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