Root/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
17 */
18
19#include <linux/kernel.h>
20#include <linux/mm.h>
21#include <linux/tty.h>
22#include <linux/tty_driver.h>
23#include <linux/console.h>
24#include <linux/init.h>
25#include <linux/jiffies.h>
26#include <linux/nmi.h>
27#include <linux/module.h>
28#include <linux/moduleparam.h>
29#include <linux/interrupt.h> /* For in_interrupt() */
30#include <linux/delay.h>
31#include <linux/smp.h>
32#include <linux/security.h>
33#include <linux/bootmem.h>
34#include <linux/memblock.h>
35#include <linux/syscalls.h>
36#include <linux/kexec.h>
37#include <linux/kdb.h>
38#include <linux/ratelimit.h>
39#include <linux/kmsg_dump.h>
40#include <linux/syslog.h>
41#include <linux/cpu.h>
42#include <linux/notifier.h>
43#include <linux/rculist.h>
44
45#include <asm/uaccess.h>
46
47/*
48 * Architectures can override it:
49 */
50void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
51{
52}
53
54#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
55
56/* printk's without a loglevel use this.. */
57#define DEFAULT_MESSAGE_LOGLEVEL CONFIG_DEFAULT_MESSAGE_LOGLEVEL
58
59/* We show everything that is MORE important than this.. */
60#define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
61#define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
62
63DECLARE_WAIT_QUEUE_HEAD(log_wait);
64
65int console_printk[4] = {
66    DEFAULT_CONSOLE_LOGLEVEL, /* console_loglevel */
67    DEFAULT_MESSAGE_LOGLEVEL, /* default_message_loglevel */
68    MINIMUM_CONSOLE_LOGLEVEL, /* minimum_console_loglevel */
69    DEFAULT_CONSOLE_LOGLEVEL, /* default_console_loglevel */
70};
71
72/*
73 * Low level drivers may need that to know if they can schedule in
74 * their unblank() callback or not. So let's export it.
75 */
76int oops_in_progress;
77EXPORT_SYMBOL(oops_in_progress);
78
79/*
80 * console_sem protects the console_drivers list, and also
81 * provides serialisation for access to the entire console
82 * driver system.
83 */
84static DEFINE_SEMAPHORE(console_sem);
85struct console *console_drivers;
86EXPORT_SYMBOL_GPL(console_drivers);
87
88/*
89 * This is used for debugging the mess that is the VT code by
90 * keeping track if we have the console semaphore held. It's
91 * definitely not the perfect debug tool (we don't know if _WE_
92 * hold it are racing, but it helps tracking those weird code
93 * path in the console code where we end up in places I want
94 * locked without the console sempahore held
95 */
96static int console_locked, console_suspended;
97
98/*
99 * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
100 * It is also used in interesting ways to provide interlocking in
101 * console_unlock();.
102 */
103static DEFINE_SPINLOCK(logbuf_lock);
104
105#define LOG_BUF_MASK (log_buf_len-1)
106#define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
107
108/*
109 * The indices into log_buf are not constrained to log_buf_len - they
110 * must be masked before subscripting
111 */
112static unsigned log_start; /* Index into log_buf: next char to be read by syslog() */
113static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
114static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */
115
116/*
117 * If exclusive_console is non-NULL then only this console is to be printed to.
118 */
119static struct console *exclusive_console;
120
121/*
122 * Array of consoles built from command line options (console=)
123 */
124struct console_cmdline
125{
126    char name[8]; /* Name of the driver */
127    int index; /* Minor dev. to use */
128    char *options; /* Options for the driver */
129#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
130    char *brl_options; /* Options for braille driver */
131#endif
132};
133
134#define MAX_CMDLINECONSOLES 8
135
136static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
137static int selected_console = -1;
138static int preferred_console = -1;
139int console_set_on_cmdline;
140EXPORT_SYMBOL(console_set_on_cmdline);
141
142/* Flag: console code may call schedule() */
143static int console_may_schedule;
144
145#ifdef CONFIG_PRINTK
146
147static char __log_buf[__LOG_BUF_LEN];
148static char *log_buf = __log_buf;
149static int log_buf_len = __LOG_BUF_LEN;
150static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
151static int saved_console_loglevel = -1;
152
153#ifdef CONFIG_KEXEC
154/*
155 * This appends the listed symbols to /proc/vmcoreinfo
156 *
157 * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
158 * obtain access to symbols that are otherwise very difficult to locate. These
159 * symbols are specifically used so that utilities can access and extract the
160 * dmesg log from a vmcore file after a crash.
161 */
162void log_buf_kexec_setup(void)
163{
164    VMCOREINFO_SYMBOL(log_buf);
165    VMCOREINFO_SYMBOL(log_end);
166    VMCOREINFO_SYMBOL(log_buf_len);
167    VMCOREINFO_SYMBOL(logged_chars);
168}
169#endif
170
171/* requested log_buf_len from kernel cmdline */
172static unsigned long __initdata new_log_buf_len;
173
174/* save requested log_buf_len since it's too early to process it */
175static int __init log_buf_len_setup(char *str)
176{
177    unsigned size = memparse(str, &str);
178
179    if (size)
180        size = roundup_pow_of_two(size);
181    if (size > log_buf_len)
182        new_log_buf_len = size;
183
184    return 0;
185}
186early_param("log_buf_len", log_buf_len_setup);
187
188void __init setup_log_buf(int early)
189{
190    unsigned long flags;
191    unsigned start, dest_idx, offset;
192    char *new_log_buf;
193    int free;
194
195    if (!new_log_buf_len)
196        return;
197
198    if (early) {
199        unsigned long mem;
200
201        mem = memblock_alloc(new_log_buf_len, PAGE_SIZE);
202        if (mem == MEMBLOCK_ERROR)
203            return;
204        new_log_buf = __va(mem);
205    } else {
206        new_log_buf = alloc_bootmem_nopanic(new_log_buf_len);
207    }
208
209    if (unlikely(!new_log_buf)) {
210        pr_err("log_buf_len: %ld bytes not available\n",
211            new_log_buf_len);
212        return;
213    }
214
215    spin_lock_irqsave(&logbuf_lock, flags);
216    log_buf_len = new_log_buf_len;
217    log_buf = new_log_buf;
218    new_log_buf_len = 0;
219    free = __LOG_BUF_LEN - log_end;
220
221    offset = start = min(con_start, log_start);
222    dest_idx = 0;
223    while (start != log_end) {
224        unsigned log_idx_mask = start & (__LOG_BUF_LEN - 1);
225
226        log_buf[dest_idx] = __log_buf[log_idx_mask];
227        start++;
228        dest_idx++;
229    }
230    log_start -= offset;
231    con_start -= offset;
232    log_end -= offset;
233    spin_unlock_irqrestore(&logbuf_lock, flags);
234
235    pr_info("log_buf_len: %d\n", log_buf_len);
236    pr_info("early log buf free: %d(%d%%)\n",
237        free, (free * 100) / __LOG_BUF_LEN);
238}
239
240#ifdef CONFIG_BOOT_PRINTK_DELAY
241
242static int boot_delay; /* msecs delay after each printk during bootup */
243static unsigned long long loops_per_msec; /* based on boot_delay */
244
245static int __init boot_delay_setup(char *str)
246{
247    unsigned long lpj;
248
249    lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
250    loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
251
252    get_option(&str, &boot_delay);
253    if (boot_delay > 10 * 1000)
254        boot_delay = 0;
255
256    pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
257        "HZ: %d, loops_per_msec: %llu\n",
258        boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
259    return 1;
260}
261__setup("boot_delay=", boot_delay_setup);
262
263static void boot_delay_msec(void)
264{
265    unsigned long long k;
266    unsigned long timeout;
267
268    if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
269        return;
270
271    k = (unsigned long long)loops_per_msec * boot_delay;
272
273    timeout = jiffies + msecs_to_jiffies(boot_delay);
274    while (k) {
275        k--;
276        cpu_relax();
277        /*
278         * use (volatile) jiffies to prevent
279         * compiler reduction; loop termination via jiffies
280         * is secondary and may or may not happen.
281         */
282        if (time_after(jiffies, timeout))
283            break;
284        touch_nmi_watchdog();
285    }
286}
287#else
288static inline void boot_delay_msec(void)
289{
290}
291#endif
292
293#ifdef CONFIG_SECURITY_DMESG_RESTRICT
294int dmesg_restrict = 1;
295#else
296int dmesg_restrict;
297#endif
298
299static int syslog_action_restricted(int type)
300{
301    if (dmesg_restrict)
302        return 1;
303    /* Unless restricted, we allow "read all" and "get buffer size" for everybody */
304    return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
305}
306
307static int check_syslog_permissions(int type, bool from_file)
308{
309    /*
310     * If this is from /proc/kmsg and we've already opened it, then we've
311     * already done the capabilities checks at open time.
312     */
313    if (from_file && type != SYSLOG_ACTION_OPEN)
314        return 0;
315
316    if (syslog_action_restricted(type)) {
317        if (capable(CAP_SYSLOG))
318            return 0;
319        /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
320        if (capable(CAP_SYS_ADMIN)) {
321            WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
322                 "but no CAP_SYSLOG (deprecated).\n");
323            return 0;
324        }
325        return -EPERM;
326    }
327    return 0;
328}
329
330int do_syslog(int type, char __user *buf, int len, bool from_file)
331{
332    unsigned i, j, limit, count;
333    int do_clear = 0;
334    char c;
335    int error;
336
337    error = check_syslog_permissions(type, from_file);
338    if (error)
339        goto out;
340
341    error = security_syslog(type);
342    if (error)
343        return error;
344
345    switch (type) {
346    case SYSLOG_ACTION_CLOSE: /* Close log */
347        break;
348    case SYSLOG_ACTION_OPEN: /* Open log */
349        break;
350    case SYSLOG_ACTION_READ: /* Read from log */
351        error = -EINVAL;
352        if (!buf || len < 0)
353            goto out;
354        error = 0;
355        if (!len)
356            goto out;
357        if (!access_ok(VERIFY_WRITE, buf, len)) {
358            error = -EFAULT;
359            goto out;
360        }
361        error = wait_event_interruptible(log_wait,
362                            (log_start - log_end));
363        if (error)
364            goto out;
365        i = 0;
366        spin_lock_irq(&logbuf_lock);
367        while (!error && (log_start != log_end) && i < len) {
368            c = LOG_BUF(log_start);
369            log_start++;
370            spin_unlock_irq(&logbuf_lock);
371            error = __put_user(c,buf);
372            buf++;
373            i++;
374            cond_resched();
375            spin_lock_irq(&logbuf_lock);
376        }
377        spin_unlock_irq(&logbuf_lock);
378        if (!error)
379            error = i;
380        break;
381    /* Read/clear last kernel messages */
382    case SYSLOG_ACTION_READ_CLEAR:
383        do_clear = 1;
384        /* FALL THRU */
385    /* Read last kernel messages */
386    case SYSLOG_ACTION_READ_ALL:
387        error = -EINVAL;
388        if (!buf || len < 0)
389            goto out;
390        error = 0;
391        if (!len)
392            goto out;
393        if (!access_ok(VERIFY_WRITE, buf, len)) {
394            error = -EFAULT;
395            goto out;
396        }
397        count = len;
398        if (count > log_buf_len)
399            count = log_buf_len;
400        spin_lock_irq(&logbuf_lock);
401        if (count > logged_chars)
402            count = logged_chars;
403        if (do_clear)
404            logged_chars = 0;
405        limit = log_end;
406        /*
407         * __put_user() could sleep, and while we sleep
408         * printk() could overwrite the messages
409         * we try to copy to user space. Therefore
410         * the messages are copied in reverse. <manfreds>
411         */
412        for (i = 0; i < count && !error; i++) {
413            j = limit-1-i;
414            if (j + log_buf_len < log_end)
415                break;
416            c = LOG_BUF(j);
417            spin_unlock_irq(&logbuf_lock);
418            error = __put_user(c,&buf[count-1-i]);
419            cond_resched();
420            spin_lock_irq(&logbuf_lock);
421        }
422        spin_unlock_irq(&logbuf_lock);
423        if (error)
424            break;
425        error = i;
426        if (i != count) {
427            int offset = count-error;
428            /* buffer overflow during copy, correct user buffer. */
429            for (i = 0; i < error; i++) {
430                if (__get_user(c,&buf[i+offset]) ||
431                    __put_user(c,&buf[i])) {
432                    error = -EFAULT;
433                    break;
434                }
435                cond_resched();
436            }
437        }
438        break;
439    /* Clear ring buffer */
440    case SYSLOG_ACTION_CLEAR:
441        logged_chars = 0;
442        break;
443    /* Disable logging to console */
444    case SYSLOG_ACTION_CONSOLE_OFF:
445        if (saved_console_loglevel == -1)
446            saved_console_loglevel = console_loglevel;
447        console_loglevel = minimum_console_loglevel;
448        break;
449    /* Enable logging to console */
450    case SYSLOG_ACTION_CONSOLE_ON:
451        if (saved_console_loglevel != -1) {
452            console_loglevel = saved_console_loglevel;
453            saved_console_loglevel = -1;
454        }
455        break;
456    /* Set level of messages printed to console */
457    case SYSLOG_ACTION_CONSOLE_LEVEL:
458        error = -EINVAL;
459        if (len < 1 || len > 8)
460            goto out;
461        if (len < minimum_console_loglevel)
462            len = minimum_console_loglevel;
463        console_loglevel = len;
464        /* Implicitly re-enable logging to console */
465        saved_console_loglevel = -1;
466        error = 0;
467        break;
468    /* Number of chars in the log buffer */
469    case SYSLOG_ACTION_SIZE_UNREAD:
470        error = log_end - log_start;
471        break;
472    /* Size of the log buffer */
473    case SYSLOG_ACTION_SIZE_BUFFER:
474        error = log_buf_len;
475        break;
476    default:
477        error = -EINVAL;
478        break;
479    }
480out:
481    return error;
482}
483
484SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
485{
486    return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
487}
488
489#ifdef CONFIG_KGDB_KDB
490/* kdb dmesg command needs access to the syslog buffer. do_syslog()
491 * uses locks so it cannot be used during debugging. Just tell kdb
492 * where the start and end of the physical and logical logs are. This
493 * is equivalent to do_syslog(3).
494 */
495void kdb_syslog_data(char *syslog_data[4])
496{
497    syslog_data[0] = log_buf;
498    syslog_data[1] = log_buf + log_buf_len;
499    syslog_data[2] = log_buf + log_end -
500        (logged_chars < log_buf_len ? logged_chars : log_buf_len);
501    syslog_data[3] = log_buf + log_end;
502}
503#endif /* CONFIG_KGDB_KDB */
504
505/*
506 * Call the console drivers on a range of log_buf
507 */
508static void __call_console_drivers(unsigned start, unsigned end)
509{
510    struct console *con;
511
512    for_each_console(con) {
513        if (exclusive_console && con != exclusive_console)
514            continue;
515        if ((con->flags & CON_ENABLED) && con->write &&
516                (cpu_online(smp_processor_id()) ||
517                (con->flags & CON_ANYTIME)))
518            con->write(con, &LOG_BUF(start), end - start);
519    }
520}
521
522static int __read_mostly ignore_loglevel;
523
524static int __init ignore_loglevel_setup(char *str)
525{
526    ignore_loglevel = 1;
527    printk(KERN_INFO "debug: ignoring loglevel setting.\n");
528
529    return 0;
530}
531
532early_param("ignore_loglevel", ignore_loglevel_setup);
533
534/*
535 * Write out chars from start to end - 1 inclusive
536 */
537static void _call_console_drivers(unsigned start,
538                unsigned end, int msg_log_level)
539{
540    if ((msg_log_level < console_loglevel || ignore_loglevel) &&
541            console_drivers && start != end) {
542        if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
543            /* wrapped write */
544            __call_console_drivers(start & LOG_BUF_MASK,
545                        log_buf_len);
546            __call_console_drivers(0, end & LOG_BUF_MASK);
547        } else {
548            __call_console_drivers(start, end);
549        }
550    }
551}
552
553/*
554 * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
555 * lower 3 bit are the log level, the rest are the log facility. In case
556 * userspace passes usual userspace syslog messages to /dev/kmsg or
557 * /dev/ttyprintk, the log prefix might contain the facility. Printk needs
558 * to extract the correct log level for in-kernel processing, and not mangle
559 * the original value.
560 *
561 * If a prefix is found, the length of the prefix is returned. If 'level' is
562 * passed, it will be filled in with the log level without a possible facility
563 * value. If 'special' is passed, the special printk prefix chars are accepted
564 * and returned. If no valid header is found, 0 is returned and the passed
565 * variables are not touched.
566 */
567static size_t log_prefix(const char *p, unsigned int *level, char *special)
568{
569    unsigned int lev = 0;
570    char sp = '\0';
571    size_t len;
572
573    if (p[0] != '<' || !p[1])
574        return 0;
575    if (p[2] == '>') {
576        /* usual single digit level number or special char */
577        switch (p[1]) {
578        case '0' ... '7':
579            lev = p[1] - '0';
580            break;
581        case 'c': /* KERN_CONT */
582        case 'd': /* KERN_DEFAULT */
583            sp = p[1];
584            break;
585        default:
586            return 0;
587        }
588        len = 3;
589    } else {
590        /* multi digit including the level and facility number */
591        char *endp = NULL;
592
593        if (p[1] < '0' && p[1] > '9')
594            return 0;
595
596        lev = (simple_strtoul(&p[1], &endp, 10) & 7);
597        if (endp == NULL || endp[0] != '>')
598            return 0;
599        len = (endp + 1) - p;
600    }
601
602    /* do not accept special char if not asked for */
603    if (sp && !special)
604        return 0;
605
606    if (special) {
607        *special = sp;
608        /* return special char, do not touch level */
609        if (sp)
610            return len;
611    }
612
613    if (level)
614        *level = lev;
615    return len;
616}
617
618/*
619 * Call the console drivers, asking them to write out
620 * log_buf[start] to log_buf[end - 1].
621 * The console_lock must be held.
622 */
623static void call_console_drivers(unsigned start, unsigned end)
624{
625    unsigned cur_index, start_print;
626    static int msg_level = -1;
627
628    BUG_ON(((int)(start - end)) > 0);
629
630    cur_index = start;
631    start_print = start;
632    while (cur_index != end) {
633        if (msg_level < 0 && ((end - cur_index) > 2)) {
634            /* strip log prefix */
635            cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
636            start_print = cur_index;
637        }
638        while (cur_index != end) {
639            char c = LOG_BUF(cur_index);
640
641            cur_index++;
642            if (c == '\n') {
643                if (msg_level < 0) {
644                    /*
645                     * printk() has already given us loglevel tags in
646                     * the buffer. This code is here in case the
647                     * log buffer has wrapped right round and scribbled
648                     * on those tags
649                     */
650                    msg_level = default_message_loglevel;
651                }
652                _call_console_drivers(start_print, cur_index, msg_level);
653                msg_level = -1;
654                start_print = cur_index;
655                break;
656            }
657        }
658    }
659    _call_console_drivers(start_print, end, msg_level);
660}
661
662static void emit_log_char(char c)
663{
664    LOG_BUF(log_end) = c;
665    log_end++;
666    if (log_end - log_start > log_buf_len)
667        log_start = log_end - log_buf_len;
668    if (log_end - con_start > log_buf_len)
669        con_start = log_end - log_buf_len;
670    if (logged_chars < log_buf_len)
671        logged_chars++;
672}
673
674/*
675 * Zap console related locks when oopsing. Only zap at most once
676 * every 10 seconds, to leave time for slow consoles to print a
677 * full oops.
678 */
679static void zap_locks(void)
680{
681    static unsigned long oops_timestamp;
682
683    if (time_after_eq(jiffies, oops_timestamp) &&
684            !time_after(jiffies, oops_timestamp + 30 * HZ))
685        return;
686
687    oops_timestamp = jiffies;
688
689    /* If a crash is occurring, make sure we can't deadlock */
690    spin_lock_init(&logbuf_lock);
691    /* And make sure that we print immediately */
692    sema_init(&console_sem, 1);
693}
694
695#if defined(CONFIG_PRINTK_TIME)
696static int printk_time = 1;
697#else
698static int printk_time = 0;
699#endif
700module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
701
702/* Check if we have any console registered that can be called early in boot. */
703static int have_callable_console(void)
704{
705    struct console *con;
706
707    for_each_console(con)
708        if (con->flags & CON_ANYTIME)
709            return 1;
710
711    return 0;
712}
713
714/**
715 * printk - print a kernel message
716 * @fmt: format string
717 *
718 * This is printk(). It can be called from any context. We want it to work.
719 *
720 * We try to grab the console_lock. If we succeed, it's easy - we log the output and
721 * call the console drivers. If we fail to get the semaphore we place the output
722 * into the log buffer and return. The current holder of the console_sem will
723 * notice the new output in console_unlock(); and will send it to the
724 * consoles before releasing the lock.
725 *
726 * One effect of this deferred printing is that code which calls printk() and
727 * then changes console_loglevel may break. This is because console_loglevel
728 * is inspected when the actual printing occurs.
729 *
730 * See also:
731 * printf(3)
732 *
733 * See the vsnprintf() documentation for format string extensions over C99.
734 */
735
736asmlinkage int printk(const char *fmt, ...)
737{
738    va_list args;
739    int r;
740
741#ifdef CONFIG_KGDB_KDB
742    if (unlikely(kdb_trap_printk)) {
743        va_start(args, fmt);
744        r = vkdb_printf(fmt, args);
745        va_end(args);
746        return r;
747    }
748#endif
749    va_start(args, fmt);
750    r = vprintk(fmt, args);
751    va_end(args);
752
753    return r;
754}
755
756/* cpu currently holding logbuf_lock */
757static volatile unsigned int printk_cpu = UINT_MAX;
758
759/*
760 * Can we actually use the console at this time on this cpu?
761 *
762 * Console drivers may assume that per-cpu resources have
763 * been allocated. So unless they're explicitly marked as
764 * being able to cope (CON_ANYTIME) don't call them until
765 * this CPU is officially up.
766 */
767static inline int can_use_console(unsigned int cpu)
768{
769    return cpu_online(cpu) || have_callable_console();
770}
771
772/*
773 * Try to get console ownership to actually show the kernel
774 * messages from a 'printk'. Return true (and with the
775 * console_lock held, and 'console_locked' set) if it
776 * is successful, false otherwise.
777 *
778 * This gets called with the 'logbuf_lock' spinlock held and
779 * interrupts disabled. It should return with 'lockbuf_lock'
780 * released but interrupts still disabled.
781 */
782static int console_trylock_for_printk(unsigned int cpu)
783    __releases(&logbuf_lock)
784{
785    int retval = 0;
786
787    if (console_trylock()) {
788        retval = 1;
789
790        /*
791         * If we can't use the console, we need to release
792         * the console semaphore by hand to avoid flushing
793         * the buffer. We need to hold the console semaphore
794         * in order to do this test safely.
795         */
796        if (!can_use_console(cpu)) {
797            console_locked = 0;
798            up(&console_sem);
799            retval = 0;
800        }
801    }
802    printk_cpu = UINT_MAX;
803    spin_unlock(&logbuf_lock);
804    return retval;
805}
806static const char recursion_bug_msg [] =
807        KERN_CRIT "BUG: recent printk recursion!\n";
808static int recursion_bug;
809static int new_text_line = 1;
810static char printk_buf[1024];
811
812int printk_delay_msec __read_mostly;
813
814static inline void printk_delay(void)
815{
816    if (unlikely(printk_delay_msec)) {
817        int m = printk_delay_msec;
818
819        while (m--) {
820            mdelay(1);
821            touch_nmi_watchdog();
822        }
823    }
824}
825
826asmlinkage int vprintk(const char *fmt, va_list args)
827{
828    int printed_len = 0;
829    int current_log_level = default_message_loglevel;
830    unsigned long flags;
831    int this_cpu;
832    char *p;
833    size_t plen;
834    char special;
835
836    boot_delay_msec();
837    printk_delay();
838
839    preempt_disable();
840    /* This stops the holder of console_sem just where we want him */
841    raw_local_irq_save(flags);
842    this_cpu = smp_processor_id();
843
844    /*
845     * Ouch, printk recursed into itself!
846     */
847    if (unlikely(printk_cpu == this_cpu)) {
848        /*
849         * If a crash is occurring during printk() on this CPU,
850         * then try to get the crash message out but make sure
851         * we can't deadlock. Otherwise just return to avoid the
852         * recursion and return - but flag the recursion so that
853         * it can be printed at the next appropriate moment:
854         */
855        if (!oops_in_progress) {
856            recursion_bug = 1;
857            goto out_restore_irqs;
858        }
859        zap_locks();
860    }
861
862    lockdep_off();
863    spin_lock(&logbuf_lock);
864    printk_cpu = this_cpu;
865
866    if (recursion_bug) {
867        recursion_bug = 0;
868        strcpy(printk_buf, recursion_bug_msg);
869        printed_len = strlen(recursion_bug_msg);
870    }
871    /* Emit the output into the temporary buffer */
872    printed_len += vscnprintf(printk_buf + printed_len,
873                  sizeof(printk_buf) - printed_len, fmt, args);
874
875    p = printk_buf;
876
877    /* Read log level and handle special printk prefix */
878    plen = log_prefix(p, &current_log_level, &special);
879    if (plen) {
880        p += plen;
881
882        switch (special) {
883        case 'c': /* Strip <c> KERN_CONT, continue line */
884            plen = 0;
885            break;
886        case 'd': /* Strip <d> KERN_DEFAULT, start new line */
887            plen = 0;
888        default:
889            if (!new_text_line) {
890                emit_log_char('\n');
891                new_text_line = 1;
892            }
893        }
894    }
895
896    /*
897     * Copy the output into log_buf. If the caller didn't provide
898     * the appropriate log prefix, we insert them here
899     */
900    for (; *p; p++) {
901        if (new_text_line) {
902            new_text_line = 0;
903
904            if (plen) {
905                /* Copy original log prefix */
906                int i;
907
908                for (i = 0; i < plen; i++)
909                    emit_log_char(printk_buf[i]);
910                printed_len += plen;
911            } else {
912                /* Add log prefix */
913                emit_log_char('<');
914                emit_log_char(current_log_level + '0');
915                emit_log_char('>');
916                printed_len += 3;
917            }
918
919            if (printk_time) {
920                /* Add the current time stamp */
921                char tbuf[50], *tp;
922                unsigned tlen;
923                unsigned long long t;
924                unsigned long nanosec_rem;
925
926                t = cpu_clock(printk_cpu);
927                nanosec_rem = do_div(t, 1000000000);
928                tlen = sprintf(tbuf, "[%5lu.%06lu] ",
929                        (unsigned long) t,
930                        nanosec_rem / 1000);
931
932                for (tp = tbuf; tp < tbuf + tlen; tp++)
933                    emit_log_char(*tp);
934                printed_len += tlen;
935            }
936
937            if (!*p)
938                break;
939        }
940
941        emit_log_char(*p);
942        if (*p == '\n')
943            new_text_line = 1;
944    }
945
946    /*
947     * Try to acquire and then immediately release the
948     * console semaphore. The release will do all the
949     * actual magic (print out buffers, wake up klogd,
950     * etc).
951     *
952     * The console_trylock_for_printk() function
953     * will release 'logbuf_lock' regardless of whether it
954     * actually gets the semaphore or not.
955     */
956    if (console_trylock_for_printk(this_cpu))
957        console_unlock();
958
959    lockdep_on();
960out_restore_irqs:
961    raw_local_irq_restore(flags);
962
963    preempt_enable();
964    return printed_len;
965}
966EXPORT_SYMBOL(printk);
967EXPORT_SYMBOL(vprintk);
968
969#else
970
971static void call_console_drivers(unsigned start, unsigned end)
972{
973}
974
975#endif
976
977static int __add_preferred_console(char *name, int idx, char *options,
978                   char *brl_options)
979{
980    struct console_cmdline *c;
981    int i;
982
983    /*
984     * See if this tty is not yet registered, and
985     * if we have a slot free.
986     */
987    for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
988        if (strcmp(console_cmdline[i].name, name) == 0 &&
989              console_cmdline[i].index == idx) {
990                if (!brl_options)
991                    selected_console = i;
992                return 0;
993        }
994    if (i == MAX_CMDLINECONSOLES)
995        return -E2BIG;
996    if (!brl_options)
997        selected_console = i;
998    c = &console_cmdline[i];
999    strlcpy(c->name, name, sizeof(c->name));
1000    c->options = options;
1001#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1002    c->brl_options = brl_options;
1003#endif
1004    c->index = idx;
1005    return 0;
1006}
1007/*
1008 * Set up a list of consoles. Called from init/main.c
1009 */
1010static int __init console_setup(char *str)
1011{
1012    char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */
1013    char *s, *options, *brl_options = NULL;
1014    int idx;
1015
1016#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1017    if (!memcmp(str, "brl,", 4)) {
1018        brl_options = "";
1019        str += 4;
1020    } else if (!memcmp(str, "brl=", 4)) {
1021        brl_options = str + 4;
1022        str = strchr(brl_options, ',');
1023        if (!str) {
1024            printk(KERN_ERR "need port name after brl=\n");
1025            return 1;
1026        }
1027        *(str++) = 0;
1028    }
1029#endif
1030
1031    /*
1032     * Decode str into name, index, options.
1033     */
1034    if (str[0] >= '0' && str[0] <= '9') {
1035        strcpy(buf, "ttyS");
1036        strncpy(buf + 4, str, sizeof(buf) - 5);
1037    } else {
1038        strncpy(buf, str, sizeof(buf) - 1);
1039    }
1040    buf[sizeof(buf) - 1] = 0;
1041    if ((options = strchr(str, ',')) != NULL)
1042        *(options++) = 0;
1043#ifdef __sparc__
1044    if (!strcmp(str, "ttya"))
1045        strcpy(buf, "ttyS0");
1046    if (!strcmp(str, "ttyb"))
1047        strcpy(buf, "ttyS1");
1048#endif
1049    for (s = buf; *s; s++)
1050        if ((*s >= '0' && *s <= '9') || *s == ',')
1051            break;
1052    idx = simple_strtoul(s, NULL, 10);
1053    *s = 0;
1054
1055    __add_preferred_console(buf, idx, options, brl_options);
1056    console_set_on_cmdline = 1;
1057    return 1;
1058}
1059__setup("console=", console_setup);
1060
1061/**
1062 * add_preferred_console - add a device to the list of preferred consoles.
1063 * @name: device name
1064 * @idx: device index
1065 * @options: options for this console
1066 *
1067 * The last preferred console added will be used for kernel messages
1068 * and stdin/out/err for init. Normally this is used by console_setup
1069 * above to handle user-supplied console arguments; however it can also
1070 * be used by arch-specific code either to override the user or more
1071 * commonly to provide a default console (ie from PROM variables) when
1072 * the user has not supplied one.
1073 */
1074int add_preferred_console(char *name, int idx, char *options)
1075{
1076    return __add_preferred_console(name, idx, options, NULL);
1077}
1078
1079int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
1080{
1081    struct console_cmdline *c;
1082    int i;
1083
1084    for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
1085        if (strcmp(console_cmdline[i].name, name) == 0 &&
1086              console_cmdline[i].index == idx) {
1087                c = &console_cmdline[i];
1088                strlcpy(c->name, name_new, sizeof(c->name));
1089                c->name[sizeof(c->name) - 1] = 0;
1090                c->options = options;
1091                c->index = idx_new;
1092                return i;
1093        }
1094    /* not found */
1095    return -1;
1096}
1097
1098int console_suspend_enabled = 1;
1099EXPORT_SYMBOL(console_suspend_enabled);
1100
1101static int __init console_suspend_disable(char *str)
1102{
1103    console_suspend_enabled = 0;
1104    return 1;
1105}
1106__setup("no_console_suspend", console_suspend_disable);
1107
1108/**
1109 * suspend_console - suspend the console subsystem
1110 *
1111 * This disables printk() while we go into suspend states
1112 */
1113void suspend_console(void)
1114{
1115    if (!console_suspend_enabled)
1116        return;
1117    printk("Suspending console(s) (use no_console_suspend to debug)\n");
1118    console_lock();
1119    console_suspended = 1;
1120    up(&console_sem);
1121}
1122
1123void resume_console(void)
1124{
1125    if (!console_suspend_enabled)
1126        return;
1127    down(&console_sem);
1128    console_suspended = 0;
1129    console_unlock();
1130}
1131
1132/**
1133 * console_cpu_notify - print deferred console messages after CPU hotplug
1134 * @self: notifier struct
1135 * @action: CPU hotplug event
1136 * @hcpu: unused
1137 *
1138 * If printk() is called from a CPU that is not online yet, the messages
1139 * will be spooled but will not show up on the console. This function is
1140 * called when a new CPU comes online (or fails to come up), and ensures
1141 * that any such output gets printed.
1142 */
1143static int __cpuinit console_cpu_notify(struct notifier_block *self,
1144    unsigned long action, void *hcpu)
1145{
1146    switch (action) {
1147    case CPU_ONLINE:
1148    case CPU_DEAD:
1149    case CPU_DYING:
1150    case CPU_DOWN_FAILED:
1151    case CPU_UP_CANCELED:
1152        console_lock();
1153        console_unlock();
1154    }
1155    return NOTIFY_OK;
1156}
1157
1158/**
1159 * console_lock - lock the console system for exclusive use.
1160 *
1161 * Acquires a lock which guarantees that the caller has
1162 * exclusive access to the console system and the console_drivers list.
1163 *
1164 * Can sleep, returns nothing.
1165 */
1166void console_lock(void)
1167{
1168    BUG_ON(in_interrupt());
1169    down(&console_sem);
1170    if (console_suspended)
1171        return;
1172    console_locked = 1;
1173    console_may_schedule = 1;
1174}
1175EXPORT_SYMBOL(console_lock);
1176
1177/**
1178 * console_trylock - try to lock the console system for exclusive use.
1179 *
1180 * Tried to acquire a lock which guarantees that the caller has
1181 * exclusive access to the console system and the console_drivers list.
1182 *
1183 * returns 1 on success, and 0 on failure to acquire the lock.
1184 */
1185int console_trylock(void)
1186{
1187    if (down_trylock(&console_sem))
1188        return 0;
1189    if (console_suspended) {
1190        up(&console_sem);
1191        return 0;
1192    }
1193    console_locked = 1;
1194    console_may_schedule = 0;
1195    return 1;
1196}
1197EXPORT_SYMBOL(console_trylock);
1198
1199int is_console_locked(void)
1200{
1201    return console_locked;
1202}
1203
1204static DEFINE_PER_CPU(int, printk_pending);
1205
1206void printk_tick(void)
1207{
1208    if (__this_cpu_read(printk_pending)) {
1209        __this_cpu_write(printk_pending, 0);
1210        wake_up_interruptible(&log_wait);
1211    }
1212}
1213
1214int printk_needs_cpu(int cpu)
1215{
1216    if (cpu_is_offline(cpu))
1217        printk_tick();
1218    return __this_cpu_read(printk_pending);
1219}
1220
1221void wake_up_klogd(void)
1222{
1223    if (waitqueue_active(&log_wait))
1224        this_cpu_write(printk_pending, 1);
1225}
1226
1227/**
1228 * console_unlock - unlock the console system
1229 *
1230 * Releases the console_lock which the caller holds on the console system
1231 * and the console driver list.
1232 *
1233 * While the console_lock was held, console output may have been buffered
1234 * by printk(). If this is the case, console_unlock(); emits
1235 * the output prior to releasing the lock.
1236 *
1237 * If there is output waiting for klogd, we wake it up.
1238 *
1239 * console_unlock(); may be called from any context.
1240 */
1241void console_unlock(void)
1242{
1243    unsigned long flags;
1244    unsigned _con_start, _log_end;
1245    unsigned wake_klogd = 0;
1246
1247    if (console_suspended) {
1248        up(&console_sem);
1249        return;
1250    }
1251
1252    console_may_schedule = 0;
1253
1254    for ( ; ; ) {
1255        spin_lock_irqsave(&logbuf_lock, flags);
1256        wake_klogd |= log_start - log_end;
1257        if (con_start == log_end)
1258            break; /* Nothing to print */
1259        _con_start = con_start;
1260        _log_end = log_end;
1261        con_start = log_end; /* Flush */
1262        spin_unlock(&logbuf_lock);
1263        stop_critical_timings(); /* don't trace print latency */
1264        call_console_drivers(_con_start, _log_end);
1265        start_critical_timings();
1266        local_irq_restore(flags);
1267    }
1268    console_locked = 0;
1269
1270    /* Release the exclusive_console once it is used */
1271    if (unlikely(exclusive_console))
1272        exclusive_console = NULL;
1273
1274    up(&console_sem);
1275    spin_unlock_irqrestore(&logbuf_lock, flags);
1276    if (wake_klogd)
1277        wake_up_klogd();
1278}
1279EXPORT_SYMBOL(console_unlock);
1280
1281/**
1282 * console_conditional_schedule - yield the CPU if required
1283 *
1284 * If the console code is currently allowed to sleep, and
1285 * if this CPU should yield the CPU to another task, do
1286 * so here.
1287 *
1288 * Must be called within console_lock();.
1289 */
1290void __sched console_conditional_schedule(void)
1291{
1292    if (console_may_schedule)
1293        cond_resched();
1294}
1295EXPORT_SYMBOL(console_conditional_schedule);
1296
1297void console_unblank(void)
1298{
1299    struct console *c;
1300
1301    /*
1302     * console_unblank can no longer be called in interrupt context unless
1303     * oops_in_progress is set to 1..
1304     */
1305    if (oops_in_progress) {
1306        if (down_trylock(&console_sem) != 0)
1307            return;
1308    } else
1309        console_lock();
1310
1311    console_locked = 1;
1312    console_may_schedule = 0;
1313    for_each_console(c)
1314        if ((c->flags & CON_ENABLED) && c->unblank)
1315            c->unblank();
1316    console_unlock();
1317}
1318
1319/*
1320 * Return the console tty driver structure and its associated index
1321 */
1322struct tty_driver *console_device(int *index)
1323{
1324    struct console *c;
1325    struct tty_driver *driver = NULL;
1326
1327    console_lock();
1328    for_each_console(c) {
1329        if (!c->device)
1330            continue;
1331        driver = c->device(c, index);
1332        if (driver)
1333            break;
1334    }
1335    console_unlock();
1336    return driver;
1337}
1338
1339/*
1340 * Prevent further output on the passed console device so that (for example)
1341 * serial drivers can disable console output before suspending a port, and can
1342 * re-enable output afterwards.
1343 */
1344void console_stop(struct console *console)
1345{
1346    console_lock();
1347    console->flags &= ~CON_ENABLED;
1348    console_unlock();
1349}
1350EXPORT_SYMBOL(console_stop);
1351
1352void console_start(struct console *console)
1353{
1354    console_lock();
1355    console->flags |= CON_ENABLED;
1356    console_unlock();
1357}
1358EXPORT_SYMBOL(console_start);
1359
1360static int __read_mostly keep_bootcon;
1361
1362static int __init keep_bootcon_setup(char *str)
1363{
1364    keep_bootcon = 1;
1365    printk(KERN_INFO "debug: skip boot console de-registration.\n");
1366
1367    return 0;
1368}
1369
1370early_param("keep_bootcon", keep_bootcon_setup);
1371
1372/*
1373 * The console driver calls this routine during kernel initialization
1374 * to register the console printing procedure with printk() and to
1375 * print any messages that were printed by the kernel before the
1376 * console driver was initialized.
1377 *
1378 * This can happen pretty early during the boot process (because of
1379 * early_printk) - sometimes before setup_arch() completes - be careful
1380 * of what kernel features are used - they may not be initialised yet.
1381 *
1382 * There are two types of consoles - bootconsoles (early_printk) and
1383 * "real" consoles (everything which is not a bootconsole) which are
1384 * handled differently.
1385 * - Any number of bootconsoles can be registered at any time.
1386 * - As soon as a "real" console is registered, all bootconsoles
1387 * will be unregistered automatically.
1388 * - Once a "real" console is registered, any attempt to register a
1389 * bootconsoles will be rejected
1390 */
1391void register_console(struct console *newcon)
1392{
1393    int i;
1394    unsigned long flags;
1395    struct console *bcon = NULL;
1396
1397    /*
1398     * before we register a new CON_BOOT console, make sure we don't
1399     * already have a valid console
1400     */
1401    if (console_drivers && newcon->flags & CON_BOOT) {
1402        /* find the last or real console */
1403        for_each_console(bcon) {
1404            if (!(bcon->flags & CON_BOOT)) {
1405                printk(KERN_INFO "Too late to register bootconsole %s%d\n",
1406                    newcon->name, newcon->index);
1407                return;
1408            }
1409        }
1410    }
1411
1412    if (console_drivers && console_drivers->flags & CON_BOOT)
1413        bcon = console_drivers;
1414
1415    if (preferred_console < 0 || bcon || !console_drivers)
1416        preferred_console = selected_console;
1417
1418    if (newcon->early_setup)
1419        newcon->early_setup();
1420
1421    /*
1422     * See if we want to use this console driver. If we
1423     * didn't select a console we take the first one
1424     * that registers here.
1425     */
1426    if (preferred_console < 0) {
1427        if (newcon->index < 0)
1428            newcon->index = 0;
1429        if (newcon->setup == NULL ||
1430            newcon->setup(newcon, NULL) == 0) {
1431            newcon->flags |= CON_ENABLED;
1432            if (newcon->device) {
1433                newcon->flags |= CON_CONSDEV;
1434                preferred_console = 0;
1435            }
1436        }
1437    }
1438
1439    /*
1440     * See if this console matches one we selected on
1441     * the command line.
1442     */
1443    for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
1444            i++) {
1445        if (strcmp(console_cmdline[i].name, newcon->name) != 0)
1446            continue;
1447        if (newcon->index >= 0 &&
1448            newcon->index != console_cmdline[i].index)
1449            continue;
1450        if (newcon->index < 0)
1451            newcon->index = console_cmdline[i].index;
1452#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1453        if (console_cmdline[i].brl_options) {
1454            newcon->flags |= CON_BRL;
1455            braille_register_console(newcon,
1456                    console_cmdline[i].index,
1457                    console_cmdline[i].options,
1458                    console_cmdline[i].brl_options);
1459            return;
1460        }
1461#endif
1462        if (newcon->setup &&
1463            newcon->setup(newcon, console_cmdline[i].options) != 0)
1464            break;
1465        newcon->flags |= CON_ENABLED;
1466        newcon->index = console_cmdline[i].index;
1467        if (i == selected_console) {
1468            newcon->flags |= CON_CONSDEV;
1469            preferred_console = selected_console;
1470        }
1471        break;
1472    }
1473
1474    if (!(newcon->flags & CON_ENABLED))
1475        return;
1476
1477    /*
1478     * If we have a bootconsole, and are switching to a real console,
1479     * don't print everything out again, since when the boot console, and
1480     * the real console are the same physical device, it's annoying to
1481     * see the beginning boot messages twice
1482     */
1483    if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
1484        newcon->flags &= ~CON_PRINTBUFFER;
1485
1486    /*
1487     * Put this console in the list - keep the
1488     * preferred driver at the head of the list.
1489     */
1490    console_lock();
1491    if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
1492        newcon->next = console_drivers;
1493        console_drivers = newcon;
1494        if (newcon->next)
1495            newcon->next->flags &= ~CON_CONSDEV;
1496    } else {
1497        newcon->next = console_drivers->next;
1498        console_drivers->next = newcon;
1499    }
1500    if (newcon->flags & CON_PRINTBUFFER) {
1501        /*
1502         * console_unlock(); will print out the buffered messages
1503         * for us.
1504         */
1505        spin_lock_irqsave(&logbuf_lock, flags);
1506        con_start = log_start;
1507        spin_unlock_irqrestore(&logbuf_lock, flags);
1508        /*
1509         * We're about to replay the log buffer. Only do this to the
1510         * just-registered console to avoid excessive message spam to
1511         * the already-registered consoles.
1512         */
1513        exclusive_console = newcon;
1514    }
1515    console_unlock();
1516    console_sysfs_notify();
1517
1518    /*
1519     * By unregistering the bootconsoles after we enable the real console
1520     * we get the "console xxx enabled" message on all the consoles -
1521     * boot consoles, real consoles, etc - this is to ensure that end
1522     * users know there might be something in the kernel's log buffer that
1523     * went to the bootconsole (that they do not see on the real console)
1524     */
1525    if (bcon &&
1526        ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
1527        !keep_bootcon) {
1528        /* we need to iterate through twice, to make sure we print
1529         * everything out, before we unregister the console(s)
1530         */
1531        printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
1532            newcon->name, newcon->index);
1533        for_each_console(bcon)
1534            if (bcon->flags & CON_BOOT)
1535                unregister_console(bcon);
1536    } else {
1537        printk(KERN_INFO "%sconsole [%s%d] enabled\n",
1538            (newcon->flags & CON_BOOT) ? "boot" : "" ,
1539            newcon->name, newcon->index);
1540    }
1541}
1542EXPORT_SYMBOL(register_console);
1543
1544int unregister_console(struct console *console)
1545{
1546        struct console *a, *b;
1547    int res = 1;
1548
1549#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
1550    if (console->flags & CON_BRL)
1551        return braille_unregister_console(console);
1552#endif
1553
1554    console_lock();
1555    if (console_drivers == console) {
1556        console_drivers=console->next;
1557        res = 0;
1558    } else if (console_drivers) {
1559        for (a=console_drivers->next, b=console_drivers ;
1560             a; b=a, a=b->next) {
1561            if (a == console) {
1562                b->next = a->next;
1563                res = 0;
1564                break;
1565            }
1566        }
1567    }
1568
1569    /*
1570     * If this isn't the last console and it has CON_CONSDEV set, we
1571     * need to set it on the next preferred console.
1572     */
1573    if (console_drivers != NULL && console->flags & CON_CONSDEV)
1574        console_drivers->flags |= CON_CONSDEV;
1575
1576    console_unlock();
1577    console_sysfs_notify();
1578    return res;
1579}
1580EXPORT_SYMBOL(unregister_console);
1581
1582static int __init printk_late_init(void)
1583{
1584    struct console *con;
1585
1586    for_each_console(con) {
1587        if (con->flags & CON_BOOT) {
1588            printk(KERN_INFO "turn off boot console %s%d\n",
1589                con->name, con->index);
1590            unregister_console(con);
1591        }
1592    }
1593    hotcpu_notifier(console_cpu_notify, 0);
1594    return 0;
1595}
1596late_initcall(printk_late_init);
1597
1598#if defined CONFIG_PRINTK
1599
1600/*
1601 * printk rate limiting, lifted from the networking subsystem.
1602 *
1603 * This enforces a rate limit: not more than 10 kernel messages
1604 * every 5s to make a denial-of-service attack impossible.
1605 */
1606DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
1607
1608int __printk_ratelimit(const char *func)
1609{
1610    return ___ratelimit(&printk_ratelimit_state, func);
1611}
1612EXPORT_SYMBOL(__printk_ratelimit);
1613
1614/**
1615 * printk_timed_ratelimit - caller-controlled printk ratelimiting
1616 * @caller_jiffies: pointer to caller's state
1617 * @interval_msecs: minimum interval between prints
1618 *
1619 * printk_timed_ratelimit() returns true if more than @interval_msecs
1620 * milliseconds have elapsed since the last time printk_timed_ratelimit()
1621 * returned true.
1622 */
1623bool printk_timed_ratelimit(unsigned long *caller_jiffies,
1624            unsigned int interval_msecs)
1625{
1626    if (*caller_jiffies == 0
1627            || !time_in_range(jiffies, *caller_jiffies,
1628                    *caller_jiffies
1629                    + msecs_to_jiffies(interval_msecs))) {
1630        *caller_jiffies = jiffies;
1631        return true;
1632    }
1633    return false;
1634}
1635EXPORT_SYMBOL(printk_timed_ratelimit);
1636
1637static DEFINE_SPINLOCK(dump_list_lock);
1638static LIST_HEAD(dump_list);
1639
1640/**
1641 * kmsg_dump_register - register a kernel log dumper.
1642 * @dumper: pointer to the kmsg_dumper structure
1643 *
1644 * Adds a kernel log dumper to the system. The dump callback in the
1645 * structure will be called when the kernel oopses or panics and must be
1646 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
1647 */
1648int kmsg_dump_register(struct kmsg_dumper *dumper)
1649{
1650    unsigned long flags;
1651    int err = -EBUSY;
1652
1653    /* The dump callback needs to be set */
1654    if (!dumper->dump)
1655        return -EINVAL;
1656
1657    spin_lock_irqsave(&dump_list_lock, flags);
1658    /* Don't allow registering multiple times */
1659    if (!dumper->registered) {
1660        dumper->registered = 1;
1661        list_add_tail_rcu(&dumper->list, &dump_list);
1662        err = 0;
1663    }
1664    spin_unlock_irqrestore(&dump_list_lock, flags);
1665
1666    return err;
1667}
1668EXPORT_SYMBOL_GPL(kmsg_dump_register);
1669
1670/**
1671 * kmsg_dump_unregister - unregister a kmsg dumper.
1672 * @dumper: pointer to the kmsg_dumper structure
1673 *
1674 * Removes a dump device from the system. Returns zero on success and
1675 * %-EINVAL otherwise.
1676 */
1677int kmsg_dump_unregister(struct kmsg_dumper *dumper)
1678{
1679    unsigned long flags;
1680    int err = -EINVAL;
1681
1682    spin_lock_irqsave(&dump_list_lock, flags);
1683    if (dumper->registered) {
1684        dumper->registered = 0;
1685        list_del_rcu(&dumper->list);
1686        err = 0;
1687    }
1688    spin_unlock_irqrestore(&dump_list_lock, flags);
1689    synchronize_rcu();
1690
1691    return err;
1692}
1693EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
1694
1695/**
1696 * kmsg_dump - dump kernel log to kernel message dumpers.
1697 * @reason: the reason (oops, panic etc) for dumping
1698 *
1699 * Iterate through each of the dump devices and call the oops/panic
1700 * callbacks with the log buffer.
1701 */
1702void kmsg_dump(enum kmsg_dump_reason reason)
1703{
1704    unsigned long end;
1705    unsigned chars;
1706    struct kmsg_dumper *dumper;
1707    const char *s1, *s2;
1708    unsigned long l1, l2;
1709    unsigned long flags;
1710
1711    /* Theoretically, the log could move on after we do this, but
1712       there's not a lot we can do about that. The new messages
1713       will overwrite the start of what we dump. */
1714    spin_lock_irqsave(&logbuf_lock, flags);
1715    end = log_end & LOG_BUF_MASK;
1716    chars = logged_chars;
1717    spin_unlock_irqrestore(&logbuf_lock, flags);
1718
1719    if (chars > end) {
1720        s1 = log_buf + log_buf_len - chars + end;
1721        l1 = chars - end;
1722
1723        s2 = log_buf;
1724        l2 = end;
1725    } else {
1726        s1 = "";
1727        l1 = 0;
1728
1729        s2 = log_buf + end - chars;
1730        l2 = chars;
1731    }
1732
1733    rcu_read_lock();
1734    list_for_each_entry_rcu(dumper, &dump_list, list)
1735        dumper->dump(dumper, reason, s1, l1, s2, l2);
1736    rcu_read_unlock();
1737}
1738#endif
1739

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