tools: use libxenlight for writing xenstore-stubdom console nodes

Instead of duplicating libxl__device_console_add() work in
init-xenstore-domain.c, just use libxenlight.

This requires to add a small wrapper function to libxenlight, as
libxl__device_console_add() is an internal function.

This at once removes a theoretical race between starting xenconsoled
and xenstore-stubdom, as the old code wasn't using a single
transaction for writing all the entries, leading to the possibility
that xenconsoled would see only some of the entries being written.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

tools/helpers/init-xenstore-domain.c

@@ -11,6 +11,7 @@
 #include <xenguest.h>
 #include <xenstore.h>
 #include <xentoollog.h>
+#include <libxl.h>
 #include <xen/sys/xenbus_dev.h>
 #include <xen-xsm/flask/flask.h>
 #include <xen/io/xenbus.h>
@@ -403,15 +404,6 @@ static void do_xs_write(struct xs_handle *xsh, char *path, char *val)
         fprintf(stderr, "writing %s to xenstore failed.\n", path);
 }
 
-static void do_xs_write_dir_node(struct xs_handle *xsh, char *dir, char *node,
-                                 char *val)
-{
-    char full_path[100];
-
-    snprintf(full_path, 100, "%s/%s", dir, node);
-    do_xs_write(xsh, full_path, val);
-}
-
 static void do_xs_write_dom(struct xs_handle *xsh, char *path, char *val)
 {
     char full_path[64];
@@ -425,9 +417,10 @@ int main(int argc, char** argv)
     int opt;
     xc_interface *xch;
     struct xs_handle *xsh;
-    char buf[16], be_path[64], fe_path[64];
+    char buf[16];
     int rv, fd;
     char *maxmem_str = NULL;
+    libxl_ctx *ctx;
 
     while ( (opt = getopt_long(argc, argv, "v", options, NULL)) != -1 )
     {
@@ -528,27 +521,18 @@ int main(int argc, char** argv)
     if (maxmem)
         snprintf(buf, 16, "%d", maxmem * 1024);
     do_xs_write_dom(xsh, "memory/static-max", buf);
-    snprintf(be_path, 64, "/local/domain/0/backend/console/%d/0", domid);
-    snprintf(fe_path, 64, "/local/domain/%d/console", domid);
-    snprintf(buf, 16, "%d", domid);
-    do_xs_write_dir_node(xsh, be_path, "frontend-id", buf);
-    do_xs_write_dir_node(xsh, be_path, "frontend", fe_path);
-    do_xs_write_dir_node(xsh, be_path, "online", "1");
-    snprintf(buf, 16, "%d", XenbusStateInitialising);
-    do_xs_write_dir_node(xsh, be_path, "state", buf);
-    do_xs_write_dir_node(xsh, be_path, "protocol", "vt100");
-    do_xs_write_dir_node(xsh, fe_path, "backend", be_path);
-    do_xs_write_dir_node(xsh, fe_path, "backend-id", "0");
-    do_xs_write_dir_node(xsh, fe_path, "limit", "1048576");
-    do_xs_write_dir_node(xsh, fe_path, "type", "xenconsoled");
-    do_xs_write_dir_node(xsh, fe_path, "output", "pty");
-    do_xs_write_dir_node(xsh, fe_path, "tty", "");
-    snprintf(buf, 16, "%d", console_evtchn);
-    do_xs_write_dir_node(xsh, fe_path, "port", buf);
-    snprintf(buf, 16, "%ld", console_gfn);
-    do_xs_write_dir_node(xsh, fe_path, "ring-ref", buf);
     xs_close(xsh);
 
+    if ( libxl_ctx_alloc(&ctx, LIBXL_VERSION, 0, logger))
+    {
+        fprintf(stderr, "libxl_ctx_alloc() failed.\n");
+        rv = 3;
+        goto out;
+    }
+    libxl_console_add_xenstore(ctx, domid, 0, console_evtchn, console_gfn,
+                               NULL);
+    libxl_ctx_free(ctx);
+
     fd = creat(XEN_RUN_DIR "/xenstored.pid", 0666);
     if ( fd < 0 )
     {

tools/include/libxl.h

@@ -547,6 +547,11 @@
  */
 #define LIBXL_HAVE_DEVICE_DISK_SPECIFICATION 1
 
+/*
+ * LIBXL_HAVE_CONSOLE_ADD_XENSTORE indicates presence of the function
+ * libxl_console_add_xenstore() in libxl.
+ */
+#define LIBXL_HAVE_CONSOLE_ADD_XENSTORE 1
 /*
  * libxl ABI compatibility
  *
@@ -1987,6 +1992,15 @@ int libxl_console_get_tty(libxl_ctx *ctx, uint32_t domid, int cons_num,
  */
 int libxl_primary_console_get_tty(libxl_ctx *ctx, uint32_t domid_vm, char **path);
 
+/* libxl_console_add_xenstore writes the Xenstore entries for a domain's
+ * primary console based on domid, event channel port and the guest frame
+ * number of the PV console's ring page.
+ */
+int libxl_console_add_xenstore(libxl_ctx *ctx, uint32_t domid, uint32_t backend,
+                               unsigned int evtch, unsigned long gfn,
+                               const libxl_asyncop_how *ao_how)
+                               LIBXL_EXTERNAL_CALLERS_ONLY;
+
 /* May be called with info_r == NULL to check for domain's existence.
  * Returns ERROR_DOMAIN_NOTFOUND if domain does not exist (used to return
  * ERROR_INVAL for this scenario). */

tools/libs/light/libxl_console.c

@@ -346,6 +346,29 @@ out:
     return rc;
 }
 
+int libxl_console_add_xenstore(libxl_ctx *ctx, uint32_t domid, uint32_t backend,
+                               unsigned int evtch, unsigned long gfn,
+                               const libxl_asyncop_how *ao_how)
+{
+    AO_CREATE(ctx, domid, ao_how);
+    int rc;
+    libxl__device_console console = { .backend_domid = backend,
+                                      .output = "pty",
+                                      .consback = LIBXL__CONSOLE_BACKEND_XENCONSOLED,
+                                    };
+    libxl__domain_build_state state = { .console_port = evtch,
+                                        .console_mfn = gfn,
+                                      };
+    libxl__device device = { };
+
+    rc = libxl__device_console_add(gc, domid, &console, &state, &device);
+    if (rc < 0)
+        LOGED(ERROR, domid, "Adding console Xenstore entries");
+
+    libxl__ao_complete(egc, ao, rc);
+    return AO_INPROGRESS;
+}
+
 int libxl__device_vuart_add(libxl__gc *gc, uint32_t domid,
                             libxl__device_console *console,
                             libxl__domain_build_state *state)