[Spice-devel] [PATCH v2 2/3] manual: Add section about debugging

[Christophe Fergeau]

This details the basics for now, but can be detailed in the future.
---
 docs/manual/manual.txt | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/docs/manual/manual.txt b/docs/manual/manual.txt
index a66554a..d7b0f30 100644
--- a/docs/manual/manual.txt
+++ b/docs/manual/manual.txt
@@ -1082,6 +1082,101 @@ You should now be able to access the qemu-system-x86_64 Spice binary.
 
 :numbered!:
 
+Debugging
+=========
+
+Server side
+-----------
+
+If the virtual machine was started using QEMU directly, SPICE server logs will be output to
+your console stdout.
+When using libvirt, logs are located in `/var/log/libvirt/qemu/` for the qemu
+system instance (`qemu:///system`), and in `~/.cache/libvirt/qemu/log` for the
+qemu session instance (`qemu:///session`).
+
+Client side
+-----------
+
+remote-viewer can be started with `SPICE_DEBUG=1` in the environment, or with
+`--spice-debug` in order to get it to output more logs on stdout. `SPICE_DEBUG`
+should work with any application using spice-gtk (virt-manager, gnome-boxes, ...).
+
+Guest side
+----------
+
+.QXL KMS driver
+
+On recent Linux kernels using the QXL kms driver, booting the kernel with the
+`drm.debug=0xf` parameter.  `journalctl -k`/`dmesg` will then contain debug
+logs for the QXL kms driver. This can also be changed at runtime by echo'ing
+this value to `/sys/module/drm/parameters/debug`.
+
+
+.qxl.guestdebug QEMU parameter
+
+It's also possible to get some host-side debugging logs from the guest QXL driver.
+The driver reads a guestdebug parameter from the rom, which can be set when starting
+the VM. Only the Windows QXL driver is using this feature, see `qxl.cmdlog` for
+something guest-agnostic.  This can be enabled with `-global
+qxl-vga.guestdebug=3`, or `-global qxl.guestdebug=3` for secondary devices.
+
+The corresponding libvirt XML is:
+
+[source,xml]
+-------------------------------------------------
+<domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
+  ....
+  <qemu:commandline>
+    <qemu:arg value='-global'/>
+    <qemu:arg value='qxl-vga.guestdebug=3'/>
+  </qemu:commandline>
+</domain>
+-------------------------------------------------
+
+(don't forget to add the
+xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0' attribute to the
+toplevel `<domain>` node)
+
+
+You can go up to 12 (or more, look for DEBUG_PRINT in the driver), you get really a lot of debug information. Interesting values are:
+
+  * 3 - will give you all the highlevel commands (DrvCopyBits, DrvBitBlt, etc.)
+  * 6 - will also show QXLGetBitMap
+  * 11 - will show caching of images (this is a driver cache, not to be confused with the server<->client shared cache).
+
+
+.qxl.cmdlog QEMU parameter
+
+This will dump all the commands passing through the ringbuffer on the device
+side. It is driver and hence guest agnostic. This can be enabled with
+`-global qxl-vga.cmdlog=1`, or `-global qxl.cmdlog=1` for secondary devices.
+See the section above for the libvirt XML to use.
+
+
+Agent
+~~~~~
+
+On Linux, `journalctl -t spice-vdagentd -t spice-vdagent` will display the agent log messages.
+spice-vdagent can also be restarted by hand with the `-d` argument in order to display more logs.
+
+Recording/replaying SPICE server traffic
+----------------------------------------
+
+Since spice-server 0.12.6, it's possible to record display traffic sent by the
+SPICE server in order to replay it afterwards for a client without needing to
+start a VM. This is achieved by setting the environment variable
+`SPICE_WORKER_RECORD_FILENAME` to the filename to write the traffic to before starting
+QEMU.
+
+Once the recording session is done, the `spice-server-replay` tool can be used
+to replay the previously recorded SPICE session, for example:
+
+[source,sh]
+-------------------------------------------------
+spice-server-replay -p 5900 -c "remote-viewer spice://localhost:5900" recorded-session.spice
+-------------------------------------------------
+
+
 [appendix]
 Manual authors
 ==============
-- 
2.5.0