[RFC] Rust Xen guest-agent

[Yann Dirson <yann.dirson@xxxxxxxx>]

XCP-ng and our friends at XenServer have a need to collect a number of informations inside guests, to give to

toolstacks and admins enough info to manage the guests properly.  Today Xen downstreams have

to implement a guest agent for this when needed (see below), and we think it would be beneficial

to have one in the Xen Project, that could be configured for the needs of various downstreams.

Playing with this idea we started on several aspects:

- document what information needs to be collected and for what need, and propose a XenStore

  structure (very preliminary ideas in [0])

- a prototype agent [1] that:

  - could be used both as a replacement for what we use now, and for any improved data set we

     would want, as well as any specific needs other downstreams may have

  - would react on event where possible, to make changes visible ASAP to the toolstack

  - would be multi-platform enough to run in (ideally) all guests

  - we decided to write in Rust for various reasons [2]

We'd like to hear from the community what you think about those ideas.

What currently exists that we are aware of are:

- description for a few xenstore paths to store VIF information (iface name, MAC, IP addresses) [3]

- Xenserver's xe-guest-utilities, also used by XCP-ng; details of collected info in [4]

  - until versions 6.x it was implemented as a Linux-specific shell-script daemon [5]

  - this version has been forked for FreeBSD support [6]

  - versions 7.x [7] are a rewrite in Go, which is slightly more efficient by using a single connection to

    XenStore throughout its lifetime, but still uses a "spawn processes every minute" approach to

    data collection; despite its design that should allow support for other OS than Linux, it has

    not been extended for any (one user started a FreeBSD port, starting with conversion of the legacy

    shell script still doing OS detection [8], but the effort stopped short of any modification of Go code).

- QubesOS' meminfo-writer [9]; only collects a "used memory" metric

- apparently nothing for OpenXT ([10] only mentions installing PV drivers for Windows)

[0] https://gitlab.com/ydirson/xen-guest-agent/-/blob/ydi/rust-proto/doc/structure.md

[1] https://gitlab.com/ydirson/xen-guest-agent/-/tree/ydi/rust-proto

    https://gitlab.com/xen-project/xen-guest-agent/-/merge_requests/2

[2] https://xcp-ng.org/blog/2023/03/17/bringing-rust-to-the-xen-project/

[3] https://xenbits.xen.org/docs/unstable/misc/xenstore-paths.html#domain-controlled-paths

[4] https://github.com/xenserver/xe-guest-utilities#collected-information-by-lifetime

[5] https://aur.archlinux.org/packages/xe-guest-utilities

[6] http://distcache.freebsd.org/local-distfiles/feld/xe-guest-utilities-6.0.2.tar.gz

[7] https://github.com/xenserver/xe-guest-utilities

[8] https://github.com/xcp-ng/xe-guest-utilities/pull/1

[9] https://gitlab.com/QubesOS/qubes-linux-utils/-/blob/master/qmemman/meminfo-writer.c

[10] https://openxt.atlassian.net/wiki/spaces/OD/pages/44924936/How+to+Install+Guest+VMs

 

 

Yann Dirson | Vates Platform Developer XCP-ng & Xen Orchestra - Vates solutions w: vates.fr | xcp-ng.org | xen-orchestra.com