libxl: Allow local access for block devices with hotplug scripts

pygrub and qemuu need to be able to access a VM's disks locally in
order to be able to pull out the kernel and provide emulated disk
access, respectively.  This can be done either by accessing the local
disk directly, or by plugging the target disk into dom0 to allow
access.

Unfortunately, while the plugging machinery works for pygrub, it does
not yet work for qemuu; this means that at the moment, disks with
hotplug scripts or disks with non-dom0 backends cannot be provided as
emulated devices to HVM domains.

Fortunately, disks using hotplug scripts created in dom0 do create a
block device as part of set-up, which can be accessed locally; and if
they use block-common.sh:write_dev, this path will be written to
physical-device-path.

Modify libxl__device_disk_setdefault() to be able to fish this path
out of xenstore and pass it to the caller.

Unfortunately, at the time pygrub runs, the devices have not yet been
set up.  Rather than try to stash the domid somewhere to pass, we just
pass INVALID_DOMID.

This allows qemuu to emulate block devices created with custom hotplug
scripts.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Tested-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index c46c2ec1fd6e0165d01d441444f1d423a3f97c03..75f00beeae73db12ac6c52e20ba3700c494bb043 100644 (file)
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2317,7 +2317,7 @@ int libxl__device_disk_setdefault(libxl__gc *gc, libxl_device_disk *disk)
 }
 
 int libxl__device_from_disk(libxl__gc *gc, uint32_t domid,
-                                   libxl_device_disk *disk,
+                                   const libxl_device_disk *disk,
                                    libxl__device *device)
 {
     int devid;
@@ -3070,8 +3070,9 @@ static char * libxl__alloc_vdev(libxl__gc *gc, void *get_vdev_user,
 /* Callbacks */
 
 char *libxl__device_disk_find_local_path(libxl__gc *gc, 
-                                         const libxl_device_disk *disk,
-                                         bool qdisk_direct)
+                                          libxl_domid guest_domid,
+                                          const libxl_device_disk *disk,
+                                          bool qdisk_direct)
 {
     char *path = NULL;
 
@@ -3100,6 +3101,38 @@ char *libxl__device_disk_find_local_path(libxl__gc *gc,
         path = libxl__strdup(gc, disk->pdev_path);
         LOG(DEBUG, "Directly accessing local QDISK target %s", path);
         goto out;
+    } 
+
+    /* 
+     * If the format isn't raw and / or we're using a script, then see
+     * if the script has written a path to the "cooked" node
+     */
+    if (disk->script && guest_domid != INVALID_DOMID) {
+        libxl__device device;
+        char *be_path, *pdpath;
+        int rc;
+
+        LOG(DEBUG,
+            "Run from a script; checking for physical-device-path (vdev %s)",
+            disk->vdev);
+
+        rc = libxl__device_from_disk(gc, guest_domid, disk, &device);
+        if (rc < 0)
+            goto out;
+
+        be_path = libxl__device_backend_path(gc, &device);
+
+        pdpath = libxl__sprintf(gc, "%s/physical-device-path", be_path);
+
+        LOG(DEBUG, "Attempting to read node %s", pdpath);
+        path = libxl__xs_read(gc, XBT_NULL, pdpath);
+
+        if (path)
+            LOG(DEBUG, "Accessing cooked block device %s", path);
+        else
+            LOG(DEBUG, "No physical-device-path, can't access locally.");
+
+        goto out;
     }
 
  out:
@@ -3126,7 +3159,8 @@ void libxl__device_disk_local_initiate_attach(libxl__egc *egc,
 
     LOG(DEBUG, "Trying to find local path");
 
-    dls->diskpath = libxl__device_disk_find_local_path(gc, in_disk, false);
+    dls->diskpath = libxl__device_disk_find_local_path(gc, INVALID_DOMID,
+                                                       in_disk, false);
     if (dls->diskpath) {
         LOG(DEBUG, "Local path found, executing callback.");
         dls->callback(egc, dls, 0);
@@ -3142,7 +3176,6 @@ void libxl__device_disk_local_initiate_attach(libxl__egc *egc,
         rc = libxl__device_disk_setdefault(gc, disk);
         if (rc) goto out;
 
-        /* If we can't find a local path, attach it */
         libxl__prepare_ao_device(ao, &dls->aodev);
         dls->aodev.callback = local_device_attach_cb;
         device_disk_add(egc, LIBXL_TOOLSTACK_DOMID, disk, &dls->aodev,

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 2a3d0326b7204b9db0c445ad3d58510c554bca18..5b79aa279f70264ffe247c4acb09e24e6064aa98 100644 (file)
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -1353,8 +1353,8 @@ static int libxl__build_device_model_args_new(libxl__gc *gc,
                     target_path = libxl__blktap_devpath(gc, disks[i].pdev_path,
                                                         disks[i].format);
                 else
-                    target_path = libxl__device_disk_find_local_path(gc, 
-                                                            &disks[i], true);
+                    target_path = libxl__device_disk_find_local_path(gc,
+                                                 guest_domid, &disks[i], true);
 
                 if (!target_path) {
                     LOG(WARN, "No way to get local access disk to image: %s\n"

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index c87c42ae6ec996b74687db842e567469c89c2d8c..7df27115009040f82c62854cfb756a4e88c03f69 100644 (file)
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1714,7 +1714,7 @@ _hidden char *libxl__blktap_devpath(libxl__gc *gc,
 _hidden int libxl__device_destroy_tapdisk(libxl__gc *gc, const char *params);
 
 _hidden int libxl__device_from_disk(libxl__gc *gc, uint32_t domid,
-                                   libxl_device_disk *disk,
+                                   const libxl_device_disk *disk,
                                    libxl__device *device);
 
 /* Calls poll() again - useful to check whether a signaled condition
@@ -2720,6 +2720,7 @@ static inline void libxl__device_disk_local_init(libxl__disk_local_state *dls)
  * See if we can find a way to access a disk locally
  */
 _hidden char * libxl__device_disk_find_local_path(libxl__gc *gc, 
+                                                  libxl_domid guest_domid,
                                                   const libxl_device_disk *disk,
                                                   bool qdisk_direct);