[Xen-changelog] [xen-3.4-testing] Fix gdbserver-xen support on older kernels.

["Xen patchbot-3.4-testing" <patchbot-3.4-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1269952592 -3600
# Node ID 17cb4b7a78e900000dc4ae4558392550d6963409
# Parent  b0aef7160eebaea9686cffd49d10823a345f0242
Fix gdbserver-xen support on older kernels.

The xc_ptrace API relies on errno for passing success/failure
indication back to callers.  However, mapping operations that fall
back on legacy APIs may leave errno set to a non-zero result even
thought the operation is successful.  This patch resets errno after
successful map operations so that xc_ptrace doesn't inadvertently
return a failure.

Signed-off-by: Justin Gibbs <gibbs@xxxxxxxxxxx>
xen-unstable changeset:   21063:0a91254533dc
xen-unstable date:        Thu Mar 25 07:41:55 2010 +0000
---
 tools/libxc/xc_ptrace.c |    7 +++++++
 1 files changed, 7 insertions(+)

diff -r b0aef7160eeb -r 17cb4b7a78e9 tools/libxc/xc_ptrace.c
--- a/tools/libxc/xc_ptrace.c   Tue Mar 30 13:36:04 2010 +0100
+++ b/tools/libxc/xc_ptrace.c   Tue Mar 30 13:36:32 2010 +0100
@@ -174,6 +174,13 @@ map_domain_va(
     if (map == NULL)
         return NULL;
 
+    /*
+     * Due to the use of API fallback code in libxc, errno may
+     * be clobberred during successful operations.  Since the caller
+     * of xc_ptrace is depending on errno for return status, clear
+     * errno here.
+     */
+    errno = 0;
     return map + (va & ~PAGE_MASK);
 }
 

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