From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <ian.campbell@citrix.com>
Subject: Re: [PATCH Remus v1 1/8] tools/libxc: adjust the memory
 allocation for migration
Date: Thu, 7 May 2015 14:57:40 +0100
Message-ID: <1431007060.2660.390.camel@citrix.com>
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To: Hongyang Yang <yanghy@cn.fujitsu.com>, David Vrabel <david.vrabel@citrix.com>
Cc: wei.liu2@citrix.com, eddie.dong@intel.com, wency@cn.fujitsu.com, Andrew Cooper <andrew.cooper3@citrix.com>, yunhong.jiang@intel.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org, rshriram@cs.ubc.ca
List-Id: xen-devel@lists.xenproject.org

On Thu, 2015-05-07 at 21:42 +0800, Hongyang Yang wrote:
> 
> On 05/07/2015 05:48 PM, Andrew Cooper wrote:
> > On 07/05/15 07:37, Yang Hongyang wrote:
> >> Move the memory allocation before the concrete live/nolive save
> >> in order to avoid the free/alloc memory loop when using Remus.
> >>
> >> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
> >> ---
> >>   tools/libxc/xc_sr_save.c | 53 +++++++++++++++++++-----------------------------
> >>   1 file changed, 21 insertions(+), 32 deletions(-)
> >>
> >> diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
> >> index 5d9c267..7fed668 100644
> >> --- a/tools/libxc/xc_sr_save.c
> >> +++ b/tools/libxc/xc_sr_save.c
> >> @@ -3,6 +3,8 @@
> >>
> >>   #include "xc_sr_common.h"
> >>
> >> +DECLARE_HYPERCALL_BUFFER(unsigned long, to_send);
> >
> > This unfortunately causes an issue when concurrent calls to
> > xc_domain_save() in the same process.  While this is a highly
> > ill-advised action, I did try to avoid breaking it.
> >
> > Please move this declaration into the ctx.save union.
> 
> I know the best way is to put this into ctx.save union, but I haven't
> found a method to put it in, the DECLARE_HYPERCALL_BUFFER macro can not
> be used there, should I just define a unsigned long var at ctx.save
> union, and use other macro(what macro?) define at save()?

I think you need a variable of type xc_hypercall_buffer_t in the struct
and then to use DECLARE_HYPERCALL_BUFFER_SHADOW in functions which need
to access it.

DECLARE_HYPERCALL_BUFFER_SHADOW seems to currently be unused, David
added it in 60572c972b8d, I suspect to be used by migration v2, although
perhaps it never was (at least not in tree yet).

Ian.