xen: defer xenstore initialization until xenstored is started

The xenstore related devices in the kernel cannot be started until
xenstored is running, which will happen later in the Dom0 case. If
start_info_t doesn't contain a valid xenstore event channel, defer all
xenstore related devices attachment to later.

Sponsored by: Citrix Systems R&D

dev/xen/xenstore/xenstore.c:
 - Prevent xenstore from trying to attach it's descendant devices if
   xenstore is not initialized.
 - Add a callback in the xenstore interrupt filter that will trigger
   the plug of xenstore descendant devices on the first received
   interrupt. This interrupt is generated when xenstored attaches to
   the event channel, and serves as a notification that xenstored is
   running.

1 files changed, 66 insertions, 2 deletions

diff --git a/sys/dev/xen/xenstore/xenstore.c b/sys/dev/xen/xenstore/xenstore.c
index f7425da7b98f..8ff766c0855a 100644
--- a/sys/dev/xen/xenstore/xenstore.c
+++ b/sys/dev/xen/xenstore/xenstore.c
@@ -48,6 +48,8 @@ __FBSDID("$FreeBSD$");
 #include <sys/sysctl.h>
 #include <sys/uio.h>
 #include <sys/unistd.h>
+#include <sys/queue.h>
+#include <sys/taskqueue.h>
 
 #include <machine/stdarg.h>
 
@@ -249,6 +251,20 @@ struct xs_softc {
 	 * with the XenStore service) are available.
 	 */
 	struct intr_config_hook xs_attachcb;
+
+	/**
+	 * Xenstore is a user-space process that usually runs in Dom0,
+	 * so if this domain is booting as Dom0, xenstore wont we accessible,
+	 * and we have to defer the initialization of xenstore related
+	 * devices to later (when xenstore is started).
+	 */
+	bool initialized;
+
+	/**
+	 * Task to run when xenstore is initialized (Dom0 only), will
+	 * take care of attaching xenstore related devices.
+	 */
+	struct task xs_late_init;
 };
 
 /*-------------------------------- Global Data ------------------------------*/
@@ -352,6 +368,16 @@ static void
 xs_intr(void * arg __unused /*__attribute__((unused))*/)
 {
 
+	/* If xenstore has not been initialized, initialize it now */
+	if (!xs.initialized) {
+		xs.initialized = true;
+		/*
+		 * Since this task is probing and attaching devices we
+		 * have to hold the Giant lock.
+		 */
+		taskqueue_enqueue(taskqueue_swi_giant, &xs.xs_late_init);
+	}
+
 	/*
 	 * Hold ring lock across wakeup so that clients
 	 * cannot miss a wakeup.
@@ -1112,6 +1138,15 @@ xs_attach_deferred(void *arg)
 	config_intrhook_disestablish(&xs.xs_attachcb);
 }
 
+static void
+xs_attach_late(void *arg, int pending)
+{
+
+	KASSERT((pending == 1), ("xs late attach queued several times"));
+	bus_generic_probe(xs.xs_dev);
+	bus_generic_attach(xs.xs_dev);
+}
+
 /**
  * Attach to the XenStore.
  *
@@ -1130,12 +1165,37 @@ xs_attach(device_t dev)
 	/* Initialize the interface to xenstore. */
 	struct proc *p;
 
+	xs.initialized = false;
 	if (xen_hvm_domain()) {
 		xs.evtchn = hvm_get_parameter(HVM_PARAM_STORE_EVTCHN);
 		xs.gpfn = hvm_get_parameter(HVM_PARAM_STORE_PFN);
 		xen_store = pmap_mapdev(xs.gpfn * PAGE_SIZE, PAGE_SIZE);
+		xs.initialized = true;
 	} else if (xen_pv_domain()) {
-		xs.evtchn = HYPERVISOR_start_info->store_evtchn;
+		if (HYPERVISOR_start_info->store_evtchn == 0) {
+			struct evtchn_alloc_unbound alloc_unbound;
+
+			/* Allocate a local event channel for xenstore */
+			alloc_unbound.dom = DOMID_SELF;
+			alloc_unbound.remote_dom = DOMID_SELF;
+			error = HYPERVISOR_event_channel_op(
+			    EVTCHNOP_alloc_unbound, &alloc_unbound);
+			if (error != 0)
+				panic(
+				   "unable to alloc event channel for Dom0: %d",
+				    error);
+
+			HYPERVISOR_start_info->store_evtchn =
+			    alloc_unbound.port;
+			xs.evtchn = alloc_unbound.port;
+
+			/* Allocate memory for the xs shared ring */
+			xen_store = malloc(PAGE_SIZE, M_XENSTORE,
+			    M_WAITOK | M_ZERO);
+		} else {
+			xs.evtchn = HYPERVISOR_start_info->store_evtchn;
+			xs.initialized = true;
+		}
 	} else {
 		panic("Unknown domain type, cannot initialize xenstore.");
 	}
@@ -1167,7 +1227,11 @@ xs_attach(device_t dev)
 
 	xs.xs_attachcb.ich_func = xs_attach_deferred;
 	xs.xs_attachcb.ich_arg = NULL;
-	config_intrhook_establish(&xs.xs_attachcb);
+	if (xs.initialized) {
+		config_intrhook_establish(&xs.xs_attachcb);
+	} else {
+		TASK_INIT(&xs.xs_late_init, 0, xs_attach_late, NULL);
+	}
 
 	return (error);
 }