[xen master] Document ioemu MiniOS stubdomain protocol

[patchbot@xxxxxxx]

commit c7c145470168c67ba45911370bd6902917e59da5
Author:     Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Mon May 18 21:54:45 2020 -0400
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Mon May 18 23:23:44 2020 +0100

    Document ioemu MiniOS stubdomain protocol
    
    Add documentation based on reverse-engineered toolstack-ioemu stubdomain
    protocol.
    
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
    Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 docs/misc/stubdom.txt | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/docs/misc/stubdom.txt b/docs/misc/stubdom.txt
index 882a18cab4..64c77d9b64 100644
--- a/docs/misc/stubdom.txt
+++ b/docs/misc/stubdom.txt
@@ -23,6 +23,59 @@ and https://wiki.xen.org/wiki/Device_Model_Stub_Domains for 
more
 information on device model stub domains
 
 
+Toolstack to MiniOS ioemu stubdomain protocol
+---------------------------------------------
+
+This section describe communication protocol between toolstack and
+qemu-traditional running in MiniOS stubdomain. The protocol include
+expectations of both qemu and stubdomain itself.
+
+Setup (done by toolstack, expected by stubdomain):
+ - Block devices for target domain are connected as PV disks to stubdomain,
+   according to configuration order, starting with xvda
+ - Network devices for target domain are connected as PV nics to stubdomain,
+   according to configuration order, starting with 0
+ - if graphics output is expected, VFB and VKB devices are set for stubdomain
+   (its backend is responsible for exposing them using appropriate protocol
+   like VNC or Spice)
+ - other target domain's devices are not connected at this point to stubdomain
+   (may be hot-plugged later)
+ - QEMU command line (space separated arguments) is stored in
+   /vm/<target-uuid>/image/dmargs xenstore path
+ - target domain id is stored in /local/domain/<stubdom-id>/target xenstore 
path
+?? - bios type is stored in /local/domain/<target-id>/hvmloader/bios
+ - stubdomain's console 0 is connected to qemu log file
+ - stubdomain's console 1 is connected to qemu save file (for saving state)
+ - stubdomain's console 2 is connected to qemu save file (for restoring state)
+ - next consoles are connected according to target guest's serial console 
configuration
+
+Startup:
+1. PV stubdomain is started with ioemu-stubdom.gz kernel and no initrd
+2. stubdomain initialize relevant devices
+3. stubdomain signal readiness by writing "running" to 
/local/domain/<stubdom-id>/device-model/<target-id>/state xenstore path
+4. now stubdomain is considered running
+
+Runtime control (hotplug etc):
+Toolstack can issue command through xenstore. The sequence is (from toolstack 
POV):
+1. Write parameter to 
/local/domain/<stubdom-id>/device-model/<target-id>/parameter.
+2. Write command to 
/local/domain/<stubdom-id>/device-model/<target-id>/command.
+3. Wait for command result in 
/local/domain/<stubdom-id>/device-model/<target-id>/state (command specific 
value).
+4. Write "running" back to 
/local/domain/<stubdom-id>/device-model/<target-id>/state.
+
+Defined commands:
+ - "pci-ins" - PCI hot plug, results:
+   - "pci-inserted" - success
+   - "pci-insert-failed" - failure
+ - "pci-rem" - PCI hot remove, results:
+   - "pci-removed" - success
+   - ??
+ - "save" - save domain state to console 1, results:
+   - "paused" - success
+ - "continue" - resume domain execution, after loading state from console 2 
(require -loadvm command argument), results:
+   - "running" - success
+
+
+
                                    PV-GRUB
                                    =======
 
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