From f2a5ddf5dc6a9f722cc6b3a66fd635d09056ad70 Mon Sep 17 00:00:00 2001 From: Cao jin Date: Thu, 1 Mar 2018 23:55:13 -0500 Subject: [PATCH] util/mmap-alloc: refactor a little bit for readability 1st mmap returns *ptr* which aligns to host page size, | size + align | ------------------------------------------ ptr input param *align* could be 1M, or 2M, or host page size. After QEMU_ALIGN_UP, offset will >= 0 2nd mmap use flag MAP_FIXED, then it return ptr+offset, or else fail. If it success, then we will have something like: | offset | size | -------------------------------------- ptr ptr1 *ptr1* is what we really want to return, it equals ptr+offset. Backports commit 6e4c890e15b23f078650499fbde11760b8eccf10 from qemu --- qemu/util/mmap-alloc.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/qemu/util/mmap-alloc.c b/qemu/util/mmap-alloc.c index 46b89c3c..86781b8e 100644 --- a/qemu/util/mmap-alloc.c +++ b/qemu/util/mmap-alloc.c @@ -60,22 +60,20 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared) return MAP_FAILED; } - ptr += offset; - total -= offset; - if (offset > 0) { - munmap(ptr - offset, offset); + munmap(ptr, offset); } /* * Leave a single PROT_NONE page allocated after the RAM block, to serve as * a guard page guarding against potential buffer overflows. */ + total -= offset; if (total > size + getpagesize()) { - munmap(ptr + size + getpagesize(), total - size - getpagesize()); + munmap(ptr1 + size + getpagesize(), total - size - getpagesize()); } - return ptr; + return ptr1; } void qemu_ram_munmap(void *ptr, size_t size)