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 #include <linux/ratelimit.h>
  37 #include <linux/kmsg_dump.h>
  38
  39 #include <asm/uaccess.h>
  40
  41 /*
  42  * for_each_console() allows you to iterate on each console
  43  */
  44 #define for_each_console(con) \
  45         for (con = console_drivers; con != NULL; con = con->next)
  46
  47 /*
  48  * Architectures can override it:
  49  */
  50 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  51 {
  52 }
  53
  54 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  55
  56 /* printk's without a loglevel use this.. */
  57 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  58
  59 /* We show everything that is MORE important than this.. */
  60 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  61 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  62
  63 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  64
  65 int console_printk[4] = {
  66         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  67         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  68         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  69         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  70 };
  71
  72 static int saved_console_loglevel = -1;
  73
  74 /*
  75  * Low level drivers may need that to know if they can schedule in
  76  * their unblank() callback or not. So let's export it.
  77  */
  78 int oops_in_progress;
  79 EXPORT_SYMBOL(oops_in_progress);
  80
  81 /*
  82  * console_sem protects the console_drivers list, and also
  83  * provides serialisation for access to the entire console
  84  * driver system.
  85  */
  86 static DECLARE_MUTEX(console_sem);
  87 struct console *console_drivers;
  88 EXPORT_SYMBOL_GPL(console_drivers);
  89
  90 /*
  91  * This is used for debugging the mess that is the VT code by
  92  * keeping track if we have the console semaphore held. It's
  93  * definitely not the perfect debug tool (we don't know if _WE_
  94  * hold it are racing, but it helps tracking those weird code
  95  * path in the console code where we end up in places I want
  96  * locked without the console sempahore held
  97  */
  98 static int console_locked, console_suspended;
  99
 100 /*
 101  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
 102  * It is also used in interesting ways to provide interlocking in
 103  * release_console_sem().
 104  */
 105 static DEFINE_SPINLOCK(logbuf_lock);
 106
 107 #define LOG_BUF_MASK (log_buf_len-1)
 108 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 109
 110 /*
 111  * The indices into log_buf are not constrained to log_buf_len - they
 112  * must be masked before subscripting
 113  */
 114 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 115 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 116 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 117
 118 /*
 119  *      Array of consoles built from command line options (console=)
 120  */
 121 struct console_cmdline
 122 {
 123         char    name[8];                        /* Name of the driver       */
 124         int     index;                          /* Minor dev. to use        */
 125         char    *options;                       /* Options for the driver   */
 126 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 127         char    *brl_options;                   /* Options for braille driver */
 128 #endif
 129 };
 130
 131 #define MAX_CMDLINECONSOLES 8
 132
 133 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 134 static int selected_console = -1;
 135 static int preferred_console = -1;
 136 int console_set_on_cmdline;
 137 EXPORT_SYMBOL(console_set_on_cmdline);
 138
 139 /* Flag: console code may call schedule() */
 140 static int console_may_schedule;
 141
 142 #ifdef CONFIG_PRINTK
 143
 144 static char __log_buf[__LOG_BUF_LEN];
 145 static char *log_buf = __log_buf;
 146 static int log_buf_len = __LOG_BUF_LEN;
 147 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 148
 149 #ifdef CONFIG_KEXEC
 150 /*
 151  * This appends the listed symbols to /proc/vmcoreinfo
 152  *
 153  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 154  * obtain access to symbols that are otherwise very difficult to locate.  These
 155  * symbols are specifically used so that utilities can access and extract the
 156  * dmesg log from a vmcore file after a crash.
 157  */
 158 void log_buf_kexec_setup(void)
 159 {
 160         VMCOREINFO_SYMBOL(log_buf);
 161         VMCOREINFO_SYMBOL(log_end);
 162         VMCOREINFO_SYMBOL(log_buf_len);
 163         VMCOREINFO_SYMBOL(logged_chars);
 164 }
 165 #endif
 166
 167 static int __init log_buf_len_setup(char *str)
 168 {
 169         unsigned size = memparse(str, &str);
 170         unsigned long flags;
 171
 172         if (size)
 173                 size = roundup_pow_of_two(size);
 174         if (size > log_buf_len) {
 175                 unsigned start, dest_idx, offset;
 176                 char *new_log_buf;
 177
 178                 new_log_buf = alloc_bootmem(size);
 179                 if (!new_log_buf) {
 180                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 181                         goto out;
 182                 }
 183
 184                 spin_lock_irqsave(&logbuf_lock, flags);
 185                 log_buf_len = size;
 186                 log_buf = new_log_buf;
 187
 188                 offset = start = min(con_start, log_start);
 189                 dest_idx = 0;
 190                 while (start != log_end) {
 191                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 192                         start++;
 193                         dest_idx++;
 194                 }
 195                 log_start -= offset;
 196                 con_start -= offset;
 197                 log_end -= offset;
 198                 spin_unlock_irqrestore(&logbuf_lock, flags);
 199
 200                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 201         }
 202 out:
 203         return 1;
 204 }
 205
 206 __setup("log_buf_len=", log_buf_len_setup);
 207
 208 #ifdef CONFIG_BOOT_PRINTK_DELAY
 209
 210 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 211 static unsigned long long loops_per_msec;       /* based on boot_delay */
 212
 213 static int __init boot_delay_setup(char *str)
 214 {
 215         unsigned long lpj;
 216
 217         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 218         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 219
 220         get_option(&str, &boot_delay);
 221         if (boot_delay > 10 * 1000)
 222                 boot_delay = 0;
 223
 224         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 225                 "HZ: %d, loops_per_msec: %llu\n",
 226                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
 227         return 1;
 228 }
 229 __setup("boot_delay=", boot_delay_setup);
 230
 231 static void boot_delay_msec(void)
 232 {
 233         unsigned long long k;
 234         unsigned long timeout;
 235
 236         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 237                 return;
 238
 239         k = (unsigned long long)loops_per_msec * boot_delay;
 240
 241         timeout = jiffies + msecs_to_jiffies(boot_delay);
 242         while (k) {
 243                 k--;
 244                 cpu_relax();
 245                 /*
 246                  * use (volatile) jiffies to prevent
 247                  * compiler reduction; loop termination via jiffies
 248                  * is secondary and may or may not happen.
 249                  */
 250                 if (time_after(jiffies, timeout))
 251                         break;
 252                 touch_nmi_watchdog();
 253         }
 254 }
 255 #else
 256 static inline void boot_delay_msec(void)
 257 {
 258 }
 259 #endif
 260
 261 /*
 262  * Commands to do_syslog:
 263  *
 264  *      0 -- Close the log.  Currently a NOP.
 265  *      1 -- Open the log. Currently a NOP.
 266  *      2 -- Read from the log.
 267  *      3 -- Read all messages remaining in the ring buffer.
 268  *      4 -- Read and clear all messages remaining in the ring buffer
 269  *      5 -- Clear ring buffer.
 270  *      6 -- Disable printk's to console
 271  *      7 -- Enable printk's to console
 272  *      8 -- Set level of messages printed to console
 273  *      9 -- Return number of unread characters in the log buffer
 274  *     10 -- Return size of the log buffer
 275  */
 276 int do_syslog(int type, char __user *buf, int len)
 277 {
 278         unsigned i, j, limit, count;
 279         int do_clear = 0;
 280         char c;
 281         int error = 0;
 282
 283         error = security_syslog(type);
 284         if (error)
 285                 return error;
 286
 287         switch (type) {
 288         case 0:         /* Close log */
 289                 break;
 290         case 1:         /* Open log */
 291                 break;
 292         case 2:         /* Read from log */
 293                 error = -EINVAL;
 294                 if (!buf || len < 0)
 295                         goto out;
 296                 error = 0;
 297                 if (!len)
 298                         goto out;
 299                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 300                         error = -EFAULT;
 301                         goto out;
 302                 }
 303                 error = wait_event_interruptible(log_wait,
 304                                                         (log_start - log_end));
 305                 if (error)
 306                         goto out;
 307                 i = 0;
 308                 spin_lock_irq(&logbuf_lock);
 309                 while (!error && (log_start != log_end) && i < len) {
 310                         c = LOG_BUF(log_start);
 311                         log_start++;
 312                         spin_unlock_irq(&logbuf_lock);
 313                         error = __put_user(c,buf);
 314                         buf++;
 315                         i++;
 316                         cond_resched();
 317                         spin_lock_irq(&logbuf_lock);
 318                 }
 319                 spin_unlock_irq(&logbuf_lock);
 320                 if (!error)
 321                         error = i;
 322                 break;
 323         case 4:         /* Read/clear last kernel messages */
 324                 do_clear = 1;
 325                 /* FALL THRU */
 326         case 3:         /* Read last kernel messages */
 327                 error = -EINVAL;
 328                 if (!buf || len < 0)
 329                         goto out;
 330                 error = 0;
 331                 if (!len)
 332                         goto out;
 333                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 334                         error = -EFAULT;
 335                         goto out;
 336                 }
 337                 count = len;
 338                 if (count > log_buf_len)
 339                         count = log_buf_len;
 340                 spin_lock_irq(&logbuf_lock);
 341                 if (count > logged_chars)
 342                         count = logged_chars;
 343                 if (do_clear)
 344                         logged_chars = 0;
 345                 limit = log_end;
 346                 /*
 347                  * __put_user() could sleep, and while we sleep
 348                  * printk() could overwrite the messages
 349                  * we try to copy to user space. Therefore
 350                  * the messages are copied in reverse. <manfreds>
 351                  */
 352                 for (i = 0; i < count && !error; i++) {
 353                         j = limit-1-i;
 354                         if (j + log_buf_len < log_end)
 355                                 break;
 356                         c = LOG_BUF(j);
 357                         spin_unlock_irq(&logbuf_lock);
 358                         error = __put_user(c,&buf[count-1-i]);
 359                         cond_resched();
 360                         spin_lock_irq(&logbuf_lock);
 361                 }
 362                 spin_unlock_irq(&logbuf_lock);
 363                 if (error)
 364                         break;
 365                 error = i;
 366                 if (i != count) {
 367                         int offset = count-error;
 368                         /* buffer overflow during copy, correct user buffer. */
 369                         for (i = 0; i < error; i++) {
 370                                 if (__get_user(c,&buf[i+offset]) ||
 371                                     __put_user(c,&buf[i])) {
 372                                         error = -EFAULT;
 373                                         break;
 374                                 }
 375                                 cond_resched();
 376                         }
 377                 }
 378                 break;
 379         case 5:         /* Clear ring buffer */
 380                 logged_chars = 0;
 381                 break;
 382         case 6:         /* Disable logging to console */
 383                 if (saved_console_loglevel == -1)
 384                         saved_console_loglevel = console_loglevel;
 385                 console_loglevel = minimum_console_loglevel;
 386                 break;
 387         case 7:         /* Enable logging to console */
 388                 if (saved_console_loglevel != -1) {
 389                         console_loglevel = saved_console_loglevel;
 390                         saved_console_loglevel = -1;
 391                 }
 392                 break;
 393         case 8:         /* Set level of messages printed to console */
 394                 error = -EINVAL;
 395                 if (len < 1 || len > 8)
 396                         goto out;
 397                 if (len < minimum_console_loglevel)
 398                         len = minimum_console_loglevel;
 399                 console_loglevel = len;
 400                 /* Implicitly re-enable logging to console */
 401                 saved_console_loglevel = -1;
 402                 error = 0;
 403                 break;
 404         case 9:         /* Number of chars in the log buffer */
 405                 error = log_end - log_start;
 406                 break;
 407         case 10:        /* Size of the log buffer */
 408                 error = log_buf_len;
 409                 break;
 410         default:
 411                 error = -EINVAL;
 412                 break;
 413         }
 414 out:
 415         return error;
 416 }
 417
 418 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 419 {
 420         return do_syslog(type, buf, len);
 421 }
 422
 423 /*
 424  * Call the console drivers on a range of log_buf
 425  */
 426 static void __call_console_drivers(unsigned start, unsigned end)
 427 {
 428         struct console *con;
 429
 430         for_each_console(con) {
 431                 if ((con->flags & CON_ENABLED) && con->write &&
 432                                 (cpu_online(smp_processor_id()) ||
 433                                 (con->flags & CON_ANYTIME)))
 434                         con->write(con, &LOG_BUF(start), end - start);
 435         }
 436 }
 437
 438 static int __read_mostly ignore_loglevel;
 439
 440 static int __init ignore_loglevel_setup(char *str)
 441 {
 442         ignore_loglevel = 1;
 443         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 444
 445         return 0;
 446 }
 447
 448 early_param("ignore_loglevel", ignore_loglevel_setup);
 449
 450 /*
 451  * Write out chars from start to end - 1 inclusive
 452  */
 453 static void _call_console_drivers(unsigned start,
 454                                 unsigned end, int msg_log_level)
 455 {
 456         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 457                         console_drivers && start != end) {
 458                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 459                         /* wrapped write */
 460                         __call_console_drivers(start & LOG_BUF_MASK,
 461                                                 log_buf_len);
 462                         __call_console_drivers(0, end & LOG_BUF_MASK);
 463                 } else {
 464                         __call_console_drivers(start, end);
 465                 }
 466         }
 467 }
 468
 469 /*
 470  * Call the console drivers, asking them to write out
 471  * log_buf[start] to log_buf[end - 1].
 472  * The console_sem must be held.
 473  */
 474 static void call_console_drivers(unsigned start, unsigned end)
 475 {
 476         unsigned cur_index, start_print;
 477         static int msg_level = -1;
 478
 479         BUG_ON(((int)(start - end)) > 0);
 480
 481         cur_index = start;
 482         start_print = start;
 483         while (cur_index != end) {
 484                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 485                                 LOG_BUF(cur_index + 0) == '<' &&
 486                                 LOG_BUF(cur_index + 1) >= '0' &&
 487                                 LOG_BUF(cur_index + 1) <= '7' &&
 488                                 LOG_BUF(cur_index + 2) == '>') {
 489                         msg_level = LOG_BUF(cur_index + 1) - '0';
 490                         cur_index += 3;
 491                         start_print = cur_index;
 492                 }
 493                 while (cur_index != end) {
 494                         char c = LOG_BUF(cur_index);
 495
 496                         cur_index++;
 497                         if (c == '\n') {
 498                                 if (msg_level < 0) {
 499                                         /*
 500                                          * printk() has already given us loglevel tags in
 501                                          * the buffer.  This code is here in case the
 502                                          * log buffer has wrapped right round and scribbled
 503                                          * on those tags
 504                                          */
 505                                         msg_level = default_message_loglevel;
 506                                 }
 507                                 _call_console_drivers(start_print, cur_index, msg_level);
 508                                 msg_level = -1;
 509                                 start_print = cur_index;
 510                                 break;
 511                         }
 512                 }
 513         }
 514         _call_console_drivers(start_print, end, msg_level);
 515 }
 516
 517 static void emit_log_char(char c)
 518 {
 519         LOG_BUF(log_end) = c;
 520         log_end++;
 521         if (log_end - log_start > log_buf_len)
 522                 log_start = log_end - log_buf_len;
 523         if (log_end - con_start > log_buf_len)
 524                 con_start = log_end - log_buf_len;
 525         if (logged_chars < log_buf_len)
 526                 logged_chars++;
 527 }
 528
 529 /*
 530  * Zap console related locks when oopsing. Only zap at most once
 531  * every 10 seconds, to leave time for slow consoles to print a
 532  * full oops.
 533  */
 534 static void zap_locks(void)
 535 {
 536         static unsigned long oops_timestamp;
 537
 538         if (time_after_eq(jiffies, oops_timestamp) &&
 539                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 540                 return;
 541
 542         oops_timestamp = jiffies;
 543
 544         /* If a crash is occurring, make sure we can't deadlock */
 545         spin_lock_init(&logbuf_lock);
 546         /* And make sure that we print immediately */
 547         init_MUTEX(&console_sem);
 548 }
 549
 550 #if defined(CONFIG_PRINTK_TIME)
 551 static int printk_time = 1;
 552 #else
 553 static int printk_time = 0;
 554 #endif
 555 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 556
 557 /* Check if we have any console registered that can be called early in boot. */
 558 static int have_callable_console(void)
 559 {
 560         struct console *con;
 561
 562         for_each_console(con)
 563                 if (con->flags & CON_ANYTIME)
 564                         return 1;
 565
 566         return 0;
 567 }
 568
 569 /**
 570  * printk - print a kernel message
 571  * @fmt: format string
 572  *
 573  * This is printk().  It can be called from any context.  We want it to work.
 574  *
 575  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 576  * call the console drivers.  If we fail to get the semaphore we place the output
 577  * into the log buffer and return.  The current holder of the console_sem will
 578  * notice the new output in release_console_sem() and will send it to the
 579  * consoles before releasing the semaphore.
 580  *
 581  * One effect of this deferred printing is that code which calls printk() and
 582  * then changes console_loglevel may break. This is because console_loglevel
 583  * is inspected when the actual printing occurs.
 584  *
 585  * See also:
 586  * printf(3)
 587  *
 588  * See the vsnprintf() documentation for format string extensions over C99.
 589  */
 590
 591 asmlinkage int printk(const char *fmt, ...)
 592 {
 593         va_list args;
 594         int r;
 595
 596         va_start(args, fmt);
 597         r = vprintk(fmt, args);
 598         va_end(args);
 599
 600         return r;
 601 }
 602
 603 /* cpu currently holding logbuf_lock */
 604 static volatile unsigned int printk_cpu = UINT_MAX;
 605
 606 /*
 607  * Can we actually use the console at this time on this cpu?
 608  *
 609  * Console drivers may assume that per-cpu resources have
 610  * been allocated. So unless they're explicitly marked as
 611  * being able to cope (CON_ANYTIME) don't call them until
 612  * this CPU is officially up.
 613  */
 614 static inline int can_use_console(unsigned int cpu)
 615 {
 616         return cpu_online(cpu) || have_callable_console();
 617 }
 618
 619 /*
 620  * Try to get console ownership to actually show the kernel
 621  * messages from a 'printk'. Return true (and with the
 622  * console_semaphore held, and 'console_locked' set) if it
 623  * is successful, false otherwise.
 624  *
 625  * This gets called with the 'logbuf_lock' spinlock held and
 626  * interrupts disabled. It should return with 'lockbuf_lock'
 627  * released but interrupts still disabled.
 628  */
 629 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 630 {
 631         int retval = 0;
 632
 633         if (!try_acquire_console_sem()) {
 634                 retval = 1;
 635
 636                 /*
 637                  * If we can't use the console, we need to release
 638                  * the console semaphore by hand to avoid flushing
 639                  * the buffer. We need to hold the console semaphore
 640                  * in order to do this test safely.
 641                  */
 642                 if (!can_use_console(cpu)) {
 643                         console_locked = 0;
 644                         up(&console_sem);
 645                         retval = 0;
 646                 }
 647         }
 648         printk_cpu = UINT_MAX;
 649         spin_unlock(&logbuf_lock);
 650         return retval;
 651 }
 652 static const char recursion_bug_msg [] =
 653                 KERN_CRIT "BUG: recent printk recursion!\n";
 654 static int recursion_bug;
 655 static int new_text_line = 1;
 656 static char printk_buf[1024];
 657
 658 int printk_delay_msec __read_mostly;
 659
 660 static inline void printk_delay(void)
 661 {
 662         if (unlikely(printk_delay_msec)) {
 663                 int m = printk_delay_msec;
 664
 665                 while (m--) {
 666                         mdelay(1);
 667                         touch_nmi_watchdog();
 668                 }
 669         }
 670 }
 671
 672 asmlinkage int vprintk(const char *fmt, va_list args)
 673 {
 674         int printed_len = 0;
 675         int current_log_level = default_message_loglevel;
 676         unsigned long flags;
 677         int this_cpu;
 678         char *p;
 679
 680         boot_delay_msec();
 681         printk_delay();
 682
 683         preempt_disable();
 684         /* This stops the holder of console_sem just where we want him */
 685         raw_local_irq_save(flags);
 686         this_cpu = smp_processor_id();
 687
 688         /*
 689          * Ouch, printk recursed into itself!
 690          */
 691         if (unlikely(printk_cpu == this_cpu)) {
 692                 /*
 693                  * If a crash is occurring during printk() on this CPU,
 694                  * then try to get the crash message out but make sure
 695                  * we can't deadlock. Otherwise just return to avoid the
 696                  * recursion and return - but flag the recursion so that
 697                  * it can be printed at the next appropriate moment:
 698                  */
 699                 if (!oops_in_progress) {
 700                         recursion_bug = 1;
 701                         goto out_restore_irqs;
 702                 }
 703                 zap_locks();
 704         }
 705
 706         lockdep_off();
 707         spin_lock(&logbuf_lock);
 708         printk_cpu = this_cpu;
 709
 710         if (recursion_bug) {
 711                 recursion_bug = 0;
 712                 strcpy(printk_buf, recursion_bug_msg);
 713                 printed_len = strlen(recursion_bug_msg);
 714         }
 715         /* Emit the output into the temporary buffer */
 716         printed_len += vscnprintf(printk_buf + printed_len,
 717                                   sizeof(printk_buf) - printed_len, fmt, args);
 718
 719
 720         p = printk_buf;
 721
 722         /* Do we have a loglevel in the string? */
 723         if (p[0] == '<') {
 724                 unsigned char c = p[1];
 725                 if (c && p[2] == '>') {
 726                         switch (c) {
 727                         case '0' ... '7': /* loglevel */
 728                                 current_log_level = c - '0';
 729                         /* Fallthrough - make sure we're on a new line */
 730                         case 'd': /* KERN_DEFAULT */
 731                                 if (!new_text_line) {
 732                                         emit_log_char('\n');
 733                                         new_text_line = 1;
 734                                 }
 735                         /* Fallthrough - skip the loglevel */
 736                         case 'c': /* KERN_CONT */
 737                                 p += 3;
 738                                 break;
 739                         }
 740                 }
 741         }
 742
 743         /*
 744          * Copy the output into log_buf.  If the caller didn't provide
 745          * appropriate log level tags, we insert them here
 746          */
 747         for ( ; *p; p++) {
 748                 if (new_text_line) {
 749                         /* Always output the token */
 750                         emit_log_char('<');
 751                         emit_log_char(current_log_level + '0');
 752                         emit_log_char('>');
 753                         printed_len += 3;
 754                         new_text_line = 0;
 755
 756                         if (printk_time) {
 757                                 /* Follow the token with the time */
 758                                 char tbuf[50], *tp;
 759                                 unsigned tlen;
 760                                 unsigned long long t;
 761                                 unsigned long nanosec_rem;
 762
 763                                 t = cpu_clock(printk_cpu);
 764                                 nanosec_rem = do_div(t, 1000000000);
 765                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 766                                                 (unsigned long) t,
 767                                                 nanosec_rem / 1000);
 768
 769                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 770                                         emit_log_char(*tp);
 771                                 printed_len += tlen;
 772                         }
 773
 774                         if (!*p)
 775                                 break;
 776                 }
 777
 778                 emit_log_char(*p);
 779                 if (*p == '\n')
 780                         new_text_line = 1;
 781         }
 782
 783         /*
 784          * Try to acquire and then immediately release the
 785          * console semaphore. The release will do all the
 786          * actual magic (print out buffers, wake up klogd,
 787          * etc).
 788          *
 789          * The acquire_console_semaphore_for_printk() function
 790          * will release 'logbuf_lock' regardless of whether it
 791          * actually gets the semaphore or not.
 792          */
 793         if (acquire_console_semaphore_for_printk(this_cpu))
 794                 release_console_sem();
 795
 796         lockdep_on();
 797 out_restore_irqs:
 798         raw_local_irq_restore(flags);
 799
 800         preempt_enable();
 801         return printed_len;
 802 }
 803 EXPORT_SYMBOL(printk);
 804 EXPORT_SYMBOL(vprintk);
 805
 806 #else
 807
 808 static void call_console_drivers(unsigned start, unsigned end)
 809 {
 810 }
 811
 812 #endif
 813
 814 static int __add_preferred_console(char *name, int idx, char *options,
 815                                    char *brl_options)
 816 {
 817         struct console_cmdline *c;
 818         int i;
 819
 820         /*
 821          *      See if this tty is not yet registered, and
 822          *      if we have a slot free.
 823          */
 824         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 825                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 826                           console_cmdline[i].index == idx) {
 827                                 if (!brl_options)
 828                                         selected_console = i;
 829                                 return 0;
 830                 }
 831         if (i == MAX_CMDLINECONSOLES)
 832                 return -E2BIG;
 833         if (!brl_options)
 834                 selected_console = i;
 835         c = &console_cmdline[i];
 836         strlcpy(c->name, name, sizeof(c->name));
 837         c->options = options;
 838 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 839         c->brl_options = brl_options;
 840 #endif
 841         c->index = idx;
 842         return 0;
 843 }
 844 /*
 845  * Set up a list of consoles.  Called from init/main.c
 846  */
 847 static int __init console_setup(char *str)
 848 {
 849         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 850         char *s, *options, *brl_options = NULL;
 851         int idx;
 852
 853 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 854         if (!memcmp(str, "brl,", 4)) {
 855                 brl_options = "";
 856                 str += 4;
 857         } else if (!memcmp(str, "brl=", 4)) {
 858                 brl_options = str + 4;
 859                 str = strchr(brl_options, ',');
 860                 if (!str) {
 861                         printk(KERN_ERR "need port name after brl=\n");
 862                         return 1;
 863                 }
 864                 *(str++) = 0;
 865         }
 866 #endif
 867
 868         /*
 869          * Decode str into name, index, options.
 870          */
 871         if (str[0] >= '0' && str[0] <= '9') {
 872                 strcpy(buf, "ttyS");
 873                 strncpy(buf + 4, str, sizeof(buf) - 5);
 874         } else {
 875                 strncpy(buf, str, sizeof(buf) - 1);
 876         }
 877         buf[sizeof(buf) - 1] = 0;
 878         if ((options = strchr(str, ',')) != NULL)
 879                 *(options++) = 0;
 880 #ifdef __sparc__
 881         if (!strcmp(str, "ttya"))
 882                 strcpy(buf, "ttyS0");
 883         if (!strcmp(str, "ttyb"))
 884                 strcpy(buf, "ttyS1");
 885 #endif
 886         for (s = buf; *s; s++)
 887                 if ((*s >= '0' && *s <= '9') || *s == ',')
 888                         break;
 889         idx = simple_strtoul(s, NULL, 10);
 890         *s = 0;
 891
 892         __add_preferred_console(buf, idx, options, brl_options);
 893         console_set_on_cmdline = 1;
 894         return 1;
 895 }
 896 __setup("console=", console_setup);
 897
 898 /**
 899  * add_preferred_console - add a device to the list of preferred consoles.
 900  * @name: device name
 901  * @idx: device index
 902  * @options: options for this console
 903  *
 904  * The last preferred console added will be used for kernel messages
 905  * and stdin/out/err for init.  Normally this is used by console_setup
 906  * above to handle user-supplied console arguments; however it can also
 907  * be used by arch-specific code either to override the user or more
 908  * commonly to provide a default console (ie from PROM variables) when
 909  * the user has not supplied one.
 910  */
 911 int add_preferred_console(char *name, int idx, char *options)
 912 {
 913         return __add_preferred_console(name, idx, options, NULL);
 914 }
 915
 916 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 917 {
 918         struct console_cmdline *c;
 919         int i;
 920
 921         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 922                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 923                           console_cmdline[i].index == idx) {
 924                                 c = &console_cmdline[i];
 925                                 strlcpy(c->name, name_new, sizeof(c->name));
 926                                 c->name[sizeof(c->name) - 1] = 0;
 927                                 c->options = options;
 928                                 c->index = idx_new;
 929                                 return i;
 930                 }
 931         /* not found */
 932         return -1;
 933 }
 934
 935 int console_suspend_enabled = 1;
 936 EXPORT_SYMBOL(console_suspend_enabled);
 937
 938 static int __init console_suspend_disable(char *str)
 939 {
 940         console_suspend_enabled = 0;
 941         return 1;
 942 }
 943 __setup("no_console_suspend", console_suspend_disable);
 944
 945 /**
 946  * suspend_console - suspend the console subsystem
 947  *
 948  * This disables printk() while we go into suspend states
 949  */
 950 void suspend_console(void)
 951 {
 952         if (!console_suspend_enabled)
 953                 return;
 954         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 955         acquire_console_sem();
 956         console_suspended = 1;
 957         up(&console_sem);
 958 }
 959
 960 void resume_console(void)
 961 {
 962         if (!console_suspend_enabled)
 963                 return;
 964         down(&console_sem);
 965         console_suspended = 0;
 966         release_console_sem();
 967 }
 968
 969 /**
 970  * acquire_console_sem - lock the console system for exclusive use.
 971  *
 972  * Acquires a semaphore which guarantees that the caller has
 973  * exclusive access to the console system and the console_drivers list.
 974  *
 975  * Can sleep, returns nothing.
 976  */
 977 void acquire_console_sem(void)
 978 {
 979         BUG_ON(in_interrupt());
 980         down(&console_sem);
 981         if (console_suspended)
 982                 return;
 983         console_locked = 1;
 984         console_may_schedule = 1;
 985 }
 986 EXPORT_SYMBOL(acquire_console_sem);
 987
 988 int try_acquire_console_sem(void)
 989 {
 990         if (down_trylock(&console_sem))
 991                 return -1;
 992         if (console_suspended) {
 993                 up(&console_sem);
 994                 return -1;
 995         }
 996         console_locked = 1;
 997         console_may_schedule = 0;
 998         return 0;
 999 }
1000 EXPORT_SYMBOL(try_acquire_console_sem);
1001
1002 int is_console_locked(void)
1003 {
1004         return console_locked;
1005 }
1006
1007 static DEFINE_PER_CPU(int, printk_pending);
1008
1009 void printk_tick(void)
1010 {
1011         if (__get_cpu_var(printk_pending)) {
1012                 __get_cpu_var(printk_pending) = 0;
1013                 wake_up_interruptible(&log_wait);
1014         }
1015 }
1016
1017 int printk_needs_cpu(int cpu)
1018 {
1019         return per_cpu(printk_pending, cpu);
1020 }
1021
1022 void wake_up_klogd(void)
1023 {
1024         if (waitqueue_active(&log_wait))
1025                 __raw_get_cpu_var(printk_pending) = 1;
1026 }
1027
1028 /**
1029  * release_console_sem - unlock the console system
1030  *
1031  * Releases the semaphore which the caller holds on the console system
1032  * and the console driver list.
1033  *
1034  * While the semaphore was held, console output may have been buffered
1035  * by printk().  If this is the case, release_console_sem() emits
1036  * the output prior to releasing the semaphore.
1037  *
1038  * If there is output waiting for klogd, we wake it up.
1039  *
1040  * release_console_sem() may be called from any context.
1041  */
1042 void release_console_sem(void)
1043 {
1044         unsigned long flags;
1045         unsigned _con_start, _log_end;
1046         unsigned wake_klogd = 0;
1047
1048         if (console_suspended) {
1049                 up(&console_sem);
1050                 return;
1051         }
1052
1053         console_may_schedule = 0;
1054
1055         for ( ; ; ) {
1056                 spin_lock_irqsave(&logbuf_lock, flags);
1057                 wake_klogd |= log_start - log_end;
1058                 if (con_start == log_end)
1059                         break;                  /* Nothing to print */
1060                 _con_start = con_start;
1061                 _log_end = log_end;
1062                 con_start = log_end;            /* Flush */
1063                 spin_unlock(&logbuf_lock);
1064                 stop_critical_timings();        /* don't trace print latency */
1065                 call_console_drivers(_con_start, _log_end);
1066                 start_critical_timings();
1067                 local_irq_restore(flags);
1068         }
1069         console_locked = 0;
1070         up(&console_sem);
1071         spin_unlock_irqrestore(&logbuf_lock, flags);
1072         if (wake_klogd)
1073                 wake_up_klogd();
1074 }
1075 EXPORT_SYMBOL(release_console_sem);
1076
1077 /**
1078  * console_conditional_schedule - yield the CPU if required
1079  *
1080  * If the console code is currently allowed to sleep, and
1081  * if this CPU should yield the CPU to another task, do
1082  * so here.
1083  *
1084  * Must be called within acquire_console_sem().
1085  */
1086 void __sched console_conditional_schedule(void)
1087 {
1088         if (console_may_schedule)
1089                 cond_resched();
1090 }
1091 EXPORT_SYMBOL(console_conditional_schedule);
1092
1093 void console_unblank(void)
1094 {
1095         struct console *c;
1096
1097         /*
1098          * console_unblank can no longer be called in interrupt context unless
1099          * oops_in_progress is set to 1..
1100          */
1101         if (oops_in_progress) {
1102                 if (down_trylock(&console_sem) != 0)
1103                         return;
1104         } else
1105                 acquire_console_sem();
1106
1107         console_locked = 1;
1108         console_may_schedule = 0;
1109         for_each_console(c)
1110                 if ((c->flags & CON_ENABLED) && c->unblank)
1111                         c->unblank();
1112         release_console_sem();
1113 }
1114
1115 /*
1116  * Return the console tty driver structure and its associated index
1117  */
1118 struct tty_driver *console_device(int *index)
1119 {
1120         struct console *c;
1121         struct tty_driver *driver = NULL;
1122
1123         acquire_console_sem();
1124         for_each_console(c) {
1125                 if (!c->device)
1126                         continue;
1127                 driver = c->device(c, index);
1128                 if (driver)
1129                         break;
1130         }
1131         release_console_sem();
1132         return driver;
1133 }
1134
1135 /*
1136  * Prevent further output on the passed console device so that (for example)
1137  * serial drivers can disable console output before suspending a port, and can
1138  * re-enable output afterwards.
1139  */
1140 void console_stop(struct console *console)
1141 {
1142         acquire_console_sem();
1143         console->flags &= ~CON_ENABLED;
1144         release_console_sem();
1145 }
1146 EXPORT_SYMBOL(console_stop);
1147
1148 void console_start(struct console *console)
1149 {
1150         acquire_console_sem();
1151         console->flags |= CON_ENABLED;
1152         release_console_sem();
1153 }
1154 EXPORT_SYMBOL(console_start);
1155
1156 /*
1157  * The console driver calls this routine during kernel initialization
1158  * to register the console printing procedure with printk() and to
1159  * print any messages that were printed by the kernel before the
1160  * console driver was initialized.
1161  *
1162  * This can happen pretty early during the boot process (because of
1163  * early_printk) - sometimes before setup_arch() completes - be careful
1164  * of what kernel features are used - they may not be initialised yet.
1165  *
1166  * There are two types of consoles - bootconsoles (early_printk) and
1167  * "real" consoles (everything which is not a bootconsole) which are
1168  * handled differently.
1169  *  - Any number of bootconsoles can be registered at any time.
1170  *  - As soon as a "real" console is registered, all bootconsoles
1171  *    will be unregistered automatically.
1172  *  - Once a "real" console is registered, any attempt to register a
1173  *    bootconsoles will be rejected
1174  */
1175 void register_console(struct console *newcon)
1176 {
1177         int i;
1178         unsigned long flags;
1179         struct console *bcon = NULL;
1180
1181         /*
1182          * before we register a new CON_BOOT console, make sure we don't
1183          * already have a valid console
1184          */
1185         if (console_drivers && newcon->flags & CON_BOOT) {
1186                 /* find the last or real console */
1187                 for_each_console(bcon) {
1188                         if (!(bcon->flags & CON_BOOT)) {
1189                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1190                                         newcon->name, newcon->index);
1191                                 return;
1192                         }
1193                 }
1194         }
1195
1196         if (console_drivers && console_drivers->flags & CON_BOOT)
1197                 bcon = console_drivers;
1198
1199         if (preferred_console < 0 || bcon || !console_drivers)
1200                 preferred_console = selected_console;
1201
1202         if (newcon->early_setup)
1203                 newcon->early_setup();
1204
1205         /*
1206          *      See if we want to use this console driver. If we
1207          *      didn't select a console we take the first one
1208          *      that registers here.
1209          */
1210         if (preferred_console < 0) {
1211                 if (newcon->index < 0)
1212                         newcon->index = 0;
1213                 if (newcon->setup == NULL ||
1214                     newcon->setup(newcon, NULL) == 0) {
1215                         newcon->flags |= CON_ENABLED;
1216                         if (newcon->device) {
1217                                 newcon->flags |= CON_CONSDEV;
1218                                 preferred_console = 0;
1219                         }
1220                 }
1221         }
1222
1223         /*
1224          *      See if this console matches one we selected on
1225          *      the command line.
1226          */
1227         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1228                         i++) {
1229                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1230                         continue;
1231                 if (newcon->index >= 0 &&
1232                     newcon->index != console_cmdline[i].index)
1233                         continue;
1234                 if (newcon->index < 0)
1235                         newcon->index = console_cmdline[i].index;
1236 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1237                 if (console_cmdline[i].brl_options) {
1238                         newcon->flags |= CON_BRL;
1239                         braille_register_console(newcon,
1240                                         console_cmdline[i].index,
1241                                         console_cmdline[i].options,
1242                                         console_cmdline[i].brl_options);
1243                         return;
1244                 }
1245 #endif
1246                 if (newcon->setup &&
1247                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1248                         break;
1249                 newcon->flags |= CON_ENABLED;
1250                 newcon->index = console_cmdline[i].index;
1251                 if (i == selected_console) {
1252                         newcon->flags |= CON_CONSDEV;
1253                         preferred_console = selected_console;
1254                 }
1255                 break;
1256         }
1257
1258         if (!(newcon->flags & CON_ENABLED))
1259                 return;
1260
1261         /*
1262          * If we have a bootconsole, and are switching to a real console,
1263          * don't print everything out again, since when the boot console, and
1264          * the real console are the same physical device, it's annoying to
1265          * see the beginning boot messages twice
1266          */
1267         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1268                 newcon->flags &= ~CON_PRINTBUFFER;
1269
1270         /*
1271          *      Put this console in the list - keep the
1272          *      preferred driver at the head of the list.
1273          */
1274         acquire_console_sem();
1275         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1276                 newcon->next = console_drivers;
1277                 console_drivers = newcon;
1278                 if (newcon->next)
1279                         newcon->next->flags &= ~CON_CONSDEV;
1280         } else {
1281                 newcon->next = console_drivers->next;
1282                 console_drivers->next = newcon;
1283         }
1284         if (newcon->flags & CON_PRINTBUFFER) {
1285                 /*
1286                  * release_console_sem() will print out the buffered messages
1287                  * for us.
1288                  */
1289                 spin_lock_irqsave(&logbuf_lock, flags);
1290                 con_start = log_start;
1291                 spin_unlock_irqrestore(&logbuf_lock, flags);
1292         }
1293         release_console_sem();
1294
1295         /*
1296          * By unregistering the bootconsoles after we enable the real console
1297          * we get the "console xxx enabled" message on all the consoles -
1298          * boot consoles, real consoles, etc - this is to ensure that end
1299          * users know there might be something in the kernel's log buffer that
1300          * went to the bootconsole (that they do not see on the real console)
1301          */
1302         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1303                 /* we need to iterate through twice, to make sure we print
1304                  * everything out, before we unregister the console(s)
1305                  */
1306                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1307                         newcon->name, newcon->index);
1308                 for_each_console(bcon)
1309                         if (bcon->flags & CON_BOOT)
1310                                 unregister_console(bcon);
1311         } else {
1312                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1313                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1314                         newcon->name, newcon->index);
1315         }
1316 }
1317 EXPORT_SYMBOL(register_console);
1318
1319 int unregister_console(struct console *console)
1320 {
1321         struct console *a, *b;
1322         int res = 1;
1323
1324 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1325         if (console->flags & CON_BRL)
1326                 return braille_unregister_console(console);
1327 #endif
1328
1329         acquire_console_sem();
1330         if (console_drivers == console) {
1331                 console_drivers=console->next;
1332                 res = 0;
1333         } else if (console_drivers) {
1334                 for (a=console_drivers->next, b=console_drivers ;
1335                      a; b=a, a=b->next) {
1336                         if (a == console) {
1337                                 b->next = a->next;
1338                                 res = 0;
1339                                 break;
1340                         }
1341                 }
1342         }
1343
1344         /*
1345          * If this isn't the last console and it has CON_CONSDEV set, we
1346          * need to set it on the next preferred console.
1347          */
1348         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1349                 console_drivers->flags |= CON_CONSDEV;
1350
1351         release_console_sem();
1352         return res;
1353 }
1354 EXPORT_SYMBOL(unregister_console);
1355
1356 static int __init disable_boot_consoles(void)
1357 {
1358         struct console *con;
1359
1360         for_each_console(con) {
1361                 if (con->flags & CON_BOOT) {
1362                         printk(KERN_INFO "turn off boot console %s%d\n",
1363                                 con->name, con->index);
1364                         unregister_console(con);
1365                 }
1366         }
1367         return 0;
1368 }
1369 late_initcall(disable_boot_consoles);
1370
1371 #if defined CONFIG_PRINTK
1372
1373 /*
1374  * printk rate limiting, lifted from the networking subsystem.
1375  *
1376  * This enforces a rate limit: not more than 10 kernel messages
1377  * every 5s to make a denial-of-service attack impossible.
1378  */
1379 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1380
1381 int __printk_ratelimit(const char *func)
1382 {
1383         return ___ratelimit(&printk_ratelimit_state, func);
1384 }
1385 EXPORT_SYMBOL(__printk_ratelimit);
1386
1387 /**
1388  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1389  * @caller_jiffies: pointer to caller's state
1390  * @interval_msecs: minimum interval between prints
1391  *
1392  * printk_timed_ratelimit() returns true if more than @interval_msecs
1393  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1394  * returned true.
1395  */
1396 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1397                         unsigned int interval_msecs)
1398 {
1399         if (*caller_jiffies == 0
1400                         || !time_in_range(jiffies, *caller_jiffies,
1401                                         *caller_jiffies
1402                                         + msecs_to_jiffies(interval_msecs))) {
1403                 *caller_jiffies = jiffies;
1404                 return true;
1405         }
1406         return false;
1407 }
1408 EXPORT_SYMBOL(printk_timed_ratelimit);
1409
1410 static DEFINE_SPINLOCK(dump_list_lock);
1411 static LIST_HEAD(dump_list);
1412
1413 /**
1414  * kmsg_dump_register - register a kernel log dumper.
1415  * @dump: pointer to the kmsg_dumper structure
1416  *
1417  * Adds a kernel log dumper to the system. The dump callback in the
1418  * structure will be called when the kernel oopses or panics and must be
1419  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1420  */
1421 int kmsg_dump_register(struct kmsg_dumper *dumper)
1422 {
1423         unsigned long flags;
1424         int err = -EBUSY;
1425
1426         /* The dump callback needs to be set */
1427         if (!dumper->dump)
1428                 return -EINVAL;
1429
1430         spin_lock_irqsave(&dump_list_lock, flags);
1431         /* Don't allow registering multiple times */
1432         if (!dumper->registered) {
1433                 dumper->registered = 1;
1434                 list_add_tail(&dumper->list, &dump_list);
1435                 err = 0;
1436         }
1437         spin_unlock_irqrestore(&dump_list_lock, flags);
1438
1439         return err;
1440 }
1441 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1442
1443 /**
1444  * kmsg_dump_unregister - unregister a kmsg dumper.
1445  * @dump: pointer to the kmsg_dumper structure
1446  *
1447  * Removes a dump device from the system. Returns zero on success and
1448  * %-EINVAL otherwise.
1449  */
1450 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1451 {
1452         unsigned long flags;
1453         int err = -EINVAL;
1454
1455         spin_lock_irqsave(&dump_list_lock, flags);
1456         if (dumper->registered) {
1457                 dumper->registered = 0;
1458                 list_del(&dumper->list);
1459                 err = 0;
1460         }
1461         spin_unlock_irqrestore(&dump_list_lock, flags);
1462
1463         return err;
1464 }
1465 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1466
1467 static const char const *kmsg_reasons[] = {
1468         [KMSG_DUMP_OOPS]        = "oops",
1469         [KMSG_DUMP_PANIC]       = "panic",
1470 };
1471
1472 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1473 {
1474         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1475                 return "unknown";
1476
1477         return kmsg_reasons[reason];
1478 }
1479
1480 /**
1481  * kmsg_dump - dump kernel log to kernel message dumpers.
1482  * @reason: the reason (oops, panic etc) for dumping
1483  *
1484  * Iterate through each of the dump devices and call the oops/panic
1485  * callbacks with the log buffer.
1486  */
1487 void kmsg_dump(enum kmsg_dump_reason reason)
1488 {
1489         unsigned long end;
1490         unsigned chars;
1491         struct kmsg_dumper *dumper;
1492         const char *s1, *s2;
1493         unsigned long l1, l2;
1494         unsigned long flags;
1495
1496         /* Theoretically, the log could move on after we do this, but
1497            there's not a lot we can do about that. The new messages
1498            will overwrite the start of what we dump. */
1499         spin_lock_irqsave(&logbuf_lock, flags);
1500         end = log_end & LOG_BUF_MASK;
1501         chars = logged_chars;
1502         spin_unlock_irqrestore(&logbuf_lock, flags);
1503
1504         if (logged_chars > end) {
1505                 s1 = log_buf + log_buf_len - logged_chars + end;
1506                 l1 = logged_chars - end;
1507
1508                 s2 = log_buf;
1509                 l2 = end;
1510         } else {
1511                 s1 = "";
1512                 l1 = 0;
1513
1514                 s2 = log_buf + end - logged_chars;
1515                 l2 = logged_chars;
1516         }
1517
1518         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1519                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1520                                 kmsg_to_str(reason));
1521                 return;
1522         }
1523         list_for_each_entry(dumper, &dump_list, list)
1524                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1525         spin_unlock_irqrestore(&dump_list_lock, flags);
1526 }
1527 #endif