[Spice-devel] Fail to create a printing channel

[Alon Levy]

On Thu, Mar 22, 2012 at 07:34:38PM +0800, Charles.Tsai-蔡清海-研究發展部 wrote:
> Alon,

Or anyone else on the list..

> 
> 	I am running the following script to create the printing channel based on the virtio device framework.
> 	When the VM is launched, it seems to block somewhere in Qemu.
> 
> 	If I remove the following two lines, the VM can be launched without any problem.		
> 	The following two lines basically are used to create the printing channel between the host and guest.
> 
> 	-chardev spicevmc,id=vdprint,name=vdprint \
> 	-device virtserialport,chardev=vdprint,name=com.redhat.print.0"
> 
> 	Can you give me some hits why Qemu does not call spice server to create the printing channel? Is there any 	function in Qemu I need to change so as to create additional channel within the Virtio device?
> 
> 	Let me know if I made anything wrong with my Qemu's command options. Thanks.

How it works right now, and it's probably not how we want it to be, is
that there is a function qemu calls to get the allowed list of names by
spice-server. That function is implemented by spice-server, so you would
need to add the "vdprint" string to it.

diff --git a/server/reds.c b/server/reds.c
index c54d30c..bb75624 100644
--- a/server/reds.c
+++ b/server/reds.c
@@ -3364,6 +3364,7 @@ SPICE_GNUC_VISIBLE void spice_server_char_device_wakeup(SpiceCharDeviceInstance*
 #define SUBTYPE_VDAGENT "vdagent"
 #define SUBTYPE_SMARTCARD "smartcard"
 #define SUBTYPE_USBREDIR "usbredir"
+#define SUBTYPE_PRINTER "printer"
 
 const char *spice_server_char_device_recognized_subtypes_list[] = {
     SUBTYPE_VDAGENT,
@@ -3371,6 +3372,7 @@ const char *spice_server_char_device_recognized_subtypes_list[] = {
     SUBTYPE_SMARTCARD,
 #endif
     SUBTYPE_USBREDIR,
+    SUBTYPE_PRINTER,
     NULL,
 };

Then you need to tell spice what to do when
spice_server_char_device_add_interface is called with this subtype
(subtype == 'name' parameter to the chardev. Another thing that should
be changed).

You could basically just use another spicevmc_device_connect call. You
will need to add the channel to the spice.proto (again, this should be
changed so adding generic channels doesn't require this - something like
having a generic channel subtype, and having a message that tells the
client which channel this is - will be a little ugly since getting a
channel list won't be enough for the client to know what channels are
available, but it's not too bad - anyway off topic)

For now you can just change the spice-protocol/spice/enums.h file
directly instead of recreating it:

U x86_64 garlic:spice-protocol alon ((1a3b563...))$ git diff
diff --git a/spice/enums.h b/spice/enums.h
index d2dbfd0..9f54ac0 100644
--- a/spice/enums.h
+++ b/spice/enums.h
@@ -330,6 +330,7 @@ enum {
     SPICE_CHANNEL_TUNNEL,
     SPICE_CHANNEL_SMARTCARD,
     SPICE_CHANNEL_USBREDIR,
+    SPICE_CHANNEL_PRINTER,
 
     SPICE_END_CHANNEL
 };

@@ -3401,9 +3403,13 @@ static int spice_server_char_device_add_interface(SpiceServer *s,
         }
     }
 #endif
+    /* all other channels use the generic spicevmc channel */
     else if (strcmp(char_device->subtype, SUBTYPE_USBREDIR) == 0) {
         spicevmc_device_connect(char_device, SPICE_CHANNEL_USBREDIR);
     }
+    else if (strcmp(char_device->subtype, SUBTYPE_PRINTER) == 0) {
+        spicevmc_device_connect(char_device, SPICE_CHANNEL_PRINTER);
+    }
     return 0;
 }

Hope you can understand my not very collected response.

Bonus points for sending patches to fix the raised issues, or starting a
discussion on how to exactly.

Alon

> ==================================
> 
> #!/bin/sh
> 
> ARGS="-localtime -spice port=5900,disable-ticketing \
> -drive file=/opt/virt/user/Win7_64.cow \
> -vga qxl \
> -device virtio-serial-pci,multifunction=on \
> -chardev spicevmc,id=vdagent,id=vdagent,name=vdagent \
> -device virtserialport,chardev=vdagent,name=com.redhat.spice.0 \
> -usbdevice tablet -smp 1,cores=2 -m 2048 -enable-kvm -net nic -net user \
> -chardev spicevmc,id=vdprint,name=vdprint \
> -device virtserialport,chardev=vdprint,name=com.redhat.print.0"