[PATCH 1 of 5] xentrace: fix t_info_pages calculation for the default case

[Olaf Hering <olaf@aepfle.de>]

# HG changeset patch
# User Olaf Hering <olaf@aepfle.de>
# Date 1300900084 -3600
# Node ID 14ac28e4656d0c235c5edf119426b1bcf3bf33d4
# Parent  8e1c737b2c44249dd1c0e4e1b8978d5d35020226
xentrace: fix t_info_pages calculation for the default case

The default tracebuffer size of 32 pages was not tested with the previous patch.
As a result, t_info_pages will become zero and alloc_xenheap_pages() fails.
Catch this case and allocate at least one page.

Signed-off-by: Olaf Hering <olaf@aepfle.de>

diff -r 8e1c737b2c44 -r 14ac28e4656d xen/common/trace.c
--- a/xen/common/trace.c	Wed Mar 23 15:24:19 2011 +0000
+++ b/xen/common/trace.c	Wed Mar 23 18:08:04 2011 +0100
@@ -29,6 +29,7 @@
 #include <xen/init.h>
 #include <xen/mm.h>
 #include <xen/percpu.h>
+#include <xen/pfn.h>
 #include <xen/cpu.h>
 #include <asm/atomic.h>
 #include <public/sysctl.h>
@@ -109,6 +110,7 @@
 {
     struct t_buf dummy;
     typeof(dummy.prod) size;
+    unsigned int t_info_bytes;
 
     /* force maximum value for an unsigned type */
     size = -1;
@@ -122,11 +124,9 @@
         pages = size;
     }
 
-    t_info_pages = num_online_cpus() * pages + t_info_first_offset;
-    t_info_pages *= sizeof(uint32_t);
-    t_info_pages /= PAGE_SIZE;
-    if ( t_info_pages % PAGE_SIZE )
-        t_info_pages++;
+    t_info_bytes = num_online_cpus() * pages + t_info_first_offset;
+    t_info_bytes *= sizeof(uint32_t);
+    t_info_pages = PFN_UP(t_info_bytes);
     return pages;
 }