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 #include <linux/syslog.h>
  39
  40 #include <asm/uaccess.h>
  41
  42 /*
  43  * for_each_console() allows you to iterate on each console
  44  */
  45 #define for_each_console(con) \
  46         for (con = console_drivers; con != NULL; con = con->next)
  47
  48 /*
  49  * Architectures can override it:
  50  */
  51 void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
  52 {
  53 }
  54
  55 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  56
  57 /* printk's without a loglevel use this.. */
  58 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  59
  60 /* We show everything that is MORE important than this.. */
  61 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  62 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  63
  64 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  65
  66 int console_printk[4] = {
  67         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  68         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  69         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  70         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  71 };
  72
  73 static int saved_console_loglevel = -1;
  74
  75 /*
  76  * Low level drivers may need that to know if they can schedule in
  77  * their unblank() callback or not. So let's export it.
  78  */
  79 int oops_in_progress;
  80 EXPORT_SYMBOL(oops_in_progress);
  81
  82 /*
  83  * console_sem protects the console_drivers list, and also
  84  * provides serialisation for access to the entire console
  85  * driver system.
  86  */
  87 static DECLARE_MUTEX(console_sem);
  88 struct console *console_drivers;
  89 EXPORT_SYMBOL_GPL(console_drivers);
  90
  91 /*
  92  * This is used for debugging the mess that is the VT code by
  93  * keeping track if we have the console semaphore held. It's
  94  * definitely not the perfect debug tool (we don't know if _WE_
  95  * hold it are racing, but it helps tracking those weird code
  96  * path in the console code where we end up in places I want
  97  * locked without the console sempahore held
  98  */
  99 static int console_locked, console_suspended;
 100
 101 /*
 102  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
 103  * It is also used in interesting ways to provide interlocking in
 104  * release_console_sem().
 105  */
 106 static DEFINE_SPINLOCK(logbuf_lock);
 107
 108 #define LOG_BUF_MASK (log_buf_len-1)
 109 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 110
 111 /*
 112  * The indices into log_buf are not constrained to log_buf_len - they
 113  * must be masked before subscripting
 114  */
 115 static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
 116 static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
 117 static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
 118
 119 /*
 120  *      Array of consoles built from command line options (console=)
 121  */
 122 struct console_cmdline
 123 {
 124         char    name[8];                        /* Name of the driver       */
 125         int     index;                          /* Minor dev. to use        */
 126         char    *options;                       /* Options for the driver   */
 127 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 128         char    *brl_options;                   /* Options for braille driver */
 129 #endif
 130 };
 131
 132 #define MAX_CMDLINECONSOLES 8
 133
 134 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 135 static int selected_console = -1;
 136 static int preferred_console = -1;
 137 int console_set_on_cmdline;
 138 EXPORT_SYMBOL(console_set_on_cmdline);
 139
 140 /* Flag: console code may call schedule() */
 141 static int console_may_schedule;
 142
 143 #ifdef CONFIG_PRINTK
 144
 145 static char __log_buf[__LOG_BUF_LEN];
 146 static char *log_buf = __log_buf;
 147 static int log_buf_len = __LOG_BUF_LEN;
 148 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 149
 150 #ifdef CONFIG_KEXEC
 151 /*
 152  * This appends the listed symbols to /proc/vmcoreinfo
 153  *
 154  * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
 155  * obtain access to symbols that are otherwise very difficult to locate.  These
 156  * symbols are specifically used so that utilities can access and extract the
 157  * dmesg log from a vmcore file after a crash.
 158  */
 159 void log_buf_kexec_setup(void)
 160 {
 161         VMCOREINFO_SYMBOL(log_buf);
 162         VMCOREINFO_SYMBOL(log_end);
 163         VMCOREINFO_SYMBOL(log_buf_len);
 164         VMCOREINFO_SYMBOL(logged_chars);
 165 }
 166 #endif
 167
 168 static int __init log_buf_len_setup(char *str)
 169 {
 170         unsigned size = memparse(str, &str);
 171         unsigned long flags;
 172
 173         if (size)
 174                 size = roundup_pow_of_two(size);
 175         if (size > log_buf_len) {
 176                 unsigned start, dest_idx, offset;
 177                 char *new_log_buf;
 178
 179                 new_log_buf = alloc_bootmem(size);
 180                 if (!new_log_buf) {
 181                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 182                         goto out;
 183                 }
 184
 185                 spin_lock_irqsave(&logbuf_lock, flags);
 186                 log_buf_len = size;
 187                 log_buf = new_log_buf;
 188
 189                 offset = start = min(con_start, log_start);
 190                 dest_idx = 0;
 191                 while (start != log_end) {
 192                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 193                         start++;
 194                         dest_idx++;
 195                 }
 196                 log_start -= offset;
 197                 con_start -= offset;
 198                 log_end -= offset;
 199                 spin_unlock_irqrestore(&logbuf_lock, flags);
 200
 201                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 202         }
 203 out:
 204         return 1;
 205 }
 206
 207 __setup("log_buf_len=", log_buf_len_setup);
 208
 209 #ifdef CONFIG_BOOT_PRINTK_DELAY
 210
 211 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 212 static unsigned long long loops_per_msec;       /* based on boot_delay */
 213
 214 static int __init boot_delay_setup(char *str)
 215 {
 216         unsigned long lpj;
 217
 218         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 219         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 220
 221         get_option(&str, &boot_delay);
 222         if (boot_delay > 10 * 1000)
 223                 boot_delay = 0;
 224
 225         pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 226                 "HZ: %d, loops_per_msec: %llu\n",
 227                 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
 228         return 1;
 229 }
 230 __setup("boot_delay=", boot_delay_setup);
 231
 232 static void boot_delay_msec(void)
 233 {
 234         unsigned long long k;
 235         unsigned long timeout;
 236
 237         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 238                 return;
 239
 240         k = (unsigned long long)loops_per_msec * boot_delay;
 241
 242         timeout = jiffies + msecs_to_jiffies(boot_delay);
 243         while (k) {
 244                 k--;
 245                 cpu_relax();
 246                 /*
 247                  * use (volatile) jiffies to prevent
 248                  * compiler reduction; loop termination via jiffies
 249                  * is secondary and may or may not happen.
 250                  */
 251                 if (time_after(jiffies, timeout))
 252                         break;
 253                 touch_nmi_watchdog();
 254         }
 255 }
 256 #else
 257 static inline void boot_delay_msec(void)
 258 {
 259 }
 260 #endif
 261
 262 /*
 263  * Commands to do_syslog:
 264  *
 265  *      0 -- Close the log.  Currently a NOP.
 266  *      1 -- Open the log. Currently a NOP.
 267  *      2 -- Read from the log.
 268  *      3 -- Read all messages remaining in the ring buffer.
 269  *      4 -- Read and clear all messages remaining in the ring buffer
 270  *      5 -- Clear ring buffer.
 271  *      6 -- Disable printk's to console
 272  *      7 -- Enable printk's to console
 273  *      8 -- Set level of messages printed to console
 274  *      9 -- Return number of unread characters in the log buffer
 275  *     10 -- Return size of the log buffer
 276  */
 277 int do_syslog(int type, char __user *buf, int len, bool from_file)
 278 {
 279         unsigned i, j, limit, count;
 280         int do_clear = 0;
 281         char c;
 282         int error = 0;
 283
 284         error = security_syslog(type, from_file);
 285         if (error)
 286                 return error;
 287
 288         switch (type) {
 289         case 0:         /* Close log */
 290                 break;
 291         case 1:         /* Open log */
 292                 break;
 293         case 2:         /* Read from log */
 294                 error = -EINVAL;
 295                 if (!buf || len < 0)
 296                         goto out;
 297                 error = 0;
 298                 if (!len)
 299                         goto out;
 300                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 301                         error = -EFAULT;
 302                         goto out;
 303                 }
 304                 error = wait_event_interruptible(log_wait,
 305                                                         (log_start - log_end));
 306                 if (error)
 307                         goto out;
 308                 i = 0;
 309                 spin_lock_irq(&logbuf_lock);
 310                 while (!error && (log_start != log_end) && i < len) {
 311                         c = LOG_BUF(log_start);
 312                         log_start++;
 313                         spin_unlock_irq(&logbuf_lock);
 314                         error = __put_user(c,buf);
 315                         buf++;
 316                         i++;
 317                         cond_resched();
 318                         spin_lock_irq(&logbuf_lock);
 319                 }
 320                 spin_unlock_irq(&logbuf_lock);
 321                 if (!error)
 322                         error = i;
 323                 break;
 324         case 4:         /* Read/clear last kernel messages */
 325                 do_clear = 1;
 326                 /* FALL THRU */
 327         case 3:         /* Read last kernel messages */
 328                 error = -EINVAL;
 329                 if (!buf || len < 0)
 330                         goto out;
 331                 error = 0;
 332                 if (!len)
 333                         goto out;
 334                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 335                         error = -EFAULT;
 336                         goto out;
 337                 }
 338                 count = len;
 339                 if (count > log_buf_len)
 340                         count = log_buf_len;
 341                 spin_lock_irq(&logbuf_lock);
 342                 if (count > logged_chars)
 343                         count = logged_chars;
 344                 if (do_clear)
 345                         logged_chars = 0;
 346                 limit = log_end;
 347                 /*
 348                  * __put_user() could sleep, and while we sleep
 349                  * printk() could overwrite the messages
 350                  * we try to copy to user space. Therefore
 351                  * the messages are copied in reverse. <manfreds>
 352                  */
 353                 for (i = 0; i < count && !error; i++) {
 354                         j = limit-1-i;
 355                         if (j + log_buf_len < log_end)
 356                                 break;
 357                         c = LOG_BUF(j);
 358                         spin_unlock_irq(&logbuf_lock);
 359                         error = __put_user(c,&buf[count-1-i]);
 360                         cond_resched();
 361                         spin_lock_irq(&logbuf_lock);
 362                 }
 363                 spin_unlock_irq(&logbuf_lock);
 364                 if (error)
 365                         break;
 366                 error = i;
 367                 if (i != count) {
 368                         int offset = count-error;
 369                         /* buffer overflow during copy, correct user buffer. */
 370                         for (i = 0; i < error; i++) {
 371                                 if (__get_user(c,&buf[i+offset]) ||
 372                                     __put_user(c,&buf[i])) {
 373                                         error = -EFAULT;
 374                                         break;
 375                                 }
 376                                 cond_resched();
 377                         }
 378                 }
 379                 break;
 380         case 5:         /* Clear ring buffer */
 381                 logged_chars = 0;
 382                 break;
 383         case 6:         /* Disable logging to console */
 384                 if (saved_console_loglevel == -1)
 385                         saved_console_loglevel = console_loglevel;
 386                 console_loglevel = minimum_console_loglevel;
 387                 break;
 388         case 7:         /* Enable logging to console */
 389                 if (saved_console_loglevel != -1) {
 390                         console_loglevel = saved_console_loglevel;
 391                         saved_console_loglevel = -1;
 392                 }
 393                 break;
 394         case 8:         /* Set level of messages printed to console */
 395                 error = -EINVAL;
 396                 if (len < 1 || len > 8)
 397                         goto out;
 398                 if (len < minimum_console_loglevel)
 399                         len = minimum_console_loglevel;
 400                 console_loglevel = len;
 401                 /* Implicitly re-enable logging to console */
 402                 saved_console_loglevel = -1;
 403                 error = 0;
 404                 break;
 405         case 9:         /* Number of chars in the log buffer */
 406                 error = log_end - log_start;
 407                 break;
 408         case 10:        /* Size of the log buffer */
 409                 error = log_buf_len;
 410                 break;
 411         default:
 412                 error = -EINVAL;
 413                 break;
 414         }
 415 out:
 416         return error;
 417 }
 418
 419 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 420 {
 421         return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
 422 }
 423
 424 /*
 425  * Call the console drivers on a range of log_buf
 426  */
 427 static void __call_console_drivers(unsigned start, unsigned end)
 428 {
 429         struct console *con;
 430
 431         for_each_console(con) {
 432                 if ((con->flags & CON_ENABLED) && con->write &&
 433                                 (cpu_online(smp_processor_id()) ||
 434                                 (con->flags & CON_ANYTIME)))
 435                         con->write(con, &LOG_BUF(start), end - start);
 436         }
 437 }
 438
 439 static int __read_mostly ignore_loglevel;
 440
 441 static int __init ignore_loglevel_setup(char *str)
 442 {
 443         ignore_loglevel = 1;
 444         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 445
 446         return 0;
 447 }
 448
 449 early_param("ignore_loglevel", ignore_loglevel_setup);
 450
 451 /*
 452  * Write out chars from start to end - 1 inclusive
 453  */
 454 static void _call_console_drivers(unsigned start,
 455                                 unsigned end, int msg_log_level)
 456 {
 457         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 458                         console_drivers && start != end) {
 459                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 460                         /* wrapped write */
 461                         __call_console_drivers(start & LOG_BUF_MASK,
 462                                                 log_buf_len);
 463                         __call_console_drivers(0, end & LOG_BUF_MASK);
 464                 } else {
 465                         __call_console_drivers(start, end);
 466                 }
 467         }
 468 }
 469
 470 /*
 471  * Call the console drivers, asking them to write out
 472  * log_buf[start] to log_buf[end - 1].
 473  * The console_sem must be held.
 474  */
 475 static void call_console_drivers(unsigned start, unsigned end)
 476 {
 477         unsigned cur_index, start_print;
 478         static int msg_level = -1;
 479
 480         BUG_ON(((int)(start - end)) > 0);
 481
 482         cur_index = start;
 483         start_print = start;
 484         while (cur_index != end) {
 485                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 486                                 LOG_BUF(cur_index + 0) == '<' &&
 487                                 LOG_BUF(cur_index + 1) >= '0' &&
 488                                 LOG_BUF(cur_index + 1) <= '7' &&
 489                                 LOG_BUF(cur_index + 2) == '>') {
 490                         msg_level = LOG_BUF(cur_index + 1) - '0';
 491                         cur_index += 3;
 492                         start_print = cur_index;
 493                 }
 494                 while (cur_index != end) {
 495                         char c = LOG_BUF(cur_index);
 496
 497                         cur_index++;
 498                         if (c == '\n') {
 499                                 if (msg_level < 0) {
 500                                         /*
 501                                          * printk() has already given us loglevel tags in
 502                                          * the buffer.  This code is here in case the
 503                                          * log buffer has wrapped right round and scribbled
 504                                          * on those tags
 505                                          */
 506                                         msg_level = default_message_loglevel;
 507                                 }
 508                                 _call_console_drivers(start_print, cur_index, msg_level);
 509                                 msg_level = -1;
 510                                 start_print = cur_index;
 511                                 break;
 512                         }
 513                 }
 514         }
 515         _call_console_drivers(start_print, end, msg_level);
 516 }
 517
 518 static void emit_log_char(char c)
 519 {
 520         LOG_BUF(log_end) = c;
 521         log_end++;
 522         if (log_end - log_start > log_buf_len)
 523                 log_start = log_end - log_buf_len;
 524         if (log_end - con_start > log_buf_len)
 525                 con_start = log_end - log_buf_len;
 526         if (logged_chars < log_buf_len)
 527                 logged_chars++;
 528 }
 529
 530 /*
 531  * Zap console related locks when oopsing. Only zap at most once
 532  * every 10 seconds, to leave time for slow consoles to print a
 533  * full oops.
 534  */
 535 static void zap_locks(void)
 536 {
 537         static unsigned long oops_timestamp;
 538
 539         if (time_after_eq(jiffies, oops_timestamp) &&
 540                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 541                 return;
 542
 543         oops_timestamp = jiffies;
 544
 545         /* If a crash is occurring, make sure we can't deadlock */
 546         spin_lock_init(&logbuf_lock);
 547         /* And make sure that we print immediately */
 548         init_MUTEX(&console_sem);
 549 }
 550
 551 #if defined(CONFIG_PRINTK_TIME)
 552 static int printk_time = 1;
 553 #else
 554 static int printk_time = 0;
 555 #endif
 556 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 557
 558 /* Check if we have any console registered that can be called early in boot. */
 559 static int have_callable_console(void)
 560 {
 561         struct console *con;
 562
 563         for_each_console(con)
 564                 if (con->flags & CON_ANYTIME)
 565                         return 1;
 566
 567         return 0;
 568 }
 569
 570 /**
 571  * printk - print a kernel message
 572  * @fmt: format string
 573  *
 574  * This is printk().  It can be called from any context.  We want it to work.
 575  *
 576  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 577  * call the console drivers.  If we fail to get the semaphore we place the output
 578  * into the log buffer and return.  The current holder of the console_sem will
 579  * notice the new output in release_console_sem() and will send it to the
 580  * consoles before releasing the semaphore.
 581  *
 582  * One effect of this deferred printing is that code which calls printk() and
 583  * then changes console_loglevel may break. This is because console_loglevel
 584  * is inspected when the actual printing occurs.
 585  *
 586  * See also:
 587  * printf(3)
 588  *
 589  * See the vsnprintf() documentation for format string extensions over C99.
 590  */
 591
 592 asmlinkage int printk(const char *fmt, ...)
 593 {
 594         va_list args;
 595         int r;
 596
 597         va_start(args, fmt);
 598         r = vprintk(fmt, args);
 599         va_end(args);
 600
 601         return r;
 602 }
 603
 604 /* cpu currently holding logbuf_lock */
 605 static volatile unsigned int printk_cpu = UINT_MAX;
 606
 607 /*
 608  * Can we actually use the console at this time on this cpu?
 609  *
 610  * Console drivers may assume that per-cpu resources have
 611  * been allocated. So unless they're explicitly marked as
 612  * being able to cope (CON_ANYTIME) don't call them until
 613  * this CPU is officially up.
 614  */
 615 static inline int can_use_console(unsigned int cpu)
 616 {
 617         return cpu_online(cpu) || have_callable_console();
 618 }
 619
 620 /*
 621  * Try to get console ownership to actually show the kernel
 622  * messages from a 'printk'. Return true (and with the
 623  * console_semaphore held, and 'console_locked' set) if it
 624  * is successful, false otherwise.
 625  *
 626  * This gets called with the 'logbuf_lock' spinlock held and
 627  * interrupts disabled. It should return with 'lockbuf_lock'
 628  * released but interrupts still disabled.
 629  */
 630 static int acquire_console_semaphore_for_printk(unsigned int cpu)
 631 {
 632         int retval = 0;
 633
 634         if (!try_acquire_console_sem()) {
 635                 retval = 1;
 636
 637                 /*
 638                  * If we can't use the console, we need to release
 639                  * the console semaphore by hand to avoid flushing
 640                  * the buffer. We need to hold the console semaphore
 641                  * in order to do this test safely.
 642                  */
 643                 if (!can_use_console(cpu)) {
 644                         console_locked = 0;
 645                         up(&console_sem);
 646                         retval = 0;
 647                 }
 648         }
 649         printk_cpu = UINT_MAX;
 650         spin_unlock(&logbuf_lock);
 651         return retval;
 652 }
 653 static const char recursion_bug_msg [] =
 654                 KERN_CRIT "BUG: recent printk recursion!\n";
 655 static int recursion_bug;
 656 static int new_text_line = 1;
 657 static char printk_buf[1024];
 658
 659 int printk_delay_msec __read_mostly;
 660
 661 static inline void printk_delay(void)
 662 {
 663         if (unlikely(printk_delay_msec)) {
 664                 int m = printk_delay_msec;
 665
 666                 while (m--) {
 667                         mdelay(1);
 668                         touch_nmi_watchdog();
 669                 }
 670         }
 671 }
 672
 673 asmlinkage int vprintk(const char *fmt, va_list args)
 674 {
 675         int printed_len = 0;
 676         int current_log_level = default_message_loglevel;
 677         unsigned long flags;
 678         int this_cpu;
 679         char *p;
 680
 681         boot_delay_msec();
 682         printk_delay();
 683
 684         preempt_disable();
 685         /* This stops the holder of console_sem just where we want him */
 686         raw_local_irq_save(flags);
 687         this_cpu = smp_processor_id();
 688
 689         /*
 690          * Ouch, printk recursed into itself!
 691          */
 692         if (unlikely(printk_cpu == this_cpu)) {
 693                 /*
 694                  * If a crash is occurring during printk() on this CPU,
 695                  * then try to get the crash message out but make sure
 696                  * we can't deadlock. Otherwise just return to avoid the
 697                  * recursion and return - but flag the recursion so that
 698                  * it can be printed at the next appropriate moment:
 699                  */
 700                 if (!oops_in_progress) {
 701                         recursion_bug = 1;
 702                         goto out_restore_irqs;
 703                 }
 704                 zap_locks();
 705         }
 706
 707         lockdep_off();
 708         spin_lock(&logbuf_lock);
 709         printk_cpu = this_cpu;
 710
 711         if (recursion_bug) {
 712                 recursion_bug = 0;
 713                 strcpy(printk_buf, recursion_bug_msg);
 714                 printed_len = strlen(recursion_bug_msg);
 715         }
 716         /* Emit the output into the temporary buffer */
 717         printed_len += vscnprintf(printk_buf + printed_len,
 718                                   sizeof(printk_buf) - printed_len, fmt, args);
 719
 720
 721         p = printk_buf;
 722
 723         /* Do we have a loglevel in the string? */
 724         if (p[0] == '<') {
 725                 unsigned char c = p[1];
 726                 if (c && p[2] == '>') {
 727                         switch (c) {
 728                         case '0' ... '7': /* loglevel */
 729                                 current_log_level = c - '0';
 730                         /* Fallthrough - make sure we're on a new line */
 731                         case 'd': /* KERN_DEFAULT */
 732                                 if (!new_text_line) {
 733                                         emit_log_char('\n');
 734                                         new_text_line = 1;
 735                                 }
 736                         /* Fallthrough - skip the loglevel */
 737                         case 'c': /* KERN_CONT */
 738                                 p += 3;
 739                                 break;
 740                         }
 741                 }
 742         }
 743
 744         /*
 745          * Copy the output into log_buf.  If the caller didn't provide
 746          * appropriate log level tags, we insert them here
 747          */
 748         for ( ; *p; p++) {
 749                 if (new_text_line) {
 750                         /* Always output the token */
 751                         emit_log_char('<');
 752                         emit_log_char(current_log_level + '0');
 753                         emit_log_char('>');
 754                         printed_len += 3;
 755                         new_text_line = 0;
 756
 757                         if (printk_time) {
 758                                 /* Follow the token with the time */
 759                                 char tbuf[50], *tp;
 760                                 unsigned tlen;
 761                                 unsigned long long t;
 762                                 unsigned long nanosec_rem;
 763
 764                                 t = cpu_clock(printk_cpu);
 765                                 nanosec_rem = do_div(t, 1000000000);
 766                                 tlen = sprintf(tbuf, "[%5lu.%06lu] ",
 767                                                 (unsigned long) t,
 768                                                 nanosec_rem / 1000);
 769
 770                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 771                                         emit_log_char(*tp);
 772                                 printed_len += tlen;
 773                         }
 774
 775                         if (!*p)
 776                                 break;
 777                 }
 778
 779                 emit_log_char(*p);
 780                 if (*p == '\n')
 781                         new_text_line = 1;
 782         }
 783
 784         /*
 785          * Try to acquire and then immediately release the
 786          * console semaphore. The release will do all the
 787          * actual magic (print out buffers, wake up klogd,
 788          * etc).
 789          *
 790          * The acquire_console_semaphore_for_printk() function
 791          * will release 'logbuf_lock' regardless of whether it
 792          * actually gets the semaphore or not.
 793          */
 794         if (acquire_console_semaphore_for_printk(this_cpu))
 795                 release_console_sem();
 796
 797         lockdep_on();
 798 out_restore_irqs:
 799         raw_local_irq_restore(flags);
 800
 801         preempt_enable();
 802         return printed_len;
 803 }
 804 EXPORT_SYMBOL(printk);
 805 EXPORT_SYMBOL(vprintk);
 806
 807 #else
 808
 809 static void call_console_drivers(unsigned start, unsigned end)
 810 {
 811 }
 812
 813 #endif
 814
 815 static int __add_preferred_console(char *name, int idx, char *options,
 816                                    char *brl_options)
 817 {
 818         struct console_cmdline *c;
 819         int i;
 820
 821         /*
 822          *      See if this tty is not yet registered, and
 823          *      if we have a slot free.
 824          */
 825         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 826                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 827                           console_cmdline[i].index == idx) {
 828                                 if (!brl_options)
 829                                         selected_console = i;
 830                                 return 0;
 831                 }
 832         if (i == MAX_CMDLINECONSOLES)
 833                 return -E2BIG;
 834         if (!brl_options)
 835                 selected_console = i;
 836         c = &console_cmdline[i];
 837         strlcpy(c->name, name, sizeof(c->name));
 838         c->options = options;
 839 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 840         c->brl_options = brl_options;
 841 #endif
 842         c->index = idx;
 843         return 0;
 844 }
 845 /*
 846  * Set up a list of consoles.  Called from init/main.c
 847  */
 848 static int __init console_setup(char *str)
 849 {
 850         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 851         char *s, *options, *brl_options = NULL;
 852         int idx;
 853
 854 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
 855         if (!memcmp(str, "brl,", 4)) {
 856                 brl_options = "";
 857                 str += 4;
 858         } else if (!memcmp(str, "brl=", 4)) {
 859                 brl_options = str + 4;
 860                 str = strchr(brl_options, ',');
 861                 if (!str) {
 862                         printk(KERN_ERR "need port name after brl=\n");
 863                         return 1;
 864                 }
 865                 *(str++) = 0;
 866         }
 867 #endif
 868
 869         /*
 870          * Decode str into name, index, options.
 871          */
 872         if (str[0] >= '0' && str[0] <= '9') {
 873                 strcpy(buf, "ttyS");
 874                 strncpy(buf + 4, str, sizeof(buf) - 5);
 875         } else {
 876                 strncpy(buf, str, sizeof(buf) - 1);
 877         }
 878         buf[sizeof(buf) - 1] = 0;
 879         if ((options = strchr(str, ',')) != NULL)
 880                 *(options++) = 0;
 881 #ifdef __sparc__
 882         if (!strcmp(str, "ttya"))
 883                 strcpy(buf, "ttyS0");
 884         if (!strcmp(str, "ttyb"))
 885                 strcpy(buf, "ttyS1");
 886 #endif
 887         for (s = buf; *s; s++)
 888                 if ((*s >= '0' && *s <= '9') || *s == ',')
 889                         break;
 890         idx = simple_strtoul(s, NULL, 10);
 891         *s = 0;
 892
 893         __add_preferred_console(buf, idx, options, brl_options);
 894         console_set_on_cmdline = 1;
 895         return 1;
 896 }
 897 __setup("console=", console_setup);
 898
 899 /**
 900  * add_preferred_console - add a device to the list of preferred consoles.
 901  * @name: device name
 902  * @idx: device index
 903  * @options: options for this console
 904  *
 905  * The last preferred console added will be used for kernel messages
 906  * and stdin/out/err for init.  Normally this is used by console_setup
 907  * above to handle user-supplied console arguments; however it can also
 908  * be used by arch-specific code either to override the user or more
 909  * commonly to provide a default console (ie from PROM variables) when
 910  * the user has not supplied one.
 911  */
 912 int add_preferred_console(char *name, int idx, char *options)
 913 {
 914         return __add_preferred_console(name, idx, options, NULL);
 915 }
 916
 917 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 918 {
 919         struct console_cmdline *c;
 920         int i;
 921
 922         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 923                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 924                           console_cmdline[i].index == idx) {
 925                                 c = &console_cmdline[i];
 926                                 strlcpy(c->name, name_new, sizeof(c->name));
 927                                 c->name[sizeof(c->name) - 1] = 0;
 928                                 c->options = options;
 929                                 c->index = idx_new;
 930                                 return i;
 931                 }
 932         /* not found */
 933         return -1;
 934 }
 935
 936 int console_suspend_enabled = 1;
 937 EXPORT_SYMBOL(console_suspend_enabled);
 938
 939 static int __init console_suspend_disable(char *str)
 940 {
 941         console_suspend_enabled = 0;
 942         return 1;
 943 }
 944 __setup("no_console_suspend", console_suspend_disable);
 945
 946 /**
 947  * suspend_console - suspend the console subsystem
 948  *
 949  * This disables printk() while we go into suspend states
 950  */
 951 void suspend_console(void)
 952 {
 953         if (!console_suspend_enabled)
 954                 return;
 955         printk("Suspending console(s) (use no_console_suspend to debug)\n");
 956         acquire_console_sem();
 957         console_suspended = 1;
 958         up(&console_sem);
 959 }
 960
 961 void resume_console(void)
 962 {
 963         if (!console_suspend_enabled)
 964                 return;
 965         down(&console_sem);
 966         console_suspended = 0;
 967         release_console_sem();
 968 }
 969
 970 /**
 971  * acquire_console_sem - lock the console system for exclusive use.
 972  *
 973  * Acquires a semaphore which guarantees that the caller has
 974  * exclusive access to the console system and the console_drivers list.
 975  *
 976  * Can sleep, returns nothing.
 977  */
 978 void acquire_console_sem(void)
 979 {
 980         BUG_ON(in_interrupt());
 981         down(&console_sem);
 982         if (console_suspended)
 983                 return;
 984         console_locked = 1;
 985         console_may_schedule = 1;
 986 }
 987 EXPORT_SYMBOL(acquire_console_sem);
 988
 989 int try_acquire_console_sem(void)
 990 {
 991         if (down_trylock(&console_sem))
 992                 return -1;
 993         if (console_suspended) {
 994                 up(&console_sem);
 995                 return -1;
 996         }
 997         console_locked = 1;
 998         console_may_schedule = 0;
 999         return 0;
1000 }
1001 EXPORT_SYMBOL(try_acquire_console_sem);
1002
1003 int is_console_locked(void)
1004 {
1005         return console_locked;
1006 }
1007
1008 static DEFINE_PER_CPU(int, printk_pending);
1009
1010 void printk_tick(void)
1011 {
1012         if (__get_cpu_var(printk_pending)) {
1013                 __get_cpu_var(printk_pending) = 0;
1014                 wake_up_interruptible(&log_wait);
1015         }
1016 }
1017
1018 int printk_needs_cpu(int cpu)
1019 {
1020         return per_cpu(printk_pending, cpu);
1021 }
1022
1023 void wake_up_klogd(void)
1024 {
1025         if (waitqueue_active(&log_wait))
1026                 __raw_get_cpu_var(printk_pending) = 1;
1027 }
1028
1029 /**
1030  * release_console_sem - unlock the console system
1031  *
1032  * Releases the semaphore which the caller holds on the console system
1033  * and the console driver list.
1034  *
1035  * While the semaphore was held, console output may have been buffered
1036  * by printk().  If this is the case, release_console_sem() emits
1037  * the output prior to releasing the semaphore.
1038  *
1039  * If there is output waiting for klogd, we wake it up.
1040  *
1041  * release_console_sem() may be called from any context.
1042  */
1043 void release_console_sem(void)
1044 {
1045         unsigned long flags;
1046         unsigned _con_start, _log_end;
1047         unsigned wake_klogd = 0;
1048
1049         if (console_suspended) {
1050                 up(&console_sem);
1051                 return;
1052         }
1053
1054         console_may_schedule = 0;
1055
1056         for ( ; ; ) {
1057                 spin_lock_irqsave(&logbuf_lock, flags);
1058                 wake_klogd |= log_start - log_end;
1059                 if (con_start == log_end)
1060                         break;                  /* Nothing to print */
1061                 _con_start = con_start;
1062                 _log_end = log_end;
1063                 con_start = log_end;            /* Flush */
1064                 spin_unlock(&logbuf_lock);
1065                 stop_critical_timings();        /* don't trace print latency */
1066                 call_console_drivers(_con_start, _log_end);
1067                 start_critical_timings();
1068                 local_irq_restore(flags);
1069         }
1070         console_locked = 0;
1071         up(&console_sem);
1072         spin_unlock_irqrestore(&logbuf_lock, flags);
1073         if (wake_klogd)
1074                 wake_up_klogd();
1075 }
1076 EXPORT_SYMBOL(release_console_sem);
1077
1078 /**
1079  * console_conditional_schedule - yield the CPU if required
1080  *
1081  * If the console code is currently allowed to sleep, and
1082  * if this CPU should yield the CPU to another task, do
1083  * so here.
1084  *
1085  * Must be called within acquire_console_sem().
1086  */
1087 void __sched console_conditional_schedule(void)
1088 {
1089         if (console_may_schedule)
1090                 cond_resched();
1091 }
1092 EXPORT_SYMBOL(console_conditional_schedule);
1093
1094 void console_unblank(void)
1095 {
1096         struct console *c;
1097
1098         /*
1099          * console_unblank can no longer be called in interrupt context unless
1100          * oops_in_progress is set to 1..
1101          */
1102         if (oops_in_progress) {
1103                 if (down_trylock(&console_sem) != 0)
1104                         return;
1105         } else
1106                 acquire_console_sem();
1107
1108         console_locked = 1;
1109         console_may_schedule = 0;
1110         for_each_console(c)
1111                 if ((c->flags & CON_ENABLED) && c->unblank)
1112                         c->unblank();
1113         release_console_sem();
1114 }
1115
1116 /*
1117  * Return the console tty driver structure and its associated index
1118  */
1119 struct tty_driver *console_device(int *index)
1120 {
1121         struct console *c;
1122         struct tty_driver *driver = NULL;
1123
1124         acquire_console_sem();
1125         for_each_console(c) {
1126                 if (!c->device)
1127                         continue;
1128                 driver = c->device(c, index);
1129                 if (driver)
1130                         break;
1131         }
1132         release_console_sem();
1133         return driver;
1134 }
1135
1136 /*
1137  * Prevent further output on the passed console device so that (for example)
1138  * serial drivers can disable console output before suspending a port, and can
1139  * re-enable output afterwards.
1140  */
1141 void console_stop(struct console *console)
1142 {
1143         acquire_console_sem();
1144         console->flags &= ~CON_ENABLED;
1145         release_console_sem();
1146 }
1147 EXPORT_SYMBOL(console_stop);
1148
1149 void console_start(struct console *console)
1150 {
1151         acquire_console_sem();
1152         console->flags |= CON_ENABLED;
1153         release_console_sem();
1154 }
1155 EXPORT_SYMBOL(console_start);
1156
1157 /*
1158  * The console driver calls this routine during kernel initialization
1159  * to register the console printing procedure with printk() and to
1160  * print any messages that were printed by the kernel before the
1161  * console driver was initialized.
1162  *
1163  * This can happen pretty early during the boot process (because of
1164  * early_printk) - sometimes before setup_arch() completes - be careful
1165  * of what kernel features are used - they may not be initialised yet.
1166  *
1167  * There are two types of consoles - bootconsoles (early_printk) and
1168  * "real" consoles (everything which is not a bootconsole) which are
1169  * handled differently.
1170  *  - Any number of bootconsoles can be registered at any time.
1171  *  - As soon as a "real" console is registered, all bootconsoles
1172  *    will be unregistered automatically.
1173  *  - Once a "real" console is registered, any attempt to register a
1174  *    bootconsoles will be rejected
1175  */
1176 void register_console(struct console *newcon)
1177 {
1178         int i;
1179         unsigned long flags;
1180         struct console *bcon = NULL;
1181
1182         /*
1183          * before we register a new CON_BOOT console, make sure we don't
1184          * already have a valid console
1185          */
1186         if (console_drivers && newcon->flags & CON_BOOT) {
1187                 /* find the last or real console */
1188                 for_each_console(bcon) {
1189                         if (!(bcon->flags & CON_BOOT)) {
1190                                 printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1191                                         newcon->name, newcon->index);
1192                                 return;
1193                         }
1194                 }
1195         }
1196
1197         if (console_drivers && console_drivers->flags & CON_BOOT)
1198                 bcon = console_drivers;
1199
1200         if (preferred_console < 0 || bcon || !console_drivers)
1201                 preferred_console = selected_console;
1202
1203         if (newcon->early_setup)
1204                 newcon->early_setup();
1205
1206         /*
1207          *      See if we want to use this console driver. If we
1208          *      didn't select a console we take the first one
1209          *      that registers here.
1210          */
1211         if (preferred_console < 0) {
1212                 if (newcon->index < 0)
1213                         newcon->index = 0;
1214                 if (newcon->setup == NULL ||
1215                     newcon->setup(newcon, NULL) == 0) {
1216                         newcon->flags |= CON_ENABLED;
1217                         if (newcon->device) {
1218                                 newcon->flags |= CON_CONSDEV;
1219                                 preferred_console = 0;
1220                         }
1221                 }
1222         }
1223
1224         /*
1225          *      See if this console matches one we selected on
1226          *      the command line.
1227          */
1228         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1229                         i++) {
1230                 if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1231                         continue;
1232                 if (newcon->index >= 0 &&
1233                     newcon->index != console_cmdline[i].index)
1234                         continue;
1235                 if (newcon->index < 0)
1236                         newcon->index = console_cmdline[i].index;
1237 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1238                 if (console_cmdline[i].brl_options) {
1239                         newcon->flags |= CON_BRL;
1240                         braille_register_console(newcon,
1241                                         console_cmdline[i].index,
1242                                         console_cmdline[i].options,
1243                                         console_cmdline[i].brl_options);
1244                         return;
1245                 }
1246 #endif
1247                 if (newcon->setup &&
1248                     newcon->setup(newcon, console_cmdline[i].options) != 0)
1249                         break;
1250                 newcon->flags |= CON_ENABLED;
1251                 newcon->index = console_cmdline[i].index;
1252                 if (i == selected_console) {
1253                         newcon->flags |= CON_CONSDEV;
1254                         preferred_console = selected_console;
1255                 }
1256                 break;
1257         }
1258
1259         if (!(newcon->flags & CON_ENABLED))
1260                 return;
1261
1262         /*
1263          * If we have a bootconsole, and are switching to a real console,
1264          * don't print everything out again, since when the boot console, and
1265          * the real console are the same physical device, it's annoying to
1266          * see the beginning boot messages twice
1267          */
1268         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1269                 newcon->flags &= ~CON_PRINTBUFFER;
1270
1271         /*
1272          *      Put this console in the list - keep the
1273          *      preferred driver at the head of the list.
1274          */
1275         acquire_console_sem();
1276         if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1277                 newcon->next = console_drivers;
1278                 console_drivers = newcon;
1279                 if (newcon->next)
1280                         newcon->next->flags &= ~CON_CONSDEV;
1281         } else {
1282                 newcon->next = console_drivers->next;
1283                 console_drivers->next = newcon;
1284         }
1285         if (newcon->flags & CON_PRINTBUFFER) {
1286                 /*
1287                  * release_console_sem() will print out the buffered messages
1288                  * for us.
1289                  */
1290                 spin_lock_irqsave(&logbuf_lock, flags);
1291                 con_start = log_start;
1292                 spin_unlock_irqrestore(&logbuf_lock, flags);
1293         }
1294         release_console_sem();
1295
1296         /*
1297          * By unregistering the bootconsoles after we enable the real console
1298          * we get the "console xxx enabled" message on all the consoles -
1299          * boot consoles, real consoles, etc - this is to ensure that end
1300          * users know there might be something in the kernel's log buffer that
1301          * went to the bootconsole (that they do not see on the real console)
1302          */
1303         if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
1304                 /* we need to iterate through twice, to make sure we print
1305                  * everything out, before we unregister the console(s)
1306                  */
1307                 printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1308                         newcon->name, newcon->index);
1309                 for_each_console(bcon)
1310                         if (bcon->flags & CON_BOOT)
1311                                 unregister_console(bcon);
1312         } else {
1313                 printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1314                         (newcon->flags & CON_BOOT) ? "boot" : "" ,
1315                         newcon->name, newcon->index);
1316         }
1317 }
1318 EXPORT_SYMBOL(register_console);
1319
1320 int unregister_console(struct console *console)
1321 {
1322         struct console *a, *b;
1323         int res = 1;
1324
1325 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1326         if (console->flags & CON_BRL)
1327                 return braille_unregister_console(console);
1328 #endif
1329
1330         acquire_console_sem();
1331         if (console_drivers == console) {
1332                 console_drivers=console->next;
1333                 res = 0;
1334         } else if (console_drivers) {
1335                 for (a=console_drivers->next, b=console_drivers ;
1336                      a; b=a, a=b->next) {
1337                         if (a == console) {
1338                                 b->next = a->next;
1339                                 res = 0;
1340                                 break;
1341                         }
1342                 }
1343         }
1344
1345         /*
1346          * If this isn't the last console and it has CON_CONSDEV set, we
1347          * need to set it on the next preferred console.
1348          */
1349         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1350                 console_drivers->flags |= CON_CONSDEV;
1351
1352         release_console_sem();
1353         return res;
1354 }
1355 EXPORT_SYMBOL(unregister_console);
1356
1357 static int __init disable_boot_consoles(void)
1358 {
1359         struct console *con;
1360
1361         for_each_console(con) {
1362                 if (con->flags & CON_BOOT) {
1363                         printk(KERN_INFO "turn off boot console %s%d\n",
1364                                 con->name, con->index);
1365                         unregister_console(con);
1366                 }
1367         }
1368         return 0;
1369 }
1370 late_initcall(disable_boot_consoles);
1371
1372 #if defined CONFIG_PRINTK
1373
1374 /*
1375  * printk rate limiting, lifted from the networking subsystem.
1376  *
1377  * This enforces a rate limit: not more than 10 kernel messages
1378  * every 5s to make a denial-of-service attack impossible.
1379  */
1380 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1381
1382 int __printk_ratelimit(const char *func)
1383 {
1384         return ___ratelimit(&printk_ratelimit_state, func);
1385 }
1386 EXPORT_SYMBOL(__printk_ratelimit);
1387
1388 /**
1389  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1390  * @caller_jiffies: pointer to caller's state
1391  * @interval_msecs: minimum interval between prints
1392  *
1393  * printk_timed_ratelimit() returns true if more than @interval_msecs
1394  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1395  * returned true.
1396  */
1397 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1398                         unsigned int interval_msecs)
1399 {
1400         if (*caller_jiffies == 0
1401                         || !time_in_range(jiffies, *caller_jiffies,
1402                                         *caller_jiffies
1403                                         + msecs_to_jiffies(interval_msecs))) {
1404                 *caller_jiffies = jiffies;
1405                 return true;
1406         }
1407         return false;
1408 }
1409 EXPORT_SYMBOL(printk_timed_ratelimit);
1410
1411 static DEFINE_SPINLOCK(dump_list_lock);
1412 static LIST_HEAD(dump_list);
1413
1414 /**
1415  * kmsg_dump_register - register a kernel log dumper.
1416  * @dumper: pointer to the kmsg_dumper structure
1417  *
1418  * Adds a kernel log dumper to the system. The dump callback in the
1419  * structure will be called when the kernel oopses or panics and must be
1420  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1421  */
1422 int kmsg_dump_register(struct kmsg_dumper *dumper)
1423 {
1424         unsigned long flags;
1425         int err = -EBUSY;
1426
1427         /* The dump callback needs to be set */
1428         if (!dumper->dump)
1429                 return -EINVAL;
1430
1431         spin_lock_irqsave(&dump_list_lock, flags);
1432         /* Don't allow registering multiple times */
1433         if (!dumper->registered) {
1434                 dumper->registered = 1;
1435                 list_add_tail(&dumper->list, &dump_list);
1436                 err = 0;
1437         }
1438         spin_unlock_irqrestore(&dump_list_lock, flags);
1439
1440         return err;
1441 }
1442 EXPORT_SYMBOL_GPL(kmsg_dump_register);
1443
1444 /**
1445  * kmsg_dump_unregister - unregister a kmsg dumper.
1446  * @dumper: pointer to the kmsg_dumper structure
1447  *
1448  * Removes a dump device from the system. Returns zero on success and
1449  * %-EINVAL otherwise.
1450  */
1451 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1452 {
1453         unsigned long flags;
1454         int err = -EINVAL;
1455
1456         spin_lock_irqsave(&dump_list_lock, flags);
1457         if (dumper->registered) {
1458                 dumper->registered = 0;
1459                 list_del(&dumper->list);
1460                 err = 0;
1461         }
1462         spin_unlock_irqrestore(&dump_list_lock, flags);
1463
1464         return err;
1465 }
1466 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1467
1468 static const char const *kmsg_reasons[] = {
1469         [KMSG_DUMP_OOPS]        = "oops",
1470         [KMSG_DUMP_PANIC]       = "panic",
1471 };
1472
1473 static const char *kmsg_to_str(enum kmsg_dump_reason reason)
1474 {
1475         if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
1476                 return "unknown";
1477
1478         return kmsg_reasons[reason];
1479 }
1480
1481 /**
1482  * kmsg_dump - dump kernel log to kernel message dumpers.
1483  * @reason: the reason (oops, panic etc) for dumping
1484  *
1485  * Iterate through each of the dump devices and call the oops/panic
1486  * callbacks with the log buffer.
1487  */
1488 void kmsg_dump(enum kmsg_dump_reason reason)
1489 {
1490         unsigned long end;
1491         unsigned chars;
1492         struct kmsg_dumper *dumper;
1493         const char *s1, *s2;
1494         unsigned long l1, l2;
1495         unsigned long flags;
1496
1497         /* Theoretically, the log could move on after we do this, but
1498            there's not a lot we can do about that. The new messages
1499            will overwrite the start of what we dump. */
1500         spin_lock_irqsave(&logbuf_lock, flags);
1501         end = log_end & LOG_BUF_MASK;
1502         chars = logged_chars;
1503         spin_unlock_irqrestore(&logbuf_lock, flags);
1504
1505         if (logged_chars > end) {
1506                 s1 = log_buf + log_buf_len - logged_chars + end;
1507                 l1 = logged_chars - end;
1508
1509                 s2 = log_buf;
1510                 l2 = end;
1511         } else {
1512                 s1 = "";
1513                 l1 = 0;
1514
1515                 s2 = log_buf + end - logged_chars;
1516                 l2 = logged_chars;
1517         }
1518
1519         if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
1520                 printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
1521                                 kmsg_to_str(reason));
1522                 return;
1523         }
1524         list_for_each_entry(dumper, &dump_list, list)
1525                 dumper->dump(dumper, reason, s1, l1, s2, l2);
1526         spin_unlock_irqrestore(&dump_list_lock, flags);
1527 }
1528 #endif