kernel/printk.c

   1 /*
   2  *  linux/kernel/printk.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  * Modified to make sys_syslog() more flexible: added commands to
   7  * return the last 4k of kernel messages, regardless of whether
   8  * they've been read or not.  Added option to suppress kernel printk's
   9  * to the console.  Added hook for sending the console messages
  10  * elsewhere, in preparation for a serial line console (someday).
  11  * Ted Ts'o, 2/11/93.
  12  * Modified for sysctl support, 1/8/97, Chris Horn.
  13  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
  14  *     manfred@colorfullife.com
  15  * Rewrote bits to get rid of console_lock
  16  *      01Mar01 Andrew Morton
  17  */
  18
  19 #include <linux/kernel.h>
  20 #include <linux/mm.h>
  21 #include <linux/tty.h>
  22 #include <linux/tty_driver.h>
  23 #include <linux/console.h>
  24 #include <linux/init.h>
  25 #include <linux/jiffies.h>
  26 #include <linux/nmi.h>
  27 #include <linux/module.h>
  28 #include <linux/moduleparam.h>
  29 #include <linux/interrupt.h>                    /* For in_interrupt() */
  30 #include <linux/delay.h>
  31 #include <linux/smp.h>
  32 #include <linux/security.h>
  33 #include <linux/bootmem.h>
  34 #include <linux/syscalls.h>
  35 #include <linux/kexec.h>
  36
  37 #include <asm/uaccess.h>
  38
  39 /*
  40  * Architectures can override it:
  41  */
  42 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  43 {
  44 }
  45
  46 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  47
  48 /* printk's without a loglevel use this.. */
  49 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  50
  51 /* We show everything that is MORE important than this.. */
  52 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  53 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  54
  55 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  56
  57 int console_printk[4] = {
  58         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  59         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  60         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  61         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  62 };
  63
  64 /*
  65  * Low level drivers may need that to know if they can schedule in
  66  * their unblank() callback or not. So let's export it.
  67  */
  68 int oops_in_progress;
  69 EXPORT_SYMBOL(oops_in_progress);
  70
  71 /*
  72  * console_sem protects the console_drivers list, and also
  73  * provides serialisation for access to the entire console
  74  * driver system.
  75  */
  76 static DECLARE_MUTEX(console_sem);
  77 struct console *console_drivers;
  78 EXPORT_SYMBOL_GPL(console_drivers);
  79
  80 /*
  81  * This is used for debugging the mess that is the VT code by
  82  * keeping track if we have the console semaphore held. It's
  83  * definitely not the perfect debug tool (we don't know if _WE_
  84  * hold it are racing, but it helps tracking those weird code
  85  * path in the console code where we end up in places I want
  86  * locked without the console sempahore held
  87  */
  88 static int console_locked, console_suspended;
  89
  90 /*
  91  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  92  * It is also used in interesting ways to provide interlocking in
  93  * release_console_sem().
  94  */
  95 static DEFINE_SPINLOCK(logbuf_lock);
  96
  97 #define LOG_BUF_MASK (log_buf_len-1)
  98 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  99
 100 /*
 101  * The indices into log_buf are not constrained to log_buf_len - they
 102  * must be masked before subscripting
 103  */
 104 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 105 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 106 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 107
 108 /*
 109  *      Array of consoles built from command line options (console=)
 110  */
 111 struct console_cmdline
 112 {
 113         char    name[8];                        /* Name of the driver       */
 114         int     index;                          /* Minor dev. to use        */
 115         char    *options;                       /* Options for the driver   */
 116 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 117         char    *brl_options;                   /* Options for braille driver */
 118 #endif
 119 };
 120
 121 #define MAX_CMDLINECONSOLES 8
 122
 123 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 124 static int selected_console = -1;
 125 static int preferred_console = -1;
 126 int console_set_on_cmdline;
 127 EXPORT_SYMBOL(console_set_on_cmdline);
 128
 129 /* Flag: console code may call schedule() */
 130 static int console_may_schedule;
 131
 132 #ifdef CONFIG_PRINTK
 133
 134 static char __log_buf[__LOG_BUF_LEN];
 135 static char *log_buf = __log_buf;
 136 static int log_buf_len = __LOG_BUF_LEN;
 137 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 138
 139 #ifdef CONFIG_KEXEC
 140 /*
 141  * This appends the listed symbols to /proc/vmcoreinfo
 142  *
 143  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 144  * obtain access to symbols that are otherwise very difficult to locate.  These
 145  * symbols are specifically used so that utilities can access and extract the
 146  * dmesg log from a vmcore file after a crash.
 147  */
 148 void log_buf_kexec_setup(void)
 149 {
 150         VMCOREINFO_SYMBOL(log_buf);
 151         VMCOREINFO_SYMBOL(log_end);
 152         VMCOREINFO_SYMBOL(log_buf_len);
 153         VMCOREINFO_SYMBOL(logged_chars);
 154 }
 155 #endif
 156
 157 static int __init log_buf_len_setup(char *str)
 158 {
 159         unsigned size = memparse(str, &str);
 160         unsigned long flags;
 161
 162         if (size)
 163                 size = roundup_pow_of_two(size);
 164         if (size > log_buf_len) {
 165                 unsigned start, dest_idx, offset;
 166                 char *new_log_buf;
 167
 168                 new_log_buf = alloc_bootmem(size);
 169                 if (!new_log_buf) {
 170                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 171                         goto out;
 172                 }
 173
 174                 spin_lock_irqsave(&logbuf_lock, flags);
 175                 log_buf_len = size;
 176                 log_buf = new_log_buf;
 177
 178                 offset = start = min(con_start, log_start);
 179                 dest_idx = 0;
 180                 while (start != log_end) {
 181                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 182                         start++;
 183                         dest_idx++;
 184                 }
 185                 log_start -= offset;
 186                 con_start -= offset;
 187                 log_end -= offset;
 188                 spin_unlock_irqrestore(&logbuf_lock, flags);
 189
 190                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 191         }
 192 out:
 193         return 1;
 194 }
 195
 196 __setup("log_buf_len=", log_buf_len_setup);
 197
 198 #ifdef CONFIG_BOOT_PRINTK_DELAY
 199
 200 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 201 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 202
 203 static int __init boot_delay_setup(char *str)
 204 {
 205         unsigned long lpj;
 206         unsigned long long loops_per_msec;
 207
 208         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 209         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 210
 211         get_option(&str, &boot_delay);
 212         if (boot_delay > 10 * 1000)
 213                 boot_delay = 0;
 214
 215         printk_delay_msec = loops_per_msec;
 216         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 217                 "HZ: %d, printk_delay_msec: %llu\n",
 218                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 219         return 1;
 220 }
 221 __setup("boot_delay=", boot_delay_setup);
 222
 223 static void boot_delay_msec(void)
 224 {
 225         unsigned long long k;
 226         unsigned long timeout;
 227
 228         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 229                 return;
 230
 231         k = (unsigned long long)printk_delay_msec * boot_delay;
 232
 233         timeout = jiffies + msecs_to_jiffies(boot_delay);
 234         while (k) {
 235                 k--;
 236                 cpu_relax();
 237                 /*
 238                  * use (volatile) jiffies to prevent
 239                  * compiler reduction; loop termination via jiffies
 240                  * is secondary and may or may not happen.
 241                  */
 242                 if (time_after(jiffies, timeout))
 243                         break;
 244                 touch_nmi_watchdog();
 245         }
 246 }
 247 #else
 248 static inline void boot_delay_msec(void)
 249 {
 250 }
 251 #endif
 252
 253 /*
 254  * Commands to do_syslog:
 255  *
 256  *      0 -- Close the log.  Currently a NOP.
 257  *      1 -- Open the log. Currently a NOP.
 258  *      2 -- Read from the log.
 259  *      3 -- Read all messages remaining in the ring buffer.
 260  *      4 -- Read and clear all messages remaining in the ring buffer
 261  *      5 -- Clear ring buffer.
 262  *      6 -- Disable printk's to console
 263  *      7 -- Enable printk's to console
 264  *      8 -- Set level of messages printed to console
 265  *      9 -- Return number of unread characters in the log buffer
 266  *     10 -- Return size of the log buffer
 267  */
 268 int do_syslog(int type, char __user *buf, int len)
 269 {
 270         unsigned i, j, limit, count;
 271         int do_clear = 0;
 272         char c;
 273         int error = 0;
 274
 275         error = security_syslog(type);
 276         if (error)
 277                 return error;
 278
 279         switch (type) {
 280         case 0:         /* Close log */
 281                 break;
 282         case 1:         /* Open log */
 283                 break;
 284         case 2:         /* Read from log */
 285                 error = -EINVAL;
 286                 if (!buf || len < 0)
 287                         goto out;
 288                 error = 0;
 289                 if (!len)
 290                         goto out;
 291                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 292                         error = -EFAULT;
 293                         goto out;
 294                 }
 295                 error = wait_event_interruptible(log_wait,
 296                                                         (log_start - log_end));
 297                 if (error)
 298                         goto out;
 299                 i = 0;
 300                 spin_lock_irq(&logbuf_lock);
 301                 while (!error && (log_start != log_end) && i < len) {
 302                         c = LOG_BUF(log_start);
 303                         log_start++;
 304                         spin_unlock_irq(&logbuf_lock);
 305                         error = __put_user(c,buf);
 306                         buf++;
 307                         i++;
 308                         cond_resched();
 309                         spin_lock_irq(&logbuf_lock);
 310                 }
 311                 spin_unlock_irq(&logbuf_lock);
 312                 if (!error)
 313                         error = i;
 314                 break;
 315         case 4:         /* Read/clear last kernel messages */
 316                 do_clear = 1;
 317                 /* FALL THRU */
 318         case 3:         /* Read last kernel messages */
 319                 error = -EINVAL;
 320                 if (!buf || len < 0)
 321                         goto out;
 322                 error = 0;
 323                 if (!len)
 324                         goto out;
 325                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 326                         error = -EFAULT;
 327                         goto out;
 328                 }
 329                 count = len;
 330                 if (count > log_buf_len)
 331                         count = log_buf_len;
 332                 spin_lock_irq(&logbuf_lock);
 333                 if (count > logged_chars)
 334                         count = logged_chars;
 335                 if (do_clear)
 336                         logged_chars = 0;
 337                 limit = log_end;
 338                 /*
 339                  * __put_user() could sleep, and while we sleep
 340                  * printk() could overwrite the messages
 341                  * we try to copy to user space. Therefore
 342                  * the messages are copied in reverse. <manfreds>
 343                  */
 344                 for (i = 0; i < count && !error; i++) {
 345                         j = limit-1-i;
 346                         if (j + log_buf_len < log_end)
 347                                 break;
 348                         c = LOG_BUF(j);
 349                         spin_unlock_irq(&logbuf_lock);
 350                         error = __put_user(c,&buf[count-1-i]);
 351                         cond_resched();
 352                         spin_lock_irq(&logbuf_lock);
 353                 }
 354                 spin_unlock_irq(&logbuf_lock);
 355                 if (error)
 356                         break;
 357                 error = i;
 358                 if (i != count) {
 359                         int offset = count-error;
 360                         /* buffer overflow during copy, correct user buffer. */
 361                         for (i = 0; i < error; i++) {
 362                                 if (__get_user(c,&buf[i+offset]) ||
 363                                     __put_user(c,&buf[i])) {
 364                                         error = -EFAULT;
 365                                         break;
 366                                 }
 367                                 cond_resched();
 368                         }
 369                 }
 370                 break;
 371         case 5:         /* Clear ring buffer */
 372                 logged_chars = 0;
 373                 break;
 374         case 6:         /* Disable logging to console */
 375                 console_loglevel = minimum_console_loglevel;
 376                 break;
 377         case 7:         /* Enable logging to console */
 378                 console_loglevel = default_console_loglevel;
 379                 break;
 380         case 8:         /* Set level of messages printed to console */
 381                 error = -EINVAL;
 382                 if (len < 1 || len > 8)
 383                         goto out;
 384                 if (len < minimum_console_loglevel)
 385                         len = minimum_console_loglevel;
 386                 console_loglevel = len;
 387                 error = 0;
 388                 break;
 389         case 9:         /* Number of chars in the log buffer */
 390                 error = log_end - log_start;
 391                 break;
 392         case 10:        /* Size of the log buffer */
 393                 error = log_buf_len;
 394                 break;
 395         default:
 396                 error = -EINVAL;
 397                 break;
 398         }
 399 out:
 400         return error;
 401 }
 402
 403 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 404 {
 405         return do_syslog(type, buf, len);
 406 }
 407
 408 /*
 409  * Call the console drivers on a range of log_buf
 410  */
 411 static void __call_console_drivers(unsigned start, unsigned end)
 412 {
 413         struct console *con;
 414
 415         for (con = console_drivers; con; con = con->next) {
 416                 if ((con->flags & CON_ENABLED) && con->write &&
 417                                 (cpu_online(smp_processor_id()) ||
 418                                 (con->flags & CON_ANYTIME)))
 419                         con->write(con, &LOG_BUF(start), end - start);
 420         }
 421 }
 422
 423 static int __read_mostly ignore_loglevel;
 424
 425 static int __init ignore_loglevel_setup(char *str)
 426 {
 427         ignore_loglevel = 1;
 428         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 429
 430         return 0;
 431 }
 432
 433 early_param("ignore_loglevel", ignore_loglevel_setup);
 434
 435 /*
 436  * Write out chars from start to end - 1 inclusive
 437  */
 438 static void _call_console_drivers(unsigned start,
 439                                 unsigned end, int msg_log_level)
 440 {
 441         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 442                         console_drivers && start != end) {
 443                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 444                         /* wrapped write */
 445                         __call_console_drivers(start & LOG_BUF_MASK,
 446                                                 log_buf_len);
 447                         __call_console_drivers(0, end & LOG_BUF_MASK);
 448                 } else {
 449                         __call_console_drivers(start, end);
 450                 }
 451         }
 452 }
 453
 454 /*
 455  * Call the console drivers, asking them to write out
 456  * log_buf[start] to log_buf[end - 1].
 457  * The console_sem must be held.
 458  */
 459 static void call_console_drivers(unsigned start, unsigned end)
 460 {
 461         unsigned cur_index, start_print;
 462         static int msg_level = -1;
 463
 464         BUG_ON(((int)(start - end)) > 0);
 465
 466         cur_index = start;
 467         start_print = start;
 468         while (cur_index != end) {
 469                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 470                                 LOG_BUF(cur_index + 0) == '<' &&
 471                                 LOG_BUF(cur_index + 1) >= '0' &&
 472                                 LOG_BUF(cur_index + 1) <= '7' &&
 473                                 LOG_BUF(cur_index + 2) == '>') {
 474                         msg_level = LOG_BUF(cur_index + 1) - '0';
 475                         cur_index += 3;
 476                         start_print = cur_index;
 477                 }
 478                 while (cur_index != end) {
 479                         char c = LOG_BUF(cur_index);
 480
 481                         cur_index++;
 482                         if (c == '\n') {
 483                                 if (msg_level < 0) {
 484                                         /*
 485                                          * printk() has already given us loglevel tags in
 486                                          * the buffer.  This code is here in case the
 487                                          * log buffer has wrapped right round and scribbled
 488                                          * on those tags
 489                                          */
 490                                         msg_level = default_message_loglevel;
 491                                 }
 492                                 _call_console_drivers(start_print, cur_index, msg_level);
 493                                 msg_level = -1;
 494                                 start_print = cur_index;
 495                                 break;
 496                         }
 497                 }
 498         }
 499         _call_console_drivers(start_print, end, msg_level);
 500 }
 501
 502 static void emit_log_char(char c)
 503 {
 504         LOG_BUF(log_end) = c;
 505         log_end++;
 506         if (log_end - log_start > log_buf_len)
 507                 log_start = log_end - log_buf_len;
 508         if (log_end - con_start > log_buf_len)
 509                 con_start = log_end - log_buf_len;
 510         if (logged_chars < log_buf_len)
 511                 logged_chars++;
 512 }
 513
 514 /*
 515  * Zap console related locks when oopsing. Only zap at most once
 516  * every 10 seconds, to leave time for slow consoles to print a
 517  * full oops.
 518  */
 519 static void zap_locks(void)
 520 {
 521         static unsigned long oops_timestamp;
 522
 523         if (time_after_eq(jiffies, oops_timestamp) &&
 524                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 525                 return;
 526
 527         oops_timestamp = jiffies;
 528
 529         /* If a crash is occurring, make sure we can't deadlock */
 530         spin_lock_init(&logbuf_lock);
 531         /* And make sure that we print immediately */
 532         init_MUTEX(&console_sem);
 533 }
 534
 535 #if defined(CONFIG_PRINTK_TIME)
 536 static int printk_time = 1;
 537 #else
 538 static int printk_time = 0;
 539 #endif
 540 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 541
 542 /* Check if we have any console registered that can be called early in boot. */
 543 static int have_callable_console(void)
 544 {
 545         struct console *con;
 546
 547         for (con = console_drivers; con; con = con->next)
 548                 if (con->flags & CON_ANYTIME)
 549                         return 1;
 550
 551         return 0;
 552 }
 553
 554 /**
 555  * printk - print a kernel message
 556  * @fmt: format string
 557  *
 558  * This is printk().  It can be called from any context.  We want it to work.
 559  *
 560  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 561  * call the console drivers.  If we fail to get the semaphore we place the output
 562  * into the log buffer and return.  The current holder of the console_sem will
 563  * notice the new output in release_console_sem() and will send it to the
 564  * consoles before releasing the semaphore.
 565  *
 566  * One effect of this deferred printing is that code which calls printk() and
 567  * then changes console_loglevel may break. This is because console_loglevel
 568  * is inspected when the actual printing occurs.
 569  *
 570  * See also:
 571  * printf(3)
 572  *
 573  * See the vsnprintf() documentation for format string extensions over C99.
 574  */
 575
 576 asmlinkage int printk(const char *fmt, ...)
 577 {
 578         va_list args;
 579         int r;
 580
 581         va_start(args, fmt);
 582         r = vprintk(fmt, args);
 583         va_end(args);
 584
 585         return r;
 586 }
 587
 588 /* cpu currently holding logbuf_lock */
 589 static volatile unsigned int printk_cpu = UINT_MAX;
 590
 591 /*
 592  * Can we actually use the console at this time on this cpu?
 593  *
 594  * Console drivers may assume that per-cpu resources have
 595  * been allocated. So unless they're explicitly marked as
 596  * being able to cope (CON_ANYTIME) don't call them until
 597  * this CPU is officially up.
 598  */
 599 static inline int can_use_console(unsigned int cpu)
 600 {
 601         return cpu_online(cpu) || have_callable_console();
 602 }
 603
 604 /*
 605  * Try to get console ownership to actually show the kernel
 606  * messages from a 'printk'. Return true (and with the
 607  * console_semaphore held, and 'console_locked' set) if it
 608  * is successful, false otherwise.
 609  *
 610  * This gets called with the 'logbuf_lock' spinlock held and
 611  * interrupts disabled. It should return with 'lockbuf_lock'
 612  * released but interrupts still disabled.
 613  */
 614 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 615 {
 616         int retval = 0;
 617
 618         if (!try_acquire_console_sem()) {
 619                 retval = 1;
 620
 621                 /*
 622                  * If we can't use the console, we need to release
 623                  * the console semaphore by hand to avoid flushing
 624                  * the buffer. We need to hold the console semaphore
 625                  * in order to do this test safely.
 626                  */
 627                 if (!can_use_console(cpu)) {
 628                         console_locked = 0;
 629                         up(&console_sem);
 630                         retval = 0;
 631                 }
 632         }
 633         printk_cpu = UINT_MAX;
 634         spin_unlock(&logbuf_lock);
 635         return retval;
 636 }
 637 static const char recursion_bug_msg [] =
 638                 KERN_CRIT "BUG: recent printk recursion!\n";
 639 static int recursion_bug;
 640 static int new_text_line = 1;
 641 static char printk_buf[1024];
 642
 643 asmlinkage int vprintk(const char *fmt, va_list args)
 644 {
 645         int printed_len = 0;
 646         int current_log_level = default_message_loglevel;
 647         unsigned long flags;
 648         int this_cpu;
 649         char *p;
 650
 651         boot_delay_msec();
 652
 653         preempt_disable();
 654         /* This stops the holder of console_sem just where we want him */
 655         raw_local_irq_save(flags);
 656         this_cpu = smp_processor_id();
 657
 658         /*
 659          * Ouch, printk recursed into itself!
 660          */
 661         if (unlikely(printk_cpu == this_cpu)) {
 662                 /*
 663                  * If a crash is occurring during printk() on this CPU,
 664                  * then try to get the crash message out but make sure
 665                  * we can't deadlock. Otherwise just return to avoid the
 666                  * recursion and return - but flag the recursion so that
 667                  * it can be printed at the next appropriate moment:
 668                  */
 669                 if (!oops_in_progress) {
 670                         recursion_bug = 1;
 671                         goto out_restore_irqs;
 672                 }
 673                 zap_locks();
 674         }
 675
 676         lockdep_off();
 677         spin_lock(&logbuf_lock);
 678         printk_cpu = this_cpu;
 679
 680         if (recursion_bug) {
 681                 recursion_bug = 0;
 682                 strcpy(printk_buf, recursion_bug_msg);
 683                 printed_len = strlen(recursion_bug_msg);
 684         }
 685         /* Emit the output into the temporary buffer */
 686         printed_len += vscnprintf(printk_buf + printed_len,
 687                                   sizeof(printk_buf) - printed_len, fmt, args);
 688
 689
 690         p = printk_buf;
 691
 692         /* Do we have a loglevel in the string? */
 693         if (p[0] == '<') {
 694                 unsigned char c = p[1];
 695                 if (c && p[2] == '>') {
 696                         switch (c) {
 697                         case '0' ... '7': /* loglevel */
 698                                 current_log_level = c - '0';
 699                                 if (!new_text_line) {
 700                                         emit_log_char('\n');
 701                                         new_text_line = 1;
 702                                 }
 703                         /* Fallthrough - skip the loglevel */
 704                         case 'c': /* KERN_CONT */
 705                                 p += 3;
 706                                 break;
 707                         }
 708                 }
 709         }
 710
 711         /*
 712          * Copy the output into log_buf.  If the caller didn't provide
 713          * appropriate log level tags, we insert them here
 714          */
 715         for ( ; *p; p++) {
 716                 if (new_text_line) {
 717                         /* Always output the token */
 718                         emit_log_char('<');
 719                         emit_log_char(current_log_level + '0');
 720                         emit_log_char('>');
 721                         printed_len += 3;
 722                         new_text_line = 0;
 723
 724                         if (printk_time) {
 725                                 /* Follow the token with the time */
 726                                 char tbuf[50], *tp;
 727                                 unsigned tlen;
 728                                 unsigned long long t;
 729                                 unsigned long nanosec_rem;
 730
 731                                 t = cpu_clock(printk_cpu);
 732                                 nanosec_rem = do_div(t, 1000000000);
 733                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 734                                                 (unsigned long) t,
 735                                                 nanosec_rem / 1000);
 736
 737                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 738                                         emit_log_char(*tp);
 739                                 printed_len += tlen;
 740                         }
 741
 742                         if (!*p)
 743                                 break;
 744                 }
 745
 746                 emit_log_char(*p);
 747                 if (*p == '\n')
 748                         new_text_line = 1;
 749         }
 750
 751         /*
 752          * Try to acquire and then immediately release the
 753          * console semaphore. The release will do all the
 754          * actual magic (print out buffers, wake up klogd,
 755          * etc).
 756          *
 757          * The acquire_console_semaphore_for_printk() function
 758          * will release 'logbuf_lock' regardless of whether it
 759          * actually gets the semaphore or not.
 760          */
 761         if (acquire_console_semaphore_for_printk(this_cpu))
 762                 release_console_sem();
 763
 764         lockdep_on();
 765 out_restore_irqs:
 766         raw_local_irq_restore(flags);
 767
 768         preempt_enable();
 769         return printed_len;
 770 }
 771 EXPORT_SYMBOL(printk);
 772 EXPORT_SYMBOL(vprintk);
 773
 774 #else
 775
 776 static void call_console_drivers(unsigned start, unsigned end)
 777 {
 778 }
 779
 780 #endif
 781
 782 static int __add_preferred_console(char *name, int idx, char *options,
 783                                    char *brl_options)
 784 {
 785         struct console_cmdline *c;
 786         int i;
 787
 788         /*
 789          *      See if this tty is not yet registered, and
 790          *      if we have a slot free.
 791          */
 792         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 793                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 794                           console_cmdline[i].index == idx) {
 795                                 if (!brl_options)
 796                                         selected_console = i;
 797                                 return 0;
 798                 }
 799         if (i == MAX_CMDLINECONSOLES)
 800                 return -E2BIG;
 801         if (!brl_options)
 802                 selected_console = i;
 803         c = &console_cmdline[i];
 804         strlcpy(c->name, name, sizeof(c->name));
 805         c->options = options;
 806 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 807         c->brl_options = brl_options;
 808 #endif
 809         c->index = idx;
 810         return 0;
 811 }
 812 /*
 813  * Set up a list of consoles.  Called from init/main.c
 814  */
 815 static int __init console_setup(char *str)
 816 {
 817         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 818         char *s, *options, *brl_options = NULL;
 819         int idx;
 820
 821 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 822         if (!memcmp(str, "brl,", 4)) {
 823                 brl_options = "";
 824                 str += 4;
 825         } else if (!memcmp(str, "brl=", 4)) {
 826                 brl_options = str + 4;
 827                 str = strchr(brl_options, ',');
 828                 if (!str) {
 829                         printk(KERN_ERR "need port name after brl=\n");
 830                         return 1;
 831                 }
 832                 *(str++) = 0;
 833         }
 834 #endif
 835
 836         /*
 837          * Decode str into name, index, options.
 838          */
 839         if (str[0] >= '0' && str[0] <= '9') {
 840                 strcpy(buf, "ttyS");
 841                 strncpy(buf + 4, str, sizeof(buf) - 5);
 842         } else {
 843                 strncpy(buf, str, sizeof(buf) - 1);
 844         }
 845         buf[sizeof(buf) - 1] = 0;
 846         if ((options = strchr(str, ',')) != NULL)
 847                 *(options++) = 0;
 848 #ifdef __sparc__
 849         if (!strcmp(str, "ttya"))
 850                 strcpy(buf, "ttyS0");
 851         if (!strcmp(str, "ttyb"))
 852                 strcpy(buf, "ttyS1");
 853 #endif
 854         for (s = buf; *s; s++)
 855                 if ((*s >= '0' && *s <= '9') || *s == ',')
 856                         break;
 857         idx = simple_strtoul(s, NULL, 10);
 858         *s = 0;
 859
 860         __add_preferred_console(buf, idx, options, brl_options);
 861         console_set_on_cmdline = 1;
 862         return 1;
 863 }
 864 __setup("console=", console_setup);
 865
 866 /**
 867  * add_preferred_console - add a device to the list of preferred consoles.
 868  * @name: device name
 869  * @idx: device index
 870  * @options: options for this console
 871  *
 872  * The last preferred console added will be used for kernel messages
 873  * and stdin/out/err for init.  Normally this is used by console_setup
 874  * above to handle user-supplied console arguments; however it can also
 875  * be used by arch-specific code either to override the user or more
 876  * commonly to provide a default console (ie from PROM variables) when
 877  * the user has not supplied one.
 878  */
 879 int add_preferred_console(char *name, int idx, char *options)
 880 {
 881         return __add_preferred_console(name, idx, options, NULL);
 882 }
 883
 884 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 885 {
 886         struct console_cmdline *c;
 887         int i;
 888
 889         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 890                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 891                           console_cmdline[i].index == idx) {
 892                                 c = &console_cmdline[i];
 893                                 strlcpy(c->name, name_new, sizeof(c->name));
 894                                 c->name[sizeof(c->name) - 1] = 0;
 895                                 c->options = options;
 896                                 c->index = idx_new;
 897                                 return i;
 898                 }
 899         /* not found */
 900         return -1;
 901 }
 902
 903 int console_suspend_enabled = 1;
 904 EXPORT_SYMBOL(console_suspend_enabled);
 905
 906 static int __init console_suspend_disable(char *str)
 907 {
 908         console_suspend_enabled = 0;
 909         return 1;
 910 }
 911 __setup("no_console_suspend", console_suspend_disable);
 912
 913 /**
 914  * suspend_console - suspend the console subsystem
 915  *
 916  * This disables printk() while we go into suspend states
 917  */
 918 void suspend_console(void)
 919 {
 920         if (!console_suspend_enabled)
 921                 return;
 922         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 923         acquire_console_sem();
 924         console_suspended = 1;
 925         up(&console_sem);
 926 }
 927
 928 void resume_console(void)
 929 {
 930         if (!console_suspend_enabled)
 931                 return;
 932         down(&console_sem);
 933         console_suspended = 0;
 934         release_console_sem();
 935 }
 936
 937 /**
 938  * acquire_console_sem - lock the console system for exclusive use.
 939  *
 940  * Acquires a semaphore which guarantees that the caller has
 941  * exclusive access to the console system and the console_drivers list.
 942  *
 943  * Can sleep, returns nothing.
 944  */
 945 void acquire_console_sem(void)
 946 {
 947         BUG_ON(in_interrupt());
 948         down(&console_sem);
 949         if (console_suspended)
 950                 return;
 951         console_locked = 1;
 952         console_may_schedule = 1;
 953 }
 954 EXPORT_SYMBOL(acquire_console_sem);
 955
 956 int try_acquire_console_sem(void)
 957 {
 958         if (down_trylock(&console_sem))
 959                 return -1;
 960         if (console_suspended) {
 961                 up(&console_sem);
 962                 return -1;
 963         }
 964         console_locked = 1;
 965         console_may_schedule = 0;
 966         return 0;
 967 }
 968 EXPORT_SYMBOL(try_acquire_console_sem);
 969
 970 int is_console_locked(void)
 971 {
 972         return console_locked;
 973 }
 974
 975 static DEFINE_PER_CPU(int, printk_pending);
 976
 977 void printk_tick(void)
 978 {
 979         if (__get_cpu_var(printk_pending)) {
 980                 __get_cpu_var(printk_pending) = 0;
 981                 wake_up_interruptible(&log_wait);
 982         }
 983 }
 984
 985 int printk_needs_cpu(int cpu)
 986 {
 987         return per_cpu(printk_pending, cpu);
 988 }
 989
 990 void wake_up_klogd(void)
 991 {
 992         if (waitqueue_active(&log_wait))
 993                 __raw_get_cpu_var(printk_pending) = 1;
 994 }
 995
 996 /**
 997  * release_console_sem - unlock the console system
 998  *
 999  * Releases the semaphore which the caller holds on the console system
1000  * and the console driver list.
1001  *
1002  * While the semaphore was held, console output may have been buffered
1003  * by printk().  If this is the case, release_console_sem() emits
1004  * the output prior to releasing the semaphore.
1005  *
1006  * If there is output waiting for klogd, we wake it up.
1007  *
1008  * release_console_sem() may be called from any context.
1009  */
1010 void release_console_sem(void)
1011 {
1012         unsigned long flags;
1013         unsigned _con_start, _log_end;
1014         unsigned wake_klogd = 0;
1015
1016         if (console_suspended) {
1017                 up(&console_sem);
1018                 return;
1019         }
1020
1021         console_may_schedule = 0;
1022
1023         for ( ; ; ) {
1024                 spin_lock_irqsave(&logbuf_lock, flags);
1025                 wake_klogd |= log_start - log_end;
1026                 if (con_start == log_end)
1027                         break;                  /* Nothing to print */
1028                 _con_start = con_start;
1029                 _log_end = log_end;
1030                 con_start = log_end;            /* Flush */
1031                 spin_unlock(&logbuf_lock);
1032                 stop_critical_timings();        /* don't trace print latency */
1033                 call_console_drivers(_con_start, _log_end);
1034                 start_critical_timings();
1035                 local_irq_restore(flags);
1036         }
1037         console_locked = 0;
1038         up(&console_sem);
1039         spin_unlock_irqrestore(&logbuf_lock, flags);
1040         if (wake_klogd)
1041                 wake_up_klogd();
1042 }
1043 EXPORT_SYMBOL(release_console_sem);
1044
1045 /**
1046  * console_conditional_schedule - yield the CPU if required
1047  *
1048  * If the console code is currently allowed to sleep, and
1049  * if this CPU should yield the CPU to another task, do
1050  * so here.
1051  *
1052  * Must be called within acquire_console_sem().
1053  */
1054 void __sched console_conditional_schedule(void)
1055 {
1056         if (console_may_schedule)
1057                 cond_resched();
1058 }
1059 EXPORT_SYMBOL(console_conditional_schedule);
1060
1061 void console_print(const char *s)
1062 {
1063         printk(KERN_EMERG "%s", s);
1064 }
1065 EXPORT_SYMBOL(console_print);
1066
1067 void console_unblank(void)
1068 {
1069         struct console *c;
1070
1071         /*
1072          * console_unblank can no longer be called in interrupt context unless
1073          * oops_in_progress is set to 1..
1074          */
1075         if (oops_in_progress) {
1076                 if (down_trylock(&console_sem) != 0)
1077                         return;
1078         } else
1079                 acquire_console_sem();
1080
1081         console_locked = 1;
1082         console_may_schedule = 0;
1083         for (c = console_drivers; c != NULL; c = c->next)
1084                 if ((c->flags & CON_ENABLED) && c->unblank)
1085                         c->unblank();
1086         release_console_sem();
1087 }
1088
1089 /*
1090  * Return the console tty driver structure and its associated index
1091  */
1092 struct tty_driver *console_device(int *index)
1093 {
1094         struct console *c;
1095         struct tty_driver *driver = NULL;
1096
1097         acquire_console_sem();
1098         for (c = console_drivers; c != NULL; c = c->next) {
1099                 if (!c->device)
1100                         continue;
1101                 driver = c->device(c, index);
1102                 if (driver)
1103                         break;
1104         }
1105         release_console_sem();
1106         return driver;
1107 }
1108
1109 /*
1110  * Prevent further output on the passed console device so that (for example)
1111  * serial drivers can disable console output before suspending a port, and can
1112  * re-enable output afterwards.
1113  */
1114 void console_stop(struct console *console)
1115 {
1116         acquire_console_sem();
1117         console->flags &= ~CON_ENABLED;
1118         release_console_sem();
1119 }
1120 EXPORT_SYMBOL(console_stop);
1121
1122 void console_start(struct console *console)
1123 {
1124         acquire_console_sem();
1125         console->flags |= CON_ENABLED;
1126         release_console_sem();
1127 }
1128 EXPORT_SYMBOL(console_start);
1129
1130 /*
1131  * The console driver calls this routine during kernel initialization
1132  * to register the console printing procedure with printk() and to
1133  * print any messages that were printed by the kernel before the
1134  * console driver was initialized.
1135  */
1136 void register_console(struct console *console)
1137 {
1138         int i;
1139         unsigned long flags;
1140         struct console *bootconsole = NULL;
1141
1142         if (console_drivers) {
1143                 if (console->flags & CON_BOOT)
1144                         return;
1145                 if (console_drivers->flags & CON_BOOT)
1146                         bootconsole = console_drivers;
1147         }
1148
1149         if (preferred_console < 0 || bootconsole || !console_drivers)
1150                 preferred_console = selected_console;
1151
1152         if (console->early_setup)
1153                 console->early_setup();
1154
1155         /*
1156          *      See if we want to use this console driver. If we
1157          *      didn't select a console we take the first one
1158          *      that registers here.
1159          */
1160         if (preferred_console < 0) {
1161                 if (console->index < 0)
1162                         console->index = 0;
1163                 if (console->setup == NULL ||
1164                     console->setup(console, NULL) == 0) {
1165                         console->flags |= CON_ENABLED;
1166                         if (console->device) {
1167                                 console->flags |= CON_CONSDEV;
1168                                 preferred_console = 0;
1169                         }
1170                 }
1171         }
1172
1173         /*
1174          *      See if this console matches one we selected on
1175          *      the command line.
1176          */
1177         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1178                         i++) {
1179                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1180                         continue;
1181                 if (console->index >= 0 &&
1182                     console->index != console_cmdline[i].index)
1183                         continue;
1184                 if (console->index < 0)
1185                         console->index = console_cmdline[i].index;
1186 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1187                 if (console_cmdline[i].brl_options) {
1188                         console->flags |= CON_BRL;
1189                         braille_register_console(console,
1190                                         console_cmdline[i].index,
1191                                         console_cmdline[i].options,
1192                                         console_cmdline[i].brl_options);
1193                         return;
1194                 }
1195 #endif
1196                 if (console->setup &&
1197                     console->setup(console, console_cmdline[i].options) != 0)
1198                         break;
1199                 console->flags |= CON_ENABLED;
1200                 console->index = console_cmdline[i].index;
1201                 if (i == selected_console) {
1202                         console->flags |= CON_CONSDEV;
1203                         preferred_console = selected_console;
1204                 }
1205                 break;
1206         }
1207
1208         if (!(console->flags & CON_ENABLED))
1209                 return;
1210
1211         if (bootconsole && (console->flags & CON_CONSDEV)) {
1212                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1213                        bootconsole->name, bootconsole->index,
1214                        console->name, console->index);
1215                 unregister_console(bootconsole);
1216                 console->flags &= ~CON_PRINTBUFFER;
1217         } else {
1218                 printk(KERN_INFO "console [%s%d] enabled\n",
1219                        console->name, console->index);
1220         }
1221
1222         /*
1223          *      Put this console in the list - keep the
1224          *      preferred driver at the head of the list.
1225          */
1226         acquire_console_sem();
1227         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1228                 console->next = console_drivers;
1229                 console_drivers = console;
1230                 if (console->next)
1231                         console->next->flags &= ~CON_CONSDEV;
1232         } else {
1233                 console->next = console_drivers->next;
1234                 console_drivers->next = console;
1235         }
1236         if (console->flags & CON_PRINTBUFFER) {
1237                 /*
1238                  * release_console_sem() will print out the buffered messages
1239                  * for us.
1240                  */
1241                 spin_lock_irqsave(&logbuf_lock, flags);
1242                 con_start = log_start;
1243                 spin_unlock_irqrestore(&logbuf_lock, flags);
1244         }
1245         release_console_sem();
1246 }
1247 EXPORT_SYMBOL(register_console);
1248
1249 int unregister_console(struct console *console)
1250 {
1251         struct console *a, *b;
1252         int res = 1;
1253
1254 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1255         if (console->flags & CON_BRL)
1256                 return braille_unregister_console(console);
1257 #endif
1258
1259         acquire_console_sem();
1260         if (console_drivers == console) {
1261                 console_drivers=console->next;
1262                 res = 0;
1263         } else if (console_drivers) {
1264                 for (a=console_drivers->next, b=console_drivers ;
1265                      a; b=a, a=b->next) {
1266                         if (a == console) {
1267                                 b->next = a->next;
1268                                 res = 0;
1269                                 break;
1270                         }
1271                 }
1272         }
1273
1274         /*
1275          * If this isn't the last console and it has CON_CONSDEV set, we
1276          * need to set it on the next preferred console.
1277          */
1278         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1279                 console_drivers->flags |= CON_CONSDEV;
1280
1281         release_console_sem();
1282         return res;
1283 }
1284 EXPORT_SYMBOL(unregister_console);
1285
1286 static int __init disable_boot_consoles(void)
1287 {
1288         if (console_drivers != NULL) {
1289                 if (console_drivers->flags & CON_BOOT) {
1290                         printk(KERN_INFO "turn off boot console %s%d\n",
1291                                 console_drivers->name, console_drivers->index);
1292                         return unregister_console(console_drivers);
1293                 }
1294         }
1295         return 0;
1296 }
1297 late_initcall(disable_boot_consoles);
1298
1299 #if defined CONFIG_PRINTK
1300
1301 /*
1302  * printk rate limiting, lifted from the networking subsystem.
1303  *
1304  * This enforces a rate limit: not more than 10 kernel messages
1305  * every 5s to make a denial-of-service attack impossible.
1306  */
1307 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1308
1309 int printk_ratelimit(void)
1310 {
1311         return __ratelimit(&printk_ratelimit_state);
1312 }
1313 EXPORT_SYMBOL(printk_ratelimit);
1314
1315 /**
1316  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1317  * @caller_jiffies: pointer to caller's state
1318  * @interval_msecs: minimum interval between prints
1319  *
1320  * printk_timed_ratelimit() returns true if more than @interval_msecs
1321  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1322  * returned true.
1323  */
1324 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1325                         unsigned int interval_msecs)
1326 {
1327         if (*caller_jiffies == 0
1328                         || !time_in_range(jiffies, *caller_jiffies,
1329                                         *caller_jiffies
1330                                         + msecs_to_jiffies(interval_msecs))) {
1331                 *caller_jiffies = jiffies;
1332                 return true;
1333         }
1334         return false;
1335 }
1336 EXPORT_SYMBOL(printk_timed_ratelimit);
1337 #endif