Re: [Xen-devel] [RFC PATCH 0/18] Xenstore stub domain

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-01-11 at 17:21 +0000, Daniel De Graaf wrote:
> This patch series allows xenstored to run in a stub domian started by
> dom0. It is based on a patch series posted by Alex Zeffertt in 2009 -
> http://old-list-archives.xen.org/archives/html/xen-devel/2009-03/msg01488.html
> 
> 
> A domain configuration for starting xenstored looks like:
> 
> kernel='/home/daniel/xen/stubdom/mini-os-x86_64-xenstore/mini-os'
> extra=''
> memory=50
> name='xenstore'
> 
> Once xenstore is started, "xenstore_dom=1" needs to be added to other
> domain's configurations in order to set up the xenstore connection to
> domain 1.

The domid should be written to xenstore so that the toolstack can pull
it back out as necessary.

> The following program handles post-creation parts of xenstored. To use
> it, run "xl create -p xenstore" and then "init-xenstore $domid". The
> running xenstored must be stopped to prevent xl using the UNIX sockets,
> and xenconsoled needs to be restarted after switching xenstores.

So the model is that you start a normal xenstored process in dom0 and
then use it to start the stub-xenstore before switching over?

How does that work wrt watches which are already registered, e.g. by
backend drivers?

I had imagined a init-xenstore.c which actually built the domain using
libxc directly from a mostly hardcoded configuration as well as
performing the necessary IOCTLs to get around the handover issue.

Ian,

> 
> /* init-xenstore.c: link with -lxenctrl */
> 
> #include <fcntl.h>
> #include <stdio.h>
> #include <string.h>
> #include <stdint.h>
> #include <stdlib.h>
> #include <sys/ioctl.h>
> #include <sys/mman.h>
> 
> #define __XEN_TOOLS__
> #include <xen/domctl.h>
> #include "xenctrl.h"
> 
> #define IOCTL_XENBUS_BACKEND_SETUP _IOC(_IOC_NONE, 'B', 1, 0)
> #define IOCTL_XENBUS_BACKEND_COMMIT _IOC(_IOC_NONE, 'B', 2, 0)
> 
> static void set_virq(int domid, int virq)
> {
>       struct xen_domctl command;
>       xc_interface *xch;
> 
>       xch = xc_interface_open(NULL, NULL, 0);
> 
>       memset(&command, 0, sizeof(command)); 
>       command.cmd               = XEN_DOMCTL_set_virq_handler;
>       command.interface_version = XEN_DOMCTL_INTERFACE_VERSION;
>       command.domain            = domid;
>       command.u.set_virq_handler.virq = virq;
>       xc_domctl(xch, &command);
>       xc_interface_close(xch);
> }
> 
> int main(int argc, char** argv)
> {
>       char buf[512];
>       int domid = atoi(argv[1]);
> 
>       set_virq(domid, VIRQ_DOM_EXC);
> 
>       int fd = open("/dev/xen/xenbus_backend", O_RDWR);
>       void *map = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
>       int rv = ioctl(fd, IOCTL_XENBUS_BACKEND_SETUP, domid);
>       *(uint16_t*)(map + 0x810) = rv;
>       snprintf(buf, 512, "xl unpause %d", domid);
>       system(buf);
>       ioctl(fd, IOCTL_XENBUS_BACKEND_COMMIT, 0);
>       return 0;
> }
> 
> -------------------------------------------------
> 
> Dom0 kernel changes:
>     [PATCH] xenbus: Add support for xenbus backend in stub domain
> 
> This is based on the new /dev/xen devices introduced in Linux 3.3.
> 
> Hypervisor changes:
>     [PATCH 01/18] xen: reinstate previously unused
>     [PATCH 02/18] xen: allow global VIRQ handlers to be delegated to
>     [PATCH 03/18] xsm: allow use of XEN_DOMCTL_getdomaininfo by
>     [PATCH 04/18] xen: Preserve reserved grant entries when switching
> 
> Patch 1 & 4 are required for setting up grant entries in new domains.
> Patch 2 & 3 allow xenstored to run in an unprivileged domain. This
> currently requires XSM to be enabled to avoid allowing all domUs access
> to XEN_DOMCTL_getdomaininfo, so the patch only allows this hypercall if
> XSM is being compiled in.
> 
> Toolstack changes:
>     [PATCH 05/18] tools/libxl: Add xenstore and console backend domain
>     [PATCH 06/18] lib{xc,xl}: Seed grant tables with xenstore and
> 
> These patches populate two of the eight reserved grant entries in new
> domains with the xenstore and console shared pages, which is required
> if xenstored is not run in a privileged domain.
> 
> Minios and xenstored:
>     [PATCH 07/18] mini-os: avoid crash if no console is provided
>     [PATCH 08/18] mini-os: avoid crash if no xenstore is provided
>     [PATCH 09/18] mini-os: remove per-fd evtchn limit
>     [PATCH 10/18] xenstored: use grant references instead of
>     [PATCH 11/18] xenstored: add NO_SOCKETS compilation option
>     [PATCH 12/18] xenstored support for in-memory rather than FS based
>     [PATCH 13/18] xenstored: support running in minios stubdom
>     [PATCH 14/18] xenstored: always use xc_gnttab_munmap in stubdom
>     [PATCH 15/18] xenstored: add --event parameter for bootstrapping
>     [PATCH 16/18] xenstored: pull dom0 event port from shared page
>     [PATCH 17/18] xenstored: use domain_is_unprivileged instead of
>     [PATCH 18/18] xenstored: add --priv-domid parameter
> 
> Support for running in a stub domain
> 
> _______________________________________________
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> http://lists.xensource.com/xen-devel



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