[PATCH v2 09/18] libxl: disallow attaching the same device more than once

[Wei Liu <wei.liu2@citrix.com>]

Originally the code allowed users to attach the same device more than
once. It just stupidly overwrites xenstore entries. This is bogus as
frontend will be very confused.

Introduce a helper function to check if the device to be written to
xenstore already exists. A new error code is also introduced.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 tools/libxl/libxl.c          |   50 ++++++++++++++++++++++++++++++++++++++++++
 tools/libxl/libxl_device.c   |   19 ++++++++++++++++
 tools/libxl/libxl_internal.h |    3 +++
 tools/libxl/libxl_pci.c      |   12 ++++++++++
 tools/libxl/libxl_types.idl  |    1 +
 5 files changed, 85 insertions(+)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 01dffa0..e6fe238 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -1906,6 +1906,15 @@ void libxl__device_vtpm_add(libxl__egc *egc, uint32_t domid,
     rc = libxl__device_from_vtpm(gc, domid, vtpm, device);
     if ( rc != 0 ) goto out;
 
+    rc = libxl__device_exists(gc, XBT_NULL, device);
+    if (rc < 0) goto out;
+    if (rc == 1) {              /* already exists in xenstore */
+        LOG(ERROR, "device already exists in xenstore");
+        aodev->action = LIBXL__DEVICE_ACTION_ADD; /* for error message */
+        rc = ERROR_DEVICE_EXISTS;
+        goto out;
+    }
+
     flexarray_append(back, "frontend-id");
     flexarray_append(back, GCSPRINTF("%d", domid));
     flexarray_append(back, "online");
@@ -2154,6 +2163,13 @@ int libxl__device_from_disk(libxl__gc *gc, uint32_t domid,
  *
  * The passed get_vdev function is also in charge of printing
  * the corresponding error message when appropiate.
+ *
+ * Note:
+ *
+ * The presence of get_vdev is also used to distinguish two
+ * cases: if get_vdev != NULL, then it is called by local attach
+ * function to run bootloader, otherwise it is called by
+ * libxl__device_disk_add wrapper.
  */
 static void device_disk_add(libxl__egc *egc, uint32_t domid,
                            libxl_device_disk *disk,
@@ -2177,6 +2193,31 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
         goto out;
     }
 
+    /* If we're not doing local attach, we're trying to do
+     * "block-attach". We already have a valid vdev at this point, and
+     * we need to check if this device already exists in xenstore.
+     */
+    if (!get_vdev) {
+        /* Construct libxl__device from libxl_device_disk */
+        libxl__device_disk_setdefault(gc, disk);
+        GCNEW(device);
+        rc = libxl__device_from_disk(gc, domid, disk, device);
+        if (rc != 0) {
+            LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Invalid or unsupported"
+                       " virtual disk identifier %s", disk->vdev);
+            goto out;
+        }
+
+        rc = libxl__device_exists(gc, XBT_NULL, device);
+        if (rc < 0) goto out;
+        if (rc == 1) {              /* already exists in xenstore */
+            LOG(ERROR, "device already exists in xenstore");
+            aodev->action = LIBXL__DEVICE_ACTION_ADD; /* for error message */
+            rc = ERROR_DEVICE_EXISTS;
+            goto out;
+        }
+    }
+
     for (;;) {
         rc = libxl__xs_transaction_start(gc, &t);
         if (rc) goto out;
@@ -3011,6 +3052,15 @@ void libxl__device_nic_add(libxl__egc *egc, uint32_t domid,
     rc = libxl__device_from_nic(gc, domid, nic, device);
     if ( rc != 0 ) goto out;
 
+    rc = libxl__device_exists(gc, XBT_NULL, device);
+    if (rc < 0) goto out;
+    if (rc == 1) {              /* already exists in xenstore */
+        LOG(ERROR, "device already exists in xenstore");
+        aodev->action = LIBXL__DEVICE_ACTION_ADD; /* for error message */
+        rc = ERROR_DEVICE_EXISTS;
+        goto out;
+    }
+
     flexarray_append(back, "frontend-id");
     flexarray_append(back, libxl__sprintf(gc, "%d", domid));
     flexarray_append(back, "online");
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index f8a2e1b..045212f 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -40,6 +40,25 @@ char *libxl__device_backend_path(libxl__gc *gc, libxl__device *device)
                      device->domid, device->devid);
 }
 
+/* Returns 1 if device exists, 0 if not, ERROR_* (<0) on error. */
+int libxl__device_exists(libxl__gc *gc, xs_transaction_t t,
+                         libxl__device *device)
+{
+    int rc;
+    char *be_path = libxl__device_backend_path(gc, device);
+    const char *dir;
+
+    be_path = libxl__device_backend_path(gc, device);
+    rc = libxl__xs_read_checked(gc, t, be_path, &dir);
+
+    if (rc)
+        return rc;
+
+    if (dir)
+        return 1;
+    return 0;
+}
+
 int libxl__parse_backend_path(libxl__gc *gc,
                               const char *path,
                               libxl__device *dev)
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 02708c7..1b44c2c 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1031,6 +1031,9 @@ _hidden int libxl__device_console_add(libxl__gc *gc, uint32_t domid,
                                       libxl__device_console *console,
                                       libxl__domain_build_state *state);
 
+/* Returns 1 if device exists, 0 if not, ERROR_* (<0) on error. */
+_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);
 _hidden char *libxl__device_backend_path(libxl__gc *gc, libxl__device *device);
diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
index 0500cf3..e05f047 100644
--- a/tools/libxl/libxl_pci.c
+++ b/tools/libxl/libxl_pci.c
@@ -1042,6 +1042,7 @@ int libxl__device_pci_add(libxl__gc *gc, uint32_t domid, libxl_device_pci *pcide
     unsigned int orig_vdev, pfunc_mask;
     libxl_device_pci *assigned;
     int num_assigned, i, rc;
+    libxl__device device;
     int stubdomid = 0;
 
     if (libxl__domain_type(gc, domid) == LIBXL_DOMAIN_TYPE_HVM) {
@@ -1059,6 +1060,17 @@ int libxl__device_pci_add(libxl__gc *gc, uint32_t domid, libxl_device_pci *pcide
     rc = libxl__device_pci_setdefault(gc, pcidev);
     if (rc) goto out;
 
+    if (!starting) {
+        libxl__device_from_pcidev(gc, domid, pcidev, &device);
+        rc = libxl__device_exists(gc, XBT_NULL, &device);
+        if (rc < 0) goto out;
+        if (rc == 1) {              /* already exists in xenstore */
+            LOG(ERROR, "device already exists in xenstore");
+            rc = ERROR_DEVICE_EXISTS;
+            goto out;
+        }
+    }
+
     if (pcidev->seize && !pciback_dev_is_assigned(gc, pcidev)) {
         rc = libxl__device_pci_assignable_add(gc, pcidev, 1);
         if ( rc )
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index d0a373b..1beb63d 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -60,6 +60,7 @@ libxl_error = Enumeration("error", [
     (-14, "UNKNOWN_CHILD"),
     (-15, "LOCK_FAIL"),
     (-16, "JSON_CONFIG_EMPTY"),
+    (-17, "DEVICE_EXISTS"),
     ], value_namespace = "")
 
 libxl_domain_type = Enumeration("domain_type", [
-- 
1.7.10.4