kernel/linux/kni/kni_misc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright(c) 2010-2014 Intel Corporation.
   4  */
   5
   6 #include <linux/version.h>
   7 #include <linux/module.h>
   8 #include <linux/miscdevice.h>
   9 #include <linux/netdevice.h>
  10 #include <linux/etherdevice.h>
  11 #include <linux/pci.h>
  12 #include <linux/kthread.h>
  13 #include <linux/rwsem.h>
  14 #include <linux/mutex.h>
  15 #include <linux/nsproxy.h>
  16 #include <net/net_namespace.h>
  17 #include <net/netns/generic.h>
  18
  19 #include <exec-env/rte_kni_common.h>
  20
  21 #include "compat.h"
  22 #include "kni_dev.h"
  23
  24 MODULE_LICENSE("Dual BSD/GPL");
  25 MODULE_AUTHOR("Intel Corporation");
  26 MODULE_DESCRIPTION("Kernel Module for managing kni devices");
  27
  28 #define KNI_RX_LOOP_NUM 1000
  29
  30 #define KNI_MAX_DEVICES 32
  31
  32 extern const struct pci_device_id ixgbe_pci_tbl[];
  33 extern const struct pci_device_id igb_pci_tbl[];
  34
  35 /* loopback mode */
  36 static char *lo_mode;
  37
  38 /* Kernel thread mode */
  39 static char *kthread_mode;
  40 static uint32_t multiple_kthread_on;
  41
  42 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
  43
  44 static int kni_net_id;
  45
  46 struct kni_net {
  47         unsigned long device_in_use; /* device in use flag */
  48         struct mutex kni_kthread_lock;
  49         struct task_struct *kni_kthread;
  50         struct rw_semaphore kni_list_lock;
  51         struct list_head kni_list_head;
  52 };
  53
  54 static int __net_init
  55 kni_init_net(struct net *net)
  56 {
  57 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
  58         struct kni_net *knet = net_generic(net, kni_net_id);
  59
  60         memset(knet, 0, sizeof(*knet));
  61 #else
  62         struct kni_net *knet;
  63         int ret;
  64
  65         knet = kzalloc(sizeof(struct kni_net), GFP_KERNEL);
  66         if (!knet) {
  67                 ret = -ENOMEM;
  68                 return ret;
  69         }
  70 #endif
  71
  72         /* Clear the bit of device in use */
  73         clear_bit(KNI_DEV_IN_USE_BIT_NUM, &knet->device_in_use);
  74
  75         mutex_init(&knet->kni_kthread_lock);
  76
  77         init_rwsem(&knet->kni_list_lock);
  78         INIT_LIST_HEAD(&knet->kni_list_head);
  79
  80 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
  81         return 0;
  82 #else
  83         ret = net_assign_generic(net, kni_net_id, knet);
  84         if (ret < 0)
  85                 kfree(knet);
  86
  87         return ret;
  88 #endif
  89 }
  90
  91 static void __net_exit
  92 kni_exit_net(struct net *net)
  93 {
  94         struct kni_net *knet __maybe_unused;
  95
  96         knet = net_generic(net, kni_net_id);
  97         mutex_destroy(&knet->kni_kthread_lock);
  98
  99 #ifndef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 100         kfree(knet);
 101 #endif
 102 }
 103
 104 static struct pernet_operations kni_net_ops = {
 105         .init = kni_init_net,
 106         .exit = kni_exit_net,
 107 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 108         .id   = &kni_net_id,
 109         .size = sizeof(struct kni_net),
 110 #endif
 111 };
 112
 113 static int
 114 kni_thread_single(void *data)
 115 {
 116         struct kni_net *knet = data;
 117         int j;
 118         struct kni_dev *dev;
 119
 120         while (!kthread_should_stop()) {
 121                 down_read(&knet->kni_list_lock);
 122                 for (j = 0; j < KNI_RX_LOOP_NUM; j++) {
 123                         list_for_each_entry(dev, &knet->kni_list_head, list) {
 124                                 kni_net_rx(dev);
 125                                 kni_net_poll_resp(dev);
 126                         }
 127                 }
 128                 up_read(&knet->kni_list_lock);
 129 #ifdef RTE_KNI_PREEMPT_DEFAULT
 130                 /* reschedule out for a while */
 131                 schedule_timeout_interruptible(
 132                         usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
 133 #endif
 134         }
 135
 136         return 0;
 137 }
 138
 139 static int
 140 kni_thread_multiple(void *param)
 141 {
 142         int j;
 143         struct kni_dev *dev = param;
 144
 145         while (!kthread_should_stop()) {
 146                 for (j = 0; j < KNI_RX_LOOP_NUM; j++) {
 147                         kni_net_rx(dev);
 148                         kni_net_poll_resp(dev);
 149                 }
 150 #ifdef RTE_KNI_PREEMPT_DEFAULT
 151                 schedule_timeout_interruptible(
 152                         usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
 153 #endif
 154         }
 155
 156         return 0;
 157 }
 158
 159 static int
 160 kni_open(struct inode *inode, struct file *file)
 161 {
 162         struct net *net = current->nsproxy->net_ns;
 163         struct kni_net *knet = net_generic(net, kni_net_id);
 164
 165         /* kni device can be opened by one user only per netns */
 166         if (test_and_set_bit(KNI_DEV_IN_USE_BIT_NUM, &knet->device_in_use))
 167                 return -EBUSY;
 168
 169         file->private_data = get_net(net);
 170         pr_debug("/dev/kni opened\n");
 171
 172         return 0;
 173 }
 174
 175 static int
 176 kni_dev_remove(struct kni_dev *dev)
 177 {
 178         if (!dev)
 179                 return -ENODEV;
 180
 181 #ifdef RTE_KNI_KMOD_ETHTOOL
 182         if (dev->pci_dev) {
 183                 if (pci_match_id(ixgbe_pci_tbl, dev->pci_dev))
 184                         ixgbe_kni_remove(dev->pci_dev);
 185                 else if (pci_match_id(igb_pci_tbl, dev->pci_dev))
 186                         igb_kni_remove(dev->pci_dev);
 187         }
 188 #endif
 189
 190         if (dev->net_dev) {
 191                 unregister_netdev(dev->net_dev);
 192                 free_netdev(dev->net_dev);
 193         }
 194
 195         kni_net_release_fifo_phy(dev);
 196
 197         return 0;
 198 }
 199
 200 static int
 201 kni_release(struct inode *inode, struct file *file)
 202 {
 203         struct net *net = file->private_data;
 204         struct kni_net *knet = net_generic(net, kni_net_id);
 205         struct kni_dev *dev, *n;
 206
 207         /* Stop kernel thread for single mode */
 208         if (multiple_kthread_on == 0) {
 209                 mutex_lock(&knet->kni_kthread_lock);
 210                 /* Stop kernel thread */
 211                 if (knet->kni_kthread != NULL) {
 212                         kthread_stop(knet->kni_kthread);
 213                         knet->kni_kthread = NULL;
 214                 }
 215                 mutex_unlock(&knet->kni_kthread_lock);
 216         }
 217
 218         down_write(&knet->kni_list_lock);
 219         list_for_each_entry_safe(dev, n, &knet->kni_list_head, list) {
 220                 /* Stop kernel thread for multiple mode */
 221                 if (multiple_kthread_on && dev->pthread != NULL) {
 222                         kthread_stop(dev->pthread);
 223                         dev->pthread = NULL;
 224                 }
 225
 226                 kni_dev_remove(dev);
 227                 list_del(&dev->list);
 228         }
 229         up_write(&knet->kni_list_lock);
 230
 231         /* Clear the bit of device in use */
 232         clear_bit(KNI_DEV_IN_USE_BIT_NUM, &knet->device_in_use);
 233
 234         put_net(net);
 235         pr_debug("/dev/kni closed\n");
 236
 237         return 0;
 238 }
 239
 240 static int
 241 kni_check_param(struct kni_dev *kni, struct rte_kni_device_info *dev)
 242 {
 243         if (!kni || !dev)
 244                 return -1;
 245
 246         /* Check if network name has been used */
 247         if (!strncmp(kni->name, dev->name, RTE_KNI_NAMESIZE)) {
 248                 pr_err("KNI name %s duplicated\n", dev->name);
 249                 return -1;
 250         }
 251
 252         return 0;
 253 }
 254
 255 static int
 256 kni_run_thread(struct kni_net *knet, struct kni_dev *kni, uint8_t force_bind)
 257 {
 258         /**
 259          * Create a new kernel thread for multiple mode, set its core affinity,
 260          * and finally wake it up.
 261          */
 262         if (multiple_kthread_on) {
 263                 kni->pthread = kthread_create(kni_thread_multiple,
 264                         (void *)kni, "kni_%s", kni->name);
 265                 if (IS_ERR(kni->pthread)) {
 266                         kni_dev_remove(kni);
 267                         return -ECANCELED;
 268                 }
 269
 270                 if (force_bind)
 271                         kthread_bind(kni->pthread, kni->core_id);
 272                 wake_up_process(kni->pthread);
 273         } else {
 274                 mutex_lock(&knet->kni_kthread_lock);
 275
 276                 if (knet->kni_kthread == NULL) {
 277                         knet->kni_kthread = kthread_create(kni_thread_single,
 278                                 (void *)knet, "kni_single");
 279                         if (IS_ERR(knet->kni_kthread)) {
 280                                 mutex_unlock(&knet->kni_kthread_lock);
 281                                 kni_dev_remove(kni);
 282                                 return -ECANCELED;
 283                         }
 284
 285                         if (force_bind)
 286                                 kthread_bind(knet->kni_kthread, kni->core_id);
 287                         wake_up_process(knet->kni_kthread);
 288                 }
 289
 290                 mutex_unlock(&knet->kni_kthread_lock);
 291         }
 292
 293         return 0;
 294 }
 295
 296 static int
 297 kni_ioctl_create(struct net *net, uint32_t ioctl_num,
 298                 unsigned long ioctl_param)
 299 {
 300         struct kni_net *knet = net_generic(net, kni_net_id);
 301         int ret;
 302         struct rte_kni_device_info dev_info;
 303         struct net_device *net_dev = NULL;
 304         struct kni_dev *kni, *dev, *n;
 305 #ifdef RTE_KNI_KMOD_ETHTOOL
 306         struct pci_dev *found_pci = NULL;
 307         struct net_device *lad_dev = NULL;
 308         struct pci_dev *pci = NULL;
 309 #endif
 310
 311         pr_info("Creating kni...\n");
 312         /* Check the buffer size, to avoid warning */
 313         if (_IOC_SIZE(ioctl_num) > sizeof(dev_info))
 314                 return -EINVAL;
 315
 316         /* Copy kni info from user space */
 317         ret = copy_from_user(&dev_info, (void *)ioctl_param, sizeof(dev_info));
 318         if (ret) {
 319                 pr_err("copy_from_user in kni_ioctl_create");
 320                 return -EIO;
 321         }
 322
 323         /* Check if name is zero-ended */
 324         if (strnlen(dev_info.name, sizeof(dev_info.name)) == sizeof(dev_info.name)) {
 325                 pr_err("kni.name not zero-terminated");
 326                 return -EINVAL;
 327         }
 328
 329         /**
 330          * Check if the cpu core id is valid for binding.
 331          */
 332         if (dev_info.force_bind && !cpu_online(dev_info.core_id)) {
 333                 pr_err("cpu %u is not online\n", dev_info.core_id);
 334                 return -EINVAL;
 335         }
 336
 337         /* Check if it has been created */
 338         down_read(&knet->kni_list_lock);
 339         list_for_each_entry_safe(dev, n, &knet->kni_list_head, list) {
 340                 if (kni_check_param(dev, &dev_info) < 0) {
 341                         up_read(&knet->kni_list_lock);
 342                         return -EINVAL;
 343                 }
 344         }
 345         up_read(&knet->kni_list_lock);
 346
 347         net_dev = alloc_netdev(sizeof(struct kni_dev), dev_info.name,
 348 #ifdef NET_NAME_USER
 349                                                         NET_NAME_USER,
 350 #endif
 351                                                         kni_net_init);
 352         if (net_dev == NULL) {
 353                 pr_err("error allocating device \"%s\"\n", dev_info.name);
 354                 return -EBUSY;
 355         }
 356
 357         dev_net_set(net_dev, net);
 358
 359         kni = netdev_priv(net_dev);
 360
 361         kni->net_dev = net_dev;
 362         kni->group_id = dev_info.group_id;
 363         kni->core_id = dev_info.core_id;
 364         strncpy(kni->name, dev_info.name, RTE_KNI_NAMESIZE);
 365
 366         /* Translate user space info into kernel space info */
 367         kni->tx_q = phys_to_virt(dev_info.tx_phys);
 368         kni->rx_q = phys_to_virt(dev_info.rx_phys);
 369         kni->alloc_q = phys_to_virt(dev_info.alloc_phys);
 370         kni->free_q = phys_to_virt(dev_info.free_phys);
 371
 372         kni->req_q = phys_to_virt(dev_info.req_phys);
 373         kni->resp_q = phys_to_virt(dev_info.resp_phys);
 374         kni->sync_va = dev_info.sync_va;
 375         kni->sync_kva = phys_to_virt(dev_info.sync_phys);
 376
 377         kni->mbuf_size = dev_info.mbuf_size;
 378
 379         pr_debug("tx_phys:      0x%016llx, tx_q addr:      0x%p\n",
 380                 (unsigned long long) dev_info.tx_phys, kni->tx_q);
 381         pr_debug("rx_phys:      0x%016llx, rx_q addr:      0x%p\n",
 382                 (unsigned long long) dev_info.rx_phys, kni->rx_q);
 383         pr_debug("alloc_phys:   0x%016llx, alloc_q addr:   0x%p\n",
 384                 (unsigned long long) dev_info.alloc_phys, kni->alloc_q);
 385         pr_debug("free_phys:    0x%016llx, free_q addr:    0x%p\n",
 386                 (unsigned long long) dev_info.free_phys, kni->free_q);
 387         pr_debug("req_phys:     0x%016llx, req_q addr:     0x%p\n",
 388                 (unsigned long long) dev_info.req_phys, kni->req_q);
 389         pr_debug("resp_phys:    0x%016llx, resp_q addr:    0x%p\n",
 390                 (unsigned long long) dev_info.resp_phys, kni->resp_q);
 391         pr_debug("mbuf_size:    %u\n", kni->mbuf_size);
 392
 393         pr_debug("PCI: %02x:%02x.%02x %04x:%04x\n",
 394                                         dev_info.bus,
 395                                         dev_info.devid,
 396                                         dev_info.function,
 397                                         dev_info.vendor_id,
 398                                         dev_info.device_id);
 399 #ifdef RTE_KNI_KMOD_ETHTOOL
 400         pci = pci_get_device(dev_info.vendor_id, dev_info.device_id, NULL);
 401
 402         /* Support Ethtool */
 403         while (pci) {
 404                 pr_debug("pci_bus: %02x:%02x:%02x\n",
 405                                         pci->bus->number,
 406                                         PCI_SLOT(pci->devfn),
 407                                         PCI_FUNC(pci->devfn));
 408
 409                 if ((pci->bus->number == dev_info.bus) &&
 410                         (PCI_SLOT(pci->devfn) == dev_info.devid) &&
 411                         (PCI_FUNC(pci->devfn) == dev_info.function)) {
 412                         found_pci = pci;
 413
 414                         if (pci_match_id(ixgbe_pci_tbl, found_pci))
 415                                 ret = ixgbe_kni_probe(found_pci, &lad_dev);
 416                         else if (pci_match_id(igb_pci_tbl, found_pci))
 417                                 ret = igb_kni_probe(found_pci, &lad_dev);
 418                         else
 419                                 ret = -1;
 420
 421                         pr_debug("PCI found: pci=0x%p, lad_dev=0x%p\n",
 422                                                         pci, lad_dev);
 423                         if (ret == 0) {
 424                                 kni->lad_dev = lad_dev;
 425                                 kni_set_ethtool_ops(kni->net_dev);
 426                         } else {
 427                                 pr_err("Device not supported by ethtool");
 428                                 kni->lad_dev = NULL;
 429                         }
 430
 431                         kni->pci_dev = found_pci;
 432                         kni->device_id = dev_info.device_id;
 433                         break;
 434                 }
 435                 pci = pci_get_device(dev_info.vendor_id,
 436                                 dev_info.device_id, pci);
 437         }
 438         if (pci)
 439                 pci_dev_put(pci);
 440 #endif
 441
 442         if (kni->lad_dev)
 443                 ether_addr_copy(net_dev->dev_addr, kni->lad_dev->dev_addr);
 444         else {
 445                 /* if user has provided a valid mac address */
 446                 if (is_valid_ether_addr((unsigned char *)(dev_info.mac_addr)))
 447                         memcpy(net_dev->dev_addr, dev_info.mac_addr, ETH_ALEN);
 448                 else
 449                         /*
 450                          * Generate random mac address. eth_random_addr() is the
 451                          * newer version of generating mac address in kernel.
 452                          */
 453                         random_ether_addr(net_dev->dev_addr);
 454         }
 455
 456         if (dev_info.mtu)
 457                 net_dev->mtu = dev_info.mtu;
 458
 459         ret = register_netdev(net_dev);
 460         if (ret) {
 461                 pr_err("error %i registering device \"%s\"\n",
 462                                         ret, dev_info.name);
 463                 kni->net_dev = NULL;
 464                 kni_dev_remove(kni);
 465                 free_netdev(net_dev);
 466                 return -ENODEV;
 467         }
 468
 469         ret = kni_run_thread(knet, kni, dev_info.force_bind);
 470         if (ret != 0)
 471                 return ret;
 472
 473         down_write(&knet->kni_list_lock);
 474         list_add(&kni->list, &knet->kni_list_head);
 475         up_write(&knet->kni_list_lock);
 476
 477         return 0;
 478 }
 479
 480 static int
 481 kni_ioctl_release(struct net *net, uint32_t ioctl_num,
 482                 unsigned long ioctl_param)
 483 {
 484         struct kni_net *knet = net_generic(net, kni_net_id);
 485         int ret = -EINVAL;
 486         struct kni_dev *dev, *n;
 487         struct rte_kni_device_info dev_info;
 488
 489         if (_IOC_SIZE(ioctl_num) > sizeof(dev_info))
 490                 return -EINVAL;
 491
 492         ret = copy_from_user(&dev_info, (void *)ioctl_param, sizeof(dev_info));
 493         if (ret) {
 494                 pr_err("copy_from_user in kni_ioctl_release");
 495                 return -EIO;
 496         }
 497
 498         /* Release the network device according to its name */
 499         if (strlen(dev_info.name) == 0)
 500                 return ret;
 501
 502         down_write(&knet->kni_list_lock);
 503         list_for_each_entry_safe(dev, n, &knet->kni_list_head, list) {
 504                 if (strncmp(dev->name, dev_info.name, RTE_KNI_NAMESIZE) != 0)
 505                         continue;
 506
 507                 if (multiple_kthread_on && dev->pthread != NULL) {
 508                         kthread_stop(dev->pthread);
 509                         dev->pthread = NULL;
 510                 }
 511
 512                 kni_dev_remove(dev);
 513                 list_del(&dev->list);
 514                 ret = 0;
 515                 break;
 516         }
 517         up_write(&knet->kni_list_lock);
 518         pr_info("%s release kni named %s\n",
 519                 (ret == 0 ? "Successfully" : "Unsuccessfully"), dev_info.name);
 520
 521         return ret;
 522 }
 523
 524 static int
 525 kni_ioctl(struct inode *inode, uint32_t ioctl_num, unsigned long ioctl_param)
 526 {
 527         int ret = -EINVAL;
 528         struct net *net = current->nsproxy->net_ns;
 529
 530         pr_debug("IOCTL num=0x%0x param=0x%0lx\n", ioctl_num, ioctl_param);
 531
 532         /*
 533          * Switch according to the ioctl called
 534          */
 535         switch (_IOC_NR(ioctl_num)) {
 536         case _IOC_NR(RTE_KNI_IOCTL_TEST):
 537                 /* For test only, not used */
 538                 break;
 539         case _IOC_NR(RTE_KNI_IOCTL_CREATE):
 540                 ret = kni_ioctl_create(net, ioctl_num, ioctl_param);
 541                 break;
 542         case _IOC_NR(RTE_KNI_IOCTL_RELEASE):
 543                 ret = kni_ioctl_release(net, ioctl_num, ioctl_param);
 544                 break;
 545         default:
 546                 pr_debug("IOCTL default\n");
 547                 break;
 548         }
 549
 550         return ret;
 551 }
 552
 553 static int
 554 kni_compat_ioctl(struct inode *inode, uint32_t ioctl_num,
 555                 unsigned long ioctl_param)
 556 {
 557         /* 32 bits app on 64 bits OS to be supported later */
 558         pr_debug("Not implemented.\n");
 559
 560         return -EINVAL;
 561 }
 562
 563 static const struct file_operations kni_fops = {
 564         .owner = THIS_MODULE,
 565         .open = kni_open,
 566         .release = kni_release,
 567         .unlocked_ioctl = (void *)kni_ioctl,
 568         .compat_ioctl = (void *)kni_compat_ioctl,
 569 };
 570
 571 static struct miscdevice kni_misc = {
 572         .minor = MISC_DYNAMIC_MINOR,
 573         .name = KNI_DEVICE,
 574         .fops = &kni_fops,
 575 };
 576
 577 static int __init
 578 kni_parse_kthread_mode(void)
 579 {
 580         if (!kthread_mode)
 581                 return 0;
 582
 583         if (strcmp(kthread_mode, "single") == 0)
 584                 return 0;
 585         else if (strcmp(kthread_mode, "multiple") == 0)
 586                 multiple_kthread_on = 1;
 587         else
 588                 return -1;
 589
 590         return 0;
 591 }
 592
 593 static int __init
 594 kni_init(void)
 595 {
 596         int rc;
 597
 598         if (kni_parse_kthread_mode() < 0) {
 599                 pr_err("Invalid parameter for kthread_mode\n");
 600                 return -EINVAL;
 601         }
 602
 603         if (multiple_kthread_on == 0)
 604                 pr_debug("Single kernel thread for all KNI devices\n");
 605         else
 606                 pr_debug("Multiple kernel thread mode enabled\n");
 607
 608 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 609         rc = register_pernet_subsys(&kni_net_ops);
 610 #else
 611         rc = register_pernet_gen_subsys(&kni_net_id, &kni_net_ops);
 612 #endif
 613         if (rc)
 614                 return -EPERM;
 615
 616         rc = misc_register(&kni_misc);
 617         if (rc != 0) {
 618                 pr_err("Misc registration failed\n");
 619                 goto out;
 620         }
 621
 622         /* Configure the lo mode according to the input parameter */
 623         kni_net_config_lo_mode(lo_mode);
 624
 625         return 0;
 626
 627 out:
 628 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 629         unregister_pernet_subsys(&kni_net_ops);
 630 #else
 631         unregister_pernet_gen_subsys(kni_net_id, &kni_net_ops);
 632 #endif
 633         return rc;
 634 }
 635
 636 static void __exit
 637 kni_exit(void)
 638 {
 639         misc_deregister(&kni_misc);
 640 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 641         unregister_pernet_subsys(&kni_net_ops);
 642 #else
 643         unregister_pernet_gen_subsys(kni_net_id, &kni_net_ops);
 644 #endif
 645 }
 646
 647 module_init(kni_init);
 648 module_exit(kni_exit);
 649
 650 module_param(lo_mode, charp, S_IRUGO | S_IWUSR);
 651 MODULE_PARM_DESC(lo_mode,
 652 "KNI loopback mode (default=lo_mode_none):\n"
 653 "    lo_mode_none        Kernel loopback disabled\n"
 654 "    lo_mode_fifo        Enable kernel loopback with fifo\n"
 655 "    lo_mode_fifo_skb    Enable kernel loopback with fifo and skb buffer\n"
 656 "\n"
 657 );
 658
 659 module_param(kthread_mode, charp, S_IRUGO);
 660 MODULE_PARM_DESC(kthread_mode,
 661 "Kernel thread mode (default=single):\n"
 662 "    single    Single kernel thread mode enabled.\n"
 663 "    multiple  Multiple kernel thread mode enabled.\n"
 664 "\n"
 665 );