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 /* printk's without a loglevel use this.. */
  41 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  42
  43 /* We show everything that is MORE important than this.. */
  44 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  45 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  46
  47 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  48
  49 int console_printk[4] = {
  50         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  51         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  52         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  53         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  54 };
  55
  56 EXPORT_UNUSED_SYMBOL(console_printk);  /*  June 2006  */
  57
  58 /*
  59  * Low lever drivers may need that to know if they can schedule in
  60  * their unblank() callback or not. So let's export it.
  61  */
  62 int oops_in_progress;
  63 EXPORT_SYMBOL(oops_in_progress);
  64
  65 /*
  66  * console_sem protects the console_drivers list, and also
  67  * provides serialisation for access to the entire console
  68  * driver system.
  69  */
  70 static DECLARE_MUTEX(console_sem);
  71 static DECLARE_MUTEX(secondary_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, console_suspended;
  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 static int __init log_buf_len_setup(char *str)
 128 {
 129         unsigned long size = memparse(str, &str);
 130         unsigned long flags;
 131
 132         if (size)
 133                 size = roundup_pow_of_two(size);
 134         if (size > log_buf_len) {
 135                 unsigned long start, dest_idx, offset;
 136                 char *new_log_buf;
 137
 138                 new_log_buf = alloc_bootmem(size);
 139                 if (!new_log_buf) {
 140                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 141                         goto out;
 142                 }
 143
 144                 spin_lock_irqsave(&logbuf_lock, flags);
 145                 log_buf_len = size;
 146                 log_buf = new_log_buf;
 147
 148                 offset = start = min(con_start, log_start);
 149                 dest_idx = 0;
 150                 while (start != log_end) {
 151                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 152                         start++;
 153                         dest_idx++;
 154                 }
 155                 log_start -= offset;
 156                 con_start -= offset;
 157                 log_end -= offset;
 158                 spin_unlock_irqrestore(&logbuf_lock, flags);
 159
 160                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 161         }
 162 out:
 163         return 1;
 164 }
 165
 166 __setup("log_buf_len=", log_buf_len_setup);
 167
 168 /*
 169  * Commands to do_syslog:
 170  *
 171  *      0 -- Close the log.  Currently a NOP.
 172  *      1 -- Open the log. Currently a NOP.
 173  *      2 -- Read from the log.
 174  *      3 -- Read all messages remaining in the ring buffer.
 175  *      4 -- Read and clear all messages remaining in the ring buffer
 176  *      5 -- Clear ring buffer.
 177  *      6 -- Disable printk's to console
 178  *      7 -- Enable printk's to console
 179  *      8 -- Set level of messages printed to console
 180  *      9 -- Return number of unread characters in the log buffer
 181  *     10 -- Return size of the log buffer
 182  */
 183 int do_syslog(int type, char __user *buf, int len)
 184 {
 185         unsigned long i, j, limit, count;
 186         int do_clear = 0;
 187         char c;
 188         int error = 0;
 189
 190         error = security_syslog(type);
 191         if (error)
 192                 return error;
 193
 194         switch (type) {
 195         case 0:         /* Close log */
 196                 break;
 197         case 1:         /* Open log */
 198                 break;
 199         case 2:         /* Read from log */
 200                 error = -EINVAL;
 201                 if (!buf || len < 0)
 202                         goto out;
 203                 error = 0;
 204                 if (!len)
 205                         goto out;
 206                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 207                         error = -EFAULT;
 208                         goto out;
 209                 }
 210                 error = wait_event_interruptible(log_wait,
 211                                                         (log_start - log_end));
 212                 if (error)
 213                         goto out;
 214                 i = 0;
 215                 spin_lock_irq(&logbuf_lock);
 216                 while (!error && (log_start != log_end) && i < len) {
 217                         c = LOG_BUF(log_start);
 218                         log_start++;
 219                         spin_unlock_irq(&logbuf_lock);
 220                         error = __put_user(c,buf);
 221                         buf++;
 222                         i++;
 223                         cond_resched();
 224                         spin_lock_irq(&logbuf_lock);
 225                 }
 226                 spin_unlock_irq(&logbuf_lock);
 227                 if (!error)
 228                         error = i;
 229                 break;
 230         case 4:         /* Read/clear last kernel messages */
 231                 do_clear = 1;
 232                 /* FALL THRU */
 233         case 3:         /* Read last kernel messages */
 234                 error = -EINVAL;
 235                 if (!buf || len < 0)
 236                         goto out;
 237                 error = 0;
 238                 if (!len)
 239                         goto out;
 240                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 241                         error = -EFAULT;
 242                         goto out;
 243                 }
 244                 count = len;
 245                 if (count > log_buf_len)
 246                         count = log_buf_len;
 247                 spin_lock_irq(&logbuf_lock);
 248                 if (count > logged_chars)
 249                         count = logged_chars;
 250                 if (do_clear)
 251                         logged_chars = 0;
 252                 limit = log_end;
 253                 /*
 254                  * __put_user() could sleep, and while we sleep
 255                  * printk() could overwrite the messages
 256                  * we try to copy to user space. Therefore
 257                  * the messages are copied in reverse. <manfreds>
 258                  */
 259                 for (i = 0; i < count && !error; i++) {
 260                         j = limit-1-i;
 261                         if (j + log_buf_len < log_end)
 262                                 break;
 263                         c = LOG_BUF(j);
 264                         spin_unlock_irq(&logbuf_lock);
 265                         error = __put_user(c,&buf[count-1-i]);
 266                         cond_resched();
 267                         spin_lock_irq(&logbuf_lock);
 268                 }
 269                 spin_unlock_irq(&logbuf_lock);
 270                 if (error)
 271                         break;
 272                 error = i;
 273                 if (i != count) {
 274                         int offset = count-error;
 275                         /* buffer overflow during copy, correct user buffer. */
 276                         for (i = 0; i < error; i++) {
 277                                 if (__get_user(c,&buf[i+offset]) ||
 278                                     __put_user(c,&buf[i])) {
 279                                         error = -EFAULT;
 280                                         break;
 281                                 }
 282                                 cond_resched();
 283                         }
 284                 }
 285                 break;
 286         case 5:         /* Clear ring buffer */
 287                 logged_chars = 0;
 288                 break;
 289         case 6:         /* Disable logging to console */
 290                 console_loglevel = minimum_console_loglevel;
 291                 break;
 292         case 7:         /* Enable logging to console */
 293                 console_loglevel = default_console_loglevel;
 294                 break;
 295         case 8:         /* Set level of messages printed to console */
 296                 error = -EINVAL;
 297                 if (len < 1 || len > 8)
 298                         goto out;
 299                 if (len < minimum_console_loglevel)
 300                         len = minimum_console_loglevel;
 301                 console_loglevel = len;
 302                 error = 0;
 303                 break;
 304         case 9:         /* Number of chars in the log buffer */
 305                 error = log_end - log_start;
 306                 break;
 307         case 10:        /* Size of the log buffer */
 308                 error = log_buf_len;
 309                 break;
 310         default:
 311                 error = -EINVAL;
 312                 break;
 313         }
 314 out:
 315         return error;
 316 }
 317
 318 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 319 {
 320         return do_syslog(type, buf, len);
 321 }
 322
 323 /*
 324  * Call the console drivers on a range of log_buf
 325  */
 326 static void __call_console_drivers(unsigned long start, unsigned long end)
 327 {
 328         struct console *con;
 329
 330         for (con = console_drivers; con; con = con->next) {
 331                 if ((con->flags & CON_ENABLED) && con->write &&
 332                                 (cpu_online(smp_processor_id()) ||
 333                                 (con->flags & CON_ANYTIME)))
 334                         con->write(con, &LOG_BUF(start), end - start);
 335         }
 336 }
 337
 338 /*
 339  * Write out chars from start to end - 1 inclusive
 340  */
 341 static void _call_console_drivers(unsigned long start,
 342                                 unsigned long end, int msg_log_level)
 343 {
 344         if (msg_log_level < console_loglevel &&
 345                         console_drivers && start != end) {
 346                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 347                         /* wrapped write */
 348                         __call_console_drivers(start & LOG_BUF_MASK,
 349                                                 log_buf_len);
 350                         __call_console_drivers(0, end & LOG_BUF_MASK);
 351                 } else {
 352                         __call_console_drivers(start, end);
 353                 }
 354         }
 355 }
 356
 357 /*
 358  * Call the console drivers, asking them to write out
 359  * log_buf[start] to log_buf[end - 1].
 360  * The console_sem must be held.
 361  */
 362 static void call_console_drivers(unsigned long start, unsigned long end)
 363 {
 364         unsigned long cur_index, start_print;
 365         static int msg_level = -1;
 366
 367         BUG_ON(((long)(start - end)) > 0);
 368
 369         cur_index = start;
 370         start_print = start;
 371         while (cur_index != end) {
 372                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 373                                 LOG_BUF(cur_index + 0) == '<' &&
 374                                 LOG_BUF(cur_index + 1) >= '0' &&
 375                                 LOG_BUF(cur_index + 1) <= '7' &&
 376                                 LOG_BUF(cur_index + 2) == '>') {
 377                         msg_level = LOG_BUF(cur_index + 1) - '0';
 378                         cur_index += 3;
 379                         start_print = cur_index;
 380                 }
 381                 while (cur_index != end) {
 382                         char c = LOG_BUF(cur_index);
 383
 384                         cur_index++;
 385                         if (c == '\n') {
 386                                 if (msg_level < 0) {
 387                                         /*
 388                                          * printk() has already given us loglevel tags in
 389                                          * the buffer.  This code is here in case the
 390                                          * log buffer has wrapped right round and scribbled
 391                                          * on those tags
 392                                          */
 393                                         msg_level = default_message_loglevel;
 394                                 }
 395                                 _call_console_drivers(start_print, cur_index, msg_level);
 396                                 msg_level = -1;
 397                                 start_print = cur_index;
 398                                 break;
 399                         }
 400                 }
 401         }
 402         _call_console_drivers(start_print, end, msg_level);
 403 }
 404
 405 static void emit_log_char(char c)
 406 {
 407         LOG_BUF(log_end) = c;
 408         log_end++;
 409         if (log_end - log_start > log_buf_len)
 410                 log_start = log_end - log_buf_len;
 411         if (log_end - con_start > log_buf_len)
 412                 con_start = log_end - log_buf_len;
 413         if (logged_chars < log_buf_len)
 414                 logged_chars++;
 415 }
 416
 417 /*
 418  * Zap console related locks when oopsing. Only zap at most once
 419  * every 10 seconds, to leave time for slow consoles to print a
 420  * full oops.
 421  */
 422 static void zap_locks(void)
 423 {
 424         static unsigned long oops_timestamp;
 425
 426         if (time_after_eq(jiffies, oops_timestamp) &&
 427                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 428                 return;
 429
 430         oops_timestamp = jiffies;
 431
 432         /* If a crash is occurring, make sure we can't deadlock */
 433         spin_lock_init(&logbuf_lock);
 434         /* And make sure that we print immediately */
 435         init_MUTEX(&console_sem);
 436 }
 437
 438 #if defined(CONFIG_PRINTK_TIME)
 439 static int printk_time = 1;
 440 #else
 441 static int printk_time = 0;
 442 #endif
 443 module_param(printk_time, int, S_IRUGO | S_IWUSR);
 444
 445 static int __init printk_time_setup(char *str)
 446 {
 447         if (*str)
 448                 return 0;
 449         printk_time = 1;
 450         return 1;
 451 }
 452
 453 __setup("time", printk_time_setup);
 454
 455 __attribute__((weak)) unsigned long long printk_clock(void)
 456 {
 457         return sched_clock();
 458 }
 459
 460 /* Check if we have any console registered that can be called early in boot. */
 461 static int have_callable_console(void)
 462 {
 463         struct console *con;
 464
 465         for (con = console_drivers; con; con = con->next)
 466                 if (con->flags & CON_ANYTIME)
 467                         return 1;
 468
 469         return 0;
 470 }
 471
 472 /**
 473  * printk - print a kernel message
 474  * @fmt: format string
 475  *
 476  * This is printk.  It can be called from any context.  We want it to work.
 477  *
 478  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 479  * call the console drivers.  If we fail to get the semaphore we place the output
 480  * into the log buffer and return.  The current holder of the console_sem will
 481  * notice the new output in release_console_sem() and will send it to the
 482  * consoles before releasing the semaphore.
 483  *
 484  * One effect of this deferred printing is that code which calls printk() and
 485  * then changes console_loglevel may break. This is because console_loglevel
 486  * is inspected when the actual printing occurs.
 487  *
 488  * See also:
 489  * printf(3)
 490  */
 491
 492 asmlinkage int printk(const char *fmt, ...)
 493 {
 494         va_list args;
 495         int r;
 496
 497         va_start(args, fmt);
 498         r = vprintk(fmt, args);
 499         va_end(args);
 500
 501         return r;
 502 }
 503
 504 /* cpu currently holding logbuf_lock */
 505 static volatile unsigned int printk_cpu = UINT_MAX;
 506
 507 asmlinkage int vprintk(const char *fmt, va_list args)
 508 {
 509         unsigned long flags;
 510         int printed_len;
 511         char *p;
 512         static char printk_buf[1024];
 513         static int log_level_unknown = 1;
 514
 515         preempt_disable();
 516         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 517                 /* If a crash is occurring during printk() on this CPU,
 518                  * make sure we can't deadlock */
 519                 zap_locks();
 520
 521         /* This stops the holder of console_sem just where we want him */
 522         local_irq_save(flags);
 523         lockdep_off();
 524         spin_lock(&logbuf_lock);
 525         printk_cpu = smp_processor_id();
 526
 527         /* Emit the output into the temporary buffer */
 528         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 529
 530         /*
 531          * Copy the output into log_buf.  If the caller didn't provide
 532          * appropriate log level tags, we insert them here
 533          */
 534         for (p = printk_buf; *p; p++) {
 535                 if (log_level_unknown) {
 536                         /* log_level_unknown signals the start of a new line */
 537                         if (printk_time) {
 538                                 int loglev_char;
 539                                 char tbuf[50], *tp;
 540                                 unsigned tlen;
 541                                 unsigned long long t;
 542                                 unsigned long nanosec_rem;
 543
 544                                 /*
 545                                  * force the log level token to be
 546                                  * before the time output.
 547                                  */
 548                                 if (p[0] == '<' && p[1] >='0' &&
 549                                    p[1] <= '7' && p[2] == '>') {
 550                                         loglev_char = p[1];
 551                                         p += 3;
 552                                         printed_len -= 3;
 553                                 } else {
 554                                         loglev_char = default_message_loglevel
 555                                                 + '0';
 556                                 }
 557                                 t = printk_clock();
 558                                 nanosec_rem = do_div(t, 1000000000);
 559                                 tlen = sprintf(tbuf,
 560                                                 "<%c>[%5lu.%06lu] ",
 561                                                 loglev_char,
 562                                                 (unsigned long)t,
 563                                                 nanosec_rem/1000);
 564
 565                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 566                                         emit_log_char(*tp);
 567                                 printed_len += tlen;
 568                         } else {
 569                                 if (p[0] != '<' || p[1] < '0' ||
 570                                    p[1] > '7' || p[2] != '>') {
 571                                         emit_log_char('<');
 572                                         emit_log_char(default_message_loglevel
 573                                                 + '0');
 574                                         emit_log_char('>');
 575                                         printed_len += 3;
 576                                 }
 577                         }
 578                         log_level_unknown = 0;
 579                         if (!*p)
 580                                 break;
 581                 }
 582                 emit_log_char(*p);
 583                 if (*p == '\n')
 584                         log_level_unknown = 1;
 585         }
 586
 587         if (!down_trylock(&console_sem)) {
 588                 /*
 589                  * We own the drivers.  We can drop the spinlock and
 590                  * let release_console_sem() print the text, maybe ...
 591                  */
 592                 console_locked = 1;
 593                 printk_cpu = UINT_MAX;
 594                 spin_unlock(&logbuf_lock);
 595
 596                 /*
 597                  * Console drivers may assume that per-cpu resources have
 598                  * been allocated. So unless they're explicitly marked as
 599                  * being able to cope (CON_ANYTIME) don't call them until
 600                  * this CPU is officially up.
 601                  */
 602                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 603                         console_may_schedule = 0;
 604                         release_console_sem();
 605                 } else {
 606                         /* Release by hand to avoid flushing the buffer. */
 607                         console_locked = 0;
 608                         up(&console_sem);
 609                 }
 610                 lockdep_on();
 611                 local_irq_restore(flags);
 612         } else {
 613                 /*
 614                  * Someone else owns the drivers.  We drop the spinlock, which
 615                  * allows the semaphore holder to proceed and to call the
 616                  * console drivers with the output which we just produced.
 617                  */
 618                 printk_cpu = UINT_MAX;
 619                 spin_unlock(&logbuf_lock);
 620                 lockdep_on();
 621                 local_irq_restore(flags);
 622         }
 623
 624         preempt_enable();
 625         return printed_len;
 626 }
 627 EXPORT_SYMBOL(printk);
 628 EXPORT_SYMBOL(vprintk);
 629
 630 #else
 631
 632 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 633 {
 634         return -ENOSYS;
 635 }
 636
 637 static void call_console_drivers(unsigned long start, unsigned long end)
 638 {
 639 }
 640
 641 #endif
 642
 643 /*
 644  * Set up a list of consoles.  Called from init/main.c
 645  */
 646 static int __init console_setup(char *str)
 647 {
 648         char name[sizeof(console_cmdline[0].name)];
 649         char *s, *options;
 650         int idx;
 651
 652         /*
 653          * Decode str into name, index, options.
 654          */
 655         if (str[0] >= '0' && str[0] <= '9') {
 656                 strcpy(name, "ttyS");
 657                 strncpy(name + 4, str, sizeof(name) - 5);
 658         } else {
 659                 strncpy(name, str, sizeof(name) - 1);
 660         }
 661         name[sizeof(name) - 1] = 0;
 662         if ((options = strchr(str, ',')) != NULL)
 663                 *(options++) = 0;
 664 #ifdef __sparc__
 665         if (!strcmp(str, "ttya"))
 666                 strcpy(name, "ttyS0");
 667         if (!strcmp(str, "ttyb"))
 668                 strcpy(name, "ttyS1");
 669 #endif
 670         for (s = name; *s; s++)
 671                 if ((*s >= '0' && *s <= '9') || *s == ',')
 672                         break;
 673         idx = simple_strtoul(s, NULL, 10);
 674         *s = 0;
 675
 676         add_preferred_console(name, idx, options);
 677         return 1;
 678 }
 679 __setup("console=", console_setup);
 680
 681 /**
 682  * add_preferred_console - add a device to the list of preferred consoles.
 683  * @name: device name
 684  * @idx: device index
 685  * @options: options for this console
 686  *
 687  * The last preferred console added will be used for kernel messages
 688  * and stdin/out/err for init.  Normally this is used by console_setup
 689  * above to handle user-supplied console arguments; however it can also
 690  * be used by arch-specific code either to override the user or more
 691  * commonly to provide a default console (ie from PROM variables) when
 692  * the user has not supplied one.
 693  */
 694 int __init add_preferred_console(char *name, int idx, char *options)
 695 {
 696         struct console_cmdline *c;
 697         int i;
 698
 699         /*
 700          *      See if this tty is not yet registered, and
 701          *      if we have a slot free.
 702          */
 703         for(i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 704                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 705                           console_cmdline[i].index == idx) {
 706                                 selected_console = i;
 707                                 return 0;
 708                 }
 709         if (i == MAX_CMDLINECONSOLES)
 710                 return -E2BIG;
 711         selected_console = i;
 712         c = &console_cmdline[i];
 713         memcpy(c->name, name, sizeof(c->name));
 714         c->name[sizeof(c->name) - 1] = 0;
 715         c->options = options;
 716         c->index = idx;
 717         return 0;
 718 }
 719
 720 #ifndef CONFIG_DISABLE_CONSOLE_SUSPEND
 721 /**
 722  * suspend_console - suspend the console subsystem
 723  *
 724  * This disables printk() while we go into suspend states
 725  */
 726 void suspend_console(void)
 727 {
 728         printk("Suspending console(s)\n");
 729         acquire_console_sem();
 730         console_suspended = 1;
 731 }
 732
 733 void resume_console(void)
 734 {
 735         console_suspended = 0;
 736         release_console_sem();
 737 }
 738 #endif /* CONFIG_DISABLE_CONSOLE_SUSPEND */
 739
 740 /**
 741  * acquire_console_sem - lock the console system for exclusive use.
 742  *
 743  * Acquires a semaphore which guarantees that the caller has
 744  * exclusive access to the console system and the console_drivers list.
 745  *
 746  * Can sleep, returns nothing.
 747  */
 748 void acquire_console_sem(void)
 749 {
 750         BUG_ON(in_interrupt());
 751         if (console_suspended) {
 752                 down(&secondary_console_sem);
 753                 return;
 754         }
 755         down(&console_sem);
 756         console_locked = 1;
 757         console_may_schedule = 1;
 758 }
 759 EXPORT_SYMBOL(acquire_console_sem);
 760
 761 int try_acquire_console_sem(void)
 762 {
 763         if (down_trylock(&console_sem))
 764                 return -1;
 765         console_locked = 1;
 766         console_may_schedule = 0;
 767         return 0;
 768 }
 769 EXPORT_SYMBOL(try_acquire_console_sem);
 770
 771 int is_console_locked(void)
 772 {
 773         return console_locked;
 774 }
 775 EXPORT_UNUSED_SYMBOL(is_console_locked);  /*  June 2006  */
 776
 777 /**
 778  * release_console_sem - unlock the console system
 779  *
 780  * Releases the semaphore which the caller holds on the console system
 781  * and the console driver list.
 782  *
 783  * While the semaphore was held, console output may have been buffered
 784  * by printk().  If this is the case, release_console_sem() emits
 785  * the output prior to releasing the semaphore.
 786  *
 787  * If there is output waiting for klogd, we wake it up.
 788  *
 789  * release_console_sem() may be called from any context.
 790  */
 791 void release_console_sem(void)
 792 {
 793         unsigned long flags;
 794         unsigned long _con_start, _log_end;
 795         unsigned long wake_klogd = 0;
 796
 797         if (console_suspended) {
 798                 up(&secondary_console_sem);
 799                 return;
 800         }
 801
 802         console_may_schedule = 0;
 803
 804         for ( ; ; ) {
 805                 spin_lock_irqsave(&logbuf_lock, flags);
 806                 wake_klogd |= log_start - log_end;
 807                 if (con_start == log_end)
 808                         break;                  /* Nothing to print */
 809                 _con_start = con_start;
 810                 _log_end = log_end;
 811                 con_start = log_end;            /* Flush */
 812                 spin_unlock(&logbuf_lock);
 813                 call_console_drivers(_con_start, _log_end);
 814                 local_irq_restore(flags);
 815         }
 816         console_locked = 0;
 817         up(&console_sem);
 818         spin_unlock_irqrestore(&logbuf_lock, flags);
 819         if (wake_klogd && !oops_in_progress && waitqueue_active(&log_wait))
 820                 wake_up_interruptible(&log_wait);
 821 }
 822 EXPORT_SYMBOL(release_console_sem);
 823
 824 /**
 825  * console_conditional_schedule - yield the CPU if required
 826  *
 827  * If the console code is currently allowed to sleep, and
 828  * if this CPU should yield the CPU to another task, do
 829  * so here.
 830  *
 831  * Must be called within acquire_console_sem().
 832  */
 833 void __sched console_conditional_schedule(void)
 834 {
 835         if (console_may_schedule)
 836                 cond_resched();
 837 }
 838 EXPORT_SYMBOL(console_conditional_schedule);
 839
 840 void console_print(const char *s)
 841 {
 842         printk(KERN_EMERG "%s", s);
 843 }
 844 EXPORT_SYMBOL(console_print);
 845
 846 void console_unblank(void)
 847 {
 848         struct console *c;
 849
 850         /*
 851          * console_unblank can no longer be called in interrupt context unless
 852          * oops_in_progress is set to 1..
 853          */
 854         if (oops_in_progress) {
 855                 if (down_trylock(&console_sem) != 0)
 856                         return;
 857         } else
 858                 acquire_console_sem();
 859
 860         console_locked = 1;
 861         console_may_schedule = 0;
 862         for (c = console_drivers; c != NULL; c = c->next)
 863                 if ((c->flags & CON_ENABLED) && c->unblank)
 864                         c->unblank();
 865         release_console_sem();
 866 }
 867
 868 /*
 869  * Return the console tty driver structure and its associated index
 870  */
 871 struct tty_driver *console_device(int *index)
 872 {
 873         struct console *c;
 874         struct tty_driver *driver = NULL;
 875
 876         acquire_console_sem();
 877         for (c = console_drivers; c != NULL; c = c->next) {
 878                 if (!c->device)
 879                         continue;
 880                 driver = c->device(c, index);
 881                 if (driver)
 882                         break;
 883         }
 884         release_console_sem();
 885         return driver;
 886 }
 887
 888 /*
 889  * Prevent further output on the passed console device so that (for example)
 890  * serial drivers can disable console output before suspending a port, and can
 891  * re-enable output afterwards.
 892  */
 893 void console_stop(struct console *console)
 894 {
 895         acquire_console_sem();
 896         console->flags &= ~CON_ENABLED;
 897         release_console_sem();
 898 }
 899 EXPORT_SYMBOL(console_stop);
 900
 901 void console_start(struct console *console)
 902 {
 903         acquire_console_sem();
 904         console->flags |= CON_ENABLED;
 905         release_console_sem();
 906 }
 907 EXPORT_SYMBOL(console_start);
 908
 909 /*
 910  * The console driver calls this routine during kernel initialization
 911  * to register the console printing procedure with printk() and to
 912  * print any messages that were printed by the kernel before the
 913  * console driver was initialized.
 914  */
 915 void register_console(struct console *console)
 916 {
 917         int i;
 918         unsigned long flags;
 919
 920         if (preferred_console < 0)
 921                 preferred_console = selected_console;
 922
 923         /*
 924          *      See if we want to use this console driver. If we
 925          *      didn't select a console we take the first one
 926          *      that registers here.
 927          */
 928         if (preferred_console < 0) {
 929                 if (console->index < 0)
 930                         console->index = 0;
 931                 if (console->setup == NULL ||
 932                     console->setup(console, NULL) == 0) {
 933                         console->flags |= CON_ENABLED | CON_CONSDEV;
 934                         preferred_console = 0;
 935                 }
 936         }
 937
 938         /*
 939          *      See if this console matches one we selected on
 940          *      the command line.
 941          */
 942         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 943                         i++) {
 944                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 945                         continue;
 946                 if (console->index >= 0 &&
 947                     console->index != console_cmdline[i].index)
 948                         continue;
 949                 if (console->index < 0)
 950                         console->index = console_cmdline[i].index;
 951                 if (console->setup &&
 952                     console->setup(console, console_cmdline[i].options) != 0)
 953                         break;
 954                 console->flags |= CON_ENABLED;
 955                 console->index = console_cmdline[i].index;
 956                 if (i == selected_console) {
 957                         console->flags |= CON_CONSDEV;
 958                         preferred_console = selected_console;
 959                 }
 960                 break;
 961         }
 962
 963         if (!(console->flags & CON_ENABLED))
 964                 return;
 965
 966         if (console_drivers && (console_drivers->flags & CON_BOOT)) {
 967                 unregister_console(console_drivers);
 968                 console->flags &= ~CON_PRINTBUFFER;
 969         }
 970
 971         /*
 972          *      Put this console in the list - keep the
 973          *      preferred driver at the head of the list.
 974          */
 975         acquire_console_sem();
 976         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
 977                 console->next = console_drivers;
 978                 console_drivers = console;
 979                 if (console->next)
 980                         console->next->flags &= ~CON_CONSDEV;
 981         } else {
 982                 console->next = console_drivers->next;
 983                 console_drivers->next = console;
 984         }
 985         if (console->flags & CON_PRINTBUFFER) {
 986                 /*
 987                  * release_console_sem() will print out the buffered messages
 988                  * for us.
 989                  */
 990                 spin_lock_irqsave(&logbuf_lock, flags);
 991                 con_start = log_start;
 992                 spin_unlock_irqrestore(&logbuf_lock, flags);
 993         }
 994         release_console_sem();
 995 }
 996 EXPORT_SYMBOL(register_console);
 997
 998 int unregister_console(struct console *console)
 999 {
1000         struct console *a, *b;
1001         int res = 1;
1002
1003         acquire_console_sem();
1004         if (console_drivers == console) {
1005                 console_drivers=console->next;
1006                 res = 0;
1007         } else if (console_drivers) {
1008                 for (a=console_drivers->next, b=console_drivers ;
1009                      a; b=a, a=b->next) {
1010                         if (a == console) {
1011                                 b->next = a->next;
1012                                 res = 0;
1013                                 break;
1014                         }
1015                 }
1016         }
1017
1018         /* If last console is removed, we re-enable picking the first
1019          * one that gets registered. Without that, pmac early boot console
1020          * would prevent fbcon from taking over.
1021          *
1022          * If this isn't the last console and it has CON_CONSDEV set, we
1023          * need to set it on the next preferred console.
1024          */
1025         if (console_drivers == NULL)
1026                 preferred_console = selected_console;
1027         else if (console->flags & CON_CONSDEV)
1028                 console_drivers->flags |= CON_CONSDEV;
1029
1030         release_console_sem();
1031         return res;
1032 }
1033 EXPORT_SYMBOL(unregister_console);
1034
1035 /**
1036  * tty_write_message - write a message to a certain tty, not just the console.
1037  * @tty: the destination tty_struct
1038  * @msg: the message to write
1039  *
1040  * This is used for messages that need to be redirected to a specific tty.
1041  * We don't put it into the syslog queue right now maybe in the future if
1042  * really needed.
1043  */
1044 void tty_write_message(struct tty_struct *tty, char *msg)
1045 {
1046         if (tty && tty->driver->write)
1047                 tty->driver->write(tty, msg, strlen(msg));
1048         return;
1049 }
1050
1051 /*
1052  * printk rate limiting, lifted from the networking subsystem.
1053  *
1054  * This enforces a rate limit: not more than one kernel message
1055  * every printk_ratelimit_jiffies to make a denial-of-service
1056  * attack impossible.
1057  */
1058 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1059 {
1060         static DEFINE_SPINLOCK(ratelimit_lock);
1061         static unsigned long toks = 10 * 5 * HZ;
1062         static unsigned long last_msg;
1063         static int missed;
1064         unsigned long flags;
1065         unsigned long now = jiffies;
1066
1067         spin_lock_irqsave(&ratelimit_lock, flags);
1068         toks += now - last_msg;
1069         last_msg = now;
1070         if (toks > (ratelimit_burst * ratelimit_jiffies))
1071                 toks = ratelimit_burst * ratelimit_jiffies;
1072         if (toks >= ratelimit_jiffies) {
1073                 int lost = missed;
1074
1075                 missed = 0;
1076                 toks -= ratelimit_jiffies;
1077                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1078                 if (lost)
1079                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1080                 return 1;
1081         }
1082         missed++;
1083         spin_unlock_irqrestore(&ratelimit_lock, flags);
1084         return 0;
1085 }
1086 EXPORT_SYMBOL(__printk_ratelimit);
1087
1088 /* minimum time in jiffies between messages */
1089 int printk_ratelimit_jiffies = 5 * HZ;
1090
1091 /* number of messages we send before ratelimiting */
1092 int printk_ratelimit_burst = 10;
1093
1094 int printk_ratelimit(void)
1095 {
1096         return __printk_ratelimit(printk_ratelimit_jiffies,
1097                                 printk_ratelimit_burst);
1098 }
1099 EXPORT_SYMBOL(printk_ratelimit);
1100
1101 /**
1102  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1103  * @caller_jiffies: pointer to caller's state
1104  * @interval_msecs: minimum interval between prints
1105  *
1106  * printk_timed_ratelimit() returns true if more than @interval_msecs
1107  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1108  * returned true.
1109  */
1110 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1111                         unsigned int interval_msecs)
1112 {
1113         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1114                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1115                 return true;
1116         }
1117         return false;
1118 }
1119 EXPORT_SYMBOL(printk_timed_ratelimit);