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/module.h>
  26 #include <linux/moduleparam.h>
  27 #include <linux/interrupt.h>                    /* For in_interrupt() */
  28 #include <linux/delay.h>
  29 #include <linux/smp.h>
  30 #include <linux/security.h>
  31 #include <linux/bootmem.h>
  32 #include <linux/syscalls.h>
  33 #include <linux/jiffies.h>
  34
  35 #include <asm/uaccess.h>
  36
  37 #define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
  38
  39 /* printk's without a loglevel use this.. */
  40 #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  41
  42 /* We show everything that is MORE important than this.. */
  43 #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  44 #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  45
  46 DECLARE_WAIT_QUEUE_HEAD(log_wait);
  47
  48 int console_printk[4] = {
  49         DEFAULT_CONSOLE_LOGLEVEL,       /* console_loglevel */
  50         DEFAULT_MESSAGE_LOGLEVEL,       /* default_message_loglevel */
  51         MINIMUM_CONSOLE_LOGLEVEL,       /* minimum_console_loglevel */
  52         DEFAULT_CONSOLE_LOGLEVEL,       /* default_console_loglevel */
  53 };
  54
  55 /*
  56  * Low level drivers may need that to know if they can schedule in
  57  * their unblank() callback or not. So let's export it.
  58  */
  59 int oops_in_progress;
  60 EXPORT_SYMBOL(oops_in_progress);
  61
  62 /*
  63  * console_sem protects the console_drivers list, and also
  64  * provides serialisation for access to the entire console
  65  * driver system.
  66  */
  67 static DECLARE_MUTEX(console_sem);
  68 static DECLARE_MUTEX(secondary_console_sem);
  69 struct console *console_drivers;
  70 /*
  71  * This is used for debugging the mess that is the VT code by
  72  * keeping track if we have the console semaphore held. It's
  73  * definitely not the perfect debug tool (we don't know if _WE_
  74  * hold it are racing, but it helps tracking those weird code
  75  * path in the console code where we end up in places I want
  76  * locked without the console sempahore held
  77  */
  78 static int console_locked, console_suspended;
  79
  80 /*
  81  * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
  82  * It is also used in interesting ways to provide interlocking in
  83  * release_console_sem().
  84  */
  85 static DEFINE_SPINLOCK(logbuf_lock);
  86
  87 #define LOG_BUF_MASK    (log_buf_len-1)
  88 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  89
  90 /*
  91  * The indices into log_buf are not constrained to log_buf_len - they
  92  * must be masked before subscripting
  93  */
  94 static unsigned long log_start; /* Index into log_buf: next char to be read by syslog() */
  95 static unsigned long con_start; /* Index into log_buf: next char to be sent to consoles */
  96 static unsigned long log_end;   /* Index into log_buf: most-recently-written-char + 1 */
  97
  98 /*
  99  *      Array of consoles built from command line options (console=)
 100  */
 101 struct console_cmdline
 102 {
 103         char    name[8];                        /* Name of the driver       */
 104         int     index;                          /* Minor dev. to use        */
 105         char    *options;                       /* Options for the driver   */
 106 };
 107
 108 #define MAX_CMDLINECONSOLES 8
 109
 110 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 111 static int selected_console = -1;
 112 static int preferred_console = -1;
 113
 114 /* Flag: console code may call schedule() */
 115 static int console_may_schedule;
 116
 117 #ifdef CONFIG_PRINTK
 118
 119 static char __log_buf[__LOG_BUF_LEN];
 120 static char *log_buf = __log_buf;
 121 static int log_buf_len = __LOG_BUF_LEN;
 122 static unsigned long logged_chars; /* Number of chars produced since last read+clear operation */
 123
 124 static int __init log_buf_len_setup(char *str)
 125 {
 126         unsigned long size = memparse(str, &str);
 127         unsigned long flags;
 128
 129         if (size)
 130                 size = roundup_pow_of_two(size);
 131         if (size > log_buf_len) {
 132                 unsigned long start, dest_idx, offset;
 133                 char *new_log_buf;
 134
 135                 new_log_buf = alloc_bootmem(size);
 136                 if (!new_log_buf) {
 137                         printk(KERN_WARNING "log_buf_len: allocation failed\n");
 138                         goto out;
 139                 }
 140
 141                 spin_lock_irqsave(&logbuf_lock, flags);
 142                 log_buf_len = size;
 143                 log_buf = new_log_buf;
 144
 145                 offset = start = min(con_start, log_start);
 146                 dest_idx = 0;
 147                 while (start != log_end) {
 148                         log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
 149                         start++;
 150                         dest_idx++;
 151                 }
 152                 log_start -= offset;
 153                 con_start -= offset;
 154                 log_end -= offset;
 155                 spin_unlock_irqrestore(&logbuf_lock, flags);
 156
 157                 printk(KERN_NOTICE "log_buf_len: %d\n", log_buf_len);
 158         }
 159 out:
 160         return 1;
 161 }
 162
 163 __setup("log_buf_len=", log_buf_len_setup);
 164
 165 /*
 166  * Commands to do_syslog:
 167  *
 168  *      0 -- Close the log.  Currently a NOP.
 169  *      1 -- Open the log. Currently a NOP.
 170  *      2 -- Read from the log.
 171  *      3 -- Read all messages remaining in the ring buffer.
 172  *      4 -- Read and clear all messages remaining in the ring buffer
 173  *      5 -- Clear ring buffer.
 174  *      6 -- Disable printk's to console
 175  *      7 -- Enable printk's to console
 176  *      8 -- Set level of messages printed to console
 177  *      9 -- Return number of unread characters in the log buffer
 178  *     10 -- Return size of the log buffer
 179  */
 180 int do_syslog(int type, char __user *buf, int len)
 181 {
 182         unsigned long i, j, limit, count;
 183         int do_clear = 0;
 184         char c;
 185         int error = 0;
 186
 187         error = security_syslog(type);
 188         if (error)
 189                 return error;
 190
 191         switch (type) {
 192         case 0:         /* Close log */
 193                 break;
 194         case 1:         /* Open log */
 195                 break;
 196         case 2:         /* Read from log */
 197                 error = -EINVAL;
 198                 if (!buf || len < 0)
 199                         goto out;
 200                 error = 0;
 201                 if (!len)
 202                         goto out;
 203                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 204                         error = -EFAULT;
 205                         goto out;
 206                 }
 207                 error = wait_event_interruptible(log_wait,
 208                                                         (log_start - log_end));
 209                 if (error)
 210                         goto out;
 211                 i = 0;
 212                 spin_lock_irq(&logbuf_lock);
 213                 while (!error && (log_start != log_end) && i < len) {
 214                         c = LOG_BUF(log_start);
 215                         log_start++;
 216                         spin_unlock_irq(&logbuf_lock);
 217                         error = __put_user(c,buf);
 218                         buf++;
 219                         i++;
 220                         cond_resched();
 221                         spin_lock_irq(&logbuf_lock);
 222                 }
 223                 spin_unlock_irq(&logbuf_lock);
 224                 if (!error)
 225                         error = i;
 226                 break;
 227         case 4:         /* Read/clear last kernel messages */
 228                 do_clear = 1;
 229                 /* FALL THRU */
 230         case 3:         /* Read last kernel messages */
 231                 error = -EINVAL;
 232                 if (!buf || len < 0)
 233                         goto out;
 234                 error = 0;
 235                 if (!len)
 236                         goto out;
 237                 if (!access_ok(VERIFY_WRITE, buf, len)) {
 238                         error = -EFAULT;
 239                         goto out;
 240                 }
 241                 count = len;
 242                 if (count > log_buf_len)
 243                         count = log_buf_len;
 244                 spin_lock_irq(&logbuf_lock);
 245                 if (count > logged_chars)
 246                         count = logged_chars;
 247                 if (do_clear)
 248                         logged_chars = 0;
 249                 limit = log_end;
 250                 /*
 251                  * __put_user() could sleep, and while we sleep
 252                  * printk() could overwrite the messages
 253                  * we try to copy to user space. Therefore
 254                  * the messages are copied in reverse. <manfreds>
 255                  */
 256                 for (i = 0; i < count && !error; i++) {
 257                         j = limit-1-i;
 258                         if (j + log_buf_len < log_end)
 259                                 break;
 260                         c = LOG_BUF(j);
 261                         spin_unlock_irq(&logbuf_lock);
 262                         error = __put_user(c,&buf[count-1-i]);
 263                         cond_resched();
 264                         spin_lock_irq(&logbuf_lock);
 265                 }
 266                 spin_unlock_irq(&logbuf_lock);
 267                 if (error)
 268                         break;
 269                 error = i;
 270                 if (i != count) {
 271                         int offset = count-error;
 272                         /* buffer overflow during copy, correct user buffer. */
 273                         for (i = 0; i < error; i++) {
 274                                 if (__get_user(c,&buf[i+offset]) ||
 275                                     __put_user(c,&buf[i])) {
 276                                         error = -EFAULT;
 277                                         break;
 278                                 }
 279                                 cond_resched();
 280                         }
 281                 }
 282                 break;
 283         case 5:         /* Clear ring buffer */
 284                 logged_chars = 0;
 285                 break;
 286         case 6:         /* Disable logging to console */
 287                 console_loglevel = minimum_console_loglevel;
 288                 break;
 289         case 7:         /* Enable logging to console */
 290                 console_loglevel = default_console_loglevel;
 291                 break;
 292         case 8:         /* Set level of messages printed to console */
 293                 error = -EINVAL;
 294                 if (len < 1 || len > 8)
 295                         goto out;
 296                 if (len < minimum_console_loglevel)
 297                         len = minimum_console_loglevel;
 298                 console_loglevel = len;
 299                 error = 0;
 300                 break;
 301         case 9:         /* Number of chars in the log buffer */
 302                 error = log_end - log_start;
 303                 break;
 304         case 10:        /* Size of the log buffer */
 305                 error = log_buf_len;
 306                 break;
 307         default:
 308                 error = -EINVAL;
 309                 break;
 310         }
 311 out:
 312         return error;
 313 }
 314
 315 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 316 {
 317         return do_syslog(type, buf, len);
 318 }
 319
 320 /*
 321  * Call the console drivers on a range of log_buf
 322  */
 323 static void __call_console_drivers(unsigned long start, unsigned long end)
 324 {
 325         struct console *con;
 326
 327         for (con = console_drivers; con; con = con->next) {
 328                 if ((con->flags & CON_ENABLED) && con->write &&
 329                                 (cpu_online(smp_processor_id()) ||
 330                                 (con->flags & CON_ANYTIME)))
 331                         con->write(con, &LOG_BUF(start), end - start);
 332         }
 333 }
 334
 335 static int __read_mostly ignore_loglevel;
 336
 337 static int __init ignore_loglevel_setup(char *str)
 338 {
 339         ignore_loglevel = 1;
 340         printk(KERN_INFO "debug: ignoring loglevel setting.\n");
 341
 342         return 1;
 343 }
 344
 345 __setup("ignore_loglevel", ignore_loglevel_setup);
 346
 347 /*
 348  * Write out chars from start to end - 1 inclusive
 349  */
 350 static void _call_console_drivers(unsigned long start,
 351                                 unsigned long end, int msg_log_level)
 352 {
 353         if ((msg_log_level < console_loglevel || ignore_loglevel) &&
 354                         console_drivers && start != end) {
 355                 if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
 356                         /* wrapped write */
 357                         __call_console_drivers(start & LOG_BUF_MASK,
 358                                                 log_buf_len);
 359                         __call_console_drivers(0, end & LOG_BUF_MASK);
 360                 } else {
 361                         __call_console_drivers(start, end);
 362                 }
 363         }
 364 }
 365
 366 /*
 367  * Call the console drivers, asking them to write out
 368  * log_buf[start] to log_buf[end - 1].
 369  * The console_sem must be held.
 370  */
 371 static void call_console_drivers(unsigned long start, unsigned long end)
 372 {
 373         unsigned long cur_index, start_print;
 374         static int msg_level = -1;
 375
 376         BUG_ON(((long)(start - end)) > 0);
 377
 378         cur_index = start;
 379         start_print = start;
 380         while (cur_index != end) {
 381                 if (msg_level < 0 && ((end - cur_index) > 2) &&
 382                                 LOG_BUF(cur_index + 0) == '<' &&
 383                                 LOG_BUF(cur_index + 1) >= '0' &&
 384                                 LOG_BUF(cur_index + 1) <= '7' &&
 385                                 LOG_BUF(cur_index + 2) == '>') {
 386                         msg_level = LOG_BUF(cur_index + 1) - '0';
 387                         cur_index += 3;
 388                         start_print = cur_index;
 389                 }
 390                 while (cur_index != end) {
 391                         char c = LOG_BUF(cur_index);
 392
 393                         cur_index++;
 394                         if (c == '\n') {
 395                                 if (msg_level < 0) {
 396                                         /*
 397                                          * printk() has already given us loglevel tags in
 398                                          * the buffer.  This code is here in case the
 399                                          * log buffer has wrapped right round and scribbled
 400                                          * on those tags
 401                                          */
 402                                         msg_level = default_message_loglevel;
 403                                 }
 404                                 _call_console_drivers(start_print, cur_index, msg_level);
 405                                 msg_level = -1;
 406                                 start_print = cur_index;
 407                                 break;
 408                         }
 409                 }
 410         }
 411         _call_console_drivers(start_print, end, msg_level);
 412 }
 413
 414 static void emit_log_char(char c)
 415 {
 416         LOG_BUF(log_end) = c;
 417         log_end++;
 418         if (log_end - log_start > log_buf_len)
 419                 log_start = log_end - log_buf_len;
 420         if (log_end - con_start > log_buf_len)
 421                 con_start = log_end - log_buf_len;
 422         if (logged_chars < log_buf_len)
 423                 logged_chars++;
 424 }
 425
 426 /*
 427  * Zap console related locks when oopsing. Only zap at most once
 428  * every 10 seconds, to leave time for slow consoles to print a
 429  * full oops.
 430  */
 431 static void zap_locks(void)
 432 {
 433         static unsigned long oops_timestamp;
 434
 435         if (time_after_eq(jiffies, oops_timestamp) &&
 436                         !time_after(jiffies, oops_timestamp + 30 * HZ))
 437                 return;
 438
 439         oops_timestamp = jiffies;
 440
 441         /* If a crash is occurring, make sure we can't deadlock */
 442         spin_lock_init(&logbuf_lock);
 443         /* And make sure that we print immediately */
 444         init_MUTEX(&console_sem);
 445 }
 446
 447 #if defined(CONFIG_PRINTK_TIME)
 448 static int printk_time = 1;
 449 #else
 450 static int printk_time = 0;
 451 #endif
 452 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
 453
 454 static int __init printk_time_setup(char *str)
 455 {
 456         if (*str)
 457                 return 0;
 458         printk_time = 1;
 459         printk(KERN_NOTICE "The 'time' option is deprecated and "
 460                 "is scheduled for removal in early 2008\n");
 461         printk(KERN_NOTICE "Use 'printk.time=<value>' instead\n");
 462         return 1;
 463 }
 464
 465 __setup("time", printk_time_setup);
 466
 467 __attribute__((weak)) unsigned long long printk_clock(void)
 468 {
 469         return sched_clock();
 470 }
 471
 472 /* Check if we have any console registered that can be called early in boot. */
 473 static int have_callable_console(void)
 474 {
 475         struct console *con;
 476
 477         for (con = console_drivers; con; con = con->next)
 478                 if (con->flags & CON_ANYTIME)
 479                         return 1;
 480
 481         return 0;
 482 }
 483
 484 /**
 485  * printk - print a kernel message
 486  * @fmt: format string
 487  *
 488  * This is printk().  It can be called from any context.  We want it to work.
 489  *
 490  * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 491  * call the console drivers.  If we fail to get the semaphore we place the output
 492  * into the log buffer and return.  The current holder of the console_sem will
 493  * notice the new output in release_console_sem() and will send it to the
 494  * consoles before releasing the semaphore.
 495  *
 496  * One effect of this deferred printing is that code which calls printk() and
 497  * then changes console_loglevel may break. This is because console_loglevel
 498  * is inspected when the actual printing occurs.
 499  *
 500  * See also:
 501  * printf(3)
 502  */
 503
 504 asmlinkage int printk(const char *fmt, ...)
 505 {
 506         va_list args;
 507         int r;
 508
 509         va_start(args, fmt);
 510         r = vprintk(fmt, args);
 511         va_end(args);
 512
 513         return r;
 514 }
 515
 516 /* cpu currently holding logbuf_lock */
 517 static volatile unsigned int printk_cpu = UINT_MAX;
 518
 519 asmlinkage int vprintk(const char *fmt, va_list args)
 520 {
 521         unsigned long flags;
 522         int printed_len;
 523         char *p;
 524         static char printk_buf[1024];
 525         static int log_level_unknown = 1;
 526
 527         preempt_disable();
 528         if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
 529                 /* If a crash is occurring during printk() on this CPU,
 530                  * make sure we can't deadlock */
 531                 zap_locks();
 532
 533         /* This stops the holder of console_sem just where we want him */
 534         raw_local_irq_save(flags);
 535         lockdep_off();
 536         spin_lock(&logbuf_lock);
 537         printk_cpu = smp_processor_id();
 538
 539         /* Emit the output into the temporary buffer */
 540         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
 541
 542         /*
 543          * Copy the output into log_buf.  If the caller didn't provide
 544          * appropriate log level tags, we insert them here
 545          */
 546         for (p = printk_buf; *p; p++) {
 547                 if (log_level_unknown) {
 548                         /* log_level_unknown signals the start of a new line */
 549                         if (printk_time) {
 550                                 int loglev_char;
 551                                 char tbuf[50], *tp;
 552                                 unsigned tlen;
 553                                 unsigned long long t;
 554                                 unsigned long nanosec_rem;
 555
 556                                 /*
 557                                  * force the log level token to be
 558                                  * before the time output.
 559                                  */
 560                                 if (p[0] == '<' && p[1] >='0' &&
 561                                    p[1] <= '7' && p[2] == '>') {
 562                                         loglev_char = p[1];
 563                                         p += 3;
 564                                         printed_len -= 3;
 565                                 } else {
 566                                         loglev_char = default_message_loglevel
 567                                                 + '0';
 568                                 }
 569                                 t = printk_clock();
 570                                 nanosec_rem = do_div(t, 1000000000);
 571                                 tlen = sprintf(tbuf,
 572                                                 "<%c>[%5lu.%06lu] ",
 573                                                 loglev_char,
 574                                                 (unsigned long)t,
 575                                                 nanosec_rem/1000);
 576
 577                                 for (tp = tbuf; tp < tbuf + tlen; tp++)
 578                                         emit_log_char(*tp);
 579                                 printed_len += tlen;
 580                         } else {
 581                                 if (p[0] != '<' || p[1] < '0' ||
 582                                    p[1] > '7' || p[2] != '>') {
 583                                         emit_log_char('<');
 584                                         emit_log_char(default_message_loglevel
 585                                                 + '0');
 586                                         emit_log_char('>');
 587                                         printed_len += 3;
 588                                 }
 589                         }
 590                         log_level_unknown = 0;
 591                         if (!*p)
 592                                 break;
 593                 }
 594                 emit_log_char(*p);
 595                 if (*p == '\n')
 596                         log_level_unknown = 1;
 597         }
 598
 599         if (!down_trylock(&console_sem)) {
 600                 /*
 601                  * We own the drivers.  We can drop the spinlock and
 602                  * let release_console_sem() print the text, maybe ...
 603                  */
 604                 console_locked = 1;
 605                 printk_cpu = UINT_MAX;
 606                 spin_unlock(&logbuf_lock);
 607
 608                 /*
 609                  * Console drivers may assume that per-cpu resources have
 610                  * been allocated. So unless they're explicitly marked as
 611                  * being able to cope (CON_ANYTIME) don't call them until
 612                  * this CPU is officially up.
 613                  */
 614                 if (cpu_online(smp_processor_id()) || have_callable_console()) {
 615                         console_may_schedule = 0;
 616                         release_console_sem();
 617                 } else {
 618                         /* Release by hand to avoid flushing the buffer. */
 619                         console_locked = 0;
 620                         up(&console_sem);
 621                 }
 622                 lockdep_on();
 623                 raw_local_irq_restore(flags);
 624         } else {
 625                 /*
 626                  * Someone else owns the drivers.  We drop the spinlock, which
 627                  * allows the semaphore holder to proceed and to call the
 628                  * console drivers with the output which we just produced.
 629                  */
 630                 printk_cpu = UINT_MAX;
 631                 spin_unlock(&logbuf_lock);
 632                 lockdep_on();
 633                 raw_local_irq_restore(flags);
 634         }
 635
 636         preempt_enable();
 637         return printed_len;
 638 }
 639 EXPORT_SYMBOL(printk);
 640 EXPORT_SYMBOL(vprintk);
 641
 642 #else
 643
 644 asmlinkage long sys_syslog(int type, char __user *buf, int len)
 645 {
 646         return -ENOSYS;
 647 }
 648
 649 static void call_console_drivers(unsigned long start, unsigned long end)
 650 {
 651 }
 652
 653 #endif
 654
 655 /*
 656  * Set up a list of consoles.  Called from init/main.c
 657  */
 658 static int __init console_setup(char *str)
 659 {
 660         char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
 661         char *s, *options;
 662         int idx;
 663
 664         /*
 665          * Decode str into name, index, options.
 666          */
 667         if (str[0] >= '0' && str[0] <= '9') {
 668                 strcpy(buf, "ttyS");
 669                 strncpy(buf + 4, str, sizeof(buf) - 5);
 670         } else {
 671                 strncpy(buf, str, sizeof(buf) - 1);
 672         }
 673         buf[sizeof(buf) - 1] = 0;
 674         if ((options = strchr(str, ',')) != NULL)
 675                 *(options++) = 0;
 676 #ifdef __sparc__
 677         if (!strcmp(str, "ttya"))
 678                 strcpy(buf, "ttyS0");
 679         if (!strcmp(str, "ttyb"))
 680                 strcpy(buf, "ttyS1");
 681 #endif
 682         for (s = buf; *s; s++)
 683                 if ((*s >= '0' && *s <= '9') || *s == ',')
 684                         break;
 685         idx = simple_strtoul(s, NULL, 10);
 686         *s = 0;
 687
 688         add_preferred_console(buf, idx, options);
 689         return 1;
 690 }
 691 __setup("console=", console_setup);
 692
 693 /**
 694  * add_preferred_console - add a device to the list of preferred consoles.
 695  * @name: device name
 696  * @idx: device index
 697  * @options: options for this console
 698  *
 699  * The last preferred console added will be used for kernel messages
 700  * and stdin/out/err for init.  Normally this is used by console_setup
 701  * above to handle user-supplied console arguments; however it can also
 702  * be used by arch-specific code either to override the user or more
 703  * commonly to provide a default console (ie from PROM variables) when
 704  * the user has not supplied one.
 705  */
 706 int __init add_preferred_console(char *name, int idx, char *options)
 707 {
 708         struct console_cmdline *c;
 709         int i;
 710
 711         /*
 712          *      See if this tty is not yet registered, and
 713          *      if we have a slot free.
 714          */
 715         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 716                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 717                           console_cmdline[i].index == idx) {
 718                                 selected_console = i;
 719                                 return 0;
 720                 }
 721         if (i == MAX_CMDLINECONSOLES)
 722                 return -E2BIG;
 723         selected_console = i;
 724         c = &console_cmdline[i];
 725         memcpy(c->name, name, sizeof(c->name));
 726         c->name[sizeof(c->name) - 1] = 0;
 727         c->options = options;
 728         c->index = idx;
 729         return 0;
 730 }
 731
 732 int __init update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
 733 {
 734         struct console_cmdline *c;
 735         int i;
 736
 737         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
 738                 if (strcmp(console_cmdline[i].name, name) == 0 &&
 739                           console_cmdline[i].index == idx) {
 740                                 c = &console_cmdline[i];
 741                                 memcpy(c->name, name_new, sizeof(c->name));
 742                                 c->name[sizeof(c->name) - 1] = 0;
 743                                 c->options = options;
 744                                 c->index = idx_new;
 745                                 return i;
 746                 }
 747         /* not found */
 748         return -1;
 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 void wake_up_klogd(void)
 808 {
 809         if (!oops_in_progress && waitqueue_active(&log_wait))
 810                 wake_up_interruptible(&log_wait);
 811 }
 812
 813 /**
 814  * release_console_sem - unlock the console system
 815  *
 816  * Releases the semaphore which the caller holds on the console system
 817  * and the console driver list.
 818  *
 819  * While the semaphore was held, console output may have been buffered
 820  * by printk().  If this is the case, release_console_sem() emits
 821  * the output prior to releasing the semaphore.
 822  *
 823  * If there is output waiting for klogd, we wake it up.
 824  *
 825  * release_console_sem() may be called from any context.
 826  */
 827 void release_console_sem(void)
 828 {
 829         unsigned long flags;
 830         unsigned long _con_start, _log_end;
 831         unsigned long wake_klogd = 0;
 832
 833         if (console_suspended) {
 834                 up(&secondary_console_sem);
 835                 return;
 836         }
 837
 838         console_may_schedule = 0;
 839
 840         for ( ; ; ) {
 841                 spin_lock_irqsave(&logbuf_lock, flags);
 842                 wake_klogd |= log_start - log_end;
 843                 if (con_start == log_end)
 844                         break;                  /* Nothing to print */
 845                 _con_start = con_start;
 846                 _log_end = log_end;
 847                 con_start = log_end;            /* Flush */
 848                 spin_unlock(&logbuf_lock);
 849                 call_console_drivers(_con_start, _log_end);
 850                 local_irq_restore(flags);
 851         }
 852         console_locked = 0;
 853         up(&console_sem);
 854         spin_unlock_irqrestore(&logbuf_lock, flags);
 855         if (wake_klogd)
 856                 wake_up_klogd();
 857 }
 858 EXPORT_SYMBOL(release_console_sem);
 859
 860 /**
 861  * console_conditional_schedule - yield the CPU if required
 862  *
 863  * If the console code is currently allowed to sleep, and
 864  * if this CPU should yield the CPU to another task, do
 865  * so here.
 866  *
 867  * Must be called within acquire_console_sem().
 868  */
 869 void __sched console_conditional_schedule(void)
 870 {
 871         if (console_may_schedule)
 872                 cond_resched();
 873 }
 874 EXPORT_SYMBOL(console_conditional_schedule);
 875
 876 void console_print(const char *s)
 877 {
 878         printk(KERN_EMERG "%s", s);
 879 }
 880 EXPORT_SYMBOL(console_print);
 881
 882 void console_unblank(void)
 883 {
 884         struct console *c;
 885
 886         /*
 887          * console_unblank can no longer be called in interrupt context unless
 888          * oops_in_progress is set to 1..
 889          */
 890         if (oops_in_progress) {
 891                 if (down_trylock(&console_sem) != 0)
 892                         return;
 893         } else
 894                 acquire_console_sem();
 895
 896         console_locked = 1;
 897         console_may_schedule = 0;
 898         for (c = console_drivers; c != NULL; c = c->next)
 899                 if ((c->flags & CON_ENABLED) && c->unblank)
 900                         c->unblank();
 901         release_console_sem();
 902 }
 903
 904 /*
 905  * Return the console tty driver structure and its associated index
 906  */
 907 struct tty_driver *console_device(int *index)
 908 {
 909         struct console *c;
 910         struct tty_driver *driver = NULL;
 911
 912         acquire_console_sem();
 913         for (c = console_drivers; c != NULL; c = c->next) {
 914                 if (!c->device)
 915                         continue;
 916                 driver = c->device(c, index);
 917                 if (driver)
 918                         break;
 919         }
 920         release_console_sem();
 921         return driver;
 922 }
 923
 924 /*
 925  * Prevent further output on the passed console device so that (for example)
 926  * serial drivers can disable console output before suspending a port, and can
 927  * re-enable output afterwards.
 928  */
 929 void console_stop(struct console *console)
 930 {
 931         acquire_console_sem();
 932         console->flags &= ~CON_ENABLED;
 933         release_console_sem();
 934 }
 935 EXPORT_SYMBOL(console_stop);
 936
 937 void console_start(struct console *console)
 938 {
 939         acquire_console_sem();
 940         console->flags |= CON_ENABLED;
 941         release_console_sem();
 942 }
 943 EXPORT_SYMBOL(console_start);
 944
 945 /*
 946  * The console driver calls this routine during kernel initialization
 947  * to register the console printing procedure with printk() and to
 948  * print any messages that were printed by the kernel before the
 949  * console driver was initialized.
 950  */
 951 void register_console(struct console *console)
 952 {
 953         int i;
 954         unsigned long flags;
 955         struct console *bootconsole = NULL;
 956
 957         if (console_drivers) {
 958                 if (console->flags & CON_BOOT)
 959                         return;
 960                 if (console_drivers->flags & CON_BOOT)
 961                         bootconsole = console_drivers;
 962         }
 963
 964         if (preferred_console < 0 || bootconsole || !console_drivers)
 965                 preferred_console = selected_console;
 966
 967         if (console->early_setup)
 968                 console->early_setup();
 969
 970         /*
 971          *      See if we want to use this console driver. If we
 972          *      didn't select a console we take the first one
 973          *      that registers here.
 974          */
 975         if (preferred_console < 0) {
 976                 if (console->index < 0)
 977                         console->index = 0;
 978                 if (console->setup == NULL ||
 979                     console->setup(console, NULL) == 0) {
 980                         console->flags |= CON_ENABLED | CON_CONSDEV;
 981                         preferred_console = 0;
 982                 }
 983         }
 984
 985         /*
 986          *      See if this console matches one we selected on
 987          *      the command line.
 988          */
 989         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
 990                         i++) {
 991                 if (strcmp(console_cmdline[i].name, console->name) != 0)
 992                         continue;
 993                 if (console->index >= 0 &&
 994                     console->index != console_cmdline[i].index)
 995                         continue;
 996                 if (console->index < 0)
 997                         console->index = console_cmdline[i].index;
 998                 if (console->setup &&
 999                     console->setup(console, console_cmdline[i].options) != 0)
1000                         break;
1001                 console->flags |= CON_ENABLED;
1002                 console->index = console_cmdline[i].index;
1003                 if (i == selected_console) {
1004                         console->flags |= CON_CONSDEV;
1005                         preferred_console = selected_console;
1006                 }
1007                 break;
1008         }
1009
1010         if (!(console->flags & CON_ENABLED))
1011                 return;
1012
1013         if (bootconsole && (console->flags & CON_CONSDEV)) {
1014                 printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
1015                        bootconsole->name, bootconsole->index,
1016                        console->name, console->index);
1017                 unregister_console(bootconsole);
1018                 console->flags &= ~CON_PRINTBUFFER;
1019         } else {
1020                 printk(KERN_INFO "console [%s%d] enabled\n",
1021                        console->name, console->index);
1022         }
1023
1024         /*
1025          *      Put this console in the list - keep the
1026          *      preferred driver at the head of the list.
1027          */
1028         acquire_console_sem();
1029         if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
1030                 console->next = console_drivers;
1031                 console_drivers = console;
1032                 if (console->next)
1033                         console->next->flags &= ~CON_CONSDEV;
1034         } else {
1035                 console->next = console_drivers->next;
1036                 console_drivers->next = console;
1037         }
1038         if (console->flags & CON_PRINTBUFFER) {
1039                 /*
1040                  * release_console_sem() will print out the buffered messages
1041                  * for us.
1042                  */
1043                 spin_lock_irqsave(&logbuf_lock, flags);
1044                 con_start = log_start;
1045                 spin_unlock_irqrestore(&logbuf_lock, flags);
1046         }
1047         release_console_sem();
1048 }
1049 EXPORT_SYMBOL(register_console);
1050
1051 int unregister_console(struct console *console)
1052 {
1053         struct console *a, *b;
1054         int res = 1;
1055
1056         acquire_console_sem();
1057         if (console_drivers == console) {
1058                 console_drivers=console->next;
1059                 res = 0;
1060         } else if (console_drivers) {
1061                 for (a=console_drivers->next, b=console_drivers ;
1062                      a; b=a, a=b->next) {
1063                         if (a == console) {
1064                                 b->next = a->next;
1065                                 res = 0;
1066                                 break;
1067                         }
1068                 }
1069         }
1070
1071         /*
1072          * If this isn't the last console and it has CON_CONSDEV set, we
1073          * need to set it on the next preferred console.
1074          */
1075         if (console_drivers != NULL && console->flags & CON_CONSDEV)
1076                 console_drivers->flags |= CON_CONSDEV;
1077
1078         release_console_sem();
1079         return res;
1080 }
1081 EXPORT_SYMBOL(unregister_console);
1082
1083 /**
1084  * tty_write_message - write a message to a certain tty, not just the console.
1085  * @tty: the destination tty_struct
1086  * @msg: the message to write
1087  *
1088  * This is used for messages that need to be redirected to a specific tty.
1089  * We don't put it into the syslog queue right now maybe in the future if
1090  * really needed.
1091  */
1092 void tty_write_message(struct tty_struct *tty, char *msg)
1093 {
1094         if (tty && tty->driver->write)
1095                 tty->driver->write(tty, msg, strlen(msg));
1096         return;
1097 }
1098
1099 /*
1100  * printk rate limiting, lifted from the networking subsystem.
1101  *
1102  * This enforces a rate limit: not more than one kernel message
1103  * every printk_ratelimit_jiffies to make a denial-of-service
1104  * attack impossible.
1105  */
1106 int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
1107 {
1108         static DEFINE_SPINLOCK(ratelimit_lock);
1109         static unsigned long toks = 10 * 5 * HZ;
1110         static unsigned long last_msg;
1111         static int missed;
1112         unsigned long flags;
1113         unsigned long now = jiffies;
1114
1115         spin_lock_irqsave(&ratelimit_lock, flags);
1116         toks += now - last_msg;
1117         last_msg = now;
1118         if (toks > (ratelimit_burst * ratelimit_jiffies))
1119                 toks = ratelimit_burst * ratelimit_jiffies;
1120         if (toks >= ratelimit_jiffies) {
1121                 int lost = missed;
1122
1123                 missed = 0;
1124                 toks -= ratelimit_jiffies;
1125                 spin_unlock_irqrestore(&ratelimit_lock, flags);
1126                 if (lost)
1127                         printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
1128                 return 1;
1129         }
1130         missed++;
1131         spin_unlock_irqrestore(&ratelimit_lock, flags);
1132         return 0;
1133 }
1134 EXPORT_SYMBOL(__printk_ratelimit);
1135
1136 /* minimum time in jiffies between messages */
1137 int printk_ratelimit_jiffies = 5 * HZ;
1138
1139 /* number of messages we send before ratelimiting */
1140 int printk_ratelimit_burst = 10;
1141
1142 int printk_ratelimit(void)
1143 {
1144         return __printk_ratelimit(printk_ratelimit_jiffies,
1145                                 printk_ratelimit_burst);
1146 }
1147 EXPORT_SYMBOL(printk_ratelimit);
1148
1149 /**
1150  * printk_timed_ratelimit - caller-controlled printk ratelimiting
1151  * @caller_jiffies: pointer to caller's state
1152  * @interval_msecs: minimum interval between prints
1153  *
1154  * printk_timed_ratelimit() returns true if more than @interval_msecs
1155  * milliseconds have elapsed since the last time printk_timed_ratelimit()
1156  * returned true.
1157  */
1158 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1159                         unsigned int interval_msecs)
1160 {
1161         if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
1162                 *caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
1163                 return true;
1164         }
1165         return false;
1166 }
1167 EXPORT_SYMBOL(printk_timed_ratelimit);