[Xen-changelog] [xen-4.0-testing] trace: improve check_tbuf_size()

["Xen patchbot-4.0-testing" <patchbot-4.0-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1278104623 -3600
# Node ID 1972b4e9f34f2144f18e22cb783f4940b0b901b7
# Parent  e26d53eb32df6227d5e893edea9cb5a2bfa5818f
trace: improve check_tbuf_size()

It didn't consider the case of the incoming size not allowing for the
2*data_size range for t_buf->{prod,cons}

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
xen-unstable changeset:   21704:1390e2ab45c7
xen-unstable date:        Fri Jul 02 18:53:10 2010 +0100
---
 xen/common/trace.c |   18 +++++++++++++-----
 1 files changed, 13 insertions(+), 5 deletions(-)

diff -r e26d53eb32df -r 1972b4e9f34f xen/common/trace.c
--- a/xen/common/trace.c        Fri Jul 02 22:02:31 2010 +0100
+++ b/xen/common/trace.c        Fri Jul 02 22:03:43 2010 +0100
@@ -91,11 +91,19 @@ static void calc_tinfo_first_offset(void
 
 /**
  * check_tbuf_size - check to make sure that the proposed size will fit
- * in the currently sized struct t_info.
- */
-static inline int check_tbuf_size(int size)
-{
-    return (num_online_cpus() * size + t_info_first_offset) > (T_INFO_SIZE / 
sizeof(uint32_t));
+ * in the currently sized struct t_info and allows prod and cons to
+ * reach double the value without overflow.
+ */
+static int check_tbuf_size(u32 pages)
+{
+    struct t_buf dummy;
+    typeof(dummy.prod) size;
+    
+    size = ((typeof(dummy.prod))pages)  * PAGE_SIZE;
+    
+    return (size / PAGE_SIZE != pages)
+           || (size + size < size)
+           || (num_online_cpus() * pages + t_info_first_offset > T_INFO_SIZE / 
sizeof(uint32_t));
 }
 
 /**

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