[Spice-devel] Read data out of the Virtqueue

Tue Apr 3 01:40:26 PDT 2012

Alon,

Our Windows client code is based on 0.10.1 release and that is, I believe, the latest one. 
"spice-gtk" is running in LINUX and I believe it is not applicable to Windows platform.

Please refer to the following trace to understand what I said. As you can see, printing channel is registered to spice server after the following trace 
"spice_server_char_device_add_interface: Connect SPICE_CHANNEL_PRINT".

Spice server report the number of channels to the client using the following main channel message "SPICE_MSG_MAIN_CHANNELS_LIST" that happens before the printing channel registers to the spice server. As such, the spice client cannot create the "print channel object" when it is launched.

I am thinking to remedy such a problem by sending a message to spice client thru the main channel. After spice client receives that message, it creates and initialize the "printing object". Although it is not good approach, it is the easy way to fix this issue for us. Let me know if you have a better idea. Thanks.

==================================================================================================================================
ctsai at ctsai-ubuntu:~$ ./Target32.sh
Starting QEMU with...
-localtime -drive file=/var/lib/libvirt/images/Windows-7-32.img -vga qxl -spice port=5900,disable-ticketing -device virtio-serial-pci,ioeventfd=off -chardev spicevmc,id=vdagent,name=vdagent,debug=2 -device virtserialport,chardev=vdagent,name=com.redhat.spice.0 -chardev spicevmc,id=vdprint,name=vdprint,debug=2 -device virtserialport,chardev=vdprint,name=com.redhat.print.0 -smp 1,cores=2 -m 2048 -enable-kvm
....
do_spice_init: starting 0.10.1
spice_server_add_interface: spice_server_add_interface: type=migration

spice_server_add_interface: SPICE_INTERFACE_MIGRATION
spice_server_add_interface: spice_server_add_interface: type=keyboard

spice_server_add_interface: SPICE_INTERFACE_KEYBOARD
spice_server_add_interface: spice_server_add_interface: type=mouse

spice_server_add_interface: SPICE_INTERFACE_MOUSE
spice_server_add_interface: spice_server_add_interface: type=qxl

spice_server_add_interface: SPICE_INTERFACE_QXL
red_worker_main: begin
display_channel_create: create display channel
cursor_channel_create: create cursor channel
scd:   1: vmc_register_interface
spice_server_add_interface: spice_server_add_interface: type=char_device

spice_server_char_device_add_interface: CHAR_DEVICE vdagent
scd:   2: vmc_register_interface
spice_server_add_interface: spice_server_add_interface: type=char_device

spice_server_char_device_add_interface: CHAR_DEVICE vdprint
spice_server_char_device_add_interface: Connect SPICE_CHANNEL_PRINT
spice_chr_write
scd:   1: spice_chr_write: 36
scd:   1: vmc_read: vdagent 0x7f7ff3f98c80 8/8/36
scd:   2: vmc_read: vdagent 0x7f7ff3f98c88 28/28/28
scd:   3: vmc_read: vdagent (nil) 8/0/0
scd:   4: vmc_read: vdagent (nil) 8/0/0
spice_chr_write
scd:   2: spice_chr_write: 36
scd:   5: vmc_read: vdagent 0x7f7ff3f98c80 8/8/36
scd:   6: vmc_read: vdagent 0x7f7ff3f98c88 28/28/28
scd:   7: vmc_read: vdagent (nil) 8/0/0
scd:   8: vmc_read: vdagent (nil) 8/0/0

-----Original Message-----
From: Alon Levy [mailto:alevy at redhat.com] 
Sent: Tuesday, April 03, 2012 3:54 PM
To: Charles.Tsai-蔡清海-研究發展部
Cc: spice-devel at lists.freedesktop.org
Subject: Re: Read data out of the Virtqueue

On Mon, Apr 02, 2012 at 07:44:46AM +0000, Charles.Tsai-蔡清海-研究發展部 wrote:
> Alon,
> 
> 	In spice client, the creation of the channel is based on "init->num_of_channels" that is returned from  the spice server.
> 	Please see the following  function to create the spice channel from 
> the client
> 
> void RedClient::handle_channels(RedPeer::InMessage* message) {
>     SpiceMsgChannels *init = (SpiceMsgChannels *)message->data();
>     SpiceChannelId* channels = init->channels;
>     for (unsigned int i = 0; i < init->num_of_channels; i++) {
>         create_channel(channels[i].type, channels[i].id);
>     }
> }
> 
> For the printing channel, it is created and registered by function 
> spicevmc_device_connect(char_device, SPICE_CHANNEL_PRINT); (see in reds.c file) Because the printing channel is registered and created in spice server lately after spice client is up, the creation of the printing channel is thus skipped by the spice client.

Two things: First, you are using the old client code base as an example.
All well and good, but if possible it's better to use spice-gtk as a base for new features, because that's the client we are going with forwward (or actually the client enabling library, with remote-viewer being the preffered client).
Second, what do you mean registered after the spice client is up? If there is some race window where the server is already listening to clients but the printing channel is not registered, that is bad and needs fixing, but in general the server is initialized *before* the client is connected. The right order is 1. server channels are registered 2. server starts listening 3. client connects

#3 cannot come before #2 so in general there is no way to have the situation you describe (unless there is a race and #1 happens after #2 and then both orders with respect to #3 are possible).

> Can you tell me how to resolve this problem based on the spice architecture? Thanks.
> 
> 
> -----Original Message-----
> From: Charles.Tsai-蔡清海-研究發展部
> Sent: Friday, March 30, 2012 9:27 AM
> To: 'Alon Levy'
> Cc: spice-devel at lists.freedesktop.org
> Subject: RE: Read data out of the Virtqueue
> 
> Alon,
> 
> It is a bug that I modified for printing channel. BTW, can a spice channel be brought up or down based on a request from a spice client?
> The reason that I am asking for such a question is because the printing channel might be brought up based on a configuration policy. I would like to know if a spice channel can be brought up dynamically during the run time.
> 
> 
> -----Original Message-----
> From: Alon Levy [mailto:alevy at redhat.com]
> Sent: Friday, March 30, 2012 4:16 AM
> To: Charles.Tsai-蔡清海-研究發展部
> Cc: spice-devel at lists.freedesktop.org
> Subject: Re: Read data out of the Virtqueue
> 
> On Thu, Mar 29, 2012 at 09:42:32AM +0000, Charles.Tsai-蔡清海-研究發展部 wrote:
> > Alon,
> > 
> > Forget my previous mail. When I dig into the vdservice, I found there was one bug to check the overlay I/O status after calling the VirtIO write function.
> > After I fixed the bug, I can see more printing raw data inside the Qemu now. Although I still find some issues, hopefully I can fix it as I debug more codes in both spice client and spice server. Thank you for your time.
> 
> Great that you managed to progress. Can you send a patch for the vdservice issue? Is it a bug in the original or just in the one you modified for printer channel?
> 
> > 
> > -----Original Message-----
> > From: Charles.Tsai-蔡清海-研究發展部
> > Sent: Wednesday, March 28, 2012 6:07 PM
> > To: 'Alon Levy'
> > Cc: spice-devel at lists.freedesktop.org
> > Subject: Read data out of the Virtqueue
> > 
> > Alon,
> > 
> > My printer driver can write the printing raw data into virtIO driver. But I cannot see the found the printing raw data in the spice server. For the vdagent, I found the following code segment which is a callback to read the data from the vdi_port. Do I need to add a similar code to read the data from the Virtio?
> > 
> > In Qemu, I do see vmc_write is called when the printer driver writes the printing raw data into the  virtIOdevice.
> > Consequently, function "spicevmc_red_channel_send_item" should be called to send the payload to the spice client. But I did not see function "spicevmc_red_channel_send_item" is called either. It looks like the printing rawa data is still inside the VirtIO queue. What function I need to add so as to pull the data out of the VirtIO queue?
> > 
> > ====================================================================
> > == ================= struct SpiceCharDeviceState 
> > vdagent_char_device_state = {
> >     .wakeup = &vdagent_char_device_wakeup, };
> > 
> > 
> > void vdagent_char_device_wakeup(SpiceCharDeviceInstance *sin) {
> >     while (read_from_vdi_port());
> > }