On 10/28/2016 10:22 PM, Michael Tokarev wrote:
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?
Because, I think there always is: ptr + offset == ptr1
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.. :)
Yes, but the 2nd mmap used MAP_FIXED, which the manpage says:
/Don't interpret addr as a hint: place the mapping at exactly that/
/address. addr must be a multiple of the page size/
/If the specified address cannot be used, mmap() will fail/
At the very least, your commit comment is a bit misleading, as it says
about readability, but it also MAY change semantics.
I don't think so, one just need dig a little deeper:)
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 :)
the change is just some simple arithmetic operation, I think it is
little difficult for me to find a decent description.
Hope this could also got other maintainer's help, review, or ack
Thanks,
/mjt
.
--
Yours Sincerely,
Cao jin
