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diff --git a/tools/ocaml/libs/xb/partial.ml b/tools/ocaml/libs/xb/partial.ml
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index 3558889..d4d1c7b 100644
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--- a/tools/ocaml/libs/xb/partial.ml
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+++ b/tools/ocaml/libs/xb/partial.ml
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@@ -27,8 +27,15 @@ external header_size: unit -> int = "stub_header_size"
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external header_of_string_internal: string -> int * int * int * int
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= "stub_header_of_string"
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+let xenstore_payload_max = 4096 (* xen/include/public/io/xs_wire.h *)
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+
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let of_string s =
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let tid, rid, opint, dlen = header_of_string_internal s in
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+ (* A packet which is bigger than xenstore_payload_max is illegal.
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+ This will leave the guest connection is a bad state and will
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+ be hard to recover from without restarting the connection
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+ (ie rebooting the guest) *)
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+ let dlen = min xenstore_payload_max dlen in
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{
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tid = tid;
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rid = rid;
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@@ -38,6 +45,7 @@ let of_string s =
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}
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let append pkt s sz =
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+ if pkt.len > 4096 then failwith "Buffer.add: cannot grow buffer";
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Buffer.add_string pkt.buf (String.sub s 0 sz)
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let to_complete pkt =
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diff --git a/tools/ocaml/libs/xb/xs_ring_stubs.c b/tools/ocaml/libs/xb/xs_ring_stubs.c
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index 00414c5..4888ac5 100644
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--- a/tools/ocaml/libs/xb/xs_ring_stubs.c
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+++ b/tools/ocaml/libs/xb/xs_ring_stubs.c
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@@ -39,21 +39,23 @@ static int xs_ring_read(struct mmap_interface *interface,
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char *buffer, int len)
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{
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struct xenstore_domain_interface *intf = interface->addr;
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- XENSTORE_RING_IDX cons, prod;
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+ XENSTORE_RING_IDX cons, prod; /* offsets only */
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int to_read;
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- cons = intf->req_cons;
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- prod = intf->req_prod;
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+ cons = *(volatile uint32*)&intf->req_cons;
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+ prod = *(volatile uint32*)&intf->req_prod;
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xen_mb();
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+ cons = MASK_XENSTORE_IDX(cons);
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+ prod = MASK_XENSTORE_IDX(prod);
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if (prod == cons)
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return 0;
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- if (MASK_XENSTORE_IDX(prod) > MASK_XENSTORE_IDX(cons))
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+ if (prod > cons)
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to_read = prod - cons;
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else
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- to_read = XENSTORE_RING_SIZE - MASK_XENSTORE_IDX(cons);
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+ to_read = XENSTORE_RING_SIZE - cons;
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if (to_read < len)
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len = to_read;
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- memcpy(buffer, intf->req + MASK_XENSTORE_IDX(cons), len);
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+ memcpy(buffer, intf->req + cons, len);
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xen_mb();
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intf->req_cons += len;
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return len;
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@@ -66,8 +68,8 @@ static int xs_ring_write(struct mmap_interface *interface,
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XENSTORE_RING_IDX cons, prod;
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int can_write;
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- cons = intf->rsp_cons;
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- prod = intf->rsp_prod;
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+ cons = *(volatile uint32*)&intf->rsp_cons;
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+ prod = *(volatile uint32*)&intf->rsp_prod;
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xen_mb();
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if ( (prod - cons) >= XENSTORE_RING_SIZE )
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return 0;
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