xen: write information about supported backends

Add a Xenstore directory for each supported pv backend. This will allow
Xen tools to decide which backend type to use in case there are
multiple possibilities.

The information is added under
/local/domain/<backend-domid>/device-model/<domid>/backends
before the "running" state is written to Xenstore. Using a directory
for each backend enables us to add parameters for specific backends
in the future.

This interface is documented in the Xen source repository in the file
docs/misc/qemu-backends.txt

In order to reuse the Xenstore directory creation already present in
hw/xen/xen_devconfig.c move the related functions to
hw/xen/xen_backend.c where they fit better.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Message-id: 1463062421-613-3-git-send-email-jgross@suse.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/xen/xen_backend.c

@@ -42,11 +42,36 @@ struct xs_handle *xenstore = NULL;
 const char *xen_protocol;
 
 /* private */
+struct xs_dirs {
+    char *xs_dir;
+    QTAILQ_ENTRY(xs_dirs) list;
+};
+static QTAILQ_HEAD(xs_dirs_head, xs_dirs) xs_cleanup =
+    QTAILQ_HEAD_INITIALIZER(xs_cleanup);
+
 static QTAILQ_HEAD(XenDeviceHead, XenDevice) xendevs = QTAILQ_HEAD_INITIALIZER(xendevs);
 static int debug = 0;
 
 /* ------------------------------------------------------------- */
 
+static void xenstore_cleanup_dir(char *dir)
+{
+    struct xs_dirs *d;
+
+    d = g_malloc(sizeof(*d));
+    d->xs_dir = dir;
+    QTAILQ_INSERT_TAIL(&xs_cleanup, d, list);
+}
+
+void xen_config_cleanup(void)
+{
+    struct xs_dirs *d;
+
+    QTAILQ_FOREACH(d, &xs_cleanup, list) {
+        xs_rm(xenstore, 0, d->xs_dir);
+    }
+}
+
 int xenstore_write_str(const char *base, const char *node, const char *val)
 {
     char abspath[XEN_BUFSIZE];
@@ -75,6 +100,30 @@ char *xenstore_read_str(const char *base, const char *node)
     return ret;
 }
 
+int xenstore_mkdir(char *path, int p)
+{
+    struct xs_permissions perms[2] = {
+        {
+            .id    = 0, /* set owner: dom0 */
+        }, {
+            .id    = xen_domid,
+            .perms = p,
+        }
+    };
+
+    if (!xs_mkdir(xenstore, 0, path)) {
+        xen_be_printf(NULL, 0, "xs_mkdir %s: failed\n", path);
+        return -1;
+    }
+    xenstore_cleanup_dir(g_strdup(path));
+
+    if (!xs_set_permissions(xenstore, 0, path, perms, 2)) {
+        xen_be_printf(NULL, 0, "xs_set_permissions %s: failed\n", path);
+        return -1;
+    }
+    return 0;
+}
+
 int xenstore_write_int(const char *base, const char *node, int ival)
 {
     char val[12];
@@ -726,6 +775,20 @@ err:
 
 int xen_be_register(const char *type, struct XenDevOps *ops)
 {
+    char path[50];
+    int rc;
+
+    if (ops->backend_register) {
+        rc = ops->backend_register();
+        if (rc) {
+            return rc;
+        }
+    }
+
+    snprintf(path, sizeof(path), "device-model/%u/backends/%s", xen_domid,
+             type);
+    xenstore_mkdir(path, XS_PERM_NONE);
+
     return xenstore_scan(type, xen_domid, ops);
 }
 

hw/xen/xen_devconfig.c

@@ -5,54 +5,6 @@
 
 /* ------------------------------------------------------------- */
 
-struct xs_dirs {
-    char *xs_dir;
-    QTAILQ_ENTRY(xs_dirs) list;
-};
-static QTAILQ_HEAD(xs_dirs_head, xs_dirs) xs_cleanup = QTAILQ_HEAD_INITIALIZER(xs_cleanup);
-
-static void xen_config_cleanup_dir(char *dir)
-{
-    struct xs_dirs *d;
-
-    d = g_malloc(sizeof(*d));
-    d->xs_dir = dir;
-    QTAILQ_INSERT_TAIL(&xs_cleanup, d, list);
-}
-
-void xen_config_cleanup(void)
-{
-    struct xs_dirs *d;
-
-    QTAILQ_FOREACH(d, &xs_cleanup, list) {
-	xs_rm(xenstore, 0, d->xs_dir);
-    }
-}
-
-/* ------------------------------------------------------------- */
-
-static int xen_config_dev_mkdir(char *dev, int p)
-{
-    struct xs_permissions perms[2] = {{
-            .id    = 0, /* set owner: dom0 */
-        },{
-            .id    = xen_domid,
-            .perms = p,
-        }};
-
-    if (!xs_mkdir(xenstore, 0, dev)) {
-	xen_be_printf(NULL, 0, "xs_mkdir %s: failed\n", dev);
-	return -1;
-    }
-    xen_config_cleanup_dir(g_strdup(dev));
-
-    if (!xs_set_permissions(xenstore, 0, dev, perms, 2)) {
-	xen_be_printf(NULL, 0, "xs_set_permissions %s: failed\n", dev);
-	return -1;
-    }
-    return 0;
-}
-
 static int xen_config_dev_dirs(const char *ftype, const char *btype, int vdev,
 			       char *fe, char *be, int len)
 {
@@ -66,8 +18,8 @@ static int xen_config_dev_dirs(const char *ftype, const char *btype, int vdev,
     snprintf(be, len, "%s/backend/%s/%d/%d", dom, btype, xen_domid, vdev);
     free(dom);
 
-    xen_config_dev_mkdir(fe, XS_PERM_READ | XS_PERM_WRITE);
+    xenstore_mkdir(fe, XS_PERM_READ | XS_PERM_WRITE);
-    xen_config_dev_mkdir(be, XS_PERM_READ);
+    xenstore_mkdir(be, XS_PERM_READ);
     return 0;
 }
 

include/hw/xen/xen_backend.h

@@ -28,6 +28,7 @@ struct XenDevOps {
     int       (*free)(struct XenDevice *xendev);
     void      (*backend_changed)(struct XenDevice *xendev, const char *node);
     void      (*frontend_changed)(struct XenDevice *xendev, const char *node);
+    int       (*backend_register)(void);
 };
 
 struct XenDevice {
@@ -63,6 +64,7 @@ extern const char *xen_protocol;
 extern DeviceState *xen_sysdev;
 
 /* xenstore helper functions */
+int xenstore_mkdir(char *path, int p);
 int xenstore_write_str(const char *base, const char *node, const char *val);
 int xenstore_write_int(const char *base, const char *node, int ival);
 int xenstore_write_int64(const char *base, const char *node, int64_t ival);