[Xen-devel] Re: [Xen-tools] [RFC] xm interface proposed changes

[harry <harry@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

I think you should move towards a model where the tools dynamically
discover the available configuration commands from components which are
installed in the system such that the tools eventually contain no
command specific code at all.

For example, on installation, the balloon driver might register itself
as a configurable component which provided a single configuration action
called (for the sake of argument) resize.  When the balloon driver was
installed in a domain, the configuration tools would discover the
balloon driver as a new configurable sub-object belonging to the domain
and query the registered configuration interface to discover the resize
method, the help text, the parameter types and the valid parameter
range.

Subsequent invocations of xm-help would list the domain-balloon-resize
method with an indication of the parameters and help text.

A mechanism like this would allow 3rd parties to extend the system
without having to modify the low-level configuration tools. Having the
entire specification and implementation of the configuration interface
in a single location (in the example, the balloon driver code) also
makes it easier to avoid incompatibilities between the tools and
configurable components since there is less coupling. In fact, the level
of coupling has been shifted from the component specific details of the
configuration interface to the component-independent aspects of the
mechanism for specifying interfaces.

I think this would naturally tend towards an object-verb form of
expression since this would be consistent with the discovery process.

Harry.

On Fri, 2005-07-29 at 09:04 -0400, Sean Dague wrote:
> In order to have this discussion in a structured way, we should figure out
> how we want commands structured in general (i.e. where is the verb).
> 
> It seems the following policy would be mostly in line with the existing
> command set.
> 
> If the command direct object is a xen domain (it does something directly to
> a domain core) then we use "verb" (i.e. create, destroy, save...).  If the
> command direct object is a part of a domain, like a block device or memory,
> we use "object-verb", mostly so the object commands cluster in a directly
> command listing.  Examples today would be "vbd-list" for instance.  If there
> is a difference of opinion here, we should hammer that out first, because
> the rest of the discussion is pretty pointless without at least these ground
> rules. :)
> 
> To make this easier, here is the command help today (with attributes added
> in to each command).
> 
> =========================================================================
> ---------XM HELP TODAY---------------------------------------------------
> call                Call xend api functions
> help                Print help.
> 
> Commands related to consoles:
> 
> console <DomainId>  Open a console to a domain.
> consoles            Get information about domain consoles.
> 
> Commands on domains:
> 
> balloon <DomainId> <Mem>  Set the domain's memory footprint using the balloon 
> driver.
> create <ConfigFile>       Create a domain.
> destroy <DomainId>        Terminate a domain immediately.
> domid   <DomainName>      Convert a domain name to a domain id.
> domname <DomainId>        Convert a domain id to a domain name.
> list                      List information about domains.
> maxmem <DomainId> <Mem>   Set domain memory limit.
> migrate [options] <DomId> <Host> Migrate a domain to another machine.
> pause  <DomainId>         Pause execution of a domain.
> pincpu <DomId> <VCpu> <CPUS>    Set which cpus a VCPU can use. 
> restore <File>            Create a domain from a saved state.
> save    <DomId> <File>    Save domain state (and config) to file.
> shutdown [options] <DomId>  Shutdown a domain.
> sysrq   <DomId> <letter>    Send a sysrq to a domain.
> unpause <DomId>           Unpause a paused domain.
> vcpu-hotplug <DomId> <VCPU> <0|1> Enable or disable a VCPU in a domain.
> 
> Commands related to the xen host (node):
> 
> dmesg   [--clear]         Read or clear Xen's message buffer.
> info                      Get information about the xen host.
> log                       Print the xend log.
> 
> Comands controlling scheduling:
> 
> bvt DOM MCUADV WARPBACK WARPVALUE WARPL WARPU   Set BVT scheduler parameters.
> bvt_ctxallow CTX_ALLOW                          Set the BVT scheduler context 
> switch allowance.
> sedf DOM PERIOD SLICE LATENCY EXTRATIME WEIGHT  Set simple EDF parameters.
> 
> Commands related to virtual block devices:
> 
> vbd-create <DomId> <BackDev> <FrontDev> <Mode> [BackDomId]    Create a new 
> virtual block device for a domain
> vbd-destroy <DomId> <DevId>  Destroy a domain's virtual block device
> vbd-list    <DomId>          List virtual block devices for a domain.
> vbd-refresh <DomId> <DevId>  Refresh a virtual block device for a domain
> 
> Commands related to virtual network interfaces:
> 
> vif-limit   <DomId> <Vif> <Credit> <Period> Limit the transmission rate of a 
> virtual network interface.
> vif-list    <DomId> List virtual network interfaces for a domain.
> 
> Try '/usr/sbin/xm help CMD' for help on CMD
> -------------------------------------------------------------------
> 
> 
> 
> The following is a proposed set of changes based on the "obj-verb" paradigm,
> plus trying to make commands make more sense to a user that may not know
> things about Xen internals.  Commands that have renames are marked with (*),
> commands that are "new" to create what seems like a complete interface are
> marked with (+).
> 
> ===================================================================
> ---------XM Proposed-----------------------------------------------
> help                Print help.
> 
> Commands related to consoles:
> 
> console <DomId>  Open a console to a domain.
> * console-list        Get information about domain consoles.
> 
> Commands on domains:
> 
> domid   <DomName>         Convert a domain name to a domain id.
> domname <DomId>           Convert a domain id to a domain name.
> 
> create  <ConfigFile>      Create a domain.
> destroy <DomId>           Terminate a domain immediately.
> restore <File>            Create a domain from a saved state.
> save    <DomId> <File>    Save domain state (and config) to file.
> * shutdown [-w|-a] <DomId>  Shutdown a domain.
> + reboot   [-w|-a] <DomId>  Reboot a domain.
> 
> list                      List information about domains.
> 
> * mem-max <DomId> <Mem>             Set domain maximum memory limit.
> * mem-set <DomId> <Mem>             Set the domain's memory dynamically.
> * cpus-set <DomId> <VCpu> <CPUS>    Set which cpus a VCPU can use. 
> + cpus-list <DomId> <VCpu>          Get the list of cpus for a VCPU
> * vcpu-enable <DomId> <VCPU>        Disable VCPU in a domain.
> + vcpu-disable <DomId> <VCPU>       Enable VCPU in a domain
> + vcpu-list <DomId>                 Get the list of VCPUs for a domain
> 
> migrate [options] <DomId> <Host> Migrate a domain to another machine.
> 
> sysrq   <DomId> <letter>    Send a sysrq to a domain.
> pause   <DomId>           Pause execution of a domain.
> unpause <DomId>           Unpause a paused domain.
> 
> Commands related to the xen host (node):
> 
> dmesg   [--clear]         Read or clear Xen's message buffer.
> info                      Get information about the xen host.
> log                       Print the xend log.
> 
> Comands controlling scheduling:
> 
> bvt DOM MCUADV WARPBACK WARPVALUE WARPL WARPU   Set BVT scheduler parameters.
> bvt_ctxallow CTX_ALLOW                          Set the BVT scheduler context 
> switch allowance.
> sedf DOM PERIOD SLICE LATENCY EXTRATIME WEIGHT  Set simple EDF parameters.
> 
> Commands related to virtual block devices:
> 
> * block-create <DomId> <BackDev> <FrontDev> <Mode> [BackDomId]    Create a 
> new virtual block device for a domain
> * block-destroy <DomId> <DevId>  Destroy a domain's virtual block device
> * block-list    <DomId>          List virtual block devices for a domain.
> * block-refresh <DomId> <DevId>  Refresh a virtual block device for a domain
> 
> Commands related to virtual network interfaces:
> 
> * network-limit   <DomId> <Vif> <Credit> <Period> Limit the transmission rate 
> of a virtual network interface.
> * network-list    <DomId> List virtual network interfaces for a domain.
> 
> Try '/usr/sbin/xm help CMD' for help on CMD
> -----------------------------------------------------------------
> 
> 
> 
> Additionally, if we are to move to a model where command aliasing can easily
> be done (for backwards compatibility), I actually think we need to majorly
> restructure main.py from an object based model to a declaritive model, where
> main() would be a dispatcher to possibly many functions that would be the
> equiv of the main methods in each object today.  I also believe that this is
> the only way to get 'xm help' to run as non-root, which I consider a goal. 
> I'd like at least tenative approval for this idea before I code it up, but I
> am *willing to volunteer* for this conversion of main.py from object based
> -> declaritive structure.
> 
> Comments welcome, flame away.
> 
>       -Sean
> 
> _______________________________________________
> Xen-tools mailing list
> Xen-tools@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-tools


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