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    SubjectRe: [RFC PATCH 12/16] xen/xenbus: support xenbus frontend/backend with xenhost_t
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    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@oracle.com>
    >> ---
    >>   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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