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Re: [libvirt] Add driver support for Native Linux KVM Tool

Sorry, I missed the title. :(

On 11/11/2011 07:56 PM, Osier Yang wrote:
Hi, all

This is a basic implementation of libvirt Native Linux KVM
Tool driver. Note that this is just made with my own interest
and spare time, it's not an endorsement/effort by Red Hat,
and it isn't supported by Red Hat officially.

Basically, the driver is designed as *stateful*, as KVM tool
doesn't maintain any info about the guest except a socket which
for its own IPC. And it's implemented by using KVM tool binary,
which is name "kvm" currently, along with cgroup controllers
"cpuacct", and "memory" support. And as one of KVM tool's
pricinple is to allow both the non-root and root user to play with.
The driver is designed to support root and non-root too, just
like QEMU does. Example of the connection URI:

     virsh -c kvmtool:///system
     virsh -c kvmtool:///session
     virsh -c kvmtool+unix:///system
     virsh -c kvmtool+unix:///session

The implementation can support more or less than 15 virsh commands
currently, including basic domain cycle operations (define/undefine,
start/destroy, suspend/resume, console, setmem, schedinfo, dumpxml,
,autostart, dominfo, etc.)

About the domain configuration:
   * "kernel": must be specified as KVM tool only support boots
      from the kernel currently (no integration with BIOS app yet).

   * "disk": only virtio bus is supported, and device type must be 'disk'.

   * "serial/console": only one console is supported, of type serial or
      virtio (can extend to support multiple console as long as kvm tool
      supports, libvirt already supported mutiple console, see upstream
      commit 0873b688c).

   * "p9fs": only support specifying the source dir, and mount tag, only
      type of 'mount' is supported.

   * "memballoon": only virtio is supported, and there is no way
      to config the addr.

   * Multiple "disk" and "p9fs" is supported.

   * Graphics and network are not supported, will explain below.

Please see "[PATCH 7/8]" for an example of the domain config. (which
contains all the XMLs supported by current implementation).

The problems of Native Linux KVM Tool from libvirt p.o.v:

   * Some destros package "qemu-kvm" as "kvm", also "kvm" is a long
     established name for "KVM" itself, so naming the project as
     "kvm" might be not a good idea. I assume it will be named
     as "kvmtool" in this implementation, never mind this if you
     don't like that, it can be updated easily. :-)

   * It still doesn't have an official package yet, even no "make install".
     means we have no way to check the dependancy and do the checking
     when 'configure'. I assume it will be installed as "/usr/bin/kvmtool"
     in this implementation. This is the main reason which can prevents
     upstream libvirt accepting the patches I guess.

   * Lacks of options for user's configuration, such as "-vnc", there
     is no option for user to configure the properties for the "vnc",
     such as the port. It hides things, doesn't provide ways to query
     the properties too, this causes problems for libvirt to add the
     vnc support, as vnc clients such as virt-manager, virt-viewer,
     have no way to connect the guest. Even vncviewer can't.

   * KVM tool manages the network completely itself (with DHCP support?),
     no way to configure, except specify the modes (user|tap|none). I
     have not test it yet, but it should need explicit script to setup
     the network rules(e.g. NAT) for the guest access outside world.
     Anyway, there is no way for libvirt to control the guest network.

   * There is a gap about the domain status between KVM tool and libvirt,
     it's caused by KVM tool unlink()s the guest socket when user exits
     from console (both text and graphic), but libvirt still think the
     guest is running.

   * KVM tool uses $HOME/.kvm_tool as the state dir, and no way to configure,
     I made a small patch to allow KVM tool accept a ENV variable,
     which is "KVM_STATE_DIR", it's used across the driver. I made a
     simple patch against kvm tool to let the whole patches work. See
     "[PATCH] kvm tools.....". As generally we want the state dir of
     a driver can be "/var/run/libvirt/kvmtool/..." for root user or
     "$HOME/.libvirt/kvmtool/run" for non-root user.

   * kvmtoolGetVersion is just broken now, as what "./kvm version" returns
     is something like "3.0.rc5.873.gb73216", however, libvirt wants things
     like "". This might be not a problem as long as KVM tool
     has a official package.

   * console connection is implemented by setup ptys in libvirt, stdout/stderr
     of kvm tool process is redirected to the master pty, and libvirt connects
     to the slave pty. This works fine now, but it might be better if kvm
     tool could provide more advanced console mechanisms. Just like QEMU

   * Not much ways existed yet for external apps or user to query the guest
     informations. But this might be changed soon per KVM tool grows up

   * It will be quite desireable if kvm tool could report the capabilities,
     of which is lacked by QEMU forever (seems so), it causes much pain for
     upper layer mgmt apps. See the RFC by Daniel Berrange in QEMU list
     for more details:


As a conclusion, it seems to me that KVM tool dosesn't consider too much
about the interface for upper layer management tools, (generally, upper
layer apps will want good interface to set/get), which might be no good
for KVM tool future development.

Thoughts, and opinions? Thanks.

[PATCH 1/7] kvmtool: Add configure support
[PATCH] kvm tools: Introduce an ENV variable for the state dir
[PATCH 2/7] kvmtool: Add documents
[PATCH 3/7] kvmtool: Add new enums and error codes for the driver
[PATCH 4/7] kvmtool: Add hook support for kvmtool domain
[PATCH 5/7] kvmtool: Add new domain type
[PATCH 6/7] conf: Set source type of the stub console
[PATCH 7/7] kvmtool: Implementation for kvm tool driver


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