Re: [Xen-devel] [PATCH RESEND] xenbus: Add support for xenbus backend in stub domain

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, May 08, 2012 at 09:46:57AM -0400, Daniel De Graaf wrote:
> Add an ioctl to the /dev/xen/xenbus_backend device allowing the xenbus
> backend to be started after the kernel has booted. This allows xenstore
> to run in a different domain from the dom0.
> 
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
>  drivers/xen/xenbus/xenbus_comms.c       |    6 ++++
>  drivers/xen/xenbus/xenbus_comms.h       |    1 +
>  drivers/xen/xenbus/xenbus_dev_backend.c |   51 
> +++++++++++++++++++++++++++++++
>  include/xen/grant_table.h               |    2 +
>  include/xen/xenbus_dev.h                |    3 ++
>  5 files changed, 63 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_comms.c 
> b/drivers/xen/xenbus/xenbus_comms.c
> index 2eff7a6..52fe7ad 100644
> --- a/drivers/xen/xenbus/xenbus_comms.c
> +++ b/drivers/xen/xenbus/xenbus_comms.c
> @@ -234,3 +234,9 @@ int xb_init_comms(void)
>  
>       return 0;
>  }
> +
> +void xb_deinit_comms(void)
> +{
> +     unbind_from_irqhandler(xenbus_irq, &xb_waitq);
> +     xenbus_irq = 0;
> +}
> diff --git a/drivers/xen/xenbus/xenbus_comms.h 
> b/drivers/xen/xenbus/xenbus_comms.h
> index 6e42800..c8abd3b 100644
> --- a/drivers/xen/xenbus/xenbus_comms.h
> +++ b/drivers/xen/xenbus/xenbus_comms.h
> @@ -35,6 +35,7 @@
>  
>  int xs_init(void);
>  int xb_init_comms(void);
> +void xb_deinit_comms(void);
>  
>  /* Low level routines. */
>  int xb_write(const void *data, unsigned len);
> diff --git a/drivers/xen/xenbus/xenbus_dev_backend.c 
> b/drivers/xen/xenbus/xenbus_dev_backend.c
> index 3d3be78..be738c4 100644
> --- a/drivers/xen/xenbus/xenbus_dev_backend.c
> +++ b/drivers/xen/xenbus/xenbus_dev_backend.c
> @@ -8,7 +8,11 @@
>  
>  #include <xen/xen.h>
>  #include <xen/page.h>
> +#include <xen/xenbus.h>
>  #include <xen/xenbus_dev.h>
> +#include <xen/grant_table.h>
> +#include <xen/events.h>
> +#include <asm/xen/hypervisor.h>
>  
>  #include "xenbus_comms.h"
>  
> @@ -22,6 +26,50 @@ static int xenbus_backend_open(struct inode *inode, struct 
> file *filp)
>       return nonseekable_open(inode, filp);
>  }
>  
> +static long xenbus_alloc(domid_t domid)
> +{
> +     struct evtchn_alloc_unbound arg;
> +     int err = -EEXIST;
> +
> +     xs_suspend();
> +
> +     /* If xenstored_ready is nonzero, that means we have already talked to
> +      * xenstore and set up watches. These watches will be restored by
> +      * xs_resume, but that requires communication over the port established
> +      * below that is not visible to anyone until the ioctl returns.
> +      *
> +      * This can be resolved by splitting the ioctl into two parts
> +      * (postponing the resume until xenstored is active) but this is
> +      * unnecessarily complex for the intended use where xenstored is only
> +      * started once - so return -EEXIST if it's already running.
> +      */
> +     if (xenstored_ready)
> +             goto out_err;
> +
> +     gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
> +                     virt_to_mfn(xen_store_interface), 0 /* writable */);
> +
> +     arg.dom = DOMID_SELF;
> +     arg.remote_dom = domid;

If I specify as domid = DOMID_SELF what will happen? Should we filter some
of the obvious no-no values? Like DOMID_IO, DOMID_SELF?
> +
> +     err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
> +     if (err)
> +             goto out_err;
> +
> +     if (xen_store_evtchn > 0)
> +             xb_deinit_comms();
> +
> +     xen_store_evtchn = arg.port;
> +
> +     xs_resume();
> +
> +     return arg.port;
> +
> + out_err:
> +     xs_suspend_cancel();
> +     return err;
> +}
> +
>  static long xenbus_backend_ioctl(struct file *file, unsigned int cmd, 
> unsigned long data)
>  {
>       if (!capable(CAP_SYS_ADMIN))
> @@ -33,6 +81,9 @@ static long xenbus_backend_ioctl(struct file *file, 
> unsigned int cmd, unsigned l
>                               return xen_store_evtchn;
>                       return -ENODEV;
>  
> +             case IOCTL_XENBUS_BACKEND_SETUP:
> +                     return xenbus_alloc(data);
> +
>               default:
>                       return -ENOTTY;
>       }
> diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
> index 15f8a00..11e27c3 100644
> --- a/include/xen/grant_table.h
> +++ b/include/xen/grant_table.h
> @@ -46,6 +46,8 @@
>  
>  #include <xen/features.h>
>  
> +#define GNTTAB_RESERVED_XENSTORE 1
> +
>  /* NR_GRANT_FRAMES must be less than or equal to that configured in Xen */
>  #define NR_GRANT_FRAMES 4
>  
> diff --git a/include/xen/xenbus_dev.h b/include/xen/xenbus_dev.h
> index ac5f0fe..bbee8c6 100644
> --- a/include/xen/xenbus_dev.h
> +++ b/include/xen/xenbus_dev.h
> @@ -38,4 +38,7 @@
>  #define IOCTL_XENBUS_BACKEND_EVTCHN                  \
>       _IOC(_IOC_NONE, 'B', 0, 0)
>  
> +#define IOCTL_XENBUS_BACKEND_SETUP                   \
> +     _IOC(_IOC_NONE, 'B', 1, 0)
> +
>  #endif /* __LINUX_XEN_XENBUS_DEV_H__ */
> -- 
> 1.7.7.6

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