init/main.c

   1 /*
   2  *  linux/init/main.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  *  GK 2/5/95  -  Changed to support mounting root fs via NFS
   7  *  Added initrd & change_root: Werner Almesberger & Hans Lermen, Feb '96
   8  *  Moan early if gcc is old, avoiding bogus kernels - Paul Gortmaker, May '96
   9  *  Simplified starting of init:  Michael A. Griffith <grif@acm.org>
  10  */
  11
  12 #define __KERNEL_SYSCALLS__
  13
  14 #include <linux/config.h>
  15 #include <linux/proc_fs.h>
  16 #include <linux/devfs_fs_kernel.h>
  17 #include <linux/unistd.h>
  18 #include <linux/string.h>
  19 #include <linux/ctype.h>
  20 #include <linux/delay.h>
  21 #include <linux/utsname.h>
  22 #include <linux/ioport.h>
  23 #include <linux/init.h>
  24 #include <linux/raid/md.h>
  25 #include <linux/smp_lock.h>
  26 #include <linux/blk.h>
  27 #include <linux/hdreg.h>
  28 #include <linux/iobuf.h>
  29 #include <linux/bootmem.h>
  30
  31 #include <asm/io.h>
  32 #include <asm/bugs.h>
  33
  34 #ifdef CONFIG_PCI
  35 #include <linux/pci.h>
  36 #endif
  37
  38 #ifdef CONFIG_DIO
  39 #include <linux/dio.h>
  40 #endif
  41
  42 #ifdef CONFIG_ZORRO
  43 #include <linux/zorro.h>
  44 #endif
  45
  46 #ifdef CONFIG_MTRR
  47 #  include <asm/mtrr.h>
  48 #endif
  49
  50 #ifdef CONFIG_3215_CONSOLE
  51 extern int con3215_activate(void);
  52 #endif
  53
  54 #ifdef CONFIG_MAC
  55 extern void nubus_init(void);
  56 #endif
  57
  58 #ifdef CONFIG_ISAPNP
  59 #include <linux/isapnp.h>
  60 #endif
  61
  62 #ifdef CONFIG_IRDA
  63 #include <net/irda/irda_device.h>
  64 #endif
  65
  66 #ifdef CONFIG_X86_IO_APIC
  67 #include <asm/smp.h>
  68 #endif
  69
  70 /*
  71  * Versions of gcc older than that listed below may actually compile
  72  * and link okay, but the end product can have subtle run time bugs.
  73  * To avoid associated bogus bug reports, we flatly refuse to compile
  74  * with a gcc that is known to be too old from the very beginning.
  75  */
  76 #if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 7)
  77 #error sorry, your GCC is too old. It builds incorrect kernels.
  78 #endif
  79
  80 extern char _stext, _etext;
  81 extern char *linux_banner;
  82
  83 extern int console_loglevel;
  84
  85 static int init(void *);
  86
  87 extern void init_IRQ(void);
  88 extern void init_modules(void);
  89 extern void sock_init(void);
  90 extern void fork_init(unsigned long);
  91 extern void mca_init(void);
  92 extern void sbus_init(void);
  93 extern void ppc_init(void);
  94 extern void sysctl_init(void);
  95 extern void filescache_init(void);
  96 extern void signals_init(void);
  97 extern void bdev_init(void);
  98 extern int init_pcmcia_ds(void);
  99 extern int usb_init(void);
 100
 101 extern void free_initmem(void);
 102 extern void filesystem_setup(void);
 103
 104 extern void ecard_init(void);
 105
 106 #if defined(CONFIG_SYSVIPC)
 107 extern void ipc_init(void);
 108 #endif
 109 #if defined(CONFIG_QUOTA)
 110 extern void dquot_init_hash(void);
 111 #endif
 112
 113 /*
 114  * Boot command-line arguments
 115  */
 116 #define MAX_INIT_ARGS 8
 117 #define MAX_INIT_ENVS 8
 118
 119 extern void time_init(void);
 120 extern void softirq_init(void);
 121
 122 int rows, cols;
 123
 124 #ifdef CONFIG_BLK_DEV_INITRD
 125 kdev_t real_root_dev;
 126 #endif
 127
 128 int root_mountflags = MS_RDONLY;
 129 char *execute_command;
 130 char root_device_name[64];
 131
 132
 133 static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
 134 static char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
 135
 136 static int __init profile_setup(char *str)
 137 {
 138     int par;
 139     if (get_option(&str,&par)) prof_shift = par;
 140         return 1;
 141 }
 142
 143 __setup("profile=", profile_setup);
 144
 145
 146 static struct dev_name_struct {
 147         const char *name;
 148         const int num;
 149 } root_dev_names[] __initdata = {
 150         { "nfs",     0x00ff },
 151         { "hda",     0x0300 },
 152         { "hdb",     0x0340 },
 153         { "hdc",     0x1600 },
 154         { "hdd",     0x1640 },
 155         { "hde",     0x2100 },
 156         { "hdf",     0x2140 },
 157         { "hdg",     0x2200 },
 158         { "hdh",     0x2240 },
 159         { "hdi",     0x3800 },
 160         { "hdj",     0x3840 },
 161         { "hdk",     0x3900 },
 162         { "hdl",     0x3940 },
 163         { "hdm",     0x5800 },
 164         { "hdn",     0x5840 },
 165         { "hdo",     0x5900 },
 166         { "hdp",     0x5940 },
 167         { "hdq",     0x5A00 },
 168         { "hdr",     0x5A40 },
 169         { "hds",     0x5B00 },
 170         { "hdt",     0x5B40 },
 171         { "sda",     0x0800 },
 172         { "sdb",     0x0810 },
 173         { "sdc",     0x0820 },
 174         { "sdd",     0x0830 },
 175         { "sde",     0x0840 },
 176         { "sdf",     0x0850 },
 177         { "sdg",     0x0860 },
 178         { "sdh",     0x0870 },
 179         { "sdi",     0x0880 },
 180         { "sdj",     0x0890 },
 181         { "sdk",     0x08a0 },
 182         { "sdl",     0x08b0 },
 183         { "sdm",     0x08c0 },
 184         { "sdn",     0x08d0 },
 185         { "sdo",     0x08e0 },
 186         { "sdp",     0x08f0 },
 187         { "ada",     0x1c00 },
 188         { "adb",     0x1c10 },
 189         { "adc",     0x1c20 },
 190         { "add",     0x1c30 },
 191         { "ade",     0x1c40 },
 192         { "fd",      0x0200 },
 193         { "md",      0x0900 },
 194         { "xda",     0x0d00 },
 195         { "xdb",     0x0d40 },
 196         { "ram",     0x0100 },
 197         { "scd",     0x0b00 },
 198         { "mcd",     0x1700 },
 199         { "cdu535",  0x1800 },
 200         { "sonycd",  0x1800 },
 201         { "aztcd",   0x1d00 },
 202         { "cm206cd", 0x2000 },
 203         { "gscd",    0x1000 },
 204         { "sbpcd",   0x1900 },
 205         { "eda",     0x2400 },
 206         { "edb",     0x2440 },
 207         { "pda",        0x2d00 },
 208         { "pdb",        0x2d10 },
 209         { "pdc",        0x2d20 },
 210         { "pdd",        0x2d30 },
 211         { "pcd",        0x2e00 },
 212         { "pf",         0x2f00 },
 213         { "apblock", APBLOCK_MAJOR << 8},
 214         { "ddv", DDV_MAJOR << 8},
 215         { "jsfd",    JSFD_MAJOR << 8},
 216 #ifdef CONFIG_MDISK
 217         { "mnda", (MDISK_MAJOR << MINORBITS)},
 218         { "mndb", (MDISK_MAJOR << MINORBITS) + 1},
 219         { "mndc", (MDISK_MAJOR << MINORBITS) + 2},
 220         { "mndd", (MDISK_MAJOR << MINORBITS) + 3},
 221         { "mnde", (MDISK_MAJOR << MINORBITS) + 4},
 222         { "mndf", (MDISK_MAJOR << MINORBITS) + 5},
 223         { "mndg", (MDISK_MAJOR << MINORBITS) + 6},
 224         { "mndh", (MDISK_MAJOR << MINORBITS) + 7},
 225 #endif
 226 #ifdef CONFIG_DASD
 227         { "dasda", (DASD_MAJOR << MINORBITS) },
 228         { "dasdb", (DASD_MAJOR << MINORBITS) + (1 << 2) },
 229         { "dasdc", (DASD_MAJOR << MINORBITS) + (2 << 2) },
 230         { "dasdd", (DASD_MAJOR << MINORBITS) + (3 << 2) },
 231         { "dasde", (DASD_MAJOR << MINORBITS) + (4 << 2) },
 232         { "dasdf", (DASD_MAJOR << MINORBITS) + (5 << 2) },
 233         { "dasdg", (DASD_MAJOR << MINORBITS) + (6 << 2) },
 234         { "dasdh", (DASD_MAJOR << MINORBITS) + (7 << 2) },
 235 #endif
 236         { NULL, 0 }
 237 };
 238
 239 kdev_t __init name_to_kdev_t(char *line)
 240 {
 241         int base = 0;
 242
 243         if (strncmp(line,"/dev/",5) == 0) {
 244                 struct dev_name_struct *dev = root_dev_names;
 245                 line += 5;
 246                 do {
 247                         int len = strlen(dev->name);
 248                         if (strncmp(line,dev->name,len) == 0) {
 249                                 line += len;
 250                                 base = dev->num;
 251                                 break;
 252                         }
 253                         dev++;
 254                 } while (dev->name);
 255         }
 256         return to_kdev_t(base + simple_strtoul(line,NULL,base?10:16));
 257 }
 258
 259 static int __init root_dev_setup(char *line)
 260 {
 261         int i;
 262         char ch;
 263
 264         ROOT_DEV = name_to_kdev_t(line);
 265         memset (root_device_name, 0, sizeof root_device_name);
 266         if (strncmp (line, "/dev/", 5) == 0) line += 5;
 267         for (i = 0; i < sizeof root_device_name - 1; ++i)
 268         {
 269             ch = line[i];
 270             if ( isspace (ch) || (ch == ',') || (ch == '\0') ) break;
 271             root_device_name[i] = ch;
 272         }
 273         return 1;
 274 }
 275
 276 __setup("root=", root_dev_setup);
 277
 278 static int __init checksetup(char *line)
 279 {
 280         struct kernel_param *p;
 281
 282         p = &__setup_start;
 283         do {
 284                 int n = strlen(p->str);
 285                 if (!strncmp(line,p->str,n)) {
 286                         if (p->setup_func(line+n))
 287                                 return 1;
 288                 }
 289                 p++;
 290         } while (p < &__setup_end);
 291         return 0;
 292 }
 293
 294 /* this should be approx 2 Bo*oMips to start (note initial shift), and will
 295    still work even if initially too large, it will just take slightly longer */
 296 unsigned long loops_per_sec = (1<<12);
 297
 298 /* This is the number of bits of precision for the loops_per_second.  Each
 299    bit takes on average 1.5/HZ seconds.  This (like the original) is a little
 300    better than 1% */
 301 #define LPS_PREC 8
 302
 303 void __init calibrate_delay(void)
 304 {
 305         unsigned long ticks, loopbit;
 306         int lps_precision = LPS_PREC;
 307
 308         loops_per_sec = (1<<12);
 309
 310         printk("Calibrating delay loop... ");
 311         while (loops_per_sec <<= 1) {
 312                 /* wait for "start of" clock tick */
 313                 ticks = jiffies;
 314                 while (ticks == jiffies)
 315                         /* nothing */;
 316                 /* Go .. */
 317                 ticks = jiffies;
 318                 __delay(loops_per_sec);
 319                 ticks = jiffies - ticks;
 320                 if (ticks)
 321                         break;
 322         }
 323
 324 /* Do a binary approximation to get loops_per_second set to equal one clock
 325    (up to lps_precision bits) */
 326         loops_per_sec >>= 1;
 327         loopbit = loops_per_sec;
 328         while ( lps_precision-- && (loopbit >>= 1) ) {
 329                 loops_per_sec |= loopbit;
 330                 ticks = jiffies;
 331                 while (ticks == jiffies);
 332                 ticks = jiffies;
 333                 __delay(loops_per_sec);
 334                 if (jiffies != ticks)   /* longer than 1 tick */
 335                         loops_per_sec &= ~loopbit;
 336         }
 337
 338 /* finally, adjust loops per second in terms of seconds instead of clocks */
 339         loops_per_sec *= HZ;
 340 /* Round the value and print it */
 341         printk("%lu.%02lu BogoMIPS\n",
 342                 (loops_per_sec+2500)/500000,
 343                 ((loops_per_sec+2500)/5000) % 100);
 344 }
 345
 346 static int __init readonly(char *str)
 347 {
 348         if (*str)
 349                 return 0;
 350         root_mountflags |= MS_RDONLY;
 351         return 1;
 352 }
 353
 354 static int __init readwrite(char *str)
 355 {
 356         if (*str)
 357                 return 0;
 358         root_mountflags &= ~MS_RDONLY;
 359         return 1;
 360 }
 361
 362 static int __init debug_kernel(char *str)
 363 {
 364         if (*str)
 365                 return 0;
 366         console_loglevel = 10;
 367         return 1;
 368 }
 369
 370 static int __init quiet_kernel(char *str)
 371 {
 372         if (*str)
 373                 return 0;
 374         console_loglevel = 4;
 375         return 1;
 376 }
 377
 378 __setup("ro", readonly);
 379 __setup("rw", readwrite);
 380 __setup("debug", debug_kernel);
 381 __setup("quiet", quiet_kernel);
 382
 383 /*
 384  * This is a simple kernel command line parsing function: it parses
 385  * the command line, and fills in the arguments/environment to init
 386  * as appropriate. Any cmd-line option is taken to be an environment
 387  * variable if it contains the character '='.
 388  *
 389  * This routine also checks for options meant for the kernel.
 390  * These options are not given to init - they are for internal kernel use only.
 391  */
 392 static void __init parse_options(char *line)
 393 {
 394         char *next,*quote;
 395         int args, envs;
 396
 397         if (!*line)
 398                 return;
 399         args = 0;
 400         envs = 1;       /* TERM is set to 'linux' by default */
 401         next = line;
 402         while ((line = next) != NULL) {
 403                 quote = strchr(line,'"');
 404                 next = strchr(line, ' ');
 405                 while (next != NULL && quote != NULL && quote < next) {
 406                         /* we found a left quote before the next blank
 407                          * now we have to find the matching right quote
 408                          */
 409                         next = strchr(quote+1, '"');
 410                         if (next != NULL) {
 411                                 quote = strchr(next+1, '"');
 412                                 next = strchr(next+1, ' ');
 413                         }
 414                 }
 415                 if (next != NULL)
 416                         *next++ = 0;
 417                 if (!strncmp(line,"init=",5)) {
 418                         line += 5;
 419                         execute_command = line;
 420                         /* In case LILO is going to boot us with default command line,
 421                          * it prepends "auto" before the whole cmdline which makes
 422                          * the shell think it should execute a script with such name.
 423                          * So we ignore all arguments entered _before_ init=... [MJ]
 424                          */
 425                         args = 0;
 426                         continue;
 427                 }
 428                 if (checksetup(line))
 429                         continue;
 430
 431                 /*
 432                  * Then check if it's an environment variable or
 433                  * an option.
 434                  */
 435                 if (strchr(line,'=')) {
 436                         if (envs >= MAX_INIT_ENVS)
 437                                 break;
 438                         envp_init[++envs] = line;
 439                 } else {
 440                         if (args >= MAX_INIT_ARGS)
 441                                 break;
 442                         if(*line)
 443                         argv_init[++args] = line;
 444                 }
 445         }
 446         argv_init[args+1] = NULL;
 447         envp_init[envs+1] = NULL;
 448 }
 449
 450
 451 extern void setup_arch(char **);
 452 extern void cpu_idle(void);
 453
 454 #ifndef CONFIG_SMP
 455
 456 #ifdef CONFIG_X86_IO_APIC
 457 static void __init smp_init(void)
 458 {
 459         IO_APIC_init_uniprocessor();
 460 }
 461 #else
 462 #define smp_init()      do { } while (0)
 463 #endif
 464
 465 #else
 466
 467 /* Called by boot processor to activate the rest. */
 468 static void __init smp_init(void)
 469 {
 470         /* Get other processors into their bootup holding patterns. */
 471         smp_boot_cpus();
 472         smp_threads_ready=1;
 473         smp_commence();
 474 }
 475
 476 #endif
 477
 478 /*
 479  *      Activate the first processor.
 480  */
 481
 482 asmlinkage void __init start_kernel(void)
 483 {
 484         char * command_line;
 485         unsigned long mempages;
 486         extern char saved_command_line[];
 487 /*
 488  * Interrupts are still disabled. Do necessary setups, then
 489  * enable them
 490  */
 491         lock_kernel();
 492         printk(linux_banner);
 493         setup_arch(&command_line);
 494         printk("Kernel command line: %s\n", saved_command_line);
 495         parse_options(command_line);
 496         trap_init();
 497         init_IRQ();
 498         sched_init();
 499         time_init();
 500         softirq_init();
 501
 502         /*
 503          * HACK ALERT! This is early. We're enabling the console before
 504          * we've done PCI setups etc, and console_init() must be aware of
 505          * this. But we do want output early, in case something goes wrong.
 506          */
 507         console_init();
 508 #ifdef CONFIG_MODULES
 509         init_modules();
 510 #endif
 511         if (prof_shift) {
 512                 unsigned int size;
 513                 /* only text is profiled */
 514                 prof_len = (unsigned long) &_etext - (unsigned long) &_stext;
 515                 prof_len >>= prof_shift;
 516
 517                 size = prof_len * sizeof(unsigned int) + PAGE_SIZE-1;
 518                 prof_buffer = (unsigned int *) alloc_bootmem(size);
 519         }
 520
 521         kmem_cache_init();
 522         sti();
 523         calibrate_delay();
 524 #ifdef CONFIG_BLK_DEV_INITRD
 525         if (initrd_start && !initrd_below_start_ok &&
 526                         initrd_start < min_low_pfn << PAGE_SHIFT) {
 527                 printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
 528                     "disabling it.\n",initrd_start,min_low_pfn << PAGE_SHIFT);
 529                 initrd_start = 0;
 530         }
 531 #endif
 532         mem_init();
 533         kmem_cache_sizes_init();
 534 #ifdef CONFIG_3215_CONSOLE
 535         con3215_activate();
 536 #endif
 537 #ifdef CONFIG_PROC_FS
 538         proc_root_init();
 539 #endif
 540         mempages = num_physpages;
 541
 542         fork_init(mempages);
 543         filescache_init();
 544         dcache_init(mempages);
 545         vma_init();
 546         buffer_init(mempages);
 547         page_cache_init(mempages);
 548         kiobuf_setup();
 549         signals_init();
 550         bdev_init();
 551         inode_init(mempages);
 552         file_table_init();
 553 #if defined(CONFIG_SYSVIPC)
 554         ipc_init();
 555 #endif
 556 #if defined(CONFIG_QUOTA)
 557         dquot_init_hash();
 558 #endif
 559         check_bugs();
 560         printk("POSIX conformance testing by UNIFIX\n");
 561
 562         /*
 563          *      We count on the initial thread going ok
 564          *      Like idlers init is an unlocked kernel thread, which will
 565          *      make syscalls (and thus be locked).
 566          */
 567         smp_init();
 568         kernel_thread(init, NULL, CLONE_FS | CLONE_FILES | CLONE_SIGHAND);
 569         unlock_kernel();
 570         current->need_resched = 1;
 571         cpu_idle();
 572 }
 573
 574 #ifdef CONFIG_BLK_DEV_INITRD
 575 static int do_linuxrc(void * shell)
 576 {
 577         static char *argv[] = { "linuxrc", NULL, };
 578
 579         close(0);close(1);close(2);
 580         setsid();
 581         (void) open("/dev/console",O_RDWR,0);
 582         (void) dup(0);
 583         (void) dup(0);
 584         return execve(shell, argv, envp_init);
 585 }
 586
 587 #endif
 588
 589 struct task_struct *child_reaper = &init_task;
 590
 591 static void __init do_initcalls(void)
 592 {
 593         initcall_t *call;
 594
 595         call = &__initcall_start;
 596         do {
 597                 (*call)();
 598                 call++;
 599         } while (call < &__initcall_end);
 600 }
 601
 602 /*
 603  * Ok, the machine is now initialized. None of the devices
 604  * have been touched yet, but the CPU subsystem is up and
 605  * running, and memory and process management works.
 606  *
 607  * Now we can finally start doing some real work..
 608  */
 609 static void __init do_basic_setup(void)
 610 {
 611 #ifdef CONFIG_BLK_DEV_INITRD
 612         int real_root_mountflags;
 613 #endif
 614
 615         /*
 616          * Tell the world that we're going to be the grim
 617          * reaper of innocent orphaned children.
 618          *
 619          * We don't want people to have to make incorrect
 620          * assumptions about where in the task array this
 621          * can be found.
 622          */
 623         child_reaper = current;
 624
 625 #if defined(CONFIG_MTRR)        /* Do this after SMP initialization */
 626 /*
 627  * We should probably create some architecture-dependent "fixup after
 628  * everything is up" style function where this would belong better
 629  * than in init/main.c..
 630  */
 631         mtrr_init();
 632 #endif
 633
 634 #ifdef CONFIG_SYSCTL
 635         sysctl_init();
 636 #endif
 637
 638         /*
 639          * Ok, at this point all CPU's should be initialized, so
 640          * we can start looking into devices..
 641          */
 642 #ifdef CONFIG_PCI
 643         pci_init();
 644 #endif
 645 #ifdef CONFIG_SBUS
 646         sbus_init();
 647 #endif
 648 #if defined(CONFIG_PPC)
 649         ppc_init();
 650 #endif
 651 #ifdef CONFIG_MCA
 652         mca_init();
 653 #endif
 654 #ifdef CONFIG_ARCH_ACORN
 655         ecard_init();
 656 #endif
 657 #ifdef CONFIG_ZORRO
 658         zorro_init();
 659 #endif
 660 #ifdef CONFIG_DIO
 661         dio_init();
 662 #endif
 663 #ifdef CONFIG_MAC
 664         nubus_init();
 665 #endif
 666 #ifdef CONFIG_ISAPNP
 667         isapnp_init();
 668 #endif
 669 #ifdef CONFIG_USB
 670         usb_init();     /* Do this before doing initcalls, so that we can make
 671                         usbcore initialize here, and all drivers initialize later */
 672 #endif
 673
 674         /* Networking initialization needs a process context */
 675         sock_init();
 676
 677 #ifdef CONFIG_BLK_DEV_INITRD
 678         real_root_dev = ROOT_DEV;
 679         real_root_mountflags = root_mountflags;
 680         if (initrd_start && mount_initrd) root_mountflags &= ~MS_RDONLY;
 681         else mount_initrd =0;
 682 #endif
 683
 684         do_initcalls();
 685
 686         /* .. filesystems .. */
 687         filesystem_setup();
 688
 689 #ifdef CONFIG_IRDA
 690         irda_device_init(); /* Must be done after protocol initialization */
 691 #endif
 692 #ifdef CONFIG_PCMCIA
 693         init_pcmcia_ds();               /* Do this last */
 694 #endif
 695         /* Mount the root filesystem.. */
 696         mount_root();
 697
 698         mount_devfs_fs ();
 699
 700 #ifdef CONFIG_BLK_DEV_INITRD
 701         root_mountflags = real_root_mountflags;
 702         if (mount_initrd && ROOT_DEV != real_root_dev
 703             && MAJOR(ROOT_DEV) == RAMDISK_MAJOR && MINOR(ROOT_DEV) == 0) {
 704                 int error;
 705                 int i, pid;
 706
 707                 pid = kernel_thread(do_linuxrc, "/linuxrc", SIGCHLD);
 708                 if (pid>0)
 709                         while (pid != wait(&i));
 710                 if (MAJOR(real_root_dev) != RAMDISK_MAJOR
 711                      || MINOR(real_root_dev) != 0) {
 712 #ifdef CONFIG_BLK_DEV_MD
 713                         md_run_setup();
 714 #endif
 715                         error = change_root(real_root_dev,"/initrd");
 716                         if (error)
 717                                 printk(KERN_ERR "Change root to /initrd: "
 718                                     "error %d\n",error);
 719                 }
 720         }
 721 #endif
 722 }
 723
 724 static int init(void * unused)
 725 {
 726         lock_kernel();
 727         do_basic_setup();
 728
 729         /*
 730          * Ok, we have completed the initial bootup, and
 731          * we're essentially up and running. Get rid of the
 732          * initmem segments and start the user-mode stuff..
 733          */
 734         free_initmem();
 735         unlock_kernel();
 736
 737         if (open("/dev/console", O_RDWR, 0) < 0)
 738                 printk("Warning: unable to open an initial console.\n");
 739
 740         (void) dup(0);
 741         (void) dup(0);
 742
 743         /*
 744          * We try each of these until one succeeds.
 745          *
 746          * The Bourne shell can be used instead of init if we are
 747          * trying to recover a really broken machine.
 748          */
 749
 750         if (execute_command)
 751                 execve(execute_command,argv_init,envp_init);
 752         execve("/sbin/init",argv_init,envp_init);
 753         execve("/etc/init",argv_init,envp_init);
 754         execve("/bin/init",argv_init,envp_init);
 755         execve("/bin/sh",argv_init,envp_init);
 756         panic("No init found.  Try passing init= option to kernel.");
 757 }