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Re: [libvirt] [PATCH] virBitmapFree: Change the function to a macro



[......]

Regardless of what the problem is......

Signed-off-by: Liuji (Jeremy) <jeremy liu huawei com>
---
   src/util/virbitmap.c | 21 ---------------------
   src/util/virbitmap.h | 21 ++++++++++++++++-----
   2 files changed, 16 insertions(+), 26 deletions(-)

diff --git a/src/util/virbitmap.c b/src/util/virbitmap.c
index 7e1cd02..cde502f 100644
--- a/src/util/virbitmap.c
+++ b/src/util/virbitmap.c
@@ -40,13 +40,6 @@

   #define VIR_FROM_THIS VIR_FROM_NONE

-struct _virBitmap {
-    size_t max_bit;
-    size_t map_len;
-    unsigned long *map;
-};
-
-
   #define VIR_BITMAP_BITS_PER_UNIT  ((int) sizeof(unsigned long) *
CHAR_BIT)
   #define VIR_BITMAP_UNIT_OFFSET(b) ((b) /
VIR_BITMAP_BITS_PER_UNIT)
   #define VIR_BITMAP_BIT_OFFSET(b)  ((b) %
VIR_BITMAP_BITS_PER_UNIT)
@@ -88,20 +81,6 @@ virBitmapPtr virBitmapNew(size_t size)
       return bitmap;
   }

-/**
- * virBitmapFree:
- * @bitmap: previously allocated bitmap
- *
- * Free @bitmap previously allocated by virBitmapNew.
- */
-void virBitmapFree(virBitmapPtr bitmap)
-{
-    if (bitmap) {
-        VIR_FREE(bitmap->map);
-        VIR_FREE(bitmap);
-    }
-}
-

   int virBitmapCopy(virBitmapPtr dst, virBitmapPtr src)
   {
diff --git a/src/util/virbitmap.h b/src/util/virbitmap.h
index b682523..9b93b88 100644
--- a/src/util/virbitmap.h
+++ b/src/util/virbitmap.h
@@ -28,6 +28,22 @@

   # include <sys/types.h>

+struct _virBitmap {
+    size_t max_bit;
+    size_t map_len;
+    unsigned long *map;
+};
+
+/*
+ * Free previously allocated bitmap
+ */
+#define virBitmapFree(bitmap)          \
+    do {                               \
+        if (bitmap) {                  \
+            VIR_FREE((bitmap)->map);   \
+            VIR_FREE(bitmap);          \
+        }                              \
+    } while (0);

... What does this make difference? Unless I missed something, what you
do is
just changing the function into a macro. And I don't see any benifit
from it.

Osier
I thought I have already clearly explained the problem.

The virBitmapFree is:
         void virBitmapFree(virBitmapPtr bitmap)
         {
             if (bitmap) {
                 VIR_FREE(bitmap->map);
                 VIR_FREE(bitmap);
             }
         }
Bitmap is a parameter (formal parameter). The address which is pointed by Bitmap is the same as argument(actual parameter) pointed.
In " VIR_FREE(bitmap);", it frees the same address. But only assigns the NULL to the Bitmap, not to the argument(actual parameter).
After calling virBitmapFree, if there is not assigning NULL to the argument(actual parameter), and using this argument(actual parameter) to call
the virBitmapFree again, it will free an already freed address. It will generate a crash.

I knew your meaning,  what I was wondering was:


There are 3 solutions:
1> After call virBitmapFree function, add a assignment which is assign NULL to the argument(actual parameter) of virBitmapFree.
2> Change the virBitmapFree to :
         void virBitmapFree(virBitmapPtr *bitmap)
         {
             if (*bitmap) {
                 VIR_FREE((*bitmap)->map);
                 VIR_FREE(*bitmap);
             }
         }
And change all virBitmapFree calling from
        virBitmapFree(abc)
to
        virBitmapFree(&abc)
3> change the virBitmapFree to a macro, like my first mail.



1) Regardless of what the problem is, and whether to change the interface of
virBitmapFree or introduce a macro, I didn't see you use it, I.E fixing the crash
    problems. Without the changes on the use of virBitmapFree, the patch is
    quite confused between the commit log and the patch itself.

2) And actually the macro still doesn't help if we don't pass a "virBitmapPtr *"
    argument for it. So the patch doesn't change things.

I prefer to change the interface of virBitmapFree instead, since it will need the
"virBitmapPtr *" argument anyway.

Osier



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