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