[xen staging] oxenstored: fix ABI breakage introduced in Xen 4.9.0

[patchbot@xxxxxxx]

commit a6ed77f1e0334c26e6e216aea45f8674d9284856
Author:     Edwin Török <edvin.torok@xxxxxxxxxx>
AuthorDate: Wed Jul 15 16:10:56 2020 +0100
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Tue Jul 21 12:31:45 2020 +0000

    oxenstored: fix ABI breakage introduced in Xen 4.9.0
    
    dbc84d2983969bb47d294131ed9e6bbbdc2aec49 (Xen >= 4.9.0) deleted XS_RESTRICT
    from oxenstored, which caused all the following opcodes to be shifted by 1:
    reset_watches became off-by-one compared to the C version of xenstored.
    
    Looking at the C code the opcode for reset watches needs:
    XS_RESET_WATCHES = XS_SET_TARGET + 2
    
    So add the placeholder `Invalid` in the OCaml<->C mapping list.
    (Note that the code here doesn't simply convert the OCaml constructor to
     an integer, so we don't need to introduce a dummy constructor).
    
    Igor says that with a suitably patched xenopsd to enable watch reset,
    we now see `reset watches` during kdump of a guest in xenstored-access.log.
    
    Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
    Tested-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Acked-by: Christian Lindig <christian.lindig@xxxxxxxxxx>
---
 tools/ocaml/libs/xb/op.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/ocaml/libs/xb/op.ml b/tools/ocaml/libs/xb/op.ml
index d4f1f08185..9bcab0f38c 100644
--- a/tools/ocaml/libs/xb/op.ml
+++ b/tools/ocaml/libs/xb/op.ml
@@ -28,7 +28,7 @@ let operation_c_mapping =
            Transaction_end; Introduce; Release;
            Getdomainpath; Write; Mkdir; Rm;
            Setperms; Watchevent; Error; Isintroduced;
-           Resume; Set_target; Reset_watches |]
+           Resume; Set_target; Invalid; Reset_watches |]
 let size = Array.length operation_c_mapping
 
 let array_search el a =
--
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