[Spice-devel] Access local network printer from guest OS

Charles.Tsai-蔡清海-工程部 charles.tsai at cloudena.com
Mon Jan 2 03:08:23 PST 2012


I have another question regarding the USB redirect for Windows client.  In current spice release, the USB redirect only support for Linux client.
If we send the printing data through the "spicevmc channel" to the Windows client(not Linux), what is the corresponding channel(file and function) in client to receive the printing data?  
Is there a files in LINUX client for us to do the design reference?

-----Original Message-----
From: Alon Levy [mailto:alevy at redhat.com] 
Sent: Monday, January 02, 2012 6:19 PM
To: Charles.Tsai-蔡清海-工程部
Cc: spice-devel at lists.freedesktop.org
Subject: Re: [Spice-devel] Access local network printer from guest OS

On Mon, Jan 02, 2012 at 10:06:34AM +0800, Charles.Tsai-蔡清海-工程部 wrote:
> Alon,
> Let me recap what you suggest in case that I missed your point.


> 1. Capturing the printing data from the virtual printer driver.
> 2. send the captured data to the " cifs/ipp server" for printing data.
> 3. send the printing data to VDI port driver(virtioserial driver).
> 4. Spicevmc(in spice server)receives the printing data from VDI port driver. 
> In the above scenario, there is nothing to be changed in spice server. Here is my questions regarding this design.
> 1. Why cannot virtual printer driver send the captured data to the VDI port driver directly? The spice agent talks to the VDI port driver directly, doesn't it?
>    The virtual printer driver I want to implement is the printer port monitor driver. It captures the printing data between user-mode print spooler and the kernel-mode port drivers that access I/O port hardware.

I didn't understand your suggestion to be so specific to windows guests.
If you intend to write a windows guest printer port monitor driver (I assume it's a windows guest thing, right?) then of course you don't need an additional guest side anything, and you are correct to point this out.

> 2. Which files or functions in virtioserial driver talks to "spicevmc channel"? 
>     This question is related to question 1. If I know the way how the virtioserial and the spicevmc talk, I can modify my design too.

You create a virtioserial port, you create a chardev, and you tell qemu to connect the port to the chardev, all from the command line:
-device virtio-serial,multifunction=on -chardev spicevmc,name=vdagent,id=vdagent -device

The first device is the virtio-serial bus (pci device), the chardev is that spicevmc chardev, id is whatever you like, name is taken from a list of possible names, see below. The third is the port device (needs to be created after the chardev, the parameters are processed by order given in the command line from left to right), the name is the guest visible device created, I don't rememer exactly the device name in windows but something like \\.\vportfoo-com.redhat.spice.0

Adding a fourth SUBTYPE (there are currently three - VDAGENT, SMARTCARD,
USBREDIR) is something like this (and yes, it looks like it might be nice to make it a switch):

diff --git a/server/reds.c b/server/reds.c index acd8495..102c254 100644
--- a/server/reds.c
+++ b/server/reds.c
@@ -3261,6 +3261,7 @@ 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[] = {
@@ -3268,6 +3269,7 @@ const char *spice_server_char_device_recognized_subtypes_list[] = {
@@ -3300,6 +3302,8 @@ static int spice_server_char_device_add_interface(SpiceServer *s,  #endif
     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;

Defining SPICE_CHANNEL_PRINTER is done via the codegen stuff, you just update spice.proto and run something to produce an updated enums.h.

> -----Original Message-----
> From: Alon Levy [mailto:alevy at redhat.com]
> Sent: Sunday, January 01, 2012 10:19 PM
> To: Charles.Tsai-蔡清海-工程部
> Cc: spice-devel at lists.freedesktop.org
> Subject: Re: [Spice-devel] Access local network printer from guest OS
> On Sun, Jan 01, 2012 at 09:08:52PM +0800, Charles.Tsai-蔡清海-工程部 wrote:
> > Hi Alon,
> > 
> > Your information is extremely valuable for us. I think adding one additional channel is a good solution.
> > Because I haven't programmed QEMU before, I have a question regarding creating a virtual printer device.
> > In spice agent, the way that the SPICE agent talks to the SPICE server is through a virtual serial port device.
> > For the virtual printer device, do I need to create a similar 
> > virtual I/O for the printer? To send the printing data to the SPICE server from guest OS, the virtual printer device driver will write the printing data to the virtual I/O like a real hardware device. In QEMU, can I find any information about this?
> > Thanks.
> > 
> I am not sure how good the idea of creating a virtual printer is. I see two options, each not optimal:
>  1. expose the real printer.
>   + all features of real printer are avaliable
>   - guest has to have real printer drivers (so each new client or new
>     printer on client side requires guest driver installation). This is
>     not neccessarily hard/bad.
>  2. expose a fixed printer (this is what you are proposing)
>   - subset / fixed set of features.
>   + no new driver to install, only one time driver install.
> We have previously intended the tunnel channel to provide the printer remoting. But you don't have to expose a whole network tunnel, you could implement a cifs/ipp server with printing services. That could be implemented as a guest daemon talking over a virtioserial port and a spicevmc channel to the client, which means you won't have to change qemu at all, but you would have to add a guest feature (so needs to be implemented and installed for every guest os you want to support). I suppose such a service could also be implemented at the qemu level, and still use a spicevmc channel so no spice server changes either way. I'm not sure what kind of virtual printer you have in mind.
> I haven't actually answer you so far:
>  - no, you don't need to create a new virtual I/O channel, virtioserial
>    is just the virtual I/O you need.
> Alon
> > 
> > 
> > -----Original Message-----
> > From: Alon Levy [mailto:alevy at redhat.com]
> > Sent: Sunday, January 01, 2012 7:45 PM
> > To: Charles.Tsai-蔡清海-工程部
> > Cc: spice-devel at lists.freedesktop.org
> > Subject: Re: [Spice-devel] Access local network printer from guest 
> > OS
> > 
> > On Sun, Jan 01, 2012 at 10:41:14AM +0800, Charles.Tsai-蔡清海-工程部 wrote:
> > >    All,
> > > 
> > >     
> > > 
> > >    We planned to implement the software to access the local network  printer
> > >    from the guest OS over the SPICE.  I did see someone post a message before
> > >    talking about the implementation of the network redirect before. But the
> > >    solution seems to be too complicated for us. Here is my design ideas to
> > >    implement the access of the local network printer from the guest OS.
> > > 
> > >     
> > > 
> > >     
> > > 
> > >    1.       Implemented a virtual printer driver in the guest OS.
> > > 
> > >    2.       Intercept the printing data from the virtual printer driver and
> > >    forward it to the spice  agent.
> > > 
> > >    3.       Deliver the printing data from the spice  agent through the
> > >    .$B!H.(Bmain channel.$B!I.(B
> > > 
> > >    4.       Spice client receives the printing data and set it to the local
> > >    network printer.
> > > 
> > >     
> > > 
> > >    Based on my design ideas, I have a couple of questions.
> > > 
> > >     
> > > 
> > >    1.       Currently, main channel is used by spice agent for enchaining the
> > >    user experience. Can I expand it to delivered printing data? Any pros and
> > >    cons?
> > > 
> > >    2.       How easily it is to expand one additional channel  for priming
> > >    data if .$B!H.(Bmain channel.$B!I.(B is not a good approach to send
> > >    printing data?
> > > 
> > 
> > I would suggest going with adding an additional channel rather then adding messages to main channel. imo the existance of agent data in the main channel is not a good thing and shouldn't be taken as an example of how to do things.
> > 
> >  To add a new channel you basically need to:
> >  1. add the channel to spice.proto (in spice repository)  There are two options here - you can use an opaque channel, and by  opaque I mean that the messages it contains are Data messages, no  additional information is in them and you have to do parsing  "yourself", without the code generation done from spice.proto. If you  want to use the code generator then you can take any other channel  message as an example. You will then need to update the spice-protocol  headers as well, common/messages.h  2. implement server side - the steps are:
> >   create the new channel. Follow the inputs channel as a good example.
> >   (server/inputs_channel.c:inputs_init)
> >   advertise the new channel. This is taken care of by calling
> >   reds_register_channel.
> >   you will need to do work based on some call backs from either
> >   direction:
> >    qemu initiated (guest did something to the virtual printer device)
> >    client initiated (callback set during channel creation, in inputs
> >    it is inputs_channel_handle_parsed)  3. client side implementation: 
> > you should be working on the spice-gtk  client, it is in it's own repository. You will have to make sure the  changes (if any) you do to the common subdirectory are copied over  since it has it's own copy. Haven't worked on spice-gtk but it looks  like again starting from some existing channel like gtk/channel-inputs  could be a good idea.
> > 
> > HTH,
> > Alon
> > >     
> > > 
> > >     
> > 
> > > _______________________________________________
> > > Spice-devel mailing list
> > > Spice-devel at lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/spice-devel
> > 

More information about the Spice-devel mailing list