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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.

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
This commit is contained in:
Cao jin 2016-11-02 21:44:47 +08:00 committed by Michael Tokarev
parent 4a3ecf201a
commit 6e4c890e15
1 changed files with 4 additions and 6 deletions
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10
util/mmap-alloc.c
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@ -84,22 +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;
}
void qemu_ram_munmap(void *ptr, size_t size)