qemu/xen: make use of xenstore relative paths

Qemu has several hardcoded xenstore paths that are only valid on Dom0.
Attempts to launch a Qemu instance (to act as a userspace backend for
PV disks) will fail because Qemu is not able to access those paths
when running on a domain different than Dom0.

Instead make the xenstore paths relative to the domain where Qemu is
actually running.
Signed-off-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: NAnthony PERARD <anthony.perard@citrix.com>
Cc: xen-devel@lists.xenproject.org
Cc: Anthony PERARD <anthony.perard@citrix.com>

hw/xen/xen_backend.c

@@ -205,7 +205,6 @@ static struct XenDevice *xen_be_get_xendev(const char *type, int dom, int dev,
                                            struct XenDevOps *ops)
 {
     struct XenDevice *xendev;
-    char *dom0;
 
     xendev = xen_be_find_xendev(type, dom, dev);
     if (xendev) {
@@ -219,12 +218,10 @@ static struct XenDevice *xen_be_get_xendev(const char *type, int dom, int dev,
     xendev->dev   = dev;
     xendev->ops   = ops;
 
-    dom0 = xs_get_domain_path(xenstore, 0);
-    snprintf(xendev->be, sizeof(xendev->be), "%s/backend/%s/%d/%d",
-             dom0, xendev->type, xendev->dom, xendev->dev);
+    snprintf(xendev->be, sizeof(xendev->be), "backend/%s/%d/%d",
+             xendev->type, xendev->dom, xendev->dev);
     snprintf(xendev->name, sizeof(xendev->name), "%s-%d",
              xendev->type, xendev->dev);
-    free(dom0);
 
     xendev->debug      = debug;
     xendev->local_port = -1;
@@ -570,14 +567,12 @@ static int xenstore_scan(const char *type, int dom, struct XenDevOps *ops)
 {
     struct XenDevice *xendev;
     char path[XEN_BUFSIZE], token[XEN_BUFSIZE];
-    char **dev = NULL, *dom0;
+    char **dev = NULL;
     unsigned int cdev, j;
 
     /* setup watch */
-    dom0 = xs_get_domain_path(xenstore, 0);
     snprintf(token, sizeof(token), "be:%p:%d:%p", type, dom, ops);
-    snprintf(path, sizeof(path), "%s/backend/%s/%d", dom0, type, dom);
-    free(dom0);
+    snprintf(path, sizeof(path), "backend/%s/%d", type, dom);
     if (!xs_watch(xenstore, path, token)) {
         xen_be_printf(NULL, 0, "xen be: watching backend path (%s) failed\n", path);
         return -1;
@@ -603,12 +598,10 @@ static void xenstore_update_be(char *watch, char *type, int dom,
                                struct XenDevOps *ops)
 {
     struct XenDevice *xendev;
-    char path[XEN_BUFSIZE], *dom0, *bepath;
+    char path[XEN_BUFSIZE], *bepath;
     unsigned int len, dev;
 
-    dom0 = xs_get_domain_path(xenstore, 0);
-    len = snprintf(path, sizeof(path), "%s/backend/%s/%d", dom0, type, dom);
-    free(dom0);
+    len = snprintf(path, sizeof(path), "backend/%s/%d", type, dom);
     if (strncmp(path, watch, len) != 0) {
         return;
     }

xen-all.c

@@ -949,7 +949,7 @@ static void xenstore_record_dm_state(struct xs_handle *xs, const char *state)
         exit(1);
     }
 
-    snprintf(path, sizeof (path), "/local/domain/0/device-model/%u/state", xen_domid);
+    snprintf(path, sizeof (path), "device-model/%u/state", xen_domid);
     if (!xs_write(xs, XBT_NULL, path, state, strlen(state))) {
         fprintf(stderr, "error recording dm state\n");
         exit(1);