hw/xen_backend.c

   1 /*
   2  *  xen backend driver infrastructure
   3  *  (c) 2008 Gerd Hoffmann <kraxel@redhat.com>
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; under version 2 of the License.
   8  *
   9  *  This program is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  *  GNU General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU General Public License along
  15  *  with this program; if not, write to the Free Software Foundation, Inc.,
  16  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  17  */
  18
  19 /*
  20  * TODO: add some xenbus / xenstore concepts overview here.
  21  */
  22
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <stdarg.h>
  26 #include <string.h>
  27 #include <unistd.h>
  28 #include <fcntl.h>
  29 #include <inttypes.h>
  30 #include <sys/types.h>
  31 #include <sys/stat.h>
  32 #include <sys/mman.h>
  33 #include <sys/signal.h>
  34
  35 #include <xs.h>
  36 #include <xenctrl.h>
  37 #include <xen/grant_table.h>
  38
  39 #include "hw.h"
  40 #include "qemu-char.h"
  41 #include "qemu-log.h"
  42 #include "xen_backend.h"
  43
  44 /* ------------------------------------------------------------- */
  45
  46 /* public */
  47 int xen_xc;
  48 struct xs_handle *xenstore = NULL;
  49 const char *xen_protocol;
  50
  51 /* private */
  52 static TAILQ_HEAD(XenDeviceHead, XenDevice) xendevs = TAILQ_HEAD_INITIALIZER(xendevs);
  53 static int debug = 0;
  54
  55 /* ------------------------------------------------------------- */
  56
  57 int xenstore_write_str(const char *base, const char *node, const char *val)
  58 {
  59     char abspath[XEN_BUFSIZE];
  60
  61     snprintf(abspath, sizeof(abspath), "%s/%s", base, node);
  62     if (!xs_write(xenstore, 0, abspath, val, strlen(val)))
  63         return -1;
  64     return 0;
  65 }
  66
  67 char *xenstore_read_str(const char *base, const char *node)
  68 {
  69     char abspath[XEN_BUFSIZE];
  70     unsigned int len;
  71     char *str, *ret = NULL;
  72
  73     snprintf(abspath, sizeof(abspath), "%s/%s", base, node);
  74     str = xs_read(xenstore, 0, abspath, &len);
  75     if (str != NULL) {
  76         /* move to qemu-allocated memory to make sure
  77          * callers can savely qemu_free() stuff. */
  78         ret = qemu_strdup(str);
  79         free(str);
  80     }
  81     return ret;
  82 }
  83
  84 int xenstore_write_int(const char *base, const char *node, int ival)
  85 {
  86     char val[32];
  87
  88     snprintf(val, sizeof(val), "%d", ival);
  89     return xenstore_write_str(base, node, val);
  90 }
  91
  92 int xenstore_read_int(const char *base, const char *node, int *ival)
  93 {
  94     char *val;
  95     int rc = -1;
  96
  97     val = xenstore_read_str(base, node);
  98     if (val && 1 == sscanf(val, "%d", ival))
  99         rc = 0;
 100     qemu_free(val);
 101     return rc;
 102 }
 103
 104 int xenstore_write_be_str(struct XenDevice *xendev, const char *node, const char *val)
 105 {
 106     return xenstore_write_str(xendev->be, node, val);
 107 }
 108
 109 int xenstore_write_be_int(struct XenDevice *xendev, const char *node, int ival)
 110 {
 111     return xenstore_write_int(xendev->be, node, ival);
 112 }
 113
 114 char *xenstore_read_be_str(struct XenDevice *xendev, const char *node)
 115 {
 116     return xenstore_read_str(xendev->be, node);
 117 }
 118
 119 int xenstore_read_be_int(struct XenDevice *xendev, const char *node, int *ival)
 120 {
 121     return xenstore_read_int(xendev->be, node, ival);
 122 }
 123
 124 char *xenstore_read_fe_str(struct XenDevice *xendev, const char *node)
 125 {
 126     return xenstore_read_str(xendev->fe, node);
 127 }
 128
 129 int xenstore_read_fe_int(struct XenDevice *xendev, const char *node, int *ival)
 130 {
 131     return xenstore_read_int(xendev->fe, node, ival);
 132 }
 133
 134 /* ------------------------------------------------------------- */
 135
 136 const char *xenbus_strstate(enum xenbus_state state)
 137 {
 138         static const char *const name[] = {
 139                 [ XenbusStateUnknown      ] = "Unknown",
 140                 [ XenbusStateInitialising ] = "Initialising",
 141                 [ XenbusStateInitWait     ] = "InitWait",
 142                 [ XenbusStateInitialised  ] = "Initialised",
 143                 [ XenbusStateConnected    ] = "Connected",
 144                 [ XenbusStateClosing      ] = "Closing",
 145                 [ XenbusStateClosed       ] = "Closed",
 146         };
 147         return (state < ARRAY_SIZE(name)) ? name[state] : "INVALID";
 148 }
 149
 150 int xen_be_set_state(struct XenDevice *xendev, enum xenbus_state state)
 151 {
 152     int rc;
 153
 154     rc = xenstore_write_be_int(xendev, "state", state);
 155     if (rc < 0)
 156         return rc;
 157     xen_be_printf(xendev, 1, "backend state: %s -> %s\n",
 158                   xenbus_strstate(xendev->be_state), xenbus_strstate(state));
 159     xendev->be_state = state;
 160     return 0;
 161 }
 162
 163 /* ------------------------------------------------------------- */
 164
 165 struct XenDevice *xen_be_find_xendev(const char *type, int dom, int dev)
 166 {
 167     struct XenDevice *xendev;
 168
 169     TAILQ_FOREACH(xendev, &xendevs, next) {
 170         if (xendev->dom != dom)
 171             continue;
 172         if (xendev->dev != dev)
 173             continue;
 174         if (strcmp(xendev->type, type) != 0)
 175             continue;
 176         return xendev;
 177     }
 178     return NULL;
 179 }
 180
 181 /*
 182  * get xen backend device, allocate a new one if it doesn't exist.
 183  */
 184 static struct XenDevice *xen_be_get_xendev(const char *type, int dom, int dev,
 185                                            struct XenDevOps *ops)
 186 {
 187     struct XenDevice *xendev;
 188     char *dom0;
 189
 190     xendev = xen_be_find_xendev(type, dom, dev);
 191     if (xendev)
 192         return xendev;
 193
 194     /* init new xendev */
 195     xendev = qemu_mallocz(ops->size);
 196     xendev->type  = type;
 197     xendev->dom   = dom;
 198     xendev->dev   = dev;
 199     xendev->ops   = ops;
 200
 201     dom0 = xs_get_domain_path(xenstore, 0);
 202     snprintf(xendev->be, sizeof(xendev->be), "%s/backend/%s/%d/%d",
 203              dom0, xendev->type, xendev->dom, xendev->dev);
 204     snprintf(xendev->name, sizeof(xendev->name), "%s-%d",
 205              xendev->type, xendev->dev);
 206     free(dom0);
 207
 208     xendev->debug      = debug;
 209     xendev->local_port = -1;
 210
 211     xendev->evtchndev = xc_evtchn_open();
 212     if (xendev->evtchndev < 0) {
 213         xen_be_printf(NULL, 0, "can't open evtchn device\n");
 214         qemu_free(xendev);
 215         return NULL;
 216     }
 217     fcntl(xc_evtchn_fd(xendev->evtchndev), F_SETFD, FD_CLOEXEC);
 218
 219     if (ops->flags & DEVOPS_FLAG_NEED_GNTDEV) {
 220         xendev->gnttabdev = xc_gnttab_open();
 221         if (xendev->gnttabdev < 0) {
 222             xen_be_printf(NULL, 0, "can't open gnttab device\n");
 223             xc_evtchn_close(xendev->evtchndev);
 224             qemu_free(xendev);
 225             return NULL;
 226         }
 227     } else {
 228         xendev->gnttabdev = -1;
 229     }
 230
 231     TAILQ_INSERT_TAIL(&xendevs, xendev, next);
 232
 233     if (xendev->ops->alloc)
 234         xendev->ops->alloc(xendev);
 235
 236     return xendev;
 237 }
 238
 239 /*
 240  * release xen backend device.
 241  */
 242 static struct XenDevice *xen_be_del_xendev(int dom, int dev)
 243 {
 244     struct XenDevice *xendev, *xnext;
 245
 246     /*
 247      * This is pretty much like TAILQ_FOREACH(xendev, &xendevs, next) but
 248      * we save the next pointer in xnext because we might free xendev.
 249      */
 250     xnext = xendevs.tqh_first;
 251     while (xnext) {
 252         xendev = xnext;
 253         xnext = xendev->next.tqe_next;
 254
 255         if (xendev->dom != dom)
 256             continue;
 257         if (xendev->dev != dev && dev != -1)
 258             continue;
 259
 260         if (xendev->ops->free)
 261             xendev->ops->free(xendev);
 262
 263         if (xendev->fe) {
 264             char token[XEN_BUFSIZE];
 265             snprintf(token, sizeof(token), "fe:%p", xendev);
 266             xs_unwatch(xenstore, xendev->fe, token);
 267             qemu_free(xendev->fe);
 268         }
 269
 270         if (xendev->evtchndev >= 0)
 271             xc_evtchn_close(xendev->evtchndev);
 272         if (xendev->gnttabdev >= 0)
 273             xc_gnttab_close(xendev->gnttabdev);
 274
 275         TAILQ_REMOVE(&xendevs, xendev, next);
 276         qemu_free(xendev);
 277     }
 278     return NULL;
 279 }
 280
 281 /*
 282  * Sync internal data structures on xenstore updates.
 283  * Node specifies the changed field.  node = NULL means
 284  * update all fields (used for initialization).
 285  */
 286 static void xen_be_backend_changed(struct XenDevice *xendev, const char *node)
 287 {
 288     if (node == NULL  ||  strcmp(node, "online") == 0) {
 289         if (xenstore_read_be_int(xendev, "online", &xendev->online) == -1)
 290             xendev->online = 0;
 291     }
 292
 293     if (node) {
 294         xen_be_printf(xendev, 2, "backend update: %s\n", node);
 295         if (xendev->ops->backend_changed)
 296             xendev->ops->backend_changed(xendev, node);
 297     }
 298 }
 299
 300 static void xen_be_frontend_changed(struct XenDevice *xendev, const char *node)
 301 {
 302     int fe_state;
 303
 304     if (node == NULL  ||  strcmp(node, "state") == 0) {
 305         if (xenstore_read_fe_int(xendev, "state", &fe_state) == -1)
 306             fe_state = XenbusStateUnknown;
 307         if (xendev->fe_state != fe_state)
 308             xen_be_printf(xendev, 1, "frontend state: %s -> %s\n",
 309                           xenbus_strstate(xendev->fe_state),
 310                           xenbus_strstate(fe_state));
 311         xendev->fe_state = fe_state;
 312     }
 313     if (node == NULL  ||  strcmp(node, "protocol") == 0) {
 314         qemu_free(xendev->protocol);
 315         xendev->protocol = xenstore_read_fe_str(xendev, "protocol");
 316         if (xendev->protocol)
 317             xen_be_printf(xendev, 1, "frontend protocol: %s\n", xendev->protocol);
 318     }
 319
 320     if (node) {
 321         xen_be_printf(xendev, 2, "frontend update: %s\n", node);
 322         if (xendev->ops->frontend_changed)
 323             xendev->ops->frontend_changed(xendev, node);
 324     }
 325 }
 326
 327 /* ------------------------------------------------------------- */
 328 /* Check for possible state transitions and perform them.        */
 329
 330 /*
 331  * Initial xendev setup.  Read frontend path, register watch for it.
 332  * Should succeed once xend finished setting up the backend device.
 333  *
 334  * Also sets initial state (-> Initializing) when done.  Which
 335  * only affects the xendev->be_state variable as xenbus should
 336  * already be put into that state by xend.
 337  */
 338 static int xen_be_try_setup(struct XenDevice *xendev)
 339 {
 340     char token[XEN_BUFSIZE];
 341     int be_state;
 342
 343     if (xenstore_read_be_int(xendev, "state", &be_state) == -1) {
 344         xen_be_printf(xendev, 0, "reading backend state failed\n");
 345         return -1;
 346     }
 347
 348     if (be_state != XenbusStateInitialising) {
 349         xen_be_printf(xendev, 0, "initial backend state is wrong (%s)\n",
 350                       xenbus_strstate(be_state));
 351         return -1;
 352     }
 353
 354     xendev->fe = xenstore_read_be_str(xendev, "frontend");
 355     if (xendev->fe == NULL) {
 356         xen_be_printf(xendev, 0, "reading frontend path failed\n");
 357         return -1;
 358     }
 359
 360     /* setup frontend watch */
 361     snprintf(token, sizeof(token), "fe:%p", xendev);
 362     if (!xs_watch(xenstore, xendev->fe, token)) {
 363         xen_be_printf(xendev, 0, "watching frontend path (%s) failed\n",
 364                       xendev->fe);
 365         return -1;
 366     }
 367     xen_be_set_state(xendev, XenbusStateInitialising);
 368
 369     xen_be_backend_changed(xendev, NULL);
 370     xen_be_frontend_changed(xendev, NULL);
 371     return 0;
 372 }
 373
 374 /*
 375  * Try initialize xendev.  Prepare everything the backend can do
 376  * without synchronizing with the frontend.  Fakes hotplug-status.  No
 377  * hotplug involved here because this is about userspace drivers, thus
 378  * there are kernel backend devices which could invoke hotplug.
 379  *
 380  * Goes to InitWait on success.
 381  */
 382 static int xen_be_try_init(struct XenDevice *xendev)
 383 {
 384     int rc = 0;
 385
 386     if (!xendev->online) {
 387         xen_be_printf(xendev, 1, "not online\n");
 388         return -1;
 389     }
 390
 391     if (xendev->ops->init)
 392         rc = xendev->ops->init(xendev);
 393     if (rc != 0) {
 394         xen_be_printf(xendev, 1, "init() failed\n");
 395         return rc;
 396     }
 397
 398     xenstore_write_be_str(xendev, "hotplug-status", "connected");
 399     xen_be_set_state(xendev, XenbusStateInitWait);
 400     return 0;
 401 }
 402
 403 /*
 404  * Try to connect xendev.  Depends on the frontend being ready
 405  * for it (shared ring and evtchn info in xenstore, state being
 406  * Initialised or Connected).
 407  *
 408  * Goes to Connected on success.
 409  */
 410 static int xen_be_try_connect(struct XenDevice *xendev)
 411 {
 412     int rc = 0;
 413
 414     if (xendev->fe_state != XenbusStateInitialised  &&
 415         xendev->fe_state != XenbusStateConnected) {
 416         if (xendev->ops->flags & DEVOPS_FLAG_IGNORE_STATE) {
 417             xen_be_printf(xendev, 2, "frontend not ready, ignoring\n");
 418         } else {
 419             xen_be_printf(xendev, 2, "frontend not ready (yet)\n");
 420             return -1;
 421         }
 422     }
 423
 424     if (xendev->ops->connect)
 425         rc = xendev->ops->connect(xendev);
 426     if (rc != 0) {
 427         xen_be_printf(xendev, 0, "connect() failed\n");
 428         return rc;
 429     }
 430
 431     xen_be_set_state(xendev, XenbusStateConnected);
 432     return 0;
 433 }
 434
 435 /*
 436  * Teardown connection.
 437  *
 438  * Goes to Closed when done.
 439  */
 440 static void xen_be_disconnect(struct XenDevice *xendev, enum xenbus_state state)
 441 {
 442     if (xendev->be_state != XenbusStateClosing &&
 443         xendev->be_state != XenbusStateClosed  &&
 444         xendev->ops->disconnect)
 445         xendev->ops->disconnect(xendev);
 446     if (xendev->be_state != state)
 447         xen_be_set_state(xendev, state);
 448 }
 449
 450 /*
 451  * Try to reset xendev, for reconnection by another frontend instance.
 452  */
 453 static int xen_be_try_reset(struct XenDevice *xendev)
 454 {
 455     if (xendev->fe_state != XenbusStateInitialising)
 456         return -1;
 457
 458     xen_be_printf(xendev, 1, "device reset (for re-connect)\n");
 459     xen_be_set_state(xendev, XenbusStateInitialising);
 460     return 0;
 461 }
 462
 463 /*
 464  * state change dispatcher function
 465  */
 466 void xen_be_check_state(struct XenDevice *xendev)
 467 {
 468     int rc = 0;
 469
 470     /* frontend may request shutdown from almost anywhere */
 471     if (xendev->fe_state == XenbusStateClosing ||
 472         xendev->fe_state == XenbusStateClosed) {
 473         xen_be_disconnect(xendev, xendev->fe_state);
 474         return;
 475     }
 476
 477     /* check for possible backend state transitions */
 478     for (;;) {
 479         switch (xendev->be_state) {
 480         case XenbusStateUnknown:
 481             rc = xen_be_try_setup(xendev);
 482             break;
 483         case XenbusStateInitialising:
 484             rc = xen_be_try_init(xendev);
 485             break;
 486         case XenbusStateInitWait:
 487             rc = xen_be_try_connect(xendev);
 488             break;
 489         case XenbusStateClosed:
 490             rc = xen_be_try_reset(xendev);
 491             break;
 492         default:
 493             rc = -1;
 494         }
 495         if (rc != 0)
 496             break;
 497     }
 498 }
 499
 500 /* ------------------------------------------------------------- */
 501
 502 static int xenstore_scan(const char *type, int dom, struct XenDevOps *ops)
 503 {
 504     struct XenDevice *xendev;
 505     char path[XEN_BUFSIZE], token[XEN_BUFSIZE];
 506     char **dev = NULL, *dom0;
 507     unsigned int cdev, j;
 508
 509     /* setup watch */
 510     dom0 = xs_get_domain_path(xenstore, 0);
 511     snprintf(token, sizeof(token), "be:%p:%d:%p", type, dom, ops);
 512     snprintf(path, sizeof(path), "%s/backend/%s/%d", dom0, type, dom);
 513     free(dom0);
 514     if (!xs_watch(xenstore, path, token)) {
 515         xen_be_printf(NULL, 0, "xen be: watching backend path (%s) failed\n", path);
 516         return -1;
 517     }
 518
 519     /* look for backends */
 520     dev = xs_directory(xenstore, 0, path, &cdev);
 521     if (!dev)
 522         return 0;
 523     for (j = 0; j < cdev; j++) {
 524         xendev = xen_be_get_xendev(type, dom, atoi(dev[j]), ops);
 525         if (xendev == NULL)
 526             continue;
 527         xen_be_check_state(xendev);
 528     }
 529     free(dev);
 530     return 0;
 531 }
 532
 533 static void xenstore_update_be(char *watch, char *type, int dom,
 534                                struct XenDevOps *ops)
 535 {
 536     struct XenDevice *xendev;
 537     char path[XEN_BUFSIZE], *dom0;
 538     unsigned int len, dev;
 539
 540     dom0 = xs_get_domain_path(xenstore, 0);
 541     len = snprintf(path, sizeof(path), "%s/backend/%s/%d", dom0, type, dom);
 542     free(dom0);
 543     if (strncmp(path, watch, len) != 0)
 544         return;
 545     if (sscanf(watch+len, "/%u/%255s", &dev, path) != 2) {
 546         strcpy(path, "");
 547         if (sscanf(watch+len, "/%u", &dev) != 1)
 548             dev = -1;
 549     }
 550     if (dev == -1)
 551         return;
 552
 553     if (0) {
 554         /* FIXME: detect devices being deleted from xenstore ... */
 555         xen_be_del_xendev(dom, dev);
 556     }
 557
 558     xendev = xen_be_get_xendev(type, dom, dev, ops);
 559     if (xendev != NULL) {
 560         xen_be_backend_changed(xendev, path);
 561         xen_be_check_state(xendev);
 562     }
 563 }
 564
 565 static void xenstore_update_fe(char *watch, struct XenDevice *xendev)
 566 {
 567     char *node;
 568     unsigned int len;
 569
 570     len = strlen(xendev->fe);
 571     if (strncmp(xendev->fe, watch, len) != 0)
 572         return;
 573     if (watch[len] != '/')
 574         return;
 575     node = watch + len + 1;
 576
 577     xen_be_frontend_changed(xendev, node);
 578     xen_be_check_state(xendev);
 579 }
 580
 581 static void xenstore_update(void *unused)
 582 {
 583     char **vec = NULL;
 584     intptr_t type, ops, ptr;
 585     unsigned int dom, count;
 586
 587     vec = xs_read_watch(xenstore, &count);
 588     if (vec == NULL)
 589         goto cleanup;
 590
 591     if (sscanf(vec[XS_WATCH_TOKEN], "be:%" PRIxPTR ":%d:%" PRIxPTR,
 592                &type, &dom, &ops) == 3)
 593         xenstore_update_be(vec[XS_WATCH_PATH], (void*)type, dom, (void*)ops);
 594     if (sscanf(vec[XS_WATCH_TOKEN], "fe:%" PRIxPTR, &ptr) == 1)
 595         xenstore_update_fe(vec[XS_WATCH_PATH], (void*)ptr);
 596
 597 cleanup:
 598     qemu_free(vec);
 599 }
 600
 601 static void xen_be_evtchn_event(void *opaque)
 602 {
 603     struct XenDevice *xendev = opaque;
 604     evtchn_port_t port;
 605
 606     port = xc_evtchn_pending(xendev->evtchndev);
 607     if (port != xendev->local_port) {
 608         xen_be_printf(xendev, 0, "xc_evtchn_pending returned %d (expected %d)\n",
 609                       port, xendev->local_port);
 610         return;
 611     }
 612     xc_evtchn_unmask(xendev->evtchndev, port);
 613
 614     if (xendev->ops->event)
 615         xendev->ops->event(xendev);
 616 }
 617
 618 /* -------------------------------------------------------------------- */
 619
 620 int xen_be_init(void)
 621 {
 622     xenstore = xs_daemon_open();
 623     if (!xenstore) {
 624         xen_be_printf(NULL, 0, "can't connect to xenstored\n");
 625         return -1;
 626     }
 627
 628     if (qemu_set_fd_handler(xs_fileno(xenstore), xenstore_update, NULL, NULL) < 0)
 629         goto err;
 630
 631     xen_xc = xc_interface_open();
 632     if (xen_xc == -1) {
 633         xen_be_printf(NULL, 0, "can't open xen interface\n");
 634         goto err;
 635     }
 636     return 0;
 637
 638 err:
 639     qemu_set_fd_handler(xs_fileno(xenstore), NULL, NULL, NULL);
 640     xs_daemon_close(xenstore);
 641     xenstore = NULL;
 642
 643     return -1;
 644 }
 645
 646 int xen_be_register(const char *type, struct XenDevOps *ops)
 647 {
 648     return xenstore_scan(type, xen_domid, ops);
 649 }
 650
 651 int xen_be_bind_evtchn(struct XenDevice *xendev)
 652 {
 653     if (xendev->local_port != -1)
 654         return 0;
 655     xendev->local_port = xc_evtchn_bind_interdomain
 656         (xendev->evtchndev, xendev->dom, xendev->remote_port);
 657     if (xendev->local_port == -1) {
 658         xen_be_printf(xendev, 0, "xc_evtchn_bind_interdomain failed\n");
 659         return -1;
 660     }
 661     xen_be_printf(xendev, 2, "bind evtchn port %d\n", xendev->local_port);
 662     qemu_set_fd_handler(xc_evtchn_fd(xendev->evtchndev),
 663                         xen_be_evtchn_event, NULL, xendev);
 664     return 0;
 665 }
 666
 667 void xen_be_unbind_evtchn(struct XenDevice *xendev)
 668 {
 669     if (xendev->local_port == -1)
 670         return;
 671     qemu_set_fd_handler(xc_evtchn_fd(xendev->evtchndev), NULL, NULL, NULL);
 672     xc_evtchn_unbind(xendev->evtchndev, xendev->local_port);
 673     xen_be_printf(xendev, 2, "unbind evtchn port %d\n", xendev->local_port);
 674     xendev->local_port = -1;
 675 }
 676
 677 int xen_be_send_notify(struct XenDevice *xendev)
 678 {
 679     return xc_evtchn_notify(xendev->evtchndev, xendev->local_port);
 680 }
 681
 682 /*
 683  * msg_level:
 684  *  0 == errors (stderr + logfile).
 685  *  1 == informative debug messages (logfile only).
 686  *  2 == noisy debug messages (logfile only).
 687  *  3 == will flood your log (logfile only).
 688  */
 689 void xen_be_printf(struct XenDevice *xendev, int msg_level, const char *fmt, ...)
 690 {
 691     va_list args;
 692
 693     if (xendev) {
 694         if (msg_level > xendev->debug)
 695             return;
 696         qemu_log("xen be: %s: ", xendev->name);
 697         if (msg_level == 0)
 698             fprintf(stderr, "xen be: %s: ", xendev->name);
 699     } else {
 700         if (msg_level > debug)
 701             return;
 702         qemu_log("xen be core: ");
 703         if (msg_level == 0)
 704             fprintf(stderr, "xen be core: ");
 705     }
 706     va_start(args, fmt);
 707     qemu_log_vprintf(fmt, args);
 708     va_end(args);
 709     if (msg_level == 0) {
 710         va_start(args, fmt);
 711         vfprintf(stderr, fmt, args);
 712         va_end(args);
 713     }
 714     qemu_log_flush();
 715 }