[PATCH v2] fix Remus failover regression

[Yang Hongyang <yanghy@cn.fujitsu.com>]

commit: c2ba706c
tools/libxc: goto correct label on error paths by Andrew Cooper
broke Remus in Xen 4.4 or earlier versions that has this commit
backported.

With Remus, this jump essentially discards the current incomplete
checkpoint received by the backup and restore backup from the
last complete checkpoint.
This is required for Remus to work and this does not break live
migration.
It has been around since Xen 4.0.

CC: Ian Jackson <ian.jackson@eu.citrix.com>
CC: Ian Campbell <ian.campbell@citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
---
 tools/libxc/xc_domain_restore.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/libxc/xc_domain_restore.c b/tools/libxc/xc_domain_restore.c
index e73e0a2..b9a56d5 100644
--- a/tools/libxc/xc_domain_restore.c
+++ b/tools/libxc/xc_domain_restore.c
@@ -1783,20 +1783,29 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t dom,
 
     if ( pagebuf_get(xch, ctx, &pagebuf, io_fd, dom) ) {
         PERROR("error when buffering batch, finishing");
-        goto out;
+        /*
+         * Remus: discard the current incomplete checkpoint and restore
+         * backup from the last complete checkpoint.
+         */
+        goto finish;
     }
     memset(&tmptail, 0, sizeof(tmptail));
     tmptail.ishvm = hvm;
     if ( buffer_tail(xch, ctx, &tmptail, io_fd, max_vcpu_id, vcpumap,
                      ext_vcpucontext, vcpuextstate_size) < 0 ) {
         ERROR ("error buffering image tail, finishing");
-        goto out;
+        /*
+         * Remus: discard the current incomplete checkpoint and restore
+         * backup from the last complete checkpoint.
+         */
+        goto finish;
     }
     tailbuf_free(&tailbuf);
     memcpy(&tailbuf, &tmptail, sizeof(tailbuf));
 
     goto loadpages;
 
+  /* With Remus: restore from last complete checkpoint */
   finish:
     if ( hvm )
         goto finish_hvm;
-- 
1.9.1