[Spice-devel] [PATCH spice-protocol] Change usbredir messages to spicevmc messages

[Hans de Goede]

While discussing various things with Alon in Vancouver, it came up that
having a channel which simply passes through data coming out of a qemu
chardev frontend unmodified, like the usbredir channel does, can be used
for a lot of other cases too. To facilitate this the usbredir channel code
will be turned into a generic spicevmc channel, which is just a passthrough
to the client, from the spicevmc chardev.

This patch renames the msg types to make clear that they are not usbredir
specific, but instead are generic spicevmc data passthrough messages. The
usbredir channel id is unmodified by this, although the same code and
messages can now be used for multiple purposes, we still need unique ids
for each purpose, so that the client knows how to interpret / represent the
passed through data.

Some examples of why having a generic spicevmc pass through is good:
1) We could add a monitor channel, allowing access to the qemu monitor from
the spice client, since the monitor is a chardev frontend we could re-use
the generic spicevmc channel server code, so all that is needed to add this
(server side) would be reserving a new channel id for this.

2) We could allow users to come up with new channels of their own, without
requiring qemu or server modification. The idea is to allow doing something
like this on the qemu startup cmdline:
-chardev spicevmc,name=generic,channelid=128

To ensure these new "generic" channels cannot conflict with newly added
official types, the must start at the SPICE_CHANNEL_USER_DEFINED_START value
this patch adds (128 or higher).

These new user defined channels could then either be used with a special
modified client, with client plugins (if we add support for those), or
by exporting them on the client side for use by an external ap, see below.

3) We could also add support to the client to make user-defined channels
end in a unix socket / pipe, allowing handling of the data by an external app,
we could for example have a new spice client cmdline argument like this:
--custom-channel unixsocket=/tmp/mysocket,channelid=128

This would allow for something like:
$random app on guest -> virtio-serial -> spicevmc chardev ->
 -> spicevmc channel -> unix socket -> $random app on client

4) On hind sight this could also have been used for the smartcard stuff,
with a 1 channel / reader model, rather then the current multiplexing code
where we've our own multiplexing protocol wrapper over the libcacard
smartcard protocol.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 spice/enums.h |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/spice/enums.h b/spice/enums.h
index ffaba5c..8d68b36 100644
--- a/spice/enums.h
+++ b/spice/enums.h
@@ -331,7 +331,9 @@ enum {
     SPICE_CHANNEL_SMARTCARD,
     SPICE_CHANNEL_USBREDIR,
 
-    SPICE_END_CHANNEL
+    SPICE_END_CHANNEL,
+
+    SPICE_CHANNEL_USER_DEFINED_START = 128
 };
 
 enum {
@@ -521,15 +523,15 @@ enum {
 };
 
 enum {
-    SPICE_MSG_USBREDIR_DATA = 101,
+    SPICE_MSG_SPICEVMC_DATA = 101,
 
-    SPICE_MSG_END_USBREDIR
+    SPICE_MSG_END_SPICEVMC
 };
 
 enum {
-    SPICE_MSGC_USBREDIR_DATA = 101,
+    SPICE_MSGC_SPICEVMC_DATA = 101,
 
-    SPICE_MSGC_END_USBREDIR
+    SPICE_MSGC_END_SPICEVMC
 };
 
 #endif /* _H_SPICE_ENUMS */
-- 
1.7.5.1