tools/libs/light: add backend type for 9pfs PV devices

Make the backend type of 9pfs PV devices configurable. The default is
"qemu" with the related Xenstore backend-side directory being "9pfs".

Add another type "xen_9pfsd" with the related Xenstore backend-side
directory "xen_9pfs".

As additional security features it is possible to specify:
- "max-space" for limiting the maximum space consumed on the filesystem
  in MBs
- "max-files" for limiting the maximum number of files in the
  filesystem
- "max-open-files" for limiting the maximum number of concurrent open
  files

For convenience "auto-delete" is available to let the backend delete the
oldest file of the guest in case otherwise "max-space" or "max-files"
would be violated.

The xen-9pfsd daemon will be started by libxenlight automatically when
the first "xen_9pfs" device is being created.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>
Acked-by: George Dunlap <george.dunlap@cloud.com> # Golang bits
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

tools/include/libxl.h

@@ -622,6 +622,13 @@
  */
 #define LIBXL_HAVE_HVM_PIRQ 1
 
+/*
+ * LIBXL_HAVE_XEN_9PFS indicates the presence of the xen-9pfsd related
+ * fields in libxl_device_p9: type, max_space, max_files, max_open_files and
+ * auto_delete.
+ */
+#define LIBXL_HAVE_XEN_9PFS 1
+
 /*
  * libxl memory management
  *

tools/libs/light/libxl_9pfs.c

@@ -33,20 +33,171 @@ static int libxl__set_xenstore_p9(libxl__gc *gc, uint32_t domid,
 
     flexarray_append_pair(front, "tag", p9->tag);
 
+    if (p9->type == LIBXL_P9_TYPE_XEN_9PFSD) {
+        flexarray_append_pair(back, "max-space",
+                              GCSPRINTF("%u", p9->max_space));
+        flexarray_append_pair(back, "max-files",
+                              GCSPRINTF("%u", p9->max_files));
+        flexarray_append_pair(back, "max-open-files",
+                              GCSPRINTF("%u", p9->max_open_files));
+        flexarray_append_pair(back, "auto-delete",
+                              p9->auto_delete ? "1" : "0");
+    }
+
+    return 0;
+}
+
+static int libxl__device_from_p9(libxl__gc *gc, uint32_t domid,
+                                 libxl_device_p9 *type, libxl__device *device)
+{
+    device->backend_devid   = type->devid;
+    device->backend_domid   = type->backend_domid;
+    device->backend_kind    = type->type == LIBXL_P9_TYPE_QEMU
+                              ? LIBXL__DEVICE_KIND_9PFS
+                              : LIBXL__DEVICE_KIND_XEN_9PFS;
+    device->devid           = type->devid;
+    device->domid           = domid;
+    device->kind            = LIBXL__DEVICE_KIND_9PFS;
+
     return 0;
 }
 
-#define libxl__add_p9s NULL
+static int libxl__device_p9_dm_needed(void *e, unsigned domid)
+{
+    libxl_device_p9 *elem = e;
+
+    return elem->type == LIBXL_P9_TYPE_QEMU && elem->backend_domid == domid;
+}
+
+typedef struct libxl__aop9_state libxl__aop9_state;
+
+struct libxl__aop9_state {
+    libxl__spawn_state spawn;
+    libxl__ao_device *aodev;
+    libxl_device_p9 p9;
+    uint32_t domid;
+};
+
+static void xen9pfsd_confirm(libxl__egc *egc, libxl__spawn_state *spawn,
+                             const char *xsdata);
+static void xen9pfsd_failed(libxl__egc *egc, libxl__spawn_state *spawn, int rc);
+static void xen9pfsd_detached(libxl__egc *egc, libxl__spawn_state *spawn);
+static void xen9pfsd_spawn_outcome(libxl__egc *egc, libxl__aop9_state *aop9,
+                                   int rc);
+
+/*
+ * Spawn the xen-9pfsd daemon if needed.
+ * returns:
+ * < 0 if error
+ * 0 if no daemon needs to be spawned
+ * 1 if daemon was spawned
+ */
+static int xen9pfsd_spawn(libxl__egc *egc, uint32_t domid, libxl_device_p9 *p9,
+                         libxl__ao_device *aodev)
+{
+    STATE_AO_GC(aodev->ao);
+    struct libxl__aop9_state *aop9;
+    int rc;
+    char *args[] = { "xen-9pfsd", NULL };
+    char *path = GCSPRINTF("/local/domain/%u/libxl/xen-9pfs",
+                           p9->backend_domid);
+
+    if (p9->type != LIBXL_P9_TYPE_XEN_9PFSD ||
+        libxl__xs_read(gc, XBT_NULL, GCSPRINTF("%s/state", path)))
+        return 0;
+
+    GCNEW(aop9);
+    aop9->aodev = aodev;
+    libxl_device_p9_copy(CTX, &aop9->p9, p9);
+    aop9->domid = domid;
+
+    aop9->spawn.ao = aodev->ao;
+    aop9->spawn.what = "xen-9pfs daemon";
+    aop9->spawn.xspath = GCSPRINTF("%s/state", path);
+    aop9->spawn.timeout_ms = LIBXL_DEVICE_MODEL_START_TIMEOUT * 1000;
+    aop9->spawn.pidpath = GCSPRINTF("%s/pid", path);
+    aop9->spawn.midproc_cb = libxl__spawn_record_pid;
+    aop9->spawn.confirm_cb = xen9pfsd_confirm;
+    aop9->spawn.failure_cb = xen9pfsd_failed;
+    aop9->spawn.detached_cb = xen9pfsd_detached;
+    rc = libxl__spawn_spawn(egc, &aop9->spawn);
+    if (rc < 0)
+        return rc;
+    if (!rc) {
+        setsid();
+        libxl__exec(gc, -1, -1, -1, LIBEXEC_BIN "/xen-9pfsd", args, NULL);
+    }
+
+    return 1;
+}
+
+static void xen9pfsd_confirm(libxl__egc *egc, libxl__spawn_state *spawn,
+                             const char *xsdata)
+{
+    STATE_AO_GC(spawn->ao);
+
+    if (!xsdata)
+        return;
+
+    if (strcmp(xsdata, "running"))
+        return;
+
+    libxl__spawn_initiate_detach(gc, spawn);
+}
+
+static void xen9pfsd_failed(libxl__egc *egc, libxl__spawn_state *spawn, int rc)
+{
+    libxl__aop9_state *aop9 = CONTAINER_OF(spawn, *aop9, spawn);
+
+    xen9pfsd_spawn_outcome(egc, aop9, rc);
+}
+
+static void xen9pfsd_detached(libxl__egc *egc, libxl__spawn_state *spawn)
+{
+    libxl__aop9_state *aop9 = CONTAINER_OF(spawn, *aop9, spawn);
+
+    xen9pfsd_spawn_outcome(egc, aop9, 0);
+}
+
+static void xen9pfsd_spawn_outcome(libxl__egc *egc, libxl__aop9_state *aop9,
+                                   int rc)
+{
+    aop9->aodev->rc = rc;
+    if (rc)
+        aop9->aodev->callback(egc, aop9->aodev);
+    else
+        libxl__device_add_async(egc, aop9->domid, &libxl__p9_devtype,
+                                &aop9->p9, aop9->aodev);
+}
+
+static void libxl__device_p9_add(libxl__egc *egc, uint32_t domid,
+                                 libxl_device_p9 *p9,
+                                 libxl__ao_device *aodev)
+{
+    int rc;
+
+    rc = xen9pfsd_spawn(egc, domid, p9, aodev);
+    if (rc == 1)
+        return;
+
+    if (rc == 0)
+        libxl__device_add_async(egc, domid, &libxl__p9_devtype, p9, aodev);
+
+    aodev->rc = rc;
+    if (rc)
+        aodev->callback(egc, aodev);
+}
+
 #define libxl_device_p9_list NULL
 #define libxl_device_p9_compare NULL
 
 static LIBXL_DEFINE_UPDATE_DEVID(p9)
-static LIBXL_DEFINE_DEVICE_FROM_TYPE(p9)
+static LIBXL_DEFINE_DEVICES_ADD(p9)
 
 LIBXL_DEFINE_DEVICE_REMOVE(p9)
 
 DEFINE_DEVICE_TYPE_STRUCT(p9, 9PFS, p9s,
-    .skip_attach = 1,
     .set_xenstore_config = (device_set_xenstore_config_fn_t)
                            libxl__set_xenstore_p9,
+    .dm_needed = libxl__device_p9_dm_needed,
 );

tools/libs/light/libxl_create.c

@@ -1761,9 +1761,6 @@ static void domcreate_launch_dm(libxl__egc *egc, libxl__multidev *multidev,
         libxl__device_console_dispose(&console);
     }
 
-    for (i = 0; i < d_config->num_p9s; i++)
-        libxl__device_add(gc, domid, &libxl__p9_devtype, &d_config->p9s[i]);
-
     for (i = 0; i < d_config->num_pvcallsifs; i++)
         libxl__device_add(gc, domid, &libxl__pvcallsif_devtype,
                           &d_config->pvcallsifs[i]);
@@ -1900,6 +1897,7 @@ const libxl__device_type *device_type_tbl[] = {
     &libxl__vdispl_devtype,
     &libxl__vsnd_devtype,
     &libxl__virtio_devtype,
+    &libxl__p9_devtype,
     NULL
 };
 

tools/libs/light/libxl_dm.c

@@ -3771,7 +3771,7 @@ int libxl__need_xenpv_qemu(libxl__gc *gc, libxl_domain_config *d_config)
         goto out;
     }
 
-    if (d_config->num_vfbs > 0 || d_config->num_p9s > 0) {
+    if (d_config->num_vfbs > 0) {
         ret = 1;
         goto out;
     }

tools/libs/light/libxl_types.idl

@@ -150,6 +150,12 @@ libxl_nic_type = Enumeration("nic_type", [
     (2, "VIF"),
     ])
 
+libxl_p9_type = Enumeration("p9_type", [
+    (0, "unknown"),
+    (1, "qemu"),
+    (2, "xen_9pfsd"),
+    ])
+
 libxl_action_on_shutdown = Enumeration("action_on_shutdown", [
     (1, "DESTROY"),
 
@@ -944,6 +950,11 @@ libxl_device_p9 = Struct("device_p9", [
     ("path",             string),
     ("security_model",   string),
     ("devid",            libxl_devid),
+    ("type",             libxl_p9_type),
+    ("max_space",        integer),
+    ("max_files",        integer),
+    ("max_open_files",   integer),
+    ("auto_delete",      bool),
 ])
 
 libxl_device_pvcallsif = Struct("device_pvcallsif", [

tools/libs/light/libxl_types_internal.idl

@@ -35,6 +35,7 @@ libxl__device_kind = Enumeration("device_kind", [
     (17, "VIRTIO_DISK"),
     (18, "VIRTIO"),
     (19, "VBD3"),
+    (20, "XEN_9PFS"),
     ])
 
 libxl__console_backend = Enumeration("console_backend", [