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[Qemu-devel] [PATCH v4 2/2] util/mmap-alloc: refactor a little bit for r


From: Cao jin
Subject: [Qemu-devel] [PATCH v4 2/2] util/mmap-alloc: refactor a little bit for readability
Date: Wed, 2 Nov 2016 21:44:47 +0800

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 <address@hidden>
---
 util/mmap-alloc.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

This one may be controversial, take it or not as you will:)

diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index d713a72..2f55f5e 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -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)
-- 
2.1.0






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