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/moduleparam.h>
  28 #include <linux/interrupt.h>                    /* For in_interrupt() */
  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/jiffies.h>
  35
  36 #include <asm/uaccess.h>
  37
  38 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  39
  40 #ifdef        CONFIG_DEBUG_LL
  41 extern void printascii(char *);
  42 #endif
  43
  44 /* printk's without a loglevel use this.. */
  45 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  46
  47 /* We show everything that is MORE important than this.. */
  48 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  49 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  50
  51 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  52
  53 int console_printk[4] = {
  54         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  55         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  56         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  57         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  58 };
  59
  60 /*
  61  * Low lever drivers may need that to know if they can schedule in
  62  * their unblank() callback or not. So let's export it.
  63  */
  64 int oops_in_progress;
  65 EXPORT_SYMBOL(oops_in_progress);
  66
  67 /*
  68  * console_sem protects the console_drivers list, and also
  69  * provides serialisation for access to the entire console
  70  * driver system.
  71  */
  72 static DECLARE_MUTEX(console_sem);
  73 static DECLARE_MUTEX(secondary_console_sem);
  74 struct console *console_drivers;
  75 /*
  76  * This is used for debugging the mess that is the VT code by
  77  * keeping track if we have the console semaphore held. It's
  78  * definitely not the perfect debug tool (we don't know if _WE_
  79  * hold it are racing, but it helps tracking those weird code
  80  * path in the console code where we end up in places I want
  81  * locked without the console sempahore held
  82  */
  83 static int console_locked, console_suspended;
  84
  85 /*
  86  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  87  * It is also used in interesting ways to provide interlocking in
  88  * release_console_sem().
  89  */
  90 static DEFINE_SPINLOCK(logbuf_lock);
  91
  92 #define LOG_BUF_MASK    (log_buf_len-1)
  93 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  94
  95 /*
  96  * The indices into log_buf are not constrained to log_buf_len - they
  97  * must be masked before subscripting
  98  */
  99 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
 100 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
 101 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
 102
 103 /*
 104  *      Array of consoles built from command line options (console=)
 105  */
 106 struct console_cmdline
 107 {
 108         char    name[8];                        /* Name of the driver       */
 109         int     index;                          /* Minor dev. to use        */
 110         char    *options;                       /* Options for the driver   */
 111 };
 112
 113 #define MAX_CMDLINECONSOLES 8
 114
 115 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 116 static int selected_console = -1;
 117 static int preferred_console = -1;
 118
 119 /* Flag: console code may call schedule() */
 120 static int console_may_schedule;
 121
 122 #ifdef CONFIG_PRINTK
 123
 124 static char __log_buf[__LOG_BUF_LEN];
 125 static char *log_buf = __log_buf;
 126 static int log_buf_len = __LOG_BUF_LEN;
 127 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 128
 129 static int __init log_buf_len_setup(char *str)
 130 {
 131         unsigned long size = memparse(str, &str);
 132         unsigned long flags;
 133
 134         if (size)
 135                 size = roundup_pow_of_two(size);
 136         if (size > log_buf_len) {
 137                 unsigned long start, dest_idx, offset;
 138                 char *new_log_buf;
 139
 140                 new_log_buf = alloc_bootmem(size);
 141                 if (!new_log_buf) {
 142                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 143                         goto out;
 144                 }
 145
 146                 spin_lock_irqsave(&logbuf_lock, flags);
 147                 log_buf_len = size;
 148                 log_buf = new_log_buf;
 149
 150                 offset = start = min(con_start, log_start);
 151                 dest_idx = 0;
 152                 while (start != log_end) {
 153                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 154                         start++;
 155                         dest_idx++;
 156                 }
 157                 log_start -= offset;
 158                 con_start -= offset;
 159                 log_end -= offset;
 160                 spin_unlock_irqrestore(&logbuf_lock, flags);
 161
 162                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 163         }
 164 out:
 165         return 1;
 166 }
 167
 168 __setup("log_buf_len=", log_buf_len_setup);
 169
 170 /*
 171  * Commands to do_syslog:
 172  *
 173  *      0 -- Close the log.  Currently a NOP.
 174  *      1 -- Open the log. Currently a NOP.
 175  *      2 -- Read from the log.
 176  *      3 -- Read all messages remaining in the ring buffer.
 177  *      4 -- Read and clear all messages remaining in the ring buffer
 178  *      5 -- Clear ring buffer.
 179  *      6 -- Disable printk's to console
 180  *      7 -- Enable printk's to console
 181  *      8 -- Set level of messages printed to console
 182  *      9 -- Return number of unread characters in the log buffer
 183  *     10 -- Return size of the log buffer
 184  */
 185 int do_syslog(int type, char __user *buf, int len)
 186 {
 187         unsigned long i, j, limit, count;
 188         int do_clear = 0;
 189         char c;
 190         int error = 0;
 191
 192         error = security_syslog(type);
 193         if (error)
 194                 return error;
 195
 196         switch (type) {
 197         case 0:         /* Close log */
 198                 break;
 199         case 1:         /* Open log */
 200                 break;
 201         case 2:         /* Read from log */
 202                 error = -EINVAL;
 203                 if (!buf || len < 0)
 204                         goto out;
 205                 error = 0;
 206                 if (!len)
 207                         goto out;
 208                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 209                         error = -EFAULT;
 210                         goto out;
 211                 }
 212                 error = wait_event_interruptible(log_wait,
 213                                                         (log_start - log_end));
 214                 if (error)
 215                         goto out;
 216                 i = 0;
 217                 spin_lock_irq(&logbuf_lock);
 218                 while (!error && (log_start != log_end) && i < len) {
 219                         c = LOG_BUF(log_start);
 220                         log_start++;
 221                         spin_unlock_irq(&logbuf_lock);
 222                         error = __put_user(c,buf);
 223                         buf++;
 224                         i++;
 225                         cond_resched();
 226                         spin_lock_irq(&logbuf_lock);
 227                 }
 228                 spin_unlock_irq(&logbuf_lock);
 229                 if (!error)
 230                         error = i;
 231                 break;
 232         case 4:         /* Read/clear last kernel messages */
 233                 do_clear = 1;
 234                 /* FALL THRU */
 235         case 3:         /* Read last kernel messages */
 236                 error = -EINVAL;
 237                 if (!buf || len < 0)
 238                         goto out;
 239                 error = 0;
 240                 if (!len)
 241                         goto out;
 242                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 243                         error = -EFAULT;
 244                         goto out;
 245                 }
 246                 count = len;
 247                 if (count > log_buf_len)
 248                         count = log_buf_len;
 249                 spin_lock_irq(&logbuf_lock);
 250                 if (count > logged_chars)
 251                         count = logged_chars;
 252                 if (do_clear)
 253                         logged_chars = 0;
 254                 limit = log_end;
 255                 /*
 256                  * __put_user() could sleep, and while we sleep
 257                  * printk() could overwrite the messages
 258                  * we try to copy to user space. Therefore
 259                  * the messages are copied in reverse. <manfreds>
 260                  */
 261                 for (i = 0; i < count && !error; i++) {
 262                         j = limit-1-i;
 263                         if (j + log_buf_len < log_end)
 264                                 break;
 265                         c = LOG_BUF(j);
 266                         spin_unlock_irq(&logbuf_lock);
 267                         error = __put_user(c,&buf[count-1-i]);
 268                         cond_resched();
 269                         spin_lock_irq(&logbuf_lock);
 270                 }
 271                 spin_unlock_irq(&logbuf_lock);
 272                 if (error)
 273                         break;
 274                 error = i;
 275                 if (i != count) {
 276                         int offset = count-error;
 277                         /* buffer overflow during copy, correct user buffer. */
 278                         for (i = 0; i < error; i++) {
 279                                 if (__get_user(c,&buf[i+offset]) ||
 280                                     __put_user(c,&buf[i])) {
 281                                         error = -EFAULT;
 282                                         break;
 283                                 }
 284                                 cond_resched();
 285                         }
 286                 }
 287                 break;
 288         case 5:         /* Clear ring buffer */
 289                 logged_chars = 0;
 290                 break;
 291         case 6:         /* Disable logging to console */
 292                 console_loglevel = minimum_console_loglevel;
 293                 break;
 294         case 7:         /* Enable logging to console */
 295                 console_loglevel = default_console_loglevel;
 296                 break;
 297         case 8:         /* Set level of messages printed to console */
 298                 error = -EINVAL;
 299                 if (len < 1 || len > 8)
 300                         goto out;
 301                 if (len < minimum_console_loglevel)
 302                         len = minimum_console_loglevel;
 303                 console_loglevel = len;
 304                 error = 0;
 305                 break;
 306         case 9:         /* Number of chars in the log buffer */
 307                 error = log_end - log_start;
 308                 break;
 309         case 10:        /* Size of the log buffer */
 310                 error = log_buf_len;
 311                 break;
 312         default:
 313                 error = -EINVAL;
 314                 break;
 315         }
 316 out:
 317         return error;
 318 }
 319
 320 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 321 {
 322         return do_syslog(type, buf, len);
 323 }
 324
 325 /*
 326  * Call the console drivers on a range of log_buf
 327  */
 328 static void __call_console_drivers(unsigned long start, unsigned long end)
 329 {
 330         struct console *con;
 331
 332         for (con = console_drivers; con; con = con->next) {
 333                 if ((con->flags & CON_ENABLED) && con->write &&
 334                                 (cpu_online(smp_processor_id()) ||
 335                                 (con->flags & CON_ANYTIME)))
 336                         con->write(con, &LOG_BUF(start), end - start);
 337         }
 338 }
 339
 340 static int __read_mostly ignore_loglevel;
 341
 342 int __init ignore_loglevel_setup(char *str)
 343 {
 344         ignore_loglevel = 1;
 345         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 346
 347         return 1;
 348 }
 349
 350 __setup("ignore_loglevel", ignore_loglevel_setup);
 351
 352 /*
 353  * Write out chars from start to end - 1 inclusive
 354  */
 355 static void _call_console_drivers(unsigned long start,
 356                                 unsigned long end, int msg_log_level)
 357 {
 358         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 359                         console_drivers && start != end) {
 360                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 361                         /* wrapped write */
 362                         __call_console_drivers(start & LOG_BUF_MASK,
 363                                                 log_buf_len);
 364                         __call_console_drivers(0, end & LOG_BUF_MASK);
 365                 } else {
 366                         __call_console_drivers(start, end);
 367                 }
 368         }
 369 }
 370
 371 /*
 372  * Call the console drivers, asking them to write out
 373  * log_buf[start] to log_buf[end - 1].
 374  * The console_sem must be held.
 375  */
 376 static void call_console_drivers(unsigned long start, unsigned long end)
 377 {
 378         unsigned long cur_index, start_print;
 379         static int msg_level = -1;
 380
 381         BUG_ON(((long)(start - end)) > 0);
 382
 383         cur_index = start;
 384         start_print = start;
 385         while (cur_index != end) {
 386                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 387                                 LOG_BUF(cur_index + 0) == '<' &&
 388                                 LOG_BUF(cur_index + 1) >= '0' &&
 389                                 LOG_BUF(cur_index + 1) <= '7' &&
 390                                 LOG_BUF(cur_index + 2) == '>') {
 391                         msg_level = LOG_BUF(cur_index + 1) - '0';
 392                         cur_index += 3;
 393                         start_print = cur_index;
 394                 }
 395                 while (cur_index != end) {
 396                         char c = LOG_BUF(cur_index);
 397
 398                         cur_index++;
 399                         if (c == '\n') {
 400                                 if (msg_level < 0) {
 401                                         /*
 402                                          * printk() has already given us loglevel tags in
 403                                          * the buffer.  This code is here in case the
 404                                          * log buffer has wrapped right round and scribbled
 405                                          * on those tags
 406                                          */
 407                                         msg_level = default_message_loglevel;
 408                                 }
 409                                 _call_console_drivers(start_print, cur_index, msg_level);
 410                                 msg_level = -1;
 411                                 start_print = cur_index;
 412                                 break;
 413                         }
 414                 }
 415         }
 416         _call_console_drivers(start_print, end, msg_level);
 417 }
 418
 419 static void emit_log_char(char c)
 420 {
 421         LOG_BUF(log_end) = c;
 422         log_end++;
 423         if (log_end - log_start > log_buf_len)
 424                 log_start = log_end - log_buf_len;
 425         if (log_end - con_start > log_buf_len)
 426                 con_start = log_end - log_buf_len;
 427         if (logged_chars < log_buf_len)
 428                 logged_chars++;
 429 }
 430
 431 /*
 432  * Zap console related locks when oopsing. Only zap at most once
 433  * every 10 seconds, to leave time for slow consoles to print a
 434  * full oops.
 435  */
 436 static void zap_locks(void)
 437 {
 438         static unsigned long oops_timestamp;
 439
 440         if (time_after_eq(jiffies, oops_timestamp) &&
 441                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 442                 return;
 443
 444         oops_timestamp = jiffies;
 445
 446         /* If a crash is occurring, make sure we can't deadlock */
 447         spin_lock_init(&logbuf_lock);
 448         /* And make sure that we print immediately */
 449         init_MUTEX(&console_sem);
 450 }
 451
 452 static int printk_time = 0;
 453
 454 #ifdef CONFIG_PRINTK_TIME
 455
 456 /*
 457  * Initialize printk time. Note that on some systems sched_clock()
 458  * does not work until timer is initialized.
 459  */
 460 static int __init printk_time_init(void)
 461 {
 462         printk_time = 1;
 463
 464         return 0;
 465 }
 466 subsys_initcall(printk_time_init);
 467
 468 #else
 469
 470 static int __init printk_time_setup(char *str)
 471 {
 472         if (*str)
 473                 return 0;
 474         printk_time = 1;
 475         return 1;
 476 }
 477
 478 __setup("time", printk_time_setup);
 479
 480 #endif
 481
 482 __attribute__((weak)) unsigned long long printk_clock(void)
 483 {
 484         return sched_clock();
 485 }
 486
 487 /* Check if we have any console registered that can be called early in boot. */
 488 static int have_callable_console(void)
 489 {
 490         struct console *con;
 491
 492         for (con = console_drivers; con; con = con->next)
 493                 if (con->flags & CON_ANYTIME)
 494                         return 1;
 495
 496         return 0;
 497 }
 498
 499 /**
 500  * printk - print a kernel message
 501  * @fmt: format string
 502  *
 503  * This is printk.  It can be called from any context.  We want it to work.
 504  *
 505  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 506  * call the console drivers.  If we fail to get the semaphore we place the output
 507  * into the log buffer and return.  The current holder of the console_sem will
 508  * notice the new output in release_console_sem() and will send it to the
 509  * consoles before releasing the semaphore.
 510  *
 511  * One effect of this deferred printing is that code which calls printk() and
 512  * then changes console_loglevel may break. This is because console_loglevel
 513  * is inspected when the actual printing occurs.
 514  *
 515  * See also:
 516  * printf(3)
 517  */
 518
 519 asmlinkage int printk(const char *fmt, ...)
 520 {
 521         va_list args;
 522         int r;
 523
 524         va_start(args, fmt);
 525         r = vprintk(fmt, args);
 526         va_end(args);
 527
 528         return r;
 529 }
 530
 531 /* cpu currently holding logbuf_lock */
 532 static volatile unsigned int printk_cpu = UINT_MAX;
 533
 534 asmlinkage int vprintk(const char *fmt, va_list args)
 535 {
 536         unsigned long flags;
 537         int printed_len;
 538         char *p;
 539         static char printk_buf[1024];
 540         static int log_level_unknown = 1;
 541
 542         preempt_disable();
 543         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 544                 /* If a crash is occurring during printk() on this CPU,
 545                  * make sure we can't deadlock */
 546                 zap_locks();
 547
 548         /* This stops the holder of console_sem just where we want him */
 549         local_irq_save(flags);
 550         lockdep_off();
 551         spin_lock(&logbuf_lock);
 552         printk_cpu = smp_processor_id();
 553
 554         /* Emit the output into the temporary buffer */
 555         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 556
 557 #ifdef  CONFIG_DEBUG_LL
 558         printascii(printk_buf);
 559 #endif
 560
 561         /*
 562          * Copy the output into log_buf.  If the caller didn't provide
 563          * appropriate log level tags, we insert them here
 564          */
 565         for (p = printk_buf; *p; p++) {
 566                 if (log_level_unknown) {
 567                         /* log_level_unknown signals the start of a new line */
 568                         if (printk_time) {
 569                                 int loglev_char;
 570                                 char tbuf[50], *tp;
 571                                 unsigned tlen;
 572                                 unsigned long long t;
 573                                 unsigned long nanosec_rem;
 574
 575                                 /*
 576                                  * force the log level token to be
 577                                  * before the time output.
 578                                  */
 579                                 if (p[0] == '<' && p[1] >='0' &&
 580                                    p[1] <= '7' && p[2] == '>') {
 581                                         loglev_char = p[1];
 582                                         p += 3;
 583                                         printed_len -= 3;
 584                                 } else {
 585                                         loglev_char = default_message_loglevel
 586                                                 + '0';
 587                                 }
 588                                 t = printk_clock();
 589                                 nanosec_rem = do_div(t, 1000000000);
 590                                 tlen = sprintf(tbuf,
 591                                                 "<%c>[%5lu.%06lu] ",
 592                                                 loglev_char,
 593                                                 (unsigned long)t,
 594                                                 nanosec_rem/1000);
 595
 596                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 597                                         emit_log_char(*tp);
 598                                 printed_len += tlen;
 599                         } else {
 600                                 if (p[0] != '<' || p[1] < '0' ||
 601                                    p[1] > '7' || p[2] != '>') {
 602                                         emit_log_char('<');
 603                                         emit_log_char(default_message_loglevel
 604                                                 + '0');
 605                                         emit_log_char('>');
 606                                         printed_len += 3;
 607                                 }
 608                         }
 609                         log_level_unknown = 0;
 610                         if (!*p)
 611                                 break;
 612                 }
 613                 emit_log_char(*p);
 614                 if (*p == '\n')
 615                         log_level_unknown = 1;
 616         }
 617
 618         if (!down_trylock(&console_sem)) {
 619                 /*
 620                  * We own the drivers.  We can drop the spinlock and
 621                  * let release_console_sem() print the text, maybe ...
 622                  */
 623                 console_locked = 1;
 624                 printk_cpu = UINT_MAX;
 625                 spin_unlock(&logbuf_lock);
 626
 627                 /*
 628                  * Console drivers may assume that per-cpu resources have
 629                  * been allocated. So unless they're explicitly marked as
 630                  * being able to cope (CON_ANYTIME) don't call them until
 631                  * this CPU is officially up.
 632                  */
 633                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 634                         console_may_schedule = 0;
 635                         release_console_sem();
 636                 } else {
 637                         /* Release by hand to avoid flushing the buffer. */
 638                         console_locked = 0;
 639                         up(&console_sem);
 640                 }
 641                 lockdep_on();
 642                 local_irq_restore(flags);
 643         } else {
 644                 /*
 645                  * Someone else owns the drivers.  We drop the spinlock, which
 646                  * allows the semaphore holder to proceed and to call the
 647                  * console drivers with the output which we just produced.
 648                  */
 649                 printk_cpu = UINT_MAX;
 650                 spin_unlock(&logbuf_lock);
 651                 lockdep_on();
 652                 local_irq_restore(flags);
 653         }
 654
 655         preempt_enable();
 656         return printed_len;
 657 }
 658 EXPORT_SYMBOL(printk);
 659 EXPORT_SYMBOL(vprintk);
 660
 661 #else
 662
 663 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 664 {
 665         return -ENOSYS;
 666 }
 667
 668 static void call_console_drivers(unsigned long start, unsigned long end)
 669 {
 670 }
 671
 672 #endif
 673
 674 /*
 675  * Set up a list of consoles.  Called from init/main.c
 676  */
 677 static int __init console_setup(char *str)
 678 {
 679         char name[sizeof(console_cmdline[0].name)];
 680         char *s, *options;
 681         int idx;
 682
 683         /*
 684          * Decode str into name, index, options.
 685          */
 686         if (str[0] >= '0' && str[0] <= '9') {
 687                 strcpy(name, "ttyS");
 688                 strncpy(name + 4, str, sizeof(name) - 5);
 689         } else {
 690                 strncpy(name, str, sizeof(name) - 1);
 691         }
 692         name[sizeof(name) - 1] = 0;
 693         if ((options = strchr(str, ',')) != NULL)
 694                 *(options++) = 0;
 695 #ifdef __sparc__
 696         if (!strcmp(str, "ttya"))
 697                 strcpy(name, "ttyS0");
 698         if (!strcmp(str, "ttyb"))
 699                 strcpy(name, "ttyS1");
 700 #endif
 701         for (s = name; *s; s++)
 702                 if ((*s >= '0' && *s <= '9') || *s == ',')
 703                         break;
 704         idx = simple_strtoul(s, NULL, 10);
 705         *s = 0;
 706
 707         add_preferred_console(name, idx, options);
 708         return 1;
 709 }
 710 __setup("console=", console_setup);
 711
 712 /**
 713  * add_preferred_console - add a device to the list of preferred consoles.
 714  * @name: device name
 715  * @idx: device index
 716  * @options: options for this console
 717  *
 718  * The last preferred console added will be used for kernel messages
 719  * and stdin/out/err for init.  Normally this is used by console_setup
 720  * above to handle user-supplied console arguments; however it can also
 721  * be used by arch-specific code either to override the user or more
 722  * commonly to provide a default console (ie from PROM variables) when
 723  * the user has not supplied one.
 724  */
 725 int __init add_preferred_console(char *name, int idx, char *options)
 726 {
 727         struct console_cmdline *c;
 728         int i;
 729
 730         /*
 731          *      See if this tty is not yet registered, and
 732          *      if we have a slot free.
 733          */
 734         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 735                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 736                           console_cmdline[i].index == idx) {
 737                                 selected_console = i;
 738                                 return 0;
 739                 }
 740         if (i == MAX_CMDLINECONSOLES)
 741                 return -E2BIG;
 742         selected_console = i;
 743         c = &console_cmdline[i];
 744         memcpy(c->name, name, sizeof(c->name));
 745         c->name[sizeof(c->name) - 1] = 0;
 746         c->options = options;
 747         c->index = idx;
 748         return 0;
 749 }
 750
 751 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 752 /**
 753  * suspend_console - suspend the console subsystem
 754  *
 755  * This disables printk() while we go into suspend states
 756  */
 757 void suspend_console(void)
 758 {
 759         printk("Suspending console(s)\n");
 760         acquire_console_sem();
 761         console_suspended = 1;
 762 }
 763
 764 void resume_console(void)
 765 {
 766         console_suspended = 0;
 767         release_console_sem();
 768 }
 769 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 770
 771 /**
 772  * acquire_console_sem - lock the console system for exclusive use.
 773  *
 774  * Acquires a semaphore which guarantees that the caller has
 775  * exclusive access to the console system and the console_drivers list.
 776  *
 777  * Can sleep, returns nothing.
 778  */
 779 void acquire_console_sem(void)
 780 {
 781         BUG_ON(in_interrupt());
 782         if (console_suspended) {
 783                 down(&secondary_console_sem);
 784                 return;
 785         }
 786         down(&console_sem);
 787         console_locked = 1;
 788         console_may_schedule = 1;
 789 }
 790 EXPORT_SYMBOL(acquire_console_sem);
 791
 792 int try_acquire_console_sem(void)
 793 {
 794         if (down_trylock(&console_sem))
 795                 return -1;
 796         console_locked = 1;
 797         console_may_schedule = 0;
 798         return 0;
 799 }
 800 EXPORT_SYMBOL(try_acquire_console_sem);
 801
 802 int is_console_locked(void)
 803 {
 804         return console_locked;
 805 }
 806
 807 /**
 808  * release_console_sem - unlock the console system
 809  *
 810  * Releases the semaphore which the caller holds on the console system
 811  * and the console driver list.
 812  *
 813  * While the semaphore was held, console output may have been buffered
 814  * by printk().  If this is the case, release_console_sem() emits
 815  * the output prior to releasing the semaphore.
 816  *
 817  * If there is output waiting for klogd, we wake it up.
 818  *
 819  * release_console_sem() may be called from any context.
 820  */
 821 void release_console_sem(void)
 822 {
 823         unsigned long flags;
 824         unsigned long _con_start, _log_end;
 825         unsigned long wake_klogd = 0;
 826
 827         if (console_suspended) {
 828                 up(&secondary_console_sem);
 829                 return;
 830         }
 831
 832         console_may_schedule = 0;
 833
 834         for ( ; ; ) {
 835                 spin_lock_irqsave(&logbuf_lock, flags);
 836                 wake_klogd |= log_start - log_end;
 837                 if (con_start == log_end)
 838                         break;                  /* Nothing to print */
 839                 _con_start = con_start;
 840                 _log_end = log_end;
 841                 con_start = log_end;            /* Flush */
 842                 spin_unlock(&logbuf_lock);
 843                 call_console_drivers(_con_start, _log_end);
 844                 local_irq_restore(flags);
 845         }
 846         console_locked = 0;
 847         up(&console_sem);
 848         spin_unlock_irqrestore(&logbuf_lock, flags);
 849         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 850                 wake_up_interruptible(&log_wait);
 851 }
 852 EXPORT_SYMBOL(release_console_sem);
 853
 854 /**
 855  * console_conditional_schedule - yield the CPU if required
 856  *
 857  * If the console code is currently allowed to sleep, and
 858  * if this CPU should yield the CPU to another task, do
 859  * so here.
 860  *
 861  * Must be called within acquire_console_sem().
 862  */
 863 void __sched console_conditional_schedule(void)
 864 {
 865         if (console_may_schedule)
 866                 cond_resched();
 867 }
 868 EXPORT_SYMBOL(console_conditional_schedule);
 869
 870 void console_print(const char *s)
 871 {
 872         printk(KERN_EMERG "%s", s);
 873 }
 874 EXPORT_SYMBOL(console_print);
 875
 876 void console_unblank(void)
 877 {
 878         struct console *c;
 879
 880         /*
 881          * console_unblank can no longer be called in interrupt context unless
 882          * oops_in_progress is set to 1..
 883          */
 884         if (oops_in_progress) {
 885                 if (down_trylock(&console_sem) != 0)
 886                         return;
 887         } else
 888                 acquire_console_sem();
 889
 890         console_locked = 1;
 891         console_may_schedule = 0;
 892         for (c = console_drivers; c != NULL; c = c->next)
 893                 if ((c->flags & CON_ENABLED) && c->unblank)
 894                         c->unblank();
 895         release_console_sem();
 896 }
 897
 898 /*
 899  * Return the console tty driver structure and its associated index
 900  */
 901 struct tty_driver *console_device(int *index)
 902 {
 903         struct console *c;
 904         struct tty_driver *driver = NULL;
 905
 906         acquire_console_sem();
 907         for (c = console_drivers; c != NULL; c = c->next) {
 908                 if (!c->device)
 909                         continue;
 910                 driver = c->device(c, index);
 911                 if (driver)
 912                         break;
 913         }
 914         release_console_sem();
 915         return driver;
 916 }
 917
 918 /*
 919  * Prevent further output on the passed console device so that (for example)
 920  * serial drivers can disable console output before suspending a port, and can
 921  * re-enable output afterwards.
 922  */
 923 void console_stop(struct console *console)
 924 {
 925         acquire_console_sem();
 926         console->flags &= ~CON_ENABLED;
 927         release_console_sem();
 928 }
 929 EXPORT_SYMBOL(console_stop);
 930
 931 void console_start(struct console *console)
 932 {
 933         acquire_console_sem();
 934         console->flags |= CON_ENABLED;
 935         release_console_sem();
 936 }
 937 EXPORT_SYMBOL(console_start);
 938
 939 /*
 940  * The console driver calls this routine during kernel initialization
 941  * to register the console printing procedure with printk() and to
 942  * print any messages that were printed by the kernel before the
 943  * console driver was initialized.
 944  */
 945 void register_console(struct console *console)
 946 {
 947         int i;
 948         unsigned long flags;
 949
 950         if (preferred_console < 0)
 951                 preferred_console = selected_console;
 952
 953         /*
 954          *      See if we want to use this console driver. If we
 955          *      didn't select a console we take the first one
 956          *      that registers here.
 957          */
 958         if (preferred_console < 0) {
 959                 if (console->index < 0)
 960                         console->index = 0;
 961                 if (console->setup == NULL ||
 962                     console->setup(console, NULL) == 0) {
 963                         console->flags |= CON_ENABLED | CON_CONSDEV;
 964                         preferred_console = 0;
 965                 }
 966         }
 967
 968         /*
 969          *      See if this console matches one we selected on
 970          *      the command line.
 971          */
 972         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 973                         i++) {
 974                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 975                         continue;
 976                 if (console->index >= 0 &&
 977                     console->index != console_cmdline[i].index)
 978                         continue;
 979                 if (console->index < 0)
 980                         console->index = console_cmdline[i].index;
 981                 if (console->setup &&
 982                     console->setup(console, console_cmdline[i].options) != 0)
 983                         break;
 984                 console->flags |= CON_ENABLED;
 985                 console->index = console_cmdline[i].index;
 986                 if (i == selected_console) {
 987                         console->flags |= CON_CONSDEV;
 988                         preferred_console = selected_console;
 989                 }
 990                 break;
 991         }
 992
 993         if (!(console->flags & CON_ENABLED))
 994                 return;
 995
 996         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 997                 unregister_console(console_drivers);
 998                 console->flags &= ~CON_PRINTBUFFER;
 999         }
1000
1001         /*
1002          *      Put this console in the list - keep the
1003          *      preferred driver at the head of the list.
1004          */
1005         acquire_console_sem();
1006         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1007                 console->next = console_drivers;
1008                 console_drivers = console;
1009                 if (console->next)
1010                         console->next->flags &= ~CON_CONSDEV;
1011         } else {
1012                 console->next = console_drivers->next;
1013                 console_drivers->next = console;
1014         }
1015         if (console->flags & CON_PRINTBUFFER) {
1016                 /*
1017                  * release_console_sem() will print out the buffered messages
1018                  * for us.
1019                  */
1020                 spin_lock_irqsave(&logbuf_lock, flags);
1021                 con_start = log_start;
1022                 spin_unlock_irqrestore(&logbuf_lock, flags);
1023         }
1024         release_console_sem();
1025 }
1026 EXPORT_SYMBOL(register_console);
1027
1028 int unregister_console(struct console *console)
1029 {
1030         struct console *a, *b;
1031         int res = 1;
1032
1033         acquire_console_sem();
1034         if (console_drivers == console) {
1035                 console_drivers=console->next;
1036                 res = 0;
1037         } else if (console_drivers) {
1038                 for (a=console_drivers->next, b=console_drivers ;
1039                      a; b=a, a=b->next) {
1040                         if (a == console) {
1041                                 b->next = a->next;
1042                                 res = 0;
1043                                 break;
1044                         }
1045                 }
1046         }
1047
1048         /* If last console is removed, we re-enable picking the first
1049          * one that gets registered. Without that, pmac early boot console
1050          * would prevent fbcon from taking over.
1051          *
1052          * If this isn't the last console and it has CON_CONSDEV set, we
1053          * need to set it on the next preferred console.
1054          */
1055         if (console_drivers == NULL)
1056                 preferred_console = selected_console;
1057         else if (console->flags & CON_CONSDEV)
1058                 console_drivers->flags |= CON_CONSDEV;
1059
1060         release_console_sem();
1061         return res;
1062 }
1063 EXPORT_SYMBOL(unregister_console);
1064
1065 /**
1066  * tty_write_message - write a message to a certain tty, not just the console.
1067  * @tty: the destination tty_struct
1068  * @msg: the message to write
1069  *
1070  * This is used for messages that need to be redirected to a specific tty.
1071  * We don't put it into the syslog queue right now maybe in the future if
1072  * really needed.
1073  */
1074 void tty_write_message(struct tty_struct *tty, char *msg)
1075 {
1076         if (tty && tty->driver->write)
1077                 tty->driver->write(tty, msg, strlen(msg));
1078         return;
1079 }
1080
1081 /*
1082  * printk rate limiting, lifted from the networking subsystem.
1083  *
1084  * This enforces a rate limit: not more than one kernel message
1085  * every printk_ratelimit_jiffies to make a denial-of-service
1086  * attack impossible.
1087  */
1088 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1089 {
1090         static DEFINE_SPINLOCK(ratelimit_lock);
1091         static unsigned long toks = 10 * 5 * HZ;
1092         static unsigned long last_msg;
1093         static int missed;
1094         unsigned long flags;
1095         unsigned long now = jiffies;
1096
1097         spin_lock_irqsave(&ratelimit_lock, flags);
1098         toks += now - last_msg;
1099         last_msg = now;
1100         if (toks > (ratelimit_burst * ratelimit_jiffies))
1101                 toks = ratelimit_burst * ratelimit_jiffies;
1102         if (toks >= ratelimit_jiffies) {
1103                 int lost = missed;
1104
1105                 missed = 0;
1106                 toks -= ratelimit_jiffies;
1107                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1108                 if (lost)
1109                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1110                 return 1;
1111         }
1112         missed++;
1113         spin_unlock_irqrestore(&ratelimit_lock, flags);
1114         return 0;
1115 }
1116 EXPORT_SYMBOL(__printk_ratelimit);
1117
1118 /* minimum time in jiffies between messages */
1119 int printk_ratelimit_jiffies = 5 * HZ;
1120
1121 /* number of messages we send before ratelimiting */
1122 int printk_ratelimit_burst = 10;
1123
1124 int printk_ratelimit(void)
1125 {
1126         return __printk_ratelimit(printk_ratelimit_jiffies,
1127                                 printk_ratelimit_burst);
1128 }
1129 EXPORT_SYMBOL(printk_ratelimit);
1130
1131 /**
1132  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1133  * @caller_jiffies: pointer to caller's state
1134  * @interval_msecs: minimum interval between prints
1135  *
1136  * printk_timed_ratelimit() returns true if more than @interval_msecs
1137  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1138  * returned true.
1139  */
1140 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1141                         unsigned int interval_msecs)
1142 {
1143         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1144                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1145                 return true;
1146         }
1147         return false;
1148 }
1149 EXPORT_SYMBOL(printk_timed_ratelimit);