void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared) { /* * Note: this always allocates at least one extra page of virtual address * space, even if size is already aligned. */ size_t total = size + align; void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; void *ptr1; if (ptr == MAP_FAILED) { return NULL; } /* Make sure align is a power of 2 */ assert(!(align & (align - 1))); /* Always align to host page size */ assert(align >= getpagesize()); ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE, MAP_FIXED | (fd == -1 ? MAP_ANONYMOUS : 0) | (shared ? MAP_SHARED : MAP_PRIVATE), fd, 0); if (ptr1 == MAP_FAILED) { munmap(ptr, total); return NULL; } ptr += offset; total -= offset; if (offset > 0) { munmap(ptr - offset, offset); } /* * Leave a single PROT_NONE page allocated after the RAM block, to serve as * a guard page guarding against potential buffer overflows. */ if (total > size + getpagesize()) { munmap(ptr + size + getpagesize(), total - size - getpagesize()); } return ptr; }