libxl: Add support for blktap vbd3

This patch re-introduces blktap support to libxl.  Unlike earlier
versions, it does not link against any blktap library.  libxl changes
are needed to write to the vbd3 backend XenStore nodes.

blktap has three components.  tapdisk is a daemon implementing the disk
IO, NBD (Network Block Device), and Xen PV interfaces.  tap-ctl is a
tool to control tapdisks - creating, starting, stopping and freeing.
tapback manages the XenStore operations and instructs tapdisk to
connect.

It is notable that tapdisk performs the grant and event channel ops, but
doesn't interact with XenStore.  tapback performs XenStore operations
and notifies tapdisks of values and changes.

The flow is: libxl writes to the "vbd3" XenStore nodes and runs the
block-tap script.  The block-tap script runs tap-ctl to create a tapdisk
instance as the physical device.  tapback then sees the tapdisk and
instructs the tapdisk to connect up the PV blkif interface.

This is expected to work without the kernel blktap driver, so the
block-tap script is modified accordingly to write the UNIX NBD path.

backendtype=tap was not fully removed previously, but it would never
succeed since it would hit the hardcoded error in disk_try_backend().
It is reused now.

An example command to attach a vhd:
xl block-attach vm 'vdev=xvdf,backendtype=tap,format=vhd,target=/srv/target.vhd'

Format raw also works to run an "aio:" tapdisk.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

diff --git a/docs/man/xl-disk-configuration.5.pod.in b/docs/man/xl-disk-configuration.5.pod.in
index bc945cc5173c11a175f0444cc87ef924960c9d95..cb442bd5b47e908ab4abc22fdf06167df689d048 100644 (file)
--- a/docs/man/xl-disk-configuration.5.pod.in
+++ b/docs/man/xl-disk-configuration.5.pod.in
@@ -232,7 +232,7 @@ Specifies the backend implementation to use
 
 =item Supported values
 
-phy, qdisk, standalone
+phy, qdisk, standalone, tap
 
 =item Mandatory
 
@@ -254,6 +254,8 @@ and "standalone" does not support specifications other than "virtio".
 Normally this option should not be specified, in which case libxl will
 automatically determine the most suitable backend.
 
+"tap" needs blktap's tapback to be running.
+
 
 =item B<script>=I<SCRIPT>
 

diff --git a/tools/libs/light/libxl_device.c b/tools/libs/light/libxl_device.c
index 13da6e057378fd571cdd6014f0ff5f611d712ad8..ae2b71b0bf368a4e781ab02128f37409332d20a3 100644 (file)
--- a/tools/libs/light/libxl_device.c
+++ b/tools/libs/light/libxl_device.c
@@ -328,9 +328,15 @@ static int disk_try_backend(disk_try_backend_args *a,
         return 0;
 
     case LIBXL_DISK_BACKEND_TAP:
-        LOG(DEBUG, "Disk vdev=%s, backend tap unsuitable because blktap "
-                   "not available", a->disk->vdev);
-        return 0;
+        if (a->disk->format != LIBXL_DISK_FORMAT_RAW &&
+            a->disk->format != LIBXL_DISK_FORMAT_VHD)
+            goto bad_format;
+
+        if (libxl_defbool_val(a->disk->colo_enable))
+            goto bad_colo;
+
+        LOG(DEBUG, "Disk vdev=%s, returning blktap", a->disk->vdev);
+        return backend;
 
     case LIBXL_DISK_BACKEND_QDISK:
         if (a->disk->script) goto bad_script;
@@ -478,7 +484,7 @@ char *libxl__device_disk_string_of_backend(libxl_disk_backend backend)
 {
     switch (backend) {
         case LIBXL_DISK_BACKEND_QDISK: return "qdisk";
-        case LIBXL_DISK_BACKEND_TAP: return "phy";
+        case LIBXL_DISK_BACKEND_TAP: return "vbd3";
         case LIBXL_DISK_BACKEND_PHY: return "phy";
         case LIBXL_DISK_BACKEND_STANDALONE: return "standalone";
         default: return NULL;

diff --git a/tools/libs/light/libxl_disk.c b/tools/libs/light/libxl_disk.c
index ea3623dd6fe5f76b5ebe21c2e3e72b72b9c8ac0e..59ff99683704294c2a42aab85352240534450450 100644 (file)
--- a/tools/libs/light/libxl_disk.c
+++ b/tools/libs/light/libxl_disk.c
@@ -56,7 +56,9 @@ static void disk_eject_xswatch_callback(libxl__egc *egc, libxl__ev_xswatch *w,
             "/local/domain/%d/backend/%" TOSTRING(BACKEND_STRING_SIZE)
            "[a-z]/%*d/%*d",
            &disk->backend_domid, backend_type);
-    if (!strcmp(backend_type, "tap") || !strcmp(backend_type, "vbd")) {
+    if (!strcmp(backend_type, "tap") ||
+        !strcmp(backend_type, "vbd") ||
+        !strcmp(backend_type, "vbd3")) {
         disk->backend = LIBXL_DISK_BACKEND_TAP;
     } else if (!strcmp(backend_type, "qdisk")) {
         disk->backend = LIBXL_DISK_BACKEND_QDISK;
@@ -224,7 +226,7 @@ static int libxl__device_from_disk(libxl__gc *gc, uint32_t domid,
             device->backend_kind = LIBXL__DEVICE_KIND_VBD;
             break;
         case LIBXL_DISK_BACKEND_TAP:
-            device->backend_kind = LIBXL__DEVICE_KIND_VBD;
+            device->backend_kind = LIBXL__DEVICE_KIND_VBD3;
             break;
         case LIBXL_DISK_BACKEND_QDISK:
             device->backend_kind = LIBXL__DEVICE_KIND_QDISK;
@@ -368,9 +370,17 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
                 assert(device->backend_kind == LIBXL__DEVICE_KIND_VIRTIO_DISK);
                 break;
             case LIBXL_DISK_BACKEND_TAP:
-                LOG(ERROR, "blktap is not supported");
-                rc = ERROR_FAIL;
-                goto out;
+                flexarray_append(back, "params");
+                flexarray_append(back, GCSPRINTF("%s:%s",
+                              libxl__device_disk_string_of_format(disk->format),
+                              disk->pdev_path ? : ""));
+
+                script = libxl__abs_path(gc, disk->script?: "block-tap",
+                                         libxl__xen_script_dir_path());
+                flexarray_append_pair(back, "script", script);
+
+                assert(device->backend_kind == LIBXL__DEVICE_KIND_VBD3);
+                break;
             case LIBXL_DISK_BACKEND_QDISK:
                 flexarray_append(back, "params");
                 flexarray_append(back, GCSPRINTF("%s:%s",

diff --git a/tools/libs/light/libxl_linux.c b/tools/libs/light/libxl_linux.c
index f7c92ba5621171b1300602f61cee8c4df9aaf819..0b4c8bd045a1bf3c4945703dbae20314953ed52c 100644 (file)
--- a/tools/libs/light/libxl_linux.c
+++ b/tools/libs/light/libxl_linux.c
@@ -207,6 +207,7 @@ int libxl__get_hotplug_script_info(libxl__gc *gc, libxl__device *dev,
 
     switch (dev->backend_kind) {
     case LIBXL__DEVICE_KIND_VBD:
+    case LIBXL__DEVICE_KIND_VBD3:
         if (num_exec != 0) {
             LOGD(DEBUG, dev->domid,
                  "num_exec %d, not running hotplug scripts", num_exec);

diff --git a/tools/libs/light/libxl_types_internal.idl b/tools/libs/light/libxl_types_internal.idl
index e24288f1a59ed4faf85948dd8c4cd4d0d82d42d7..56dccac15377688b7cb6801aaa92dd504e5c70e6 100644 (file)
--- a/tools/libs/light/libxl_types_internal.idl
+++ b/tools/libs/light/libxl_types_internal.idl
@@ -34,6 +34,7 @@ libxl__device_kind = Enumeration("device_kind", [
     (16, "VINPUT"),
     (17, "VIRTIO_DISK"),
     (18, "VIRTIO"),
+    (19, "VBD3"),
     ])
 
 libxl__console_backend = Enumeration("console_backend", [

diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
index e403bd9bcf6acae4f6ededb6141cdcd11de27af9..10398a6c86110c44a14c8d574c7a7e683f24577b 100644 (file)
--- a/tools/libs/light/libxl_utils.c
+++ b/tools/libs/light/libxl_utils.c
@@ -295,6 +295,8 @@ int libxl_string_to_backend(libxl_ctx *ctx, char *s, libxl_disk_backend *backend
         *backend = LIBXL_DISK_BACKEND_PHY;
     } else if (!strcmp(s, "file")) {
         *backend = LIBXL_DISK_BACKEND_TAP;
+    } else if (!strcmp(s, "vbd3")) {
+        *backend = LIBXL_DISK_BACKEND_TAP;
     } else if (!strcmp(s, "qdisk")) {
         *backend = LIBXL_DISK_BACKEND_QDISK;
     } else if (!strcmp(s, "standalone")) {