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 <andrewm@uow.edu.au>
  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/smp_lock.h>
  24 #include <linux/console.h>
  25 #include <linux/init.h>
  26 #include <linux/module.h>
  27 #include <linux/interrupt.h>                    /* For in_interrupt() */
  28 #include <linux/config.h>
  29 #include <linux/delay.h>
  30 #include <linux/smp.h>
  31 #include <linux/security.h>
  32 #include <linux/bootmem.h>
  33 #include <linux/syscalls.h>
  34 #include <linux/vs_base.h>
  35 #include <linux/vs_cvirt.h>
  36
  37 #include <asm/uaccess.h>
  38
  39 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  40
  41 /* printk's without a loglevel use this.. */
  42 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  43
  44 /* We show everything that is MORE important than this.. */
  45 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  46 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  47
  48 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  49
  50 int console_printk[4] = {
  51         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  52         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  53         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  54         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  55 };
  56
  57 EXPORT_SYMBOL(console_printk);
  58
  59 /*
  60  * Low lever drivers may need that to know if they can schedule in
  61  * their unblank() callback or not. So let's export it.
  62  */
  63 int oops_in_progress;
  64 EXPORT_SYMBOL(oops_in_progress);
  65
  66 /*
  67  * console_sem protects the console_drivers list, and also
  68  * provides serialisation for access to the entire console
  69  * driver system.
  70  */
  71 static DECLARE_MUTEX(console_sem);
  72 struct console *console_drivers;
  73 /*
  74  * This is used for debugging the mess that is the VT code by
  75  * keeping track if we have the console semaphore held. It's
  76  * definitely not the perfect debug tool (we don't know if _WE_
  77  * hold it are racing, but it helps tracking those weird code
  78  * path in the console code where we end up in places I want
  79  * locked without the console sempahore held
  80  */
  81 static int console_locked;
  82
  83 /*
  84  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  85  * It is also used in interesting ways to provide interlocking in
  86  * release_console_sem().
  87  */
  88 static DEFINE_SPINLOCK(logbuf_lock);
  89
  90 #define LOG_BUF_MASK    (log_buf_len-1)
  91 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  92
  93 /*
  94  * The indices into log_buf are not constrained to log_buf_len - they
  95  * must be masked before subscripting
  96  */
  97 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  98 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  99 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
 100
 101 /*
 102  *      Array of consoles built from command line options (console=)
 103  */
 104 struct console_cmdline
 105 {
 106         char    name[8];                        /* Name of the driver       */
 107         int     index;                          /* Minor dev. to use        */
 108         char    *options;                       /* Options for the driver   */
 109 };
 110
 111 #define MAX_CMDLINECONSOLES 8
 112
 113 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 114 static int selected_console = -1;
 115 static int preferred_console = -1;
 116
 117 /* Flag: console code may call schedule() */
 118 static int console_may_schedule;
 119
 120 #ifdef CONFIG_PRINTK
 121
 122 static char __log_buf[__LOG_BUF_LEN];
 123 static char *log_buf = __log_buf;
 124 static int log_buf_len = __LOG_BUF_LEN;
 125 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 126
 127 /*
 128  *      Setup a list of consoles. Called from init/main.c
 129  */
 130 static int __init console_setup(char *str)
 131 {
 132         char name[sizeof(console_cmdline[0].name)];
 133         char *s, *options;
 134         int idx;
 135
 136         /*
 137          *      Decode str into name, index, options.
 138          */
 139         if (str[0] >= '0' && str[0] <= '9') {
 140                 strcpy(name, "ttyS");
 141                 strncpy(name + 4, str, sizeof(name) - 5);
 142         } else
 143                 strncpy(name, str, sizeof(name) - 1);
 144         name[sizeof(name) - 1] = 0;
 145         if ((options = strchr(str, ',')) != NULL)
 146                 *(options++) = 0;
 147 #ifdef __sparc__
 148         if (!strcmp(str, "ttya"))
 149                 strcpy(name, "ttyS0");
 150         if (!strcmp(str, "ttyb"))
 151                 strcpy(name, "ttyS1");
 152 #endif
 153         for (s = name; *s; s++)
 154                 if ((*s >= '0' && *s <= '9') || *s == ',')
 155                         break;
 156         idx = simple_strtoul(s, NULL, 10);
 157         *s = 0;
 158
 159         add_preferred_console(name, idx, options);
 160         return 1;
 161 }
 162
 163 __setup("console=", console_setup);
 164
 165 static int __init log_buf_len_setup(char *str)
 166 {
 167         unsigned long size = memparse(str, &str);
 168         unsigned long flags;
 169
 170         if (size)
 171                 size = roundup_pow_of_two(size);
 172         if (size > log_buf_len) {
 173                 unsigned long start, dest_idx, offset;
 174                 char *new_log_buf;
 175
 176                 new_log_buf = alloc_bootmem(size);
 177                 if (!new_log_buf) {
 178                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 179                         goto out;
 180                 }
 181
 182                 spin_lock_irqsave(&logbuf_lock, flags);
 183                 log_buf_len = size;
 184                 log_buf = new_log_buf;
 185
 186                 offset = start = min(con_start, log_start);
 187                 dest_idx = 0;
 188                 while (start != log_end) {
 189                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 190                         start++;
 191                         dest_idx++;
 192                 }
 193                 log_start -= offset;
 194                 con_start -= offset;
 195                 log_end -= offset;
 196                 spin_unlock_irqrestore(&logbuf_lock, flags);
 197
 198                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 199         }
 200 out:
 201         return 1;
 202 }
 203
 204 __setup("log_buf_len=", log_buf_len_setup);
 205
 206 /*
 207  * Commands to do_syslog:
 208  *
 209  *      0 -- Close the log.  Currently a NOP.
 210  *      1 -- Open the log. Currently a NOP.
 211  *      2 -- Read from the log.
 212  *      3 -- Read all messages remaining in the ring buffer.
 213  *      4 -- Read and clear all messages remaining in the ring buffer
 214  *      5 -- Clear ring buffer.
 215  *      6 -- Disable printk's to console
 216  *      7 -- Enable printk's to console
 217  *      8 -- Set level of messages printed to console
 218  *      9 -- Return number of unread characters in the log buffer
 219  *     10 -- Return size of the log buffer
 220  */
 221 int do_syslog(int type, char __user *buf, int len)
 222 {
 223         unsigned long i, j, limit, count;
 224         int do_clear = 0;
 225         char c;
 226         int error;
 227
 228         error = security_syslog(type);
 229         if (error)
 230                 return error;
 231
 232         if ((type >= 2) && (type <= 4)) {
 233                 error = -EINVAL;
 234                 if (!buf || len < 0)
 235                         goto out;
 236                 error = 0;
 237                 if (!len)
 238                         goto out;
 239                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 240                         error = -EFAULT;
 241                         goto out;
 242                 }
 243         }
 244         if (!vx_check(0, VX_ADMIN|VX_WATCH))
 245                 return vx_do_syslog(type, buf, len);
 246
 247         switch (type) {
 248         case 0:         /* Close log */
 249                 break;
 250         case 1:         /* Open log */
 251                 break;
 252         case 2:         /* Read from log */
 253                 error = wait_event_interruptible(log_wait,
 254                                                         (log_start - log_end));
 255                 if (error)
 256                         goto out;
 257                 i = 0;
 258                 spin_lock_irq(&logbuf_lock);
 259                 while (!error && (log_start != log_end) && i < len) {
 260                         c = LOG_BUF(log_start);
 261                         log_start++;
 262                         spin_unlock_irq(&logbuf_lock);
 263                         error = __put_user(c,buf);
 264                         buf++;
 265                         i++;
 266                         cond_resched();
 267                         spin_lock_irq(&logbuf_lock);
 268                 }
 269                 spin_unlock_irq(&logbuf_lock);
 270                 if (!error)
 271                         error = i;
 272                 break;
 273         case 4:         /* Read/clear last kernel messages */
 274                 do_clear = 1;
 275                 /* FALL THRU */
 276         case 3:         /* Read last kernel messages */
 277                 count = len;
 278                 if (count > log_buf_len)
 279                         count = log_buf_len;
 280                 spin_lock_irq(&logbuf_lock);
 281                 if (count > logged_chars)
 282                         count = logged_chars;
 283                 if (do_clear)
 284                         logged_chars = 0;
 285                 limit = log_end;
 286                 /*
 287                  * __put_user() could sleep, and while we sleep
 288                  * printk() could overwrite the messages
 289                  * we try to copy to user space. Therefore
 290                  * the messages are copied in reverse. <manfreds>
 291                  */
 292                 for (i = 0; i < count && !error; i++) {
 293                         j = limit-1-i;
 294                         if (j + log_buf_len < log_end)
 295                                 break;
 296                         c = LOG_BUF(j);
 297                         spin_unlock_irq(&logbuf_lock);
 298                         error = __put_user(c,&buf[count-1-i]);
 299                         cond_resched();
 300                         spin_lock_irq(&logbuf_lock);
 301                 }
 302                 spin_unlock_irq(&logbuf_lock);
 303                 if (error)
 304                         break;
 305                 error = i;
 306                 if (i != count) {
 307                         int offset = count-error;
 308                         /* buffer overflow during copy, correct user buffer. */
 309                         for (i = 0; i < error; i++) {
 310                                 if (__get_user(c,&buf[i+offset]) ||
 311                                     __put_user(c,&buf[i])) {
 312                                         error = -EFAULT;
 313                                         break;
 314                                 }
 315                                 cond_resched();
 316                         }
 317                 }
 318                 break;
 319         case 5:         /* Clear ring buffer */
 320                 logged_chars = 0;
 321                 break;
 322         case 6:         /* Disable logging to console */
 323                 console_loglevel = minimum_console_loglevel;
 324                 break;
 325         case 7:         /* Enable logging to console */
 326                 console_loglevel = default_console_loglevel;
 327                 break;
 328         case 8:         /* Set level of messages printed to console */
 329                 error = -EINVAL;
 330                 if (len < 1 || len > 8)
 331                         goto out;
 332                 if (len < minimum_console_loglevel)
 333                         len = minimum_console_loglevel;
 334                 console_loglevel = len;
 335                 error = 0;
 336                 break;
 337         case 9:         /* Number of chars in the log buffer */
 338                 error = log_end - log_start;
 339                 break;
 340         case 10:        /* Size of the log buffer */
 341                 error = log_buf_len;
 342                 break;
 343         default:
 344                 error = -EINVAL;
 345                 break;
 346         }
 347 out:
 348         return error;
 349 }
 350
 351 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 352 {
 353         return do_syslog(type, buf, len);
 354 }
 355
 356 /*
 357  * Call the console drivers on a range of log_buf
 358  */
 359 static void __call_console_drivers(unsigned long start, unsigned long end)
 360 {
 361         struct console *con;
 362
 363         for (con = console_drivers; con; con = con->next) {
 364                 if ((con->flags & CON_ENABLED) && con->write)
 365                         con->write(con, &LOG_BUF(start), end - start);
 366         }
 367 }
 368
 369 /*
 370  * Write out chars from start to end - 1 inclusive
 371  */
 372 static void _call_console_drivers(unsigned long start,
 373                                 unsigned long end, int msg_log_level)
 374 {
 375         if (msg_log_level < console_loglevel &&
 376                         console_drivers && start != end) {
 377                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 378                         /* wrapped write */
 379                         __call_console_drivers(start & LOG_BUF_MASK,
 380                                                 log_buf_len);
 381                         __call_console_drivers(0, end & LOG_BUF_MASK);
 382                 } else {
 383                         __call_console_drivers(start, end);
 384                 }
 385         }
 386 }
 387
 388 /*
 389  * Call the console drivers, asking them to write out
 390  * log_buf[start] to log_buf[end - 1].
 391  * The console_sem must be held.
 392  */
 393 static void call_console_drivers(unsigned long start, unsigned long end)
 394 {
 395         unsigned long cur_index, start_print;
 396         static int msg_level = -1;
 397
 398         if (((long)(start - end)) > 0)
 399                 BUG();
 400
 401         cur_index = start;
 402         start_print = start;
 403         while (cur_index != end) {
 404                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 405                                 LOG_BUF(cur_index + 0) == '<' &&
 406                                 LOG_BUF(cur_index + 1) >= '0' &&
 407                                 LOG_BUF(cur_index + 1) <= '7' &&
 408                                 LOG_BUF(cur_index + 2) == '>') {
 409                         msg_level = LOG_BUF(cur_index + 1) - '0';
 410                         cur_index += 3;
 411                         start_print = cur_index;
 412                 }
 413                 while (cur_index != end) {
 414                         char c = LOG_BUF(cur_index);
 415
 416                         cur_index++;
 417                         if (c == '\n') {
 418                                 if (msg_level < 0) {
 419                                         /*
 420                                          * printk() has already given us loglevel tags in
 421                                          * the buffer.  This code is here in case the
 422                                          * log buffer has wrapped right round and scribbled
 423                                          * on those tags
 424                                          */
 425                                         msg_level = default_message_loglevel;
 426                                 }
 427                                 _call_console_drivers(start_print, cur_index, msg_level);
 428                                 msg_level = -1;
 429                                 start_print = cur_index;
 430                                 break;
 431                         }
 432                 }
 433         }
 434         _call_console_drivers(start_print, end, msg_level);
 435 }
 436
 437 static void emit_log_char(char c)
 438 {
 439         LOG_BUF(log_end) = c;
 440         log_end++;
 441         if (log_end - log_start > log_buf_len)
 442                 log_start = log_end - log_buf_len;
 443         if (log_end - con_start > log_buf_len)
 444                 con_start = log_end - log_buf_len;
 445         if (logged_chars < log_buf_len)
 446                 logged_chars++;
 447 }
 448
 449 /*
 450  * Zap console related locks when oopsing. Only zap at most once
 451  * every 10 seconds, to leave time for slow consoles to print a
 452  * full oops.
 453  */
 454 static void zap_locks(void)
 455 {
 456         static unsigned long oops_timestamp;
 457
 458         if (time_after_eq(jiffies, oops_timestamp) &&
 459                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 460                 return;
 461
 462         oops_timestamp = jiffies;
 463
 464         /* If a crash is occurring, make sure we can't deadlock */
 465         spin_lock_init(&logbuf_lock);
 466         /* And make sure that we print immediately */
 467         init_MUTEX(&console_sem);
 468 }
 469
 470 #if defined(CONFIG_PRINTK_TIME)
 471 static int printk_time = 1;
 472 #else
 473 static int printk_time = 0;
 474 #endif
 475
 476 static int __init printk_time_setup(char *str)
 477 {
 478         if (*str)
 479                 return 0;
 480         printk_time = 1;
 481         return 1;
 482 }
 483
 484 __setup("time", printk_time_setup);
 485
 486 __attribute__((weak)) unsigned long long printk_clock(void)
 487 {
 488         return sched_clock();
 489 }
 490
 491 /**
 492  * printk - print a kernel message
 493  * @fmt: format string
 494  *
 495  * This is printk.  It can be called from any context.  We want it to work.
 496  *
 497  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 498  * call the console drivers.  If we fail to get the semaphore we place the output
 499  * into the log buffer and return.  The current holder of the console_sem will
 500  * notice the new output in release_console_sem() and will send it to the
 501  * consoles before releasing the semaphore.
 502  *
 503  * One effect of this deferred printing is that code which calls printk() and
 504  * then changes console_loglevel may break. This is because console_loglevel
 505  * is inspected when the actual printing occurs.
 506  *
 507  * See also:
 508  * printf(3)
 509  */
 510
 511 asmlinkage int printk(const char *fmt, ...)
 512 {
 513         va_list args;
 514         int r;
 515
 516         va_start(args, fmt);
 517         r = vprintk(fmt, args);
 518         va_end(args);
 519
 520         return r;
 521 }
 522
 523 /* cpu currently holding logbuf_lock */
 524 static volatile unsigned int printk_cpu = UINT_MAX;
 525
 526 asmlinkage int vprintk(const char *fmt, va_list args)
 527 {
 528         unsigned long flags;
 529         int printed_len;
 530         char *p;
 531         static char printk_buf[1024];
 532         static int log_level_unknown = 1;
 533
 534         preempt_disable();
 535         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 536                 /* If a crash is occurring during printk() on this CPU,
 537                  * make sure we can't deadlock */
 538                 zap_locks();
 539
 540         /* This stops the holder of console_sem just where we want him */
 541         spin_lock_irqsave(&logbuf_lock, flags);
 542         printk_cpu = smp_processor_id();
 543
 544         /* Emit the output into the temporary buffer */
 545         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 546
 547         /*
 548          * Copy the output into log_buf.  If the caller didn't provide
 549          * appropriate log level tags, we insert them here
 550          */
 551         for (p = printk_buf; *p; p++) {
 552                 if (log_level_unknown) {
 553                         /* log_level_unknown signals the start of a new line */
 554                         if (printk_time) {
 555                                 int loglev_char;
 556                                 char tbuf[50], *tp;
 557                                 unsigned tlen;
 558                                 unsigned long long t;
 559                                 unsigned long nanosec_rem;
 560
 561                                 /*
 562                                  * force the log level token to be
 563                                  * before the time output.
 564                                  */
 565                                 if (p[0] == '<' && p[1] >='0' &&
 566                                    p[1] <= '7' && p[2] == '>') {
 567                                         loglev_char = p[1];
 568                                         p += 3;
 569                                         printed_len -= 3;
 570                                 } else {
 571                                         loglev_char = default_message_loglevel
 572                                                 + '0';
 573                                 }
 574                                 t = printk_clock();
 575                                 nanosec_rem = do_div(t, 1000000000);
 576                                 tlen = sprintf(tbuf,
 577                                                 "<%c>[%5lu.%06lu] ",
 578                                                 loglev_char,
 579                                                 (unsigned long)t,
 580                                                 nanosec_rem/1000);
 581
 582                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 583                                         emit_log_char(*tp);
 584                                 printed_len += tlen;
 585                         } else {
 586                                 if (p[0] != '<' || p[1] < '0' ||
 587                                    p[1] > '7' || p[2] != '>') {
 588                                         emit_log_char('<');
 589                                         emit_log_char(default_message_loglevel
 590                                                 + '0');
 591                                         emit_log_char('>');
 592                                         printed_len += 3;
 593                                 }
 594                         }
 595                         log_level_unknown = 0;
 596                         if (!*p)
 597                                 break;
 598                 }
 599                 emit_log_char(*p);
 600                 if (*p == '\n')
 601                         log_level_unknown = 1;
 602         }
 603
 604         if (!cpu_online(smp_processor_id())) {
 605                 /*
 606                  * Some console drivers may assume that per-cpu resources have
 607                  * been allocated.  So don't allow them to be called by this
 608                  * CPU until it is officially up.  We shouldn't be calling into
 609                  * random console drivers on a CPU which doesn't exist yet..
 610                  */
 611                 printk_cpu = UINT_MAX;
 612                 spin_unlock_irqrestore(&logbuf_lock, flags);
 613                 goto out;
 614         }
 615         if (!down_trylock(&console_sem)) {
 616                 console_locked = 1;
 617                 /*
 618                  * We own the drivers.  We can drop the spinlock and let
 619                  * release_console_sem() print the text
 620                  */
 621                 printk_cpu = UINT_MAX;
 622                 spin_unlock_irqrestore(&logbuf_lock, flags);
 623                 console_may_schedule = 0;
 624                 release_console_sem();
 625         } else {
 626                 /*
 627                  * Someone else owns the drivers.  We drop the spinlock, which
 628                  * allows the semaphore holder to proceed and to call the
 629                  * console drivers with the output which we just produced.
 630                  */
 631                 printk_cpu = UINT_MAX;
 632                 spin_unlock_irqrestore(&logbuf_lock, flags);
 633         }
 634 out:
 635         preempt_enable();
 636         return printed_len;
 637 }
 638 EXPORT_SYMBOL(printk);
 639 EXPORT_SYMBOL(vprintk);
 640
 641 #else
 642
 643 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 644 {
 645         return 0;
 646 }
 647
 648 int do_syslog(int type, char __user *buf, int len)
 649 {
 650         return 0;
 651 }
 652
 653 static void call_console_drivers(unsigned long start, unsigned long end)
 654 {
 655 }
 656
 657 #endif
 658
 659 /**
 660  * add_preferred_console - add a device to the list of preferred consoles.
 661  * @name: device name
 662  * @idx: device index
 663  * @options: options for this console
 664  *
 665  * The last preferred console added will be used for kernel messages
 666  * and stdin/out/err for init.  Normally this is used by console_setup
 667  * above to handle user-supplied console arguments; however it can also
 668  * be used by arch-specific code either to override the user or more
 669  * commonly to provide a default console (ie from PROM variables) when
 670  * the user has not supplied one.
 671  */
 672 int __init add_preferred_console(char *name, int idx, char *options)
 673 {
 674         struct console_cmdline *c;
 675         int i;
 676
 677         /*
 678          *      See if this tty is not yet registered, and
 679          *      if we have a slot free.
 680          */
 681         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 682                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 683                           console_cmdline[i].index == idx) {
 684                                 selected_console = i;
 685                                 return 0;
 686                 }
 687         if (i == MAX_CMDLINECONSOLES)
 688                 return -E2BIG;
 689         selected_console = i;
 690         c = &console_cmdline[i];
 691         memcpy(c->name, name, sizeof(c->name));
 692         c->name[sizeof(c->name) - 1] = 0;
 693         c->options = options;
 694         c->index = idx;
 695         return 0;
 696 }
 697
 698 /**
 699  * acquire_console_sem - lock the console system for exclusive use.
 700  *
 701  * Acquires a semaphore which guarantees that the caller has
 702  * exclusive access to the console system and the console_drivers list.
 703  *
 704  * Can sleep, returns nothing.
 705  */
 706 void acquire_console_sem(void)
 707 {
 708         if (in_interrupt())
 709                 BUG();
 710         down(&console_sem);
 711         console_locked = 1;
 712         console_may_schedule = 1;
 713 }
 714 EXPORT_SYMBOL(acquire_console_sem);
 715
 716 int try_acquire_console_sem(void)
 717 {
 718         if (down_trylock(&console_sem))
 719                 return -1;
 720         console_locked = 1;
 721         console_may_schedule = 0;
 722         return 0;
 723 }
 724 EXPORT_SYMBOL(try_acquire_console_sem);
 725
 726 int is_console_locked(void)
 727 {
 728         return console_locked;
 729 }
 730 EXPORT_SYMBOL(is_console_locked);
 731
 732 /**
 733  * release_console_sem - unlock the console system
 734  *
 735  * Releases the semaphore which the caller holds on the console system
 736  * and the console driver list.
 737  *
 738  * While the semaphore was held, console output may have been buffered
 739  * by printk().  If this is the case, release_console_sem() emits
 740  * the output prior to releasing the semaphore.
 741  *
 742  * If there is output waiting for klogd, we wake it up.
 743  *
 744  * release_console_sem() may be called from any context.
 745  */
 746 void release_console_sem(void)
 747 {
 748         unsigned long flags;
 749         unsigned long _con_start, _log_end;
 750         unsigned long wake_klogd = 0;
 751
 752         for ( ; ; ) {
 753                 spin_lock_irqsave(&logbuf_lock, flags);
 754                 wake_klogd |= log_start - log_end;
 755                 if (con_start == log_end)
 756                         break;                  /* Nothing to print */
 757                 _con_start = con_start;
 758                 _log_end = log_end;
 759                 con_start = log_end;            /* Flush */
 760                 spin_unlock(&logbuf_lock);
 761                 call_console_drivers(_con_start, _log_end);
 762                 local_irq_restore(flags);
 763         }
 764         console_locked = 0;
 765         console_may_schedule = 0;
 766         up(&console_sem);
 767         spin_unlock_irqrestore(&logbuf_lock, flags);
 768         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 769                 wake_up_interruptible(&log_wait);
 770 }
 771 EXPORT_SYMBOL(release_console_sem);
 772
 773 /**
 774  * console_conditional_schedule - yield the CPU if required
 775  *
 776  * If the console code is currently allowed to sleep, and
 777  * if this CPU should yield the CPU to another task, do
 778  * so here.
 779  *
 780  * Must be called within acquire_console_sem().
 781  */
 782 void __sched console_conditional_schedule(void)
 783 {
 784         if (console_may_schedule)
 785                 cond_resched();
 786 }
 787 EXPORT_SYMBOL(console_conditional_schedule);
 788
 789 void console_print(const char *s)
 790 {
 791         printk(KERN_EMERG "%s", s);
 792 }
 793 EXPORT_SYMBOL(console_print);
 794
 795 void console_unblank(void)
 796 {
 797         struct console *c;
 798
 799         /*
 800          * console_unblank can no longer be called in interrupt context unless
 801          * oops_in_progress is set to 1..
 802          */
 803         if (oops_in_progress) {
 804                 if (down_trylock(&console_sem) != 0)
 805                         return;
 806         } else
 807                 acquire_console_sem();
 808
 809         console_locked = 1;
 810         console_may_schedule = 0;
 811         for (c = console_drivers; c != NULL; c = c->next)
 812                 if ((c->flags & CON_ENABLED) && c->unblank)
 813                         c->unblank();
 814         release_console_sem();
 815 }
 816
 817 /*
 818  * Return the console tty driver structure and its associated index
 819  */
 820 struct tty_driver *console_device(int *index)
 821 {
 822         struct console *c;
 823         struct tty_driver *driver = NULL;
 824
 825         acquire_console_sem();
 826         for (c = console_drivers; c != NULL; c = c->next) {
 827                 if (!c->device)
 828                         continue;
 829                 driver = c->device(c, index);
 830                 if (driver)
 831                         break;
 832         }
 833         release_console_sem();
 834         return driver;
 835 }
 836
 837 /*
 838  * Prevent further output on the passed console device so that (for example)
 839  * serial drivers can disable console output before suspending a port, and can
 840  * re-enable output afterwards.
 841  */
 842 void console_stop(struct console *console)
 843 {
 844         acquire_console_sem();
 845         console->flags &= ~CON_ENABLED;
 846         release_console_sem();
 847 }
 848 EXPORT_SYMBOL(console_stop);
 849
 850 void console_start(struct console *console)
 851 {
 852         acquire_console_sem();
 853         console->flags |= CON_ENABLED;
 854         release_console_sem();
 855 }
 856 EXPORT_SYMBOL(console_start);
 857
 858 /*
 859  * The console driver calls this routine during kernel initialization
 860  * to register the console printing procedure with printk() and to
 861  * print any messages that were printed by the kernel before the
 862  * console driver was initialized.
 863  */
 864 void register_console(struct console *console)
 865 {
 866         int i;
 867         unsigned long flags;
 868
 869         if (preferred_console < 0)
 870                 preferred_console = selected_console;
 871
 872         /*
 873          *      See if we want to use this console driver. If we
 874          *      didn't select a console we take the first one
 875          *      that registers here.
 876          */
 877         if (preferred_console < 0) {
 878                 if (console->index < 0)
 879                         console->index = 0;
 880                 if (console->setup == NULL ||
 881                     console->setup(console, NULL) == 0) {
 882                         console->flags |= CON_ENABLED | CON_CONSDEV;
 883                         preferred_console = 0;
 884                 }
 885         }
 886
 887         /*
 888          *      See if this console matches one we selected on
 889          *      the command line.
 890          */
 891         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 892                         i++) {
 893                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 894                         continue;
 895                 if (console->index >= 0 &&
 896                     console->index != console_cmdline[i].index)
 897                         continue;
 898                 if (console->index < 0)
 899                         console->index = console_cmdline[i].index;
 900                 if (console->setup &&
 901                     console->setup(console, console_cmdline[i].options) != 0)
 902                         break;
 903                 console->flags |= CON_ENABLED;
 904                 console->index = console_cmdline[i].index;
 905                 if (i == selected_console) {
 906                         console->flags |= CON_CONSDEV;
 907                         preferred_console = selected_console;
 908                 }
 909                 break;
 910         }
 911
 912         if (!(console->flags & CON_ENABLED))
 913                 return;
 914
 915         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 916                 unregister_console(console_drivers);
 917                 console->flags &= ~CON_PRINTBUFFER;
 918         }
 919
 920         /*
 921          *      Put this console in the list - keep the
 922          *      preferred driver at the head of the list.
 923          */
 924         acquire_console_sem();
 925         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 926                 console->next = console_drivers;
 927                 console_drivers = console;
 928                 if (console->next)
 929                         console->next->flags &= ~CON_CONSDEV;
 930         } else {
 931                 console->next = console_drivers->next;
 932                 console_drivers->next = console;
 933         }
 934         if (console->flags & CON_PRINTBUFFER) {
 935                 /*
 936                  * release_console_sem() will print out the buffered messages
 937                  * for us.
 938                  */
 939                 spin_lock_irqsave(&logbuf_lock, flags);
 940                 con_start = log_start;
 941                 spin_unlock_irqrestore(&logbuf_lock, flags);
 942         }
 943         release_console_sem();
 944 }
 945 EXPORT_SYMBOL(register_console);
 946
 947 int unregister_console(struct console *console)
 948 {
 949         struct console *a, *b;
 950         int res = 1;
 951
 952         acquire_console_sem();
 953         if (console_drivers == console) {
 954                 console_drivers=console->next;
 955                 res = 0;
 956         } else if (console_drivers) {
 957                 for (a=console_drivers->next, b=console_drivers ;
 958                      a; b=a, a=b->next) {
 959                         if (a == console) {
 960                                 b->next = a->next;
 961                                 res = 0;
 962                                 break;
 963                         }
 964                 }
 965         }
 966
 967         /* If last console is removed, we re-enable picking the first
 968          * one that gets registered. Without that, pmac early boot console
 969          * would prevent fbcon from taking over.
 970          *
 971          * If this isn't the last console and it has CON_CONSDEV set, we
 972          * need to set it on the next preferred console.
 973          */
 974         if (console_drivers == NULL)
 975                 preferred_console = selected_console;
 976         else if (console->flags & CON_CONSDEV)
 977                 console_drivers->flags |= CON_CONSDEV;
 978
 979         release_console_sem();
 980         return res;
 981 }
 982 EXPORT_SYMBOL(unregister_console);
 983
 984 /**
 985  * tty_write_message - write a message to a certain tty, not just the console.
 986  * @tty: the destination tty_struct
 987  * @msg: the message to write
 988  *
 989  * This is used for messages that need to be redirected to a specific tty.
 990  * We don't put it into the syslog queue right now maybe in the future if
 991  * really needed.
 992  */
 993 void tty_write_message(struct tty_struct *tty, char *msg)
 994 {
 995         if (tty && tty->driver->write)
 996                 tty->driver->write(tty, msg, strlen(msg));
 997         return;
 998 }
 999
1000 /*
1001  * printk rate limiting, lifted from the networking subsystem.
1002  *
1003  * This enforces a rate limit: not more than one kernel message
1004  * every printk_ratelimit_jiffies to make a denial-of-service
1005  * attack impossible.
1006  */
1007 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1008 {
1009         static DEFINE_SPINLOCK(ratelimit_lock);
1010         static unsigned long toks = 10 * 5 * HZ;
1011         static unsigned long last_msg;
1012         static int missed;
1013         unsigned long flags;
1014         unsigned long now = jiffies;
1015
1016         spin_lock_irqsave(&ratelimit_lock, flags);
1017         toks += now - last_msg;
1018         last_msg = now;
1019         if (toks > (ratelimit_burst * ratelimit_jiffies))
1020                 toks = ratelimit_burst * ratelimit_jiffies;
1021         if (toks >= ratelimit_jiffies) {
1022                 int lost = missed;
1023
1024                 missed = 0;
1025                 toks -= ratelimit_jiffies;
1026                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1027                 if (lost)
1028                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1029                 return 1;
1030         }
1031         missed++;
1032         spin_unlock_irqrestore(&ratelimit_lock, flags);
1033         return 0;
1034 }
1035 EXPORT_SYMBOL(__printk_ratelimit);
1036
1037 /* minimum time in jiffies between messages */
1038 int printk_ratelimit_jiffies = 5 * HZ;
1039
1040 /* number of messages we send before ratelimiting */
1041 int printk_ratelimit_burst = 10;
1042
1043 int printk_ratelimit(void)
1044 {
1045         return __printk_ratelimit(printk_ratelimit_jiffies,
1046                                 printk_ratelimit_burst);
1047 }
1048 EXPORT_SYMBOL(printk_ratelimit);