============= Shared Memory ============= Shared memory interfaces are only available with the NuttX kernel build (``CONFIG_BUILD_KERNEL=y``). These interfaces support user memory regions that can be shared between multiple user processes. The user interfaces are provided in the standard header file ``include/sys/shm.h>``. All logic to support shared memory is implemented within the NuttX kernel with the exception of two low-level functions that are require to configure the platform-specific MMU resources. Those interfaces are described below: .. c:function:: int up_shmat(FAR uintptr_t *pages, unsigned int npages, uintptr_t vaddr) Attach, i.e, map, on shared memory region to a user virtual address. :param pages: A pointer to the first element in a array of physical address, each corresponding to one page of memory. :param npages: The number of pages in the list of physical pages to be mapped. :param vaddr: The virtual address corresponding to the beginning of the (contiguous) virtual address region. :return: Zero (OK) is returned on success; a negated errno value is returned on failure. .. c:function:: int up_shmdt(uintptr_t vaddr, unsigned int npages) Detach, i.e, unmap, on shared memory region from a user virtual address. :param vaddr: The virtual address corresponding to the beginning of the (contiguous) virtual address region. :param npages: T The number of pages to be unmapped. :return: Zero (OK) is returned on success; a negated errno value is returned on failure.