[Spice-devel] [PATCH 1/1] Allow missing capabilities from source host

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert at redhat.com>

When loading a USB redirection stream during a qemu
migration, the source QEMU might be earlier and be missing
a bunch of capabilities that are now available in a more modern
version; allow this migration to work as long as the source
isn't claiming any capabilities that we don't have.

(We should be a bit more careful about this in future in qemu;
we could tie any new capabilities we ask for to machine types).

Signed-off-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
---
 usbredirparser/usbredirparser.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/usbredirparser/usbredirparser.c b/usbredirparser/usbredirparser.c
index 8076b72..d1f9850 100644
--- a/usbredirparser/usbredirparser.c
+++ b/usbredirparser/usbredirparser.c
@@ -1682,10 +1682,24 @@ int usbredirparser_unserialize(struct usbredirparser *parser_pub,
     memcpy(orig_caps, parser->our_caps, i);
     if (unserialize_data(parser, &state, &remain, &data, &i, "our_caps"))
         return -1;
-    if (memcmp(parser->our_caps, orig_caps,
-               USB_REDIR_CAPS_SIZE * sizeof(int32_t)) != 0) {
-        ERROR("error unserialize caps mismatch");
-        return -1;
+    for (i =0; i < USB_REDIR_CAPS_SIZE; i++) {
+        if (parser->our_caps[i] != orig_caps[i]) {
+            /* orig_caps is our original settings
+             * parser->our_caps is off the wire.
+             * We want to allow reception from an older
+             * usbredir that doesn't have all our features.
+             */
+            if (parser->our_caps[i] & ~orig_caps[i]) {
+                /* Source has a cap we don't */
+                ERROR("error unserialize caps mismatch ours: %x recv: %x",
+                      orig_caps[i], parser->our_caps[i]);
+                return -1;
+            } else {
+                /* We've got a cap the source doesn't - that's OK */
+                WARNING("unserialize missing some caps; ours: %x recv: %x",
+                      orig_caps[i], parser->our_caps[i]);
+            }
+        }
     }
 
     data = (uint8_t *)parser->peer_caps;
-- 
2.5.0