[Xen-devel] [Patch v2] tools/migrate: Fix regression when migrating from older version of Xen

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Commit 00a4b65f8534c9e6521eab2e6ce796ae36037774 Sep 7 2010
  "libxc: provide notification of final checkpoint to restore end"
broke migration from any version of Xen using tools from prior to that commit

Older tools have no idea about an XC_SAVE_ID_LAST_CHECKPOINT, causing newer
tools xc_domain_restore() to start reading the qemu save record, as
ctx->last_checkpoint is 0.

The failure looks like:
  xc: error: Max batch size exceeded (1970103633). Giving up.
where 1970103633 = 0x756d6551 = *(uint32_t*)"Qemu"

Sadly, the simple fix of just setting ctx->last_checkpoint = 1 will cause an
opposite function regresson for anyone using the current behaviour of
save_callbacks->checkpoint().

The only safe fix is to rely on the toolstack to provide this information.

Passing 0 results in unchanged behaviour, while passing nonzero means "the
other end of the migration stream does not know about
XC_SAVE_ID_LAST_CHECKPOINT but is performing a normal migrate"

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

---
Changes since v1:
 * Rename "last_checkpoint_unaware" to "checkpointed_stream" to be more
   generic yet still accurate as to the meaning and fix for the issue
---
 tools/libxc/xc_domain_restore.c |    3 ++-
 tools/libxc/xc_nomigrate.c      |    2 +-
 tools/libxc/xenguest.h          |    3 ++-
 tools/libxl/libxl_save_helper.c |    2 +-
 tools/xcutils/xc_restore.c      |    2 +-
 5 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/tools/libxc/xc_domain_restore.c b/tools/libxc/xc_domain_restore.c
index 63d36cd..e50b185 100644
--- a/tools/libxc/xc_domain_restore.c
+++ b/tools/libxc/xc_domain_restore.c
@@ -1401,7 +1401,7 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
uint32_t dom,
                       domid_t store_domid, unsigned int console_evtchn,
                       unsigned long *console_mfn, domid_t console_domid,
                       unsigned int hvm, unsigned int pae, int superpages,
-                      int no_incr_generationid,
+                      int no_incr_generationid, int checkpointed_stream,
                       unsigned long *vm_generationid_addr,
                       struct restore_callbacks *callbacks)
 {
@@ -1472,6 +1472,7 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
uint32_t dom,
 
     ctx->superpages = superpages;
     ctx->hvm = hvm;
+    ctx->last_checkpoint = !!checkpointed_stream;
 
     ctxt = xc_hypercall_buffer_alloc(xch, ctxt, sizeof(*ctxt));
 
diff --git a/tools/libxc/xc_nomigrate.c b/tools/libxc/xc_nomigrate.c
index 73e7566..fb6d53e 100644
--- a/tools/libxc/xc_nomigrate.c
+++ b/tools/libxc/xc_nomigrate.c
@@ -35,7 +35,7 @@ int xc_domain_restore(xc_interface *xch, int io_fd, uint32_t 
dom,
                       domid_t store_domid, unsigned int console_evtchn,
                       unsigned long *console_mfn, domid_t console_domid,
                       unsigned int hvm, unsigned int pae, int superpages,
-                      int no_incr_generationid,
+                      int no_incr_generationid, int checkpointed_stream,
                       unsigned long *vm_generationid_addr,
                       struct restore_callbacks *callbacks)
 {
diff --git a/tools/libxc/xenguest.h b/tools/libxc/xenguest.h
index 4714bd2..2101810 100644
--- a/tools/libxc/xenguest.h
+++ b/tools/libxc/xenguest.h
@@ -114,6 +114,7 @@ struct restore_callbacks {
  * @parm pae non-zero if this HVM domain has PAE support enabled
  * @parm superpages non-zero to allocate guest memory with superpages
  * @parm no_incr_generationid non-zero if generation id is NOT to be 
incremented
+ * @parm checkpointed_stream non-zero if the far end of the stream is using 
checkpointing
  * @parm vm_generationid_addr returned with the address of the generation id 
buffer
  * @parm callbacks non-NULL to receive a callback to restore toolstack
  *       specific data
@@ -124,7 +125,7 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
uint32_t dom,
                       domid_t store_domid, unsigned int console_evtchn,
                       unsigned long *console_mfn, domid_t console_domid,
                       unsigned int hvm, unsigned int pae, int superpages,
-                      int no_incr_generationid,
+                      int no_incr_generationid, int checkpointed_stream,
                       unsigned long *vm_generationid_addr,
                       struct restore_callbacks *callbacks);
 /**
diff --git a/tools/libxl/libxl_save_helper.c b/tools/libxl/libxl_save_helper.c
index 772251a..8f14b8b 100644
--- a/tools/libxl/libxl_save_helper.c
+++ b/tools/libxl/libxl_save_helper.c
@@ -264,7 +264,7 @@ int main(int argc, char **argv)
         r = xc_domain_restore(xch, io_fd, dom, store_evtchn, &store_mfn,
                               store_domid, console_evtchn, &console_mfn,
                               console_domid, hvm, pae, superpages,
-                              no_incr_genidad, &genidad,
+                              no_incr_genidad, 0, &genidad,
                               &helper_restore_callbacks);
         helper_stub_restore_results(store_mfn,console_mfn,genidad,0);
         complete(r);
diff --git a/tools/xcutils/xc_restore.c b/tools/xcutils/xc_restore.c
index 35d725c..e657c7f 100644
--- a/tools/xcutils/xc_restore.c
+++ b/tools/xcutils/xc_restore.c
@@ -52,7 +52,7 @@ main(int argc, char **argv)
 
     ret = xc_domain_restore(xch, io_fd, domid, store_evtchn, &store_mfn, 0,
                             console_evtchn, &console_mfn, 0, hvm, pae, 
superpages,
-                            0, NULL, NULL);
+                            0, 0, NULL, NULL);
 
     if ( ret == 0 )
     {
-- 
1.7.10.4


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