Re: [Xen-devel] [RFC PATCH 12/16] xen/xenbus: support xenbus frontend/backend with xenhost_t

[Ankur Arora <ankur.a.arora@xxxxxxxxxx>]

On 6/17/19 2:50 AM, Juergen Gross wrote:
> On 09.05.19 19:25, Ankur Arora wrote:
> > As part of xenbus init, both frontend, backend interfaces need to talk
> > on the correct xenbus. This might be a local xenstore (backend) or might
> > be a XS_PV/XS_HVM interface (frontend) which needs to talk over xenbus
> > with the remote xenstored. We bootstrap all of these with evtchn/gfn
> > parameters from (*setup_xs)().
> >
> > Given this we can do appropriate device discovery (in case of frontend)
> > and device connectivity for the backend.
> > Once done, we stash the xenhost_t * in xen_bus_type, xenbus_device or
> > xenbus_watch and then the frontend and backend devices implicitly use
> > the correct interface.
> >
> > The rest of patch is just changing the interfaces where needed.
> >
> > Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
> > ---
> >   drivers/block/xen-blkback/blkback.c        |  10 +-
> >   drivers/net/xen-netfront.c                 |  14 +-
> >   drivers/pci/xen-pcifront.c                 |   4 +-
> >   drivers/xen/cpu_hotplug.c                  |   4 +-
> >   drivers/xen/manage.c                       |  28 +--
> >   drivers/xen/xen-balloon.c                  |   8 +-
> >   drivers/xen/xenbus/xenbus.h                |  45 ++--
> >   drivers/xen/xenbus/xenbus_client.c         |  32 +--
> >   drivers/xen/xenbus/xenbus_comms.c          | 121 +++++-----
> >   drivers/xen/xenbus/xenbus_dev_backend.c    |  30 ++-
> >   drivers/xen/xenbus/xenbus_dev_frontend.c   |  22 +-
> >   drivers/xen/xenbus/xenbus_probe.c          | 246 +++++++++++++--------
> >   drivers/xen/xenbus/xenbus_probe_backend.c  |  19 +-
> >   drivers/xen/xenbus/xenbus_probe_frontend.c |  65 +++---
> >   drivers/xen/xenbus/xenbus_xs.c             | 188 +++++++++-------
> >   include/xen/xen-ops.h                      |   3 +
> >   include/xen/xenbus.h                       |  54 +++--
> >   include/xen/xenhost.h                      |  20 ++
> >   18 files changed, 536 insertions(+), 377 deletions(-)
> >
> > diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c 
> > b/drivers/xen/xenbus/xenbus_dev_frontend.c
> > index c3e201025ef0..d6e0c397c6a0 100644
> > --- a/drivers/xen/xenbus/xenbus_dev_frontend.c
> > +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
> > @@ -58,10 +58,14 @@
> >   #include <xen/xenbus.h>
> >   #include <xen/xen.h>
> > +#include <xen/interface/xen.h>
> > +#include <xen/xenhost.h>
> >   #include <asm/xen/hypervisor.h>
> >   #include "xenbus.h"
> > +static xenhost_t *xh;
> > +
> >   /*
> >    * An element of a list of outstanding transactions, for which we're
> >    * still waiting a reply.
> > @@ -312,13 +316,13 @@ static void xenbus_file_free(struct kref *kref)
> >        */
> >       list_for_each_entry_safe(trans, tmp, &u->transactions, list) {
> > -        xenbus_transaction_end(trans->handle, 1);
> > +        xenbus_transaction_end(xh, trans->handle, 1);
> >           list_del(&trans->list);
> >           kfree(trans);
> >       }
> >       list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
> > -        unregister_xenbus_watch(&watch->watch);
> > +        unregister_xenbus_watch(xh, &watch->watch);
> >           list_del(&watch->list);
> >           free_watch_adapter(watch);
> >       }
> > @@ -450,7 +454,7 @@ static int xenbus_write_transaction(unsigned 
> > msg_type,
> >              (!strcmp(msg->body, "T") || !strcmp(msg->body, "F"))))
> >           return xenbus_command_reply(u, XS_ERROR, "EINVAL");
> > -    rc = xenbus_dev_request_and_reply(&msg->hdr, u);
> > +    rc = xenbus_dev_request_and_reply(xh, &msg->hdr, u);
> >       if (rc && trans) {
> >           list_del(&trans->list);
> >           kfree(trans);
> > @@ -489,7 +493,7 @@ static int xenbus_write_watch(unsigned msg_type, 
> > struct xenbus_file_priv *u)
> >           watch->watch.callback = watch_fired;
> >           watch->dev_data = u;
> > -        err = register_xenbus_watch(&watch->watch);
> > +        err = register_xenbus_watch(xh, &watch->watch);
> >           if (err) {
> >               free_watch_adapter(watch);
> >               rc = err;
> > @@ -500,7 +504,7 @@ static int xenbus_write_watch(unsigned msg_type, 
> > struct xenbus_file_priv *u)
> >           list_for_each_entry(watch, &u->watches, list) {
> >               if (!strcmp(watch->token, token) &&
> >                   !strcmp(watch->watch.node, path)) {
> > -                unregister_xenbus_watch(&watch->watch);
> > +                unregister_xenbus_watch(xh, &watch->watch);
> >                   list_del(&watch->list);
> >                   free_watch_adapter(watch);
> >                   break;
> > @@ -618,8 +622,9 @@ static ssize_t xenbus_file_write(struct file *filp,
> >   static int xenbus_file_open(struct inode *inode, struct file *filp)
> >   {
> >       struct xenbus_file_priv *u;
> > +    struct xenstore_private *xs = xs_priv(xh);
> > -    if (xen_store_evtchn == 0)
> > +    if (xs->store_evtchn == 0)
> >           return -ENOENT;
> >       nonseekable_open(inode, filp);
> > @@ -687,6 +692,11 @@ static int __init xenbus_init(void)
> >       if (!xen_domain())
> >           return -ENODEV;
> > +    if (xen_driver_domain() && xen_nested())
> > +        xh = xh_remote;
> > +    else
> > +        xh = xh_default;
> This precludes any mixed use of L0 and L1 frontends. With this move you
> make it impossible to e.g. use a driver domain for networking in L1 with
> a L1-local PV disk, or pygrub in L1 dom0.
Ah, yes. I hadn't thought about that case.

Let me see how I can rework this interface.

Ankur

> Juergen
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