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/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/jiffies.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 /*
  58  * Low level drivers may need that to know if they can schedule in
  59  * their unblank() callback or not. So let's export it.
  60  */
  61 int oops_in_progress;
  62 EXPORT_SYMBOL(oops_in_progress);
  63
  64 /*
  65  * console_sem protects the console_drivers list, and also
  66  * provides serialisation for access to the entire console
  67  * driver system.
  68  */
  69 static DECLARE_MUTEX(console_sem);
  70 static DECLARE_MUTEX(secondary_console_sem);
  71 struct console *console_drivers;
  72 /*
  73  * This is used for debugging the mess that is the VT code by
  74  * keeping track if we have the console semaphore held. It's
  75  * definitely not the perfect debug tool (we don't know if _WE_
  76  * hold it are racing, but it helps tracking those weird code
  77  * path in the console code where we end up in places I want
  78  * locked without the console sempahore held
  79  */
  80 static int console_locked, console_suspended;
  81
  82 /*
  83  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  84  * It is also used in interesting ways to provide interlocking in
  85  * release_console_sem().
  86  */
  87 static DEFINE_SPINLOCK(logbuf_lock);
  88
  89 #define LOG_BUF_MASK    (log_buf_len-1)
  90 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  91
  92 /*
  93  * The indices into log_buf are not constrained to log_buf_len - they
  94  * must be masked before subscripting
  95  */
  96 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  97 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  98 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  99
 100 /*
 101  *      Array of consoles built from command line options (console=)
 102  */
 103 struct console_cmdline
 104 {
 105         char    name[8];                        /* Name of the driver       */
 106         int     index;                          /* Minor dev. to use        */
 107         char    *options;                       /* Options for the driver   */
 108 };
 109
 110 #define MAX_CMDLINECONSOLES 8
 111
 112 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 113 static int selected_console = -1;
 114 static int preferred_console = -1;
 115
 116 /* Flag: console code may call schedule() */
 117 static int console_may_schedule;
 118
 119 #ifdef CONFIG_PRINTK
 120
 121 static char __log_buf[__LOG_BUF_LEN];
 122 static char *log_buf = __log_buf;
 123 static int log_buf_len = __LOG_BUF_LEN;
 124 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 125
 126 static int __init log_buf_len_setup(char *str)
 127 {
 128         unsigned long size = memparse(str, &str);
 129         unsigned long flags;
 130
 131         if (size)
 132                 size = roundup_pow_of_two(size);
 133         if (size > log_buf_len) {
 134                 unsigned long start, dest_idx, offset;
 135                 char *new_log_buf;
 136
 137                 new_log_buf = alloc_bootmem(size);
 138                 if (!new_log_buf) {
 139                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 140                         goto out;
 141                 }
 142
 143                 spin_lock_irqsave(&logbuf_lock, flags);
 144                 log_buf_len = size;
 145                 log_buf = new_log_buf;
 146
 147                 offset = start = min(con_start, log_start);
 148                 dest_idx = 0;
 149                 while (start != log_end) {
 150                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 151                         start++;
 152                         dest_idx++;
 153                 }
 154                 log_start -= offset;
 155                 con_start -= offset;
 156                 log_end -= offset;
 157                 spin_unlock_irqrestore(&logbuf_lock, flags);
 158
 159                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 160         }
 161 out:
 162         return 1;
 163 }
 164
 165 __setup("log_buf_len=", log_buf_len_setup);
 166
 167 #ifdef CONFIG_BOOT_PRINTK_DELAY
 168
 169 static unsigned int boot_delay; /* msecs delay after each printk during bootup */
 170 static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
 171
 172 static int __init boot_delay_setup(char *str)
 173 {
 174         unsigned long lpj;
 175         unsigned long long loops_per_msec;
 176
 177         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
 178         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
 179
 180         get_option(&str, &boot_delay);
 181         if (boot_delay > 10 * 1000)
 182                 boot_delay = 0;
 183
 184         printk_delay_msec = loops_per_msec;
 185         printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
 186                 "HZ: %d, printk_delay_msec: %llu\n",
 187                 boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
 188         return 1;
 189 }
 190 __setup("boot_delay=", boot_delay_setup);
 191
 192 static void boot_delay_msec(void)
 193 {
 194         unsigned long long k;
 195         unsigned long timeout;
 196
 197         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
 198                 return;
 199
 200         k = (unsigned long long)printk_delay_msec * boot_delay;
 201
 202         timeout = jiffies + msecs_to_jiffies(boot_delay);
 203         while (k) {
 204                 k--;
 205                 cpu_relax();
 206                 /*
 207                  * use (volatile) jiffies to prevent
 208                  * compiler reduction; loop termination via jiffies
 209                  * is secondary and may or may not happen.
 210                  */
 211                 if (time_after(jiffies, timeout))
 212                         break;
 213                 touch_nmi_watchdog();
 214         }
 215 }
 216 #else
 217 static inline void boot_delay_msec(void)
 218 {
 219 }
 220 #endif
 221
 222 /*
 223  * Commands to do_syslog:
 224  *
 225  *      0 -- Close the log.  Currently a NOP.
 226  *      1 -- Open the log. Currently a NOP.
 227  *      2 -- Read from the log.
 228  *      3 -- Read all messages remaining in the ring buffer.
 229  *      4 -- Read and clear all messages remaining in the ring buffer
 230  *      5 -- Clear ring buffer.
 231  *      6 -- Disable printk's to console
 232  *      7 -- Enable printk's to console
 233  *      8 -- Set level of messages printed to console
 234  *      9 -- Return number of unread characters in the log buffer
 235  *     10 -- Return size of the log buffer
 236  */
 237 int do_syslog(int type, char __user *buf, int len)
 238 {
 239         unsigned long i, j, limit, count;
 240         int do_clear = 0;
 241         char c;
 242         int error = 0;
 243
 244         error = security_syslog(type);
 245         if (error)
 246                 return error;
 247
 248         switch (type) {
 249         case 0:         /* Close log */
 250                 break;
 251         case 1:         /* Open log */
 252                 break;
 253         case 2:         /* Read from log */
 254                 error = -EINVAL;
 255                 if (!buf || len < 0)
 256                         goto out;
 257                 error = 0;
 258                 if (!len)
 259                         goto out;
 260                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 261                         error = -EFAULT;
 262                         goto out;
 263                 }
 264                 error = wait_event_interruptible(log_wait,
 265                                                         (log_start - log_end));
 266                 if (error)
 267                         goto out;
 268                 i = 0;
 269                 spin_lock_irq(&logbuf_lock);
 270                 while (!error && (log_start != log_end) && i < len) {
 271                         c = LOG_BUF(log_start);
 272                         log_start++;
 273                         spin_unlock_irq(&logbuf_lock);
 274                         error = __put_user(c,buf);
 275                         buf++;
 276                         i++;
 277                         cond_resched();
 278                         spin_lock_irq(&logbuf_lock);
 279                 }
 280                 spin_unlock_irq(&logbuf_lock);
 281                 if (!error)
 282                         error = i;
 283                 break;
 284         case 4:         /* Read/clear last kernel messages */
 285                 do_clear = 1;
 286                 /* FALL THRU */
 287         case 3:         /* Read last kernel messages */
 288                 error = -EINVAL;
 289                 if (!buf || len < 0)
 290                         goto out;
 291                 error = 0;
 292                 if (!len)
 293                         goto out;
 294                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 295                         error = -EFAULT;
 296                         goto out;
 297                 }
 298                 count = len;
 299                 if (count > log_buf_len)
 300                         count = log_buf_len;
 301                 spin_lock_irq(&logbuf_lock);
 302                 if (count > logged_chars)
 303                         count = logged_chars;
 304                 if (do_clear)
 305                         logged_chars = 0;
 306                 limit = log_end;
 307                 /*
 308                  * __put_user() could sleep, and while we sleep
 309                  * printk() could overwrite the messages
 310                  * we try to copy to user space. Therefore
 311                  * the messages are copied in reverse. <manfreds>
 312                  */
 313                 for (i = 0; i < count && !error; i++) {
 314                         j = limit-1-i;
 315                         if (j + log_buf_len < log_end)
 316                                 break;
 317                         c = LOG_BUF(j);
 318                         spin_unlock_irq(&logbuf_lock);
 319                         error = __put_user(c,&buf[count-1-i]);
 320                         cond_resched();
 321                         spin_lock_irq(&logbuf_lock);
 322                 }
 323                 spin_unlock_irq(&logbuf_lock);
 324                 if (error)
 325                         break;
 326                 error = i;
 327                 if (i != count) {
 328                         int offset = count-error;
 329                         /* buffer overflow during copy, correct user buffer. */
 330                         for (i = 0; i < error; i++) {
 331                                 if (__get_user(c,&buf[i+offset]) ||
 332                                     __put_user(c,&buf[i])) {
 333                                         error = -EFAULT;
 334                                         break;
 335                                 }
 336                                 cond_resched();
 337                         }
 338                 }
 339                 break;
 340         case 5:         /* Clear ring buffer */
 341                 logged_chars = 0;
 342                 break;
 343         case 6:         /* Disable logging to console */
 344                 console_loglevel = minimum_console_loglevel;
 345                 break;
 346         case 7:         /* Enable logging to console */
 347                 console_loglevel = default_console_loglevel;
 348                 break;
 349         case 8:         /* Set level of messages printed to console */
 350                 error = -EINVAL;
 351                 if (len < 1 || len > 8)
 352                         goto out;
 353                 if (len < minimum_console_loglevel)
 354                         len = minimum_console_loglevel;
 355                 console_loglevel = len;
 356                 error = 0;
 357                 break;
 358         case 9:         /* Number of chars in the log buffer */
 359                 error = log_end - log_start;
 360                 break;
 361         case 10:        /* Size of the log buffer */
 362                 error = log_buf_len;
 363                 break;
 364         default:
 365                 error = -EINVAL;
 366                 break;
 367         }
 368 out:
 369         return error;
 370 }
 371
 372 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 373 {
 374         return do_syslog(type, buf, len);
 375 }
 376
 377 /*
 378  * Call the console drivers on a range of log_buf
 379  */
 380 static void __call_console_drivers(unsigned long start, unsigned long end)
 381 {
 382         struct console *con;
 383
 384         for (con = console_drivers; con; con = con->next) {
 385                 if ((con->flags & CON_ENABLED) && con->write &&
 386                                 (cpu_online(smp_processor_id()) ||
 387                                 (con->flags & CON_ANYTIME)))
 388                         con->write(con, &LOG_BUF(start), end - start);
 389         }
 390 }
 391
 392 static int __read_mostly ignore_loglevel;
 393
 394 static int __init ignore_loglevel_setup(char *str)
 395 {
 396         ignore_loglevel = 1;
 397         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 398
 399         return 1;
 400 }
 401
 402 __setup("ignore_loglevel", ignore_loglevel_setup);
 403
 404 /*
 405  * Write out chars from start to end - 1 inclusive
 406  */
 407 static void _call_console_drivers(unsigned long start,
 408                                 unsigned long end, int msg_log_level)
 409 {
 410         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 411                         console_drivers && start != end) {
 412                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 413                         /* wrapped write */
 414                         __call_console_drivers(start & LOG_BUF_MASK,
 415                                                 log_buf_len);
 416                         __call_console_drivers(0, end & LOG_BUF_MASK);
 417                 } else {
 418                         __call_console_drivers(start, end);
 419                 }
 420         }
 421 }
 422
 423 /*
 424  * Call the console drivers, asking them to write out
 425  * log_buf[start] to log_buf[end - 1].
 426  * The console_sem must be held.
 427  */
 428 static void call_console_drivers(unsigned long start, unsigned long end)
 429 {
 430         unsigned long cur_index, start_print;
 431         static int msg_level = -1;
 432
 433         BUG_ON(((long)(start - end)) > 0);
 434
 435         cur_index = start;
 436         start_print = start;
 437         while (cur_index != end) {
 438                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 439                                 LOG_BUF(cur_index + 0) == '<' &&
 440                                 LOG_BUF(cur_index + 1) >= '0' &&
 441                                 LOG_BUF(cur_index + 1) <= '7' &&
 442                                 LOG_BUF(cur_index + 2) == '>') {
 443                         msg_level = LOG_BUF(cur_index + 1) - '0';
 444                         cur_index += 3;
 445                         start_print = cur_index;
 446                 }
 447                 while (cur_index != end) {
 448                         char c = LOG_BUF(cur_index);
 449
 450                         cur_index++;
 451                         if (c == '\n') {
 452                                 if (msg_level < 0) {
 453                                         /*
 454                                          * printk() has already given us loglevel tags in
 455                                          * the buffer.  This code is here in case the
 456                                          * log buffer has wrapped right round and scribbled
 457                                          * on those tags
 458                                          */
 459                                         msg_level = default_message_loglevel;
 460                                 }
 461                                 _call_console_drivers(start_print, cur_index, msg_level);
 462                                 msg_level = -1;
 463                                 start_print = cur_index;
 464                                 break;
 465                         }
 466                 }
 467         }
 468         _call_console_drivers(start_print, end, msg_level);
 469 }
 470
 471 static void emit_log_char(char c)
 472 {
 473         LOG_BUF(log_end) = c;
 474         log_end++;
 475         if (log_end - log_start > log_buf_len)
 476                 log_start = log_end - log_buf_len;
 477         if (log_end - con_start > log_buf_len)
 478                 con_start = log_end - log_buf_len;
 479         if (logged_chars < log_buf_len)
 480                 logged_chars++;
 481 }
 482
 483 /*
 484  * Zap console related locks when oopsing. Only zap at most once
 485  * every 10 seconds, to leave time for slow consoles to print a
 486  * full oops.
 487  */
 488 static void zap_locks(void)
 489 {
 490         static unsigned long oops_timestamp;
 491
 492         if (time_after_eq(jiffies, oops_timestamp) &&
 493                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 494                 return;
 495
 496         oops_timestamp = jiffies;
 497
 498         /* If a crash is occurring, make sure we can't deadlock */
 499         spin_lock_init(&logbuf_lock);
 500         /* And make sure that we print immediately */
 501         init_MUTEX(&console_sem);
 502 }
 503
 504 #if defined(CONFIG_PRINTK_TIME)
 505 static int printk_time = 1;
 506 #else
 507 static int printk_time = 0;
 508 #endif
 509 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 510
 511 static int __init printk_time_setup(char *str)
 512 {
 513         if (*str)
 514                 return 0;
 515         printk_time = 1;
 516         printk(KERN_NOTICE "The 'time' option is deprecated and "
 517                 "is scheduled for removal in early 2008\n");
 518         printk(KERN_NOTICE "Use 'printk.time=<value>' instead\n");
 519         return 1;
 520 }
 521
 522 __setup("time", printk_time_setup);
 523
 524 __attribute__((weak)) unsigned long long printk_clock(void)
 525 {
 526         return sched_clock();
 527 }
 528
 529 /* Check if we have any console registered that can be called early in boot. */
 530 static int have_callable_console(void)
 531 {
 532         struct console *con;
 533
 534         for (con = console_drivers; con; con = con->next)
 535                 if (con->flags & CON_ANYTIME)
 536                         return 1;
 537
 538         return 0;
 539 }
 540
 541 /**
 542  * printk - print a kernel message
 543  * @fmt: format string
 544  *
 545  * This is printk().  It can be called from any context.  We want it to work.
 546  * Be aware of the fact that if oops_in_progress is not set, we might try to
 547  * wake klogd up which could deadlock on runqueue lock if printk() is called
 548  * from scheduler code.
 549  *
 550  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 551  * call the console drivers.  If we fail to get the semaphore we place the output
 552  * into the log buffer and return.  The current holder of the console_sem will
 553  * notice the new output in release_console_sem() and will send it to the
 554  * consoles before releasing the semaphore.
 555  *
 556  * One effect of this deferred printing is that code which calls printk() and
 557  * then changes console_loglevel may break. This is because console_loglevel
 558  * is inspected when the actual printing occurs.
 559  *
 560  * See also:
 561  * printf(3)
 562  */
 563
 564 asmlinkage int printk(const char *fmt, ...)
 565 {
 566         va_list args;
 567         int r;
 568
 569         va_start(args, fmt);
 570         r = vprintk(fmt, args);
 571         va_end(args);
 572
 573         return r;
 574 }
 575
 576 /* cpu currently holding logbuf_lock */
 577 static volatile unsigned int printk_cpu = UINT_MAX;
 578
 579 asmlinkage int vprintk(const char *fmt, va_list args)
 580 {
 581         unsigned long flags;
 582         int printed_len;
 583         char *p;
 584         static char printk_buf[1024];
 585         static int log_level_unknown = 1;
 586
 587         boot_delay_msec();
 588
 589         preempt_disable();
 590         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 591                 /* If a crash is occurring during printk() on this CPU,
 592                  * make sure we can't deadlock */
 593                 zap_locks();
 594
 595         /* This stops the holder of console_sem just where we want him */
 596         raw_local_irq_save(flags);
 597         lockdep_off();
 598         spin_lock(&logbuf_lock);
 599         printk_cpu = smp_processor_id();
 600
 601         /* Emit the output into the temporary buffer */
 602         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 603
 604         /*
 605          * Copy the output into log_buf.  If the caller didn't provide
 606          * appropriate log level tags, we insert them here
 607          */
 608         for (p = printk_buf; *p; p++) {
 609                 if (log_level_unknown) {
 610                         /* log_level_unknown signals the start of a new line */
 611                         if (printk_time) {
 612                                 int loglev_char;
 613                                 char tbuf[50], *tp;
 614                                 unsigned tlen;
 615                                 unsigned long long t;
 616                                 unsigned long nanosec_rem;
 617
 618                                 /*
 619                                  * force the log level token to be
 620                                  * before the time output.
 621                                  */
 622                                 if (p[0] == '<' && p[1] >='0' &&
 623                                    p[1] <= '7' && p[2] == '>') {
 624                                         loglev_char = p[1];
 625                                         p += 3;
 626                                         printed_len -= 3;
 627                                 } else {
 628                                         loglev_char = default_message_loglevel
 629                                                 + '0';
 630                                 }
 631                                 t = printk_clock();
 632                                 nanosec_rem = do_div(t, 1000000000);
 633                                 tlen = sprintf(tbuf,
 634                                                 "<%c>[%5lu.%06lu] ",
 635                                                 loglev_char,
 636                                                 (unsigned long)t,
 637                                                 nanosec_rem/1000);
 638
 639                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 640                                         emit_log_char(*tp);
 641                                 printed_len += tlen;
 642                         } else {
 643                                 if (p[0] != '<' || p[1] < '0' ||
 644                                    p[1] > '7' || p[2] != '>') {
 645                                         emit_log_char('<');
 646                                         emit_log_char(default_message_loglevel
 647                                                 + '0');
 648                                         emit_log_char('>');
 649                                         printed_len += 3;
 650                                 }
 651                         }
 652                         log_level_unknown = 0;
 653                         if (!*p)
 654                                 break;
 655                 }
 656                 emit_log_char(*p);
 657                 if (*p == '\n')
 658                         log_level_unknown = 1;
 659         }
 660
 661         if (!down_trylock(&console_sem)) {
 662                 /*
 663                  * We own the drivers.  We can drop the spinlock and
 664                  * let release_console_sem() print the text, maybe ...
 665                  */
 666                 console_locked = 1;
 667                 printk_cpu = UINT_MAX;
 668                 spin_unlock(&logbuf_lock);
 669
 670                 /*
 671                  * Console drivers may assume that per-cpu resources have
 672                  * been allocated. So unless they're explicitly marked as
 673                  * being able to cope (CON_ANYTIME) don't call them until
 674                  * this CPU is officially up.
 675                  */
 676                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 677                         console_may_schedule = 0;
 678                         release_console_sem();
 679                 } else {
 680                         /* Release by hand to avoid flushing the buffer. */
 681                         console_locked = 0;
 682                         up(&console_sem);
 683                 }
 684                 lockdep_on();
 685                 raw_local_irq_restore(flags);
 686         } else {
 687                 /*
 688                  * Someone else owns the drivers.  We drop the spinlock, which
 689                  * allows the semaphore holder to proceed and to call the
 690                  * console drivers with the output which we just produced.
 691                  */
 692                 printk_cpu = UINT_MAX;
 693                 spin_unlock(&logbuf_lock);
 694                 lockdep_on();
 695                 raw_local_irq_restore(flags);
 696         }
 697
 698         preempt_enable();
 699         return printed_len;
 700 }
 701 EXPORT_SYMBOL(printk);
 702 EXPORT_SYMBOL(vprintk);
 703
 704 #else
 705
 706 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 707 {
 708         return -ENOSYS;
 709 }
 710
 711 static void call_console_drivers(unsigned long start, unsigned long end)
 712 {
 713 }
 714
 715 #endif
 716
 717 /*
 718  * Set up a list of consoles.  Called from init/main.c
 719  */
 720 static int __init console_setup(char *str)
 721 {
 722         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 723         char *s, *options;
 724         int idx;
 725
 726         /*
 727          * Decode str into name, index, options.
 728          */
 729         if (str[0] >= '0' && str[0] <= '9') {
 730                 strcpy(buf, "ttyS");
 731                 strncpy(buf + 4, str, sizeof(buf) - 5);
 732         } else {
 733                 strncpy(buf, str, sizeof(buf) - 1);
 734         }
 735         buf[sizeof(buf) - 1] = 0;
 736         if ((options = strchr(str, ',')) != NULL)
 737                 *(options++) = 0;
 738 #ifdef __sparc__
 739         if (!strcmp(str, "ttya"))
 740                 strcpy(buf, "ttyS0");
 741         if (!strcmp(str, "ttyb"))
 742                 strcpy(buf, "ttyS1");
 743 #endif
 744         for (s = buf; *s; s++)
 745                 if ((*s >= '0' && *s <= '9') || *s == ',')
 746                         break;
 747         idx = simple_strtoul(s, NULL, 10);
 748         *s = 0;
 749
 750         add_preferred_console(buf, idx, options);
 751         return 1;
 752 }
 753 __setup("console=", console_setup);
 754
 755 /**
 756  * add_preferred_console - add a device to the list of preferred consoles.
 757  * @name: device name
 758  * @idx: device index
 759  * @options: options for this console
 760  *
 761  * The last preferred console added will be used for kernel messages
 762  * and stdin/out/err for init.  Normally this is used by console_setup
 763  * above to handle user-supplied console arguments; however it can also
 764  * be used by arch-specific code either to override the user or more
 765  * commonly to provide a default console (ie from PROM variables) when
 766  * the user has not supplied one.
 767  */
 768 int __init add_preferred_console(char *name, int idx, char *options)
 769 {
 770         struct console_cmdline *c;
 771         int i;
 772
 773         /*
 774          *      See if this tty is not yet registered, and
 775          *      if we have a slot free.
 776          */
 777         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 778                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 779                           console_cmdline[i].index == idx) {
 780                                 selected_console = i;
 781                                 return 0;
 782                 }
 783         if (i == MAX_CMDLINECONSOLES)
 784                 return -E2BIG;
 785         selected_console = i;
 786         c = &console_cmdline[i];
 787         memcpy(c->name, name, sizeof(c->name));
 788         c->name[sizeof(c->name) - 1] = 0;
 789         c->options = options;
 790         c->index = idx;
 791         return 0;
 792 }
 793
 794 int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 795 {
 796         struct console_cmdline *c;
 797         int i;
 798
 799         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 800                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 801                           console_cmdline[i].index == idx) {
 802                                 c = &console_cmdline[i];
 803                                 memcpy(c->name, name_new, sizeof(c->name));
 804                                 c->name[sizeof(c->name) - 1] = 0;
 805                                 c->options = options;
 806                                 c->index = idx_new;
 807                                 return i;
 808                 }
 809         /* not found */
 810         return -1;
 811 }
 812
 813 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 814 /**
 815  * suspend_console - suspend the console subsystem
 816  *
 817  * This disables printk() while we go into suspend states
 818  */
 819 void suspend_console(void)
 820 {
 821         printk("Suspending console(s)\n");
 822         acquire_console_sem();
 823         console_suspended = 1;
 824 }
 825
 826 void resume_console(void)
 827 {
 828         console_suspended = 0;
 829         release_console_sem();
 830 }
 831 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 832
 833 /**
 834  * acquire_console_sem - lock the console system for exclusive use.
 835  *
 836  * Acquires a semaphore which guarantees that the caller has
 837  * exclusive access to the console system and the console_drivers list.
 838  *
 839  * Can sleep, returns nothing.
 840  */
 841 void acquire_console_sem(void)
 842 {
 843         BUG_ON(in_interrupt());
 844         if (console_suspended) {
 845                 down(&secondary_console_sem);
 846                 return;
 847         }
 848         down(&console_sem);
 849         console_locked = 1;
 850         console_may_schedule = 1;
 851 }
 852 EXPORT_SYMBOL(acquire_console_sem);
 853
 854 int try_acquire_console_sem(void)
 855 {
 856         if (down_trylock(&console_sem))
 857                 return -1;
 858         console_locked = 1;
 859         console_may_schedule = 0;
 860         return 0;
 861 }
 862 EXPORT_SYMBOL(try_acquire_console_sem);
 863
 864 int is_console_locked(void)
 865 {
 866         return console_locked;
 867 }
 868
 869 void wake_up_klogd(void)
 870 {
 871         if (!oops_in_progress && waitqueue_active(&log_wait))
 872                 wake_up_interruptible(&log_wait);
 873 }
 874
 875 /**
 876  * release_console_sem - unlock the console system
 877  *
 878  * Releases the semaphore which the caller holds on the console system
 879  * and the console driver list.
 880  *
 881  * While the semaphore was held, console output may have been buffered
 882  * by printk().  If this is the case, release_console_sem() emits
 883  * the output prior to releasing the semaphore.
 884  *
 885  * If there is output waiting for klogd, we wake it up.
 886  *
 887  * release_console_sem() may be called from any context.
 888  */
 889 void release_console_sem(void)
 890 {
 891         unsigned long flags;
 892         unsigned long _con_start, _log_end;
 893         unsigned long wake_klogd = 0;
 894
 895         if (console_suspended) {
 896                 up(&secondary_console_sem);
 897                 return;
 898         }
 899
 900         console_may_schedule = 0;
 901
 902         for ( ; ; ) {
 903                 spin_lock_irqsave(&logbuf_lock, flags);
 904                 wake_klogd |= log_start - log_end;
 905                 if (con_start == log_end)
 906                         break;                  /* Nothing to print */
 907                 _con_start = con_start;
 908                 _log_end = log_end;
 909                 con_start = log_end;            /* Flush */
 910                 spin_unlock(&logbuf_lock);
 911                 call_console_drivers(_con_start, _log_end);
 912                 local_irq_restore(flags);
 913         }
 914         console_locked = 0;
 915         up(&console_sem);
 916         spin_unlock_irqrestore(&logbuf_lock, flags);
 917         if (wake_klogd)
 918                 wake_up_klogd();
 919 }
 920 EXPORT_SYMBOL(release_console_sem);
 921
 922 /**
 923  * console_conditional_schedule - yield the CPU if required
 924  *
 925  * If the console code is currently allowed to sleep, and
 926  * if this CPU should yield the CPU to another task, do
 927  * so here.
 928  *
 929  * Must be called within acquire_console_sem().
 930  */
 931 void __sched console_conditional_schedule(void)
 932 {
 933         if (console_may_schedule)
 934                 cond_resched();
 935 }
 936 EXPORT_SYMBOL(console_conditional_schedule);
 937
 938 void console_print(const char *s)
 939 {
 940         printk(KERN_EMERG "%s", s);
 941 }
 942 EXPORT_SYMBOL(console_print);
 943
 944 void console_unblank(void)
 945 {
 946         struct console *c;
 947
 948         /*
 949          * console_unblank can no longer be called in interrupt context unless
 950          * oops_in_progress is set to 1..
 951          */
 952         if (oops_in_progress) {
 953                 if (down_trylock(&console_sem) != 0)
 954                         return;
 955         } else
 956                 acquire_console_sem();
 957
 958         console_locked = 1;
 959         console_may_schedule = 0;
 960         for (c = console_drivers; c != NULL; c = c->next)
 961                 if ((c->flags & CON_ENABLED) && c->unblank)
 962                         c->unblank();
 963         release_console_sem();
 964 }
 965
 966 /*
 967  * Return the console tty driver structure and its associated index
 968  */
 969 struct tty_driver *console_device(int *index)
 970 {
 971         struct console *c;
 972         struct tty_driver *driver = NULL;
 973
 974         acquire_console_sem();
 975         for (c = console_drivers; c != NULL; c = c->next) {
 976                 if (!c->device)
 977                         continue;
 978                 driver = c->device(c, index);
 979                 if (driver)
 980                         break;
 981         }
 982         release_console_sem();
 983         return driver;
 984 }
 985
 986 /*
 987  * Prevent further output on the passed console device so that (for example)
 988  * serial drivers can disable console output before suspending a port, and can
 989  * re-enable output afterwards.
 990  */
 991 void console_stop(struct console *console)
 992 {
 993         acquire_console_sem();
 994         console->flags &= ~CON_ENABLED;
 995         release_console_sem();
 996 }
 997 EXPORT_SYMBOL(console_stop);
 998
 999 void console_start(struct console *console)
1000 {
1001         acquire_console_sem();
1002         console->flags |= CON_ENABLED;
1003         release_console_sem();
1004 }
1005 EXPORT_SYMBOL(console_start);
1006
1007 /*
1008  * The console driver calls this routine during kernel initialization
1009  * to register the console printing procedure with printk() and to
1010  * print any messages that were printed by the kernel before the
1011  * console driver was initialized.
1012  */
1013 void register_console(struct console *console)
1014 {
1015         int i;
1016         unsigned long flags;
1017         struct console *bootconsole = NULL;
1018
1019         if (console_drivers) {
1020                 if (console->flags & CON_BOOT)
1021                         return;
1022                 if (console_drivers->flags & CON_BOOT)
1023                         bootconsole = console_drivers;
1024         }
1025
1026         if (preferred_console < 0 || bootconsole || !console_drivers)
1027                 preferred_console = selected_console;
1028
1029         if (console->early_setup)
1030                 console->early_setup();
1031
1032         /*
1033          *      See if we want to use this console driver. If we
1034          *      didn't select a console we take the first one
1035          *      that registers here.
1036          */
1037         if (preferred_console < 0) {
1038                 if (console->index < 0)
1039                         console->index = 0;
1040                 if (console->setup == NULL ||
1041                     console->setup(console, NULL) == 0) {
1042                         console->flags |= CON_ENABLED | CON_CONSDEV;
1043                         preferred_console = 0;
1044                 }
1045         }
1046
1047         /*
1048          *      See if this console matches one we selected on
1049          *      the command line.
1050          */
1051         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1052                         i++) {
1053                 if (strcmp(console_cmdline[i].name, console->name) != 0)
1054                         continue;
1055                 if (console->index >= 0 &&
1056                     console->index != console_cmdline[i].index)
1057                         continue;
1058                 if (console->index < 0)
1059                         console->index = console_cmdline[i].index;
1060                 if (console->setup &&
1061                     console->setup(console, console_cmdline[i].options) != 0)
1062                         break;
1063                 console->flags |= CON_ENABLED;
1064                 console->index = console_cmdline[i].index;
1065                 if (i == selected_console) {
1066                         console->flags |= CON_CONSDEV;
1067                         preferred_console = selected_console;
1068                 }
1069                 break;
1070         }
1071
1072         if (!(console->flags & CON_ENABLED))
1073                 return;
1074
1075         if (bootconsole && (console->flags & CON_CONSDEV)) {
1076                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1077                        bootconsole->name, bootconsole->index,
1078                        console->name, console->index);
1079                 unregister_console(bootconsole);
1080                 console->flags &= ~CON_PRINTBUFFER;
1081         } else {
1082                 printk(KERN_INFO "console [%s%d] enabled\n",
1083                        console->name, console->index);
1084         }
1085
1086         /*
1087          *      Put this console in the list - keep the
1088          *      preferred driver at the head of the list.
1089          */
1090         acquire_console_sem();
1091         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1092                 console->next = console_drivers;
1093                 console_drivers = console;
1094                 if (console->next)
1095                         console->next->flags &= ~CON_CONSDEV;
1096         } else {
1097                 console->next = console_drivers->next;
1098                 console_drivers->next = console;
1099         }
1100         if (console->flags & CON_PRINTBUFFER) {
1101                 /*
1102                  * release_console_sem() will print out the buffered messages
1103                  * for us.
1104                  */
1105                 spin_lock_irqsave(&logbuf_lock, flags);
1106                 con_start = log_start;
1107                 spin_unlock_irqrestore(&logbuf_lock, flags);
1108         }
1109         release_console_sem();
1110 }
1111 EXPORT_SYMBOL(register_console);
1112
1113 int unregister_console(struct console *console)
1114 {
1115         struct console *a, *b;
1116         int res = 1;
1117
1118         acquire_console_sem();
1119         if (console_drivers == console) {
1120                 console_drivers=console->next;
1121                 res = 0;
1122         } else if (console_drivers) {
1123                 for (a=console_drivers->next, b=console_drivers ;
1124                      a; b=a, a=b->next) {
1125                         if (a == console) {
1126                                 b->next = a->next;
1127                                 res = 0;
1128                                 break;
1129                         }
1130                 }
1131         }
1132
1133         /*
1134          * If this isn't the last console and it has CON_CONSDEV set, we
1135          * need to set it on the next preferred console.
1136          */
1137         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1138                 console_drivers->flags |= CON_CONSDEV;
1139
1140         release_console_sem();
1141         return res;
1142 }
1143 EXPORT_SYMBOL(unregister_console);
1144
1145 static int __init disable_boot_consoles(void)
1146 {
1147         if (console_drivers != NULL) {
1148                 if (console_drivers->flags & CON_BOOT) {
1149                         printk(KERN_INFO "turn off boot console %s%d\n",
1150                                 console_drivers->name, console_drivers->index);
1151                         return unregister_console(console_drivers);
1152                 }
1153         }
1154         return 0;
1155 }
1156 late_initcall(disable_boot_consoles);
1157
1158 /**
1159  * tty_write_message - write a message to a certain tty, not just the console.
1160  * @tty: the destination tty_struct
1161  * @msg: the message to write
1162  *
1163  * This is used for messages that need to be redirected to a specific tty.
1164  * We don't put it into the syslog queue right now maybe in the future if
1165  * really needed.
1166  */
1167 void tty_write_message(struct tty_struct *tty, char *msg)
1168 {
1169         if (tty && tty->driver->write)
1170                 tty->driver->write(tty, msg, strlen(msg));
1171         return;
1172 }
1173
1174 /*
1175  * printk rate limiting, lifted from the networking subsystem.
1176  *
1177  * This enforces a rate limit: not more than one kernel message
1178  * every printk_ratelimit_jiffies to make a denial-of-service
1179  * attack impossible.
1180  */
1181 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1182 {
1183         static DEFINE_SPINLOCK(ratelimit_lock);
1184         static unsigned long toks = 10 * 5 * HZ;
1185         static unsigned long last_msg;
1186         static int missed;
1187         unsigned long flags;
1188         unsigned long now = jiffies;
1189
1190         spin_lock_irqsave(&ratelimit_lock, flags);
1191         toks += now - last_msg;
1192         last_msg = now;
1193         if (toks > (ratelimit_burst * ratelimit_jiffies))
1194                 toks = ratelimit_burst * ratelimit_jiffies;
1195         if (toks >= ratelimit_jiffies) {
1196                 int lost = missed;
1197
1198                 missed = 0;
1199                 toks -= ratelimit_jiffies;
1200                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1201                 if (lost)
1202                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1203                 return 1;
1204         }
1205         missed++;
1206         spin_unlock_irqrestore(&ratelimit_lock, flags);
1207         return 0;
1208 }
1209 EXPORT_SYMBOL(__printk_ratelimit);
1210
1211 /* minimum time in jiffies between messages */
1212 int printk_ratelimit_jiffies = 5 * HZ;
1213
1214 /* number of messages we send before ratelimiting */
1215 int printk_ratelimit_burst = 10;
1216
1217 int printk_ratelimit(void)
1218 {
1219         return __printk_ratelimit(printk_ratelimit_jiffies,
1220                                 printk_ratelimit_burst);
1221 }
1222 EXPORT_SYMBOL(printk_ratelimit);
1223
1224 /**
1225  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1226  * @caller_jiffies: pointer to caller's state
1227  * @interval_msecs: minimum interval between prints
1228  *
1229  * printk_timed_ratelimit() returns true if more than @interval_msecs
1230  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1231  * returned true.
1232  */
1233 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1234                         unsigned int interval_msecs)
1235 {
1236         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1237                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1238                 return true;
1239         }
1240         return false;
1241 }
1242 EXPORT_SYMBOL(printk_timed_ratelimit);