmap(nullptr, size, m_prot, m_flags, -1, 0);
    return addr;
}

Fw::MmapAllocator my_alloc(PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_LOCKED);

Rationale

The MmapAllocator type is useful for allocating anonymous memory with the mmap system call. However I would like to allocate pages with the MAP_LOCKED flag set. Instead of creating a custom instance I think it would be more useful to amend the existing allocator for this strategy.

Open questions

• Does the PROT field need to be exposed here? Any reason to allocate memory the allocator that isn't marked RW? Does adding the option just add noise?
• Should custom fpp enums be used for the prot and flags arguments?
  • I think not. Just use the Posix defined flags. I don't believe this is intended to be an OS agnostic interface