[libvirt] [PATCH] util:qemu: fix IOThreadinfo always get failed when get running vm status

[Peter Krempa]

On Mon, Jun 29, 2015 at 16:22:54 +0800, Luyao Huang wrote:
> When we use iothreadinfo to get iothread information, we will get
> error like this:
> 
>  # virsh iothreadinfo rhel7.0 --live
>  error: Unable to get domain IOThreads information
>  error: Unable to encode message payload
> 
> This is because virProcessGetAffinity() return a bitmap which map_len
> is too big to send via rpc:
> 
>  (gdb) p *map
>  $7 = {max_bit = 262144, map_len = 4096, map = 0x7f9b6c2c0a20}
> 
> To fix this issue add a new parameter &maxcpu to virProcessGetAffinity()
> to let callers specify the maxcpu (also in most machine, no need loop
> 262144 times to check if cpu is set), if set &maxcpu to zero,
> virProcessGetAffinity() will use default value (262144 or 1024) to
> create bitmap. This issue was introduced in commit 825df8c.
> 
> Signed-off-by: Luyao Huang <lhuang at redhat.com>
> ---
>  src/qemu/qemu_driver.c | 4 ++--
>  src/util/virprocess.c  | 7 ++++---
>  src/util/virprocess.h  | 2 +-
>  3 files changed, 7 insertions(+), 6 deletions(-)
> 

I think a better fix will be to make virBitmapToData smarter when
formatting a bitmap by finding the last set bit rather than formatting
the full bitmap.

This will avoid re-introducing the maxcpu argument.

The diff for such change is following:

diff --git a/src/util/virbitmap.c b/src/util/virbitmap.c
index 9abc807..7234f7e 100644
--- a/src/util/virbitmap.c
+++ b/src/util/virbitmap.c
@@ -498,9 +498,12 @@ virBitmapPtr virBitmapNewData(void *data, int len)
  */
 int virBitmapToData(virBitmapPtr bitmap, unsigned char **data, int *dataLen)
 {
-    int len;
+    ssize_t len;

-    len = (bitmap->max_bit + CHAR_BIT - 1) / CHAR_BIT;
+    if ((len = virBitmapLastSetBit(bitmap)) < 0)
+        len = 1;
+    else
+        len = (len + CHAR_BIT - 1) / CHAR_BIT;

     if (VIR_ALLOC_N(*data, len) < 0)
         return -1;

Peter
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