libxl: call hotplug scripts for disk devices from libxl

Since most of the needed work is already done in previous patches,
this patch only contains the necessary code to call hotplug scripts
for disk devices, that should be called when the device is added or
removed from a guest.

We will chain the launch of the disk hotplug scripts after the
device_backend_callback callback, or directly from
libxl__initiate_device_{add,remove} if the device is already in the
desired state.

Signed-off-by: Roger Pau Monne <roger.pau@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

7 files changed, 273 insertions, 6 deletions

diff --git a/tools/hotplug/Linux/xen-backend.rules b/tools/hotplug/Linux/xen-backend.rules
index 405387f1a9..d55ff11309 100644
--- a/tools/hotplug/Linux/xen-backend.rules
+++ b/tools/hotplug/Linux/xen-backend.rules
@@ -1,11 +1,11 @@
-SUBSYSTEM=="xen-backend", KERNEL=="tap*", RUN+="/etc/xen/scripts/blktap $env{ACTION}"
-SUBSYSTEM=="xen-backend", KERNEL=="vbd*", RUN+="/etc/xen/scripts/block $env{ACTION}"
+SUBSYSTEM=="xen-backend", KERNEL=="tap*", ENV{UDEV_CALL}="1", RUN+="/etc/xen/scripts/blktap $env{ACTION}"
+SUBSYSTEM=="xen-backend", KERNEL=="vbd*", ENV{UDEV_CALL}="1", RUN+="/etc/xen/scripts/block $env{ACTION}"
 SUBSYSTEM=="xen-backend", KERNEL=="vtpm*", RUN+="/etc/xen/scripts/vtpm $env{ACTION}"
 SUBSYSTEM=="xen-backend", KERNEL=="vif2-*", RUN+="/etc/xen/scripts/vif2 $env{ACTION}"
 SUBSYSTEM=="xen-backend", KERNEL=="vif-*", ACTION=="online", RUN+="/etc/xen/scripts/vif-setup online type_if=vif"
 SUBSYSTEM=="xen-backend", KERNEL=="vif-*", ACTION=="offline", RUN+="/etc/xen/scripts/vif-setup offline type_if=vif"
 SUBSYSTEM=="xen-backend", KERNEL=="vscsi*", RUN+="/etc/xen/scripts/vscsi $env{ACTION}"
-SUBSYSTEM=="xen-backend", ACTION=="remove", RUN+="/etc/xen/scripts/xen-hotplug-cleanup"
+SUBSYSTEM=="xen-backend", ACTION=="remove", ENV{UDEV_CALL}="1", RUN+="/etc/xen/scripts/xen-hotplug-cleanup"
 KERNEL=="evtchn", NAME="xen/%k"
 SUBSYSTEM=="xen", KERNEL=="blktap[0-9]*", NAME="xen/%k", MODE="0600"
 SUBSYSTEM=="blktap2", KERNEL=="blktap[0-9]*", NAME="xen/blktap-2/%k", MODE="0600"
diff --git a/tools/hotplug/Linux/xen-hotplug-common.sh b/tools/hotplug/Linux/xen-hotplug-common.sh
index 8f6557df73..4a7bc7349f 100644
--- a/tools/hotplug/Linux/xen-hotplug-common.sh
+++ b/tools/hotplug/Linux/xen-hotplug-common.sh
@@ -15,6 +15,12 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 #
 
+# Hack to prevent the execution of hotplug scripts from udev if the domain
+# has been launched from libxl
+if [ -n "${UDEV_CALL}" ] && \
+   xenstore-read "libxl/disable_udev" >/dev/null 2>&1; then
+    exit 0
+fi
 
 dir=$(dirname "$0")
 . "$dir/hotplugpath.sh"
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index da9ddff4aa..1f79865958 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -1858,6 +1858,11 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
                 flexarray_append(back, "params");
                 flexarray_append(back, dev);
 
+                flexarray_append(back, "script");
+                flexarray_append(back, GCSPRINTF("%s/%s",
+                                                 libxl__xen_script_dir_path(),
+                                                 "block"));
+
                 assert(device->backend_kind == LIBXL__DEVICE_KIND_VBD);
                 break;
             case LIBXL_DISK_BACKEND_TAP:
@@ -1873,6 +1878,11 @@ static void device_disk_add(libxl__egc *egc, uint32_t domid,
                     libxl__device_disk_string_of_format(disk->format),
                     disk->pdev_path));
 
+                flexarray_append(back, "script");
+                flexarray_append(back, GCSPRINTF("%s/%s",
+                                                 libxl__xen_script_dir_path(),
+                                                 "blktap"));
+
                 /* now create a phy device to export the device to the guest */
                 goto do_backend_phy;
             case LIBXL_DISK_BACKEND_QDISK:
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index ed33f6f644..a80dee846f 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -412,9 +412,12 @@ void libxl__prepare_ao_device(libxl__ao *ao, libxl__ao_device *aodev)
     aodev->ao = ao;
     aodev->rc = 0;
     aodev->dev = NULL;
-    /* Initialize timer for QEMU Bodge */
+    /* Initialize timer for QEMU Bodge and hotplug execution */
     libxl__ev_time_init(&aodev->timeout);
     aodev->active = 1;
+    /* We init this here because we might call device_hotplug_done
+     * without actually calling any hotplug script */
+    libxl__ev_child_init(&aodev->child);
 }
 
 void libxl__prepare_ao_devices(libxl__ao *ao, libxl__ao_devices *aodevs)
@@ -624,6 +627,15 @@ static void device_backend_callback(libxl__egc *egc, libxl__ev_devstate *ds,
 static void device_backend_cleanup(libxl__gc *gc,
                                    libxl__ao_device *aodev);
 
+static void device_hotplug(libxl__egc *egc, libxl__ao_device *aodev);
+
+static void device_hotplug_timeout_cb(libxl__egc *egc, libxl__ev_time *ev,
+                                      const struct timeval *requested_abs);
+
+static void device_hotplug_child_death_cb(libxl__egc *egc,
+                                          libxl__ev_child *child,
+                                          pid_t pid, int status);
+
 static void device_hotplug_done(libxl__egc *egc, libxl__ao_device *aodev);
 
 void libxl__wait_device_connection(libxl__egc *egc, libxl__ao_device *aodev)
@@ -649,7 +661,7 @@ void libxl__wait_device_connection(libxl__egc *egc, libxl__ao_device *aodev)
          * If Qemu is running, it will set the state of the device to
          * 4 directly, without waiting in state 2 for any hotplug execution.
          */
-        device_hotplug_done(egc, aodev);
+        device_hotplug(egc, aodev);
         return;
     }
 
@@ -783,6 +795,9 @@ static void device_qemu_timeout(libxl__egc *egc, libxl__ev_time *ev,
     rc = libxl__xs_write_checked(gc, XBT_NULL, state_path, "6");
     if (rc) goto out;
 
+    device_hotplug(egc, aodev);
+    return;
+
 out:
     aodev->rc = rc;
     device_hotplug_done(egc, aodev);
@@ -808,6 +823,9 @@ static void device_backend_callback(libxl__egc *egc, libxl__ev_devstate *ds,
         goto out;
     }
 
+    device_hotplug(egc, aodev);
+    return;
+
 out:
     aodev->rc = rc;
     device_hotplug_done(egc, aodev);
@@ -820,6 +838,111 @@ static void device_backend_cleanup(libxl__gc *gc, libxl__ao_device *aodev)
     libxl__ev_devstate_cancel(gc, &aodev->backend_ds);
 }
 
+static void device_hotplug(libxl__egc *egc, libxl__ao_device *aodev)
+{
+    STATE_AO_GC(aodev->ao);
+    char *be_path = libxl__device_backend_path(gc, aodev->dev);
+    char **args = NULL, **env = NULL;
+    int rc = 0;
+    int hotplug;
+    pid_t pid;
+
+    /* Check if we have to execute hotplug scripts for this device
+     * and return the necessary args/env vars for execution */
+    hotplug = libxl__get_hotplug_script_info(gc, aodev->dev, &args, &env,
+                                             aodev->action);
+    switch (hotplug) {
+    case 0:
+        /* no hotplug script to execute */
+        goto out;
+    case 1:
+        /* execute hotplug script */
+        break;
+    default:
+        /* everything else is an error */
+        LOG(ERROR, "unable to get args/env to execute hotplug script for "
+                   "device %s", libxl__device_backend_path(gc, aodev->dev));
+        rc = hotplug;
+        goto out;
+    }
+
+    /* Set hotplug timeout */
+    rc = libxl__ev_time_register_rel(gc, &aodev->timeout,
+                                     device_hotplug_timeout_cb,
+                                     LIBXL_HOTPLUG_TIMEOUT * 1000);
+    if (rc) {
+        LOG(ERROR, "unable to register timeout for hotplug device %s", be_path);
+        goto out;
+    }
+
+    aodev->what = GCSPRINTF("%s %s", args[0], args[1]);
+    LOG(DEBUG, "calling hotplug script: %s %s", args[0], args[1]);
+
+    /* fork and execute hotplug script */
+    pid = libxl__ev_child_fork(gc, &aodev->child, device_hotplug_child_death_cb);
+    if (pid == -1) {
+        LOG(ERROR, "unable to fork");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    if (!pid) {
+        /* child */
+        libxl__exec(gc, -1, -1, -1, args[0], args, env);
+        /* notreached */
+        abort();
+    }
+
+    assert(libxl__ev_child_inuse(&aodev->child));
+
+    return;
+
+out:
+    aodev->rc = rc;
+    device_hotplug_done(egc, aodev);
+    return;
+}
+
+static void device_hotplug_timeout_cb(libxl__egc *egc, libxl__ev_time *ev,
+                                      const struct timeval *requested_abs)
+{
+    libxl__ao_device *aodev = CONTAINER_OF(ev, *aodev, timeout);
+    STATE_AO_GC(aodev->ao);
+
+    libxl__ev_time_deregister(gc, &aodev->timeout);
+
+    assert(libxl__ev_child_inuse(&aodev->child));
+    LOG(DEBUG, "killing hotplug script %s because of timeout", aodev->what);
+    if (kill(aodev->child.pid, SIGKILL)) {
+        LOGEV(ERROR, errno, "unable to kill hotplug script %s [%ld]",
+                            aodev->what, (unsigned long)aodev->child.pid);
+    }
+
+    return;
+}
+
+static void device_hotplug_child_death_cb(libxl__egc *egc,
+                                          libxl__ev_child *child,
+                                          pid_t pid, int status)
+{
+    libxl__ao_device *aodev = CONTAINER_OF(child, *aodev, child);
+    STATE_AO_GC(aodev->ao);
+    char *be_path = libxl__device_backend_path(gc, aodev->dev);
+    char *hotplug_error;
+
+    if (status) {
+        libxl_report_child_exitstatus(CTX, LIBXL__LOG_ERROR,
+                                      aodev->what, pid, status);
+        hotplug_error = libxl__xs_read(gc, XBT_NULL,
+                                       GCSPRINTF("%s/hotplug-error", be_path));
+        if (hotplug_error)
+            LOG(ERROR, "script: %s", hotplug_error);
+        aodev->rc = ERROR_FAIL;
+    }
+
+    device_hotplug_done(egc, aodev);
+}
+
 static void device_hotplug_done(libxl__egc *egc, libxl__ao_device *aodev)
 {
     STATE_AO_GC(aodev->ao);
@@ -828,6 +951,11 @@ static void device_hotplug_done(libxl__egc *egc, libxl__ao_device *aodev)
     xs_transaction_t t = 0;
     int rc;
 
+    /* Clean events and check reentrancy */
+    libxl__ev_time_deregister(gc, &aodev->timeout);
+    assert(!libxl__ev_child_inuse(&aodev->child));
+
+    /* Clean xenstore if it's a disconnection */
     if (aodev->action == DEVICE_DISCONNECT) {
         for (;;) {
             rc = libxl__xs_transaction_start(gc, &t);
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 382ec79dd7..2567c4d38a 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -74,6 +74,7 @@
 
 #define LIBXL_INIT_TIMEOUT 10
 #define LIBXL_DESTROY_TIMEOUT 10
+#define LIBXL_HOTPLUG_TIMEOUT 10
 #define LIBXL_DEVICE_MODEL_START_TIMEOUT 10
 #define LIBXL_QEMU_BODGE_TIMEOUT 2
 #define LIBXL_XENCONSOLE_LIMIT 1048576
@@ -1832,11 +1833,14 @@ struct libxl__ao_device {
     int active;
     int rc;
     libxl__ev_devstate backend_ds;
-    /* Bodge for Qemu devices */
+    /* Bodge for Qemu devices, also used for timeout of hotplug execution */
     libxl__ev_time timeout;
     /* Used internally to have a reference to the upper libxl__ao_devices
      * struct when present */
     libxl__ao_devices *aodevs;
+    /* device hotplug execution */
+    const char *what;
+    libxl__ev_child child;
 };
 
 /* Helper struct to simply the plug/unplug of multiple devices at the same
@@ -1966,6 +1970,20 @@ _hidden void libxl__wait_device_connection(libxl__egc*,
 _hidden void libxl__initiate_device_remove(libxl__egc *egc,
                                            libxl__ao_device *aodev);
 
+/*
+ * libxl__get_hotplug_script_info returns the args and env that should
+ * be passed to the hotplug script for the requested device.
+ *
+ * Since a device might not need to execute any hotplug script, this function
+ * can return the following values:
+ * < 0: Error
+ * 0: No need to execute hotplug script
+ * 1: Execute hotplug script
+ */
+_hidden int libxl__get_hotplug_script_info(libxl__gc *gc, libxl__device *dev,
+                                           char ***args, char ***env,
+                                           libxl__device_action action);
+
 /*----- local disk attach: attach a disk locally to run the bootloader -----*/
 
 typedef struct libxl__disk_local_state libxl__disk_local_state;
diff --git a/tools/libxl/libxl_linux.c b/tools/libxl/libxl_linux.c
index 0169b2ff0b..97b3fd4a64 100644
--- a/tools/libxl/libxl_linux.c
+++ b/tools/libxl/libxl_linux.c
@@ -77,3 +77,100 @@ char *libxl__devid_to_localdev(libxl__gc *gc, int devid)
                 "%d", minor & (nr_parts - 1));
     return ret;
 }
+
+/* Hotplug scripts helpers */
+
+static char **get_hotplug_env(libxl__gc *gc, libxl__device *dev)
+{
+    char *be_path = libxl__device_backend_path(gc, dev);
+    char *script;
+    const char *type = libxl__device_kind_to_string(dev->backend_kind);
+    char **env;
+    int nr = 0;
+
+    script = libxl__xs_read(gc, XBT_NULL,
+                            GCSPRINTF("%s/%s", be_path, "script"));
+    if (!script) {
+        LOGEV(ERROR, errno, "unable to read script from %s", be_path);
+        return NULL;
+    }
+
+    const int arraysize = 9;
+    GCNEW_ARRAY(env, arraysize);
+    env[nr++] = "script";
+    env[nr++] = script;
+    env[nr++] = "XENBUS_TYPE";
+    env[nr++] = libxl__strdup(gc, type);
+    env[nr++] = "XENBUS_PATH";
+    env[nr++] = GCSPRINTF("backend/%s/%u/%d", type, dev->domid, dev->devid);
+    env[nr++] = "XENBUS_BASE_PATH";
+    env[nr++] = "backend";
+    env[nr++] = NULL;
+    assert(nr == arraysize);
+
+    return env;
+}
+
+/* Hotplug scripts caller functions */
+
+static int libxl__hotplug_disk(libxl__gc *gc, libxl__device *dev,
+                               char ***args, char ***env,
+                               libxl__device_action action)
+{
+    char *be_path = libxl__device_backend_path(gc, dev);
+    char *script;
+    int nr = 0, rc = 0;
+
+    script = libxl__xs_read(gc, XBT_NULL,
+                            GCSPRINTF("%s/%s", be_path, "script"));
+    if (!script) {
+        LOGEV(ERROR, errno, "unable to read script from %s", be_path);
+        rc = ERROR_FAIL;
+        goto error;
+    }
+
+    *env = get_hotplug_env(gc, dev);
+    if (!*env) {
+        rc = ERROR_FAIL;
+        goto error;
+    }
+
+    const int arraysize = 3;
+    GCNEW_ARRAY(*args, arraysize);
+    (*args)[nr++] = script;
+    (*args)[nr++] = action == DEVICE_CONNECT ? "add" : "remove";
+    (*args)[nr++] = NULL;
+    assert(nr == arraysize);
+
+    rc = 1;
+
+error:
+    return rc;
+}
+
+int libxl__get_hotplug_script_info(libxl__gc *gc, libxl__device *dev,
+                                   char ***args, char ***env,
+                                   libxl__device_action action)
+{
+    char *disable_udev = libxl__xs_read(gc, XBT_NULL, DISABLE_UDEV_PATH);
+    int rc;
+
+    /* Check if we have to run hotplug scripts */
+    if (!disable_udev) {
+        rc = 0;
+        goto out;
+    }
+
+    switch (dev->backend_kind) {
+    case LIBXL__DEVICE_KIND_VBD:
+        rc = libxl__hotplug_disk(gc, dev, args, env, action);
+        break;
+    default:
+        /* No need to execute any hotplug scripts */
+        rc = 0;
+        break;
+    }
+
+out:
+    return rc;
+}
diff --git a/tools/libxl/libxl_netbsd.c b/tools/libxl/libxl_netbsd.c
index dbf5f7177a..a2f8d3f0c5 100644
--- a/tools/libxl/libxl_netbsd.c
+++ b/tools/libxl/libxl_netbsd.c
@@ -30,3 +30,11 @@ char *libxl__devid_to_localdev(libxl__gc *gc, int devid)
     /* TODO */
     return NULL;
 }
+
+/* Hotplug scripts caller functions */
+int libxl__get_hotplug_script_info(libxl__gc *gc, libxl__device *dev,
+                                   char ***args, char ***env,
+                                   libxl__device_action action)
+{
+    return 0;
+}