qubes-doc/debugging/vm-interface.md

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VM Configuration Interface

Qubes VM have some settings set by dom0 based on VM settings. There are multiple configuration channels, which includes:

• XenStore
• QubesDB - replacing most of xenstore (in R3 or later)
• Qubes RPC (called at VM startup, or when configuration changed)
• GUI protocol

xenstore

Keys exposed by dom0 to VM (only Qubes specific included):

• qubes-vm-type - VM type, the same as type field in qvm-prefs. One of AppVM, ProxyVM, NetVM, TemplateVM, HVM, TemplateHVM
• qubes-vm-updatable - flag whether VM is updatable (whether changes in root.img will survive VM restart). One of True, False
• qubes-vm-persistence - what data do persist between VM restarts:
  • full - all disks
  • rw-only - only /rw disk
  • none - none
• qubes-timezone - name of timezone based on dom0 timezone. For example Europe/Warsaw`
• qubes-keyboard - keyboard layout based on dom0 layout. Its syntax is suitable for xkbcomp command (after expanding escape sequences like \n or \t). This is meant only as some default value, VM can ignore this option and choose its own keyboard layout (this is what keyboard setting from Qubes Manager does). This entry is created as part of gui-daemon initialization (so not available when gui-daemon disabled, or not started yet).
• qubes-debug-mode - flag whether VM have debug mode enabled (qvm-prefs setting). One of 1, 0
• qubes-service/SERVICE_NAME - subtree for VM services controlled from dom0 (using qvm-service command or Qubes Manager). One of 1, 0. Note that not every service will be listed here, if entry is missing, it means "use VM default". List of currently supported services is in qvm-service man page
• qubes-netmask - network mask (only when VM has netvm set); currently hardcoded "255.255.255.0"
• `qubes-ip - IP address for this VM (only when VM has netvm set)
• qubes-gateway - default gateway IP and primary DNS address (only when VM has netvm set); VM should add host route to this address directly via eth0 (or whatever default interface name is)
• qubes-secondary-dns - secondary DNS address (only when VM has netvm set)
• qubes-netvm-gateway - same as qubes-gateway in connected VMs (only when VM serves as network backend - ProxyVM and NetVM); because this is also set as primary DNS in connected VMs, traffic sent to this IP on port 53 should be redirected to DNS server
• qubes-netvm-netmask - same as qubes-netmask in connected VMs (only when VM serves as network backend - ProxyVM and NetVM)
• qubes-netvm-network - network address (only when VM serves as network backend - ProxyVM and NetVM); can be also calculated from qubes-netvm-gateway and qubes-netvm-netmask
• qubes-netvm-secondary-dns - same as qubes-secondary-dns in connected VMs (only when VM serves as network backend - ProxyVM and NetVM); traffic sent to this IP on port 53 should be redirected to secondary DNS server

Keys set by VM for passing info to dom0:

• memory/meminfo - used memory (updated by qubes-meminfo-writer), input information for qmemman; Format: 6 lines (EOL encoded as \n), each in format "FIELD: VALUE kB"; fields: MemTotal, MemFree, Buffers, Cached, SwapTotal, SwapFree; meaning the same as in /proc/meminfo in Linux
• qubes-block-devices - list of block devices exposed by this VM, each device (subdirectory) should be named in a way that VM can attach the device based on it. Each should contain those entries:
  • desc - device description (ASCII text)
  • size - device size in bytes
  • mode - default connection mode; r for read-only, w for read-write
• qubes-usb-devices - list of USB devices exposed by this VM, each device (subdirectory) should contain:
  • desc - device description (ASCII text)
  • usb-ver - USB version (1, 2 or 3)

Qubes RPC

Services called by dom0 to provide some VM configuration:

• qubes.SetMonitorLayout - provide list of monitors, one in a line, each line contains four numbers: width height X Y width_mm height_mm (physical dimensions - width_mm and height_mm - are optional)

• qubes.WaitForSession - called to wait for full VM startup

• qubes.GetAppmenus - receive appmenus from given VM (template); TODO: describe format here

• qubes.GetImageRGBA - receive image/application icon. Protocol:

  1. Caller sends name of requested icon. This can be one of:
     • xdgicon:NAME - search for NAME in standard icons theme
     • - - get icon data from stdin (the caller), can be prefixed with format name, for example png:-
     • file name
  2. The service responds with image dimensions: width and height as decimal numbers, separated with space and with EOL marker at the and; then image data in RGBA format (32 bits per pixel)

• qubes.SetDateTime - set VM time, called periodically by dom0 (can be triggered manually from dom0 by calling qvm-sync-clock). The service receives one line at stdin - time in format of date -u -Iseconds, for example 2015-07-31T16:10:43+0000.

• qubes.SetGuiMode - called in HVM to switch between fullscreen and seamless GUI mode. The service receives a single word on stdin - either FULLSCREEN or SEAMLESS

Other Qrexec services installed by default:

• qubes.Backup - store Qubes backup. The service receives location chosen by the user (one line, terminated by '\n'), the backup archive (description of backup format)
• qubes.DetachPciDevice - service called in reaction to qvm-pci -d call on running VM. The service receives one word - BDF of device to detach. When the service call ends, the device will be detached
• qubes.Filecopy - receive some files from other VM. Files sent in qfile format
• qubes.OpenInVM - open a file in called VM. Service receives a single file on stdin (in qfile format. After a file viewer/editor is terminated, if the file was modified, can be sent back (just raw content, without any headers); otherwise service should just terminate without sending anything. This service is used by both qvm-open-in-vm and qvm-open-in-dvm tools. When called in DispVM, service termination will trigger DispVM cleanup.
• qubes.Restore - retrieve Qubes backup. The service receives backup location entered by the user (one line, terminated by '\n'), then should output backup archive in qfile format (core-agent-linux component contains tar2qfile utility to do the conversion
• qubes.SelectDirectory, qubes.SelectFile - services which should show file/directory selection dialog and return (to stdout) a single line containing selected path, or nothing in case of cancellation
• qubes.SuspendPre - service called in every VM with PCI device attached just before system suspend
• qubes.SuspendPost - service called in every VM with PCI device attached just after system resume
• qubes.SyncNtpClock - service called to trigger network time synchronization. Service should synchronize local VM time and terminate when done.
• qubes.WindowIconUpdater - service called by VM to send icons of individual windows. The protocol there is simple one direction stream: VM sends window ID followed by icon in qubes.GetImageRGBA format, then next window ID etc. VM can send icon for the same window multiple times to replace previous one (for example for animated icons)
• qubes.VMShell - call any command in the VM; the command(s) is passed one per line

Currently Qubes still calls few tools in VM directly, not using service abstraction. This will change in the future. Those tools are:

• /usr/lib/qubes/qubes-download-dom0-updates.sh - script to download updates (or new packages to be installed) for dom0 (qubes-dom0-update tool)
• date -u -Iseconds - called directly to retrieve time after calling qubes.SyncNtpClock service (qvm-sync-clock tool)
• nm-online -x - called before qubes.SyncNtpClock service call by qvm-sync-clock tool
• resize2fs - called to resize filesystem on /rw partition by qvm-grow-private tool
• gpk-update-viewer - called by Qubes Manager to display available updates in a TemplateVM
• systemctl start qubes-update-check.timer (and similarly stop) - called when enabling/disabling updates checking in given VM (qubes-update-check qvm-service)

Additionally automatic tests extensively calls various commands directly in VMs. We do not plan to change that.

GUI protocol

GUI initialization includes passing the whole screen dimensions from dom0 to VM. This will most likely be overwritten by qubes.SetMonitorLayout Qubes RPC call.