libxl_dm: Pre-open QMP socket for QEMU

This patch moves the creation of the QMP unix socket from QEMU to libxl.
But libxl doesn't rely on this yet.

When starting QEMU with dm_restrict=1, pre-open the QMP socket before
exec QEMU. That socket will be useful to find out if QEMU is ready, and
pre-opening it means that libxl can connect to it without waiting for
QEMU to create it.

The pre-opening is conditional, based on the use of dm_restrict
because it is using a new command line option of QEMU, and dm_restrict
support in QEMU is newer.

-chardev socket,fd=X is available with QEMU 2.12, since commit:
> char: allow passing pre-opened socket file descriptor at startup
> 0935700f8544033ebbd41e1f13cd528f8a58d24d

dm_restrict is available in QEMU 3.0.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 4ca25f56a6da135fbf0fd52a6384d4da46aad90b..89f4766a27752507b335670a0e5de52954955454 100644 (file)
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -763,12 +763,17 @@ static int store_libxl_entry(libxl__gc *gc, uint32_t domid,
 
 void libxl__domain_build_state_init(libxl__domain_build_state *state)
 {
+    state->dm_monitor_fd = -1;
 }
 
 void libxl__domain_build_state_dispose(libxl__domain_build_state *state)
 {
     libxl__file_reference_unmap(&state->pv_kernel);
     libxl__file_reference_unmap(&state->pv_ramdisk);
+    if (state->dm_monitor_fd >= 0) {
+        close(state->dm_monitor_fd);
+        state->dm_monitor_fd = -1;
+    }
 }
 
 /*----- main domain creation -----*/

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 200310083fb1948b8212e9f5cf5bfb6331b98b9e..b9921eb885a45592cab990127f33be4ab464e08e 100644 (file)
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -670,6 +670,8 @@ static int libxl__build_device_model_args_old(libxl__gc *gc,
     dm_args = flexarray_make(gc, 16, 1);
     dm_envs = flexarray_make(gc, 16, 1);
 
+    assert(state->dm_monitor_fd == -1);
+
     libxl__set_qemu_env_for_xsa_180(gc, dm_envs);
 
     flexarray_vappend(dm_args, dm,
@@ -1100,6 +1102,51 @@ static char *qemu_disk_ide_drive_string(libxl__gc *gc, const char *target_path,
     return drive;
 }
 
+static int libxl__pre_open_qmp_socket(libxl__gc *gc, libxl_domid domid,
+                                      int *fd_r)
+{
+    int rc, r;
+    int fd;
+    struct sockaddr_un un;
+    const char *path = libxl__qemu_qmp_path(gc, domid);
+
+    fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    if (fd < 0) {
+        LOGED(ERROR, domid, "socket() failed");
+        return ERROR_FAIL;
+    }
+
+    rc = libxl__prepare_sockaddr_un(gc, &un, path, "QEMU's QMP socket");
+    if (rc)
+        goto out;
+
+    rc = libxl__remove_file(gc, path);
+    if (rc)
+        goto out;
+
+    r = bind(fd, (struct sockaddr *) &un, sizeof(un));
+    if (r < 0) {
+        LOGED(ERROR, domid, "bind('%s') failed", path);
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    r = listen(fd, 1);
+    if (r < 0) {
+        LOGED(ERROR, domid, "listen() failed");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    *fd_r = fd;
+    rc = 0;
+
+out:
+    if (rc && fd >= 0)
+        close(fd);
+    return rc;
+}
+
 static int libxl__build_device_model_args_new(libxl__gc *gc,
                                         const char *dm, int guest_domid,
                                         const libxl_domain_config *guest_config,
@@ -1132,10 +1179,16 @@ static int libxl__build_device_model_args_new(libxl__gc *gc,
                       GCSPRINTF("%d", guest_domid), NULL);
 
     flexarray_append(dm_args, "-chardev");
-    flexarray_append(dm_args,
-                     GCSPRINTF("socket,id=libxl-cmd,"
-                               "path=%s,server,nowait",
-                               libxl__qemu_qmp_path(gc, guest_domid)));
+    if (state->dm_monitor_fd >= 0) {
+        flexarray_append(dm_args,
+            GCSPRINTF("socket,id=libxl-cmd,fd=%d,server,nowait",
+                      state->dm_monitor_fd));
+    } else {
+        flexarray_append(dm_args,
+                         GCSPRINTF("socket,id=libxl-cmd,"
+                                   "path=%s,server,nowait",
+                                   libxl__qemu_qmp_path(gc, guest_domid)));
+    }
 
     flexarray_append(dm_args, "-no-shutdown");
     flexarray_append(dm_args, "-mon");
@@ -2437,6 +2490,16 @@ void libxl__spawn_local_dm(libxl__egc *egc, libxl__dm_spawn_state *dmss)
     if (rc)
         goto out;
 
+    if (b_info->device_model_version
+            == LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN &&
+        libxl_defbool_val(b_info->dm_restrict)) {
+        /* If we have to use dm_restrict, QEMU needs to be new enough
+         * and will have the new interface where we can pre-open the
+         * QMP socket. */
+        rc = libxl__pre_open_qmp_socket(gc, domid, &state->dm_monitor_fd);
+        if (rc) goto out;
+    }
+
     rc = libxl__build_device_model_args(gc, dm, domid, guest_config,
                                           &args, &envs, state,
                                           &dm_state_fd);

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 3d12748cbbf76ed7c28bda35fc47b9310e92cb3a..b50234482c99f49470b87ccb8dcc6a59d1c059fa 100644 (file)
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1240,6 +1240,7 @@ typedef struct {
     char *console_tty;
 
     char *saved_state;
+    int dm_monitor_fd;
 
     libxl__file_reference pv_kernel;
     libxl__file_reference pv_ramdisk;