[PATCH RFC 3/8] libxl: add backend_features to libxl_device_disk

[Joao Martins <joao.m.martins@oracle.com>]

The function libxl__device_generic_add will have an additional
argument whereby it adds a second set of entries visible to the
backend only. These entries will then be used for devices
thus overriding backend maximum feature set with this user-defined ones.

libxl_device_disk.backend_features are a key value store storing:
 <feature-name> = <feature-value>

xl|libxl are stateless with respect to feature names therefore is up to the
admin to carefully select those. If backend isn't supported therefore the
features won't be overwritten.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 tools/libxl/libxl.h          |  8 ++++++++
 tools/libxl/libxl_console.c  |  5 +++--
 tools/libxl/libxl_device.c   | 37 +++++++++++++++++++++++++++++++++----
 tools/libxl/libxl_disk.c     | 17 +++++++++++++++--
 tools/libxl/libxl_internal.h |  4 +++-
 tools/libxl/libxl_pci.c      |  2 +-
 tools/libxl/libxl_types.idl  |  1 +
 tools/libxl/libxl_usb.c      |  2 +-
 8 files changed, 65 insertions(+), 11 deletions(-)

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 5e9aed739d..82990089ef 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -1101,6 +1101,14 @@ void libxl_mac_copy(libxl_ctx *ctx, libxl_mac *dst, const libxl_mac *src);
  */
 #define LIBXL_HAVE_SET_PARAMETERS 1
 
+/*
+ * LIBXL_HAVE_DISK_BACKEND_FEATURES
+ *
+ * libxl_device_disk contains backend_features which can be used to control
+ * what features are exposed to guest vbds.
+ */
+#define LIBXL_HAVE_DISK_BACKEND_FEATURES 1
+
 typedef char **libxl_string_list;
 void libxl_string_list_dispose(libxl_string_list *sl);
 int libxl_string_list_length(const libxl_string_list *sl);
diff --git a/tools/libxl/libxl_console.c b/tools/libxl/libxl_console.c
index c05dc28b99..f40def1276 100644
--- a/tools/libxl/libxl_console.c
+++ b/tools/libxl/libxl_console.c
@@ -339,7 +339,7 @@ int libxl__device_console_add(libxl__gc *gc, uint32_t domid,
     libxl__device_generic_add(gc, XBT_NULL, device,
                               libxl__xs_kvs_of_flexarray(gc, back),
                               libxl__xs_kvs_of_flexarray(gc, front),
-                              libxl__xs_kvs_of_flexarray(gc, ro_front));
+                              libxl__xs_kvs_of_flexarray(gc, ro_front), NULL);
     rc = 0;
 out:
     return rc;
@@ -385,7 +385,8 @@ int libxl__device_vuart_add(libxl__gc *gc, uint32_t domid,
     rc = libxl__device_generic_add(gc, XBT_NULL, &device,
                                    libxl__xs_kvs_of_flexarray(gc, back),
                                    NULL,
-                                   libxl__xs_kvs_of_flexarray(gc, ro_front));
+                                   libxl__xs_kvs_of_flexarray(gc, ro_front),
+                                   NULL);
     return rc;
 }
 
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index 5438577c3c..05178fb480 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -43,6 +43,15 @@ char *libxl__device_backend_path(libxl__gc *gc, libxl__device *device)
                      device->domid, device->devid);
 }
 
+char *libxl__device_require_path(libxl__gc *gc, libxl__device *device)
+{
+    char *dom_path = libxl__xs_get_dompath(gc, device->backend_domid);
+
+    return GCSPRINTF("%s/backend/%s/%u/%d/require", dom_path,
+                     libxl__device_kind_to_string(device->backend_kind),
+                     device->domid, device->devid);
+}
+
 char *libxl__device_libxl_path(libxl__gc *gc, libxl__device *device)
 {
     char *libxl_dom_path = libxl__xs_libxl_path(gc, device->domid);
@@ -114,13 +123,16 @@ out:
 }
 
 int libxl__device_generic_add(libxl__gc *gc, xs_transaction_t t,
-        libxl__device *device, char **bents, char **fents, char **ro_fents)
+        libxl__device *device, char **bents, char **fents, char **ro_fents,
+        char **brents)
 {
     libxl_ctx *ctx = libxl__gc_owner(gc);
-    char *frontend_path = NULL, *backend_path = NULL, *libxl_path;
+    char *frontend_path = NULL, *backend_path = NULL, *require_path = NULL,
+         *libxl_path;
     struct xs_permissions frontend_perms[2];
     struct xs_permissions ro_frontend_perms[2];
     struct xs_permissions backend_perms[2];
+    struct xs_permissions require_perms[1];
     int create_transaction = t == XBT_NULL;
     int libxl_only = device->backend_kind == LIBXL__DEVICE_KIND_NONE;
     int rc;
@@ -131,6 +143,7 @@ int libxl__device_generic_add(libxl__gc *gc, xs_transaction_t t,
     } else {
         frontend_path = libxl__device_frontend_path(gc, device);
         backend_path = libxl__device_backend_path(gc, device);
+        require_path = libxl__device_require_path(gc, device);
     }
     libxl_path = libxl__device_libxl_path(gc, device);
 
@@ -144,6 +157,9 @@ int libxl__device_generic_add(libxl__gc *gc, xs_transaction_t t,
     ro_frontend_perms[1].id = backend_perms[1].id = device->domid;
     ro_frontend_perms[1].perms = backend_perms[1].perms = XS_PERM_READ;
 
+    require_perms[0].id = device->backend_domid;
+    require_perms[0].perms = XS_PERM_NONE;
+
 retry_transaction:
     if (create_transaction)
         t = xs_transaction_start(ctx->xsh);
@@ -200,6 +216,12 @@ retry_transaction:
                      frontend_path, strlen(frontend_path));
             libxl__xs_writev(gc, t, backend_path, bents);
         }
+        if (brents) {
+            xs_mkdir(ctx->xsh, t, require_path);
+            xs_set_permissions(ctx->xsh, t, require_path, require_perms,
+                               ARRAY_SIZE(require_perms));
+            libxl__xs_writev(gc, t, require_path, brents);
+        }
 
         /*
          * We make a copy of everything for the backend in the libxl
@@ -226,6 +248,11 @@ retry_transaction:
          */
         rc = libxl__xs_writev(gc, t, libxl_path, bents);
         if (rc) goto out;
+
+        if (brents) {
+            rc = libxl__xs_writev(gc, t, libxl_path, brents);
+            if (rc) goto out;
+        }
     }
 
     if (!create_transaction)
@@ -1920,7 +1947,8 @@ void libxl__device_add_async(libxl__egc *egc, uint32_t domid,
         libxl__device_generic_add(gc, t, device,
                                   libxl__xs_kvs_of_flexarray(gc, back),
                                   libxl__xs_kvs_of_flexarray(gc, front),
-                                  libxl__xs_kvs_of_flexarray(gc, ro_front));
+                                  libxl__xs_kvs_of_flexarray(gc, ro_front),
+                                  NULL);
 
         rc = libxl__xs_transaction_commit(gc, &t);
         if (!rc) break;
@@ -1984,7 +2012,8 @@ int libxl__device_add(libxl__gc *gc, uint32_t domid,
     rc = libxl__device_generic_add(gc, XBT_NULL, device,
                                    libxl__xs_kvs_of_flexarray(gc, back),
                                    libxl__xs_kvs_of_flexarray(gc, front),
-                                   libxl__xs_kvs_of_flexarray(gc, ro_front));
+                                   libxl__xs_kvs_of_flexarray(gc, ro_front),
+                                   NULL);
     if (rc) goto out;
 
     rc = 0;
diff --git a/tools/libxl/libxl_disk.c b/tools/libxl/libxl_disk.c
index 895bf4f89a..8caf763c88 100644
--- a/tools/libxl/libxl_disk.c
+++ b/tools/libxl/libxl_disk.c
@@ -239,14 +239,16 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
     STATE_AO_GC(aodev->ao);
     flexarray_t *front = NULL;
     flexarray_t *back = NULL;
+    flexarray_t *require = NULL;
     char *dev = NULL, *script;
     libxl__device *device;
-    int rc;
+    int rc, i;
     libxl_ctx *ctx = gc->owner;
     xs_transaction_t t = XBT_NULL;
     libxl_domain_config d_config;
     libxl_device_disk disk_saved;
     libxl__domain_userdata_lock *lock = NULL;
+    libxl_key_value_list back_features = disk->backend_features;
 
     libxl_domain_config_init(&d_config);
     libxl_device_disk_init(&disk_saved);
@@ -300,6 +302,7 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
 
         front = flexarray_make(gc, 16, 1);
         back = flexarray_make(gc, 16, 1);
+        require = flexarray_make(gc, 16, 1);
 
         GCNEW(device);
         rc = libxl__device_from_disk(gc, domid, disk, device);
@@ -433,6 +436,15 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
             }
         }
 
+        if (back_features) {
+            for (i = 0; back_features[i] != NULL; i += 2) {
+                flexarray_append(require, libxl__strdup(gc, back_features[i]));
+                if (back_features[i + 1])
+                    flexarray_append(require,
+                                     libxl__strdup(gc, back_features[i + 1]));
+            }
+        }
+
         if (!get_vdev && aodev->update_json) {
             rc = libxl__set_domain_configuration(gc, domid, &d_config);
             if (rc) goto out;
@@ -441,7 +453,8 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
         libxl__device_generic_add(gc, t, device,
                                   libxl__xs_kvs_of_flexarray(gc, back),
                                   libxl__xs_kvs_of_flexarray(gc, front),
-                                  NULL);
+                                  NULL,
+                                  libxl__xs_kvs_of_flexarray(gc, require));
 
         rc = libxl__xs_transaction_commit(gc, &t);
         if (!rc) break;
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 45e6df6c82..19c02e27a0 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1216,8 +1216,10 @@ _hidden int libxl__device_vuart_add(libxl__gc *gc, uint32_t domid,
 _hidden int libxl__device_exists(libxl__gc *gc, xs_transaction_t t,
                                  libxl__device *device);
 _hidden int libxl__device_generic_add(libxl__gc *gc, xs_transaction_t t,
-        libxl__device *device, char **bents, char **fents, char **ro_fents);
+                                      libxl__device *device, char **bents,
+                                      char **fents, char **ro_fents, char **brents);
 _hidden char *libxl__device_backend_path(libxl__gc *gc, libxl__device *device);
+_hidden char *libxl__device_require_path(libxl__gc *gc, libxl__device *device);
 _hidden char *libxl__device_libxl_path(libxl__gc *gc, libxl__device *device);
 _hidden int libxl__parse_backend_path(libxl__gc *gc, const char *path,
                                       libxl__device *dev);
diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
index 88a55ce8bd..1d595513f5 100644
--- a/tools/libxl/libxl_pci.c
+++ b/tools/libxl/libxl_pci.c
@@ -106,7 +106,7 @@ int libxl__create_pci_backend(libxl__gc *gc, uint32_t domid,
     return libxl__device_generic_add(gc, XBT_NULL, &device,
                                      libxl__xs_kvs_of_flexarray(gc, back),
                                      libxl__xs_kvs_of_flexarray(gc, front),
-                                     NULL);
+                                     NULL, NULL);
 }
 
 static int libxl__device_pci_add_xenstore(libxl__gc *gc, uint32_t domid, libxl_device_pci *pcidev, int starting)
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index a239324341..949a797402 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -627,6 +627,7 @@ libxl_device_vkb = Struct("device_vkb", [
 libxl_device_disk = Struct("device_disk", [
     ("backend_domid", libxl_domid),
     ("backend_domname", string),
+    ("backend_features", libxl_key_value_list),
     ("pdev_path", string),
     ("vdev", string),
     ("backend", libxl_disk_backend),
diff --git a/tools/libxl/libxl_usb.c b/tools/libxl/libxl_usb.c
index cb0e792724..97e54272f1 100644
--- a/tools/libxl/libxl_usb.c
+++ b/tools/libxl/libxl_usb.c
@@ -283,7 +283,7 @@ static int libxl__device_usbctrl_add_xenstore(libxl__gc *gc, uint32_t domid,
         libxl__device_generic_add(gc, t, device,
                                   libxl__xs_kvs_of_flexarray(gc, back),
                                   libxl__xs_kvs_of_flexarray(gc, front),
-                                  NULL);
+                                  NULL, NULL);
 
         rc = libxl__xs_transaction_commit(gc, &t);
         if (!rc) break;
-- 
2.11.0


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