28.10.2016 11:56, Cao jin wrote:
> Also refactor a little bit for readability
See comments below...
> Signed-off-by: Cao jin <caoj.f...@cn.fujitsu.com>
> ---
> util/mmap-alloc.c | 17 ++++++++---------
> 1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 5a85aa3..2f55f5e 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -12,6 +12,7 @@
>
> #include "qemu/osdep.h"
> #include "qemu/mmap-alloc.h"
> +#include "qemu/host-utils.h"
>
> #define HUGETLBFS_MAGIC 0x958458f6
>
> @@ -61,18 +62,18 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
> bool shared)
> #else
> void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1,
> 0);
> #endif
> - size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
> + size_t offset;
> void *ptr1;
>
> if (ptr == MAP_FAILED) {
> return MAP_FAILED;
> }
>
> - /* Make sure align is a power of 2 */
> - assert(!(align & (align - 1)));
> + assert(is_power_of_2(align));
> /* Always align to host page size */
> assert(align >= getpagesize());
>
> + offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
> ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
> MAP_FIXED |
> (fd == -1 ? MAP_ANONYMOUS : 0) |
> @@ -83,22 +84,20 @@ 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;
Why did you change ptr to ptr1 here and above?
On linux, mmap(2) manpage says that address serves as hint, and the
system create the mapping at a nearby page boundary. Generally, this
address is just a hint. So I'm not really sure if this code is actually
right.. :)
At the very least, your commit comment is a bit misleading, as it says
about readability, but it also MAY change semantics.
Maybe just move BOTH "ptr+=, total-=" parts down the line and keep
using ptr instead of ptr1?
It'd be very good, in my opinion, to document how this whole thing
is supposed to work :)
Thanks,
/mjt
