1 // SPDX-License-Identifier: GPL-2.0-only
3 * linux/kernel/printk.c
5 * Copyright (C) 1991, 1992 Linus Torvalds
7 * Modified to make sys_syslog() more flexible: added commands to
8 * return the last 4k of kernel messages, regardless of whether
9 * they've been read or not. Added option to suppress kernel printk's
10 * to the console. Added hook for sending the console messages
11 * elsewhere, in preparation for a serial line console (someday).
13 * Modified for sysctl support, 1/8/97, Chris Horn.
14 * Fixed SMP synchronization, 08/08/99, Manfred Spraul
15 * manfred@colorfullife.com
16 * Rewrote bits to get rid of console_lock
17 * 01Mar01 Andrew Morton
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
22 #include <linux/kernel.h>
24 #include <linux/tty.h>
25 #include <linux/tty_driver.h>
26 #include <linux/console.h>
27 #include <linux/init.h>
28 #include <linux/jiffies.h>
29 #include <linux/nmi.h>
30 #include <linux/module.h>
31 #include <linux/moduleparam.h>
32 #include <linux/delay.h>
33 #include <linux/smp.h>
34 #include <linux/security.h>
35 #include <linux/memblock.h>
36 #include <linux/syscalls.h>
37 #include <linux/crash_core.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/rculist.h>
43 #include <linux/poll.h>
44 #include <linux/irq_work.h>
45 #include <linux/ctype.h>
46 #include <linux/uio.h>
47 #include <linux/sched/clock.h>
48 #include <linux/sched/debug.h>
49 #include <linux/sched/task_stack.h>
51 #include <linux/uaccess.h>
52 #include <asm/sections.h>
54 #include <trace/events/initcall.h>
55 #define CREATE_TRACE_POINTS
56 #include <trace/events/printk.h>
58 #include "console_cmdline.h"
62 int console_printk[4] = {
63 CONSOLE_LOGLEVEL_DEFAULT, /* console_loglevel */
64 MESSAGE_LOGLEVEL_DEFAULT, /* default_message_loglevel */
65 CONSOLE_LOGLEVEL_MIN, /* minimum_console_loglevel */
66 CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
68 EXPORT_SYMBOL_GPL(console_printk);
70 atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
71 EXPORT_SYMBOL(ignore_console_lock_warning);
74 * Low level drivers may need that to know if they can schedule in
75 * their unblank() callback or not. So let's export it.
78 EXPORT_SYMBOL(oops_in_progress);
81 * console_sem protects the console_drivers list, and also
82 * provides serialisation for access to the entire console
85 static DEFINE_SEMAPHORE(console_sem);
86 struct console *console_drivers;
87 EXPORT_SYMBOL_GPL(console_drivers);
90 * System may need to suppress printk message under certain
91 * circumstances, like after kernel panic happens.
93 int __read_mostly suppress_printk;
96 static struct lockdep_map console_lock_dep_map = {
97 .name = "console_lock"
101 enum devkmsg_log_bits {
102 __DEVKMSG_LOG_BIT_ON = 0,
103 __DEVKMSG_LOG_BIT_OFF,
104 __DEVKMSG_LOG_BIT_LOCK,
107 enum devkmsg_log_masks {
108 DEVKMSG_LOG_MASK_ON = BIT(__DEVKMSG_LOG_BIT_ON),
109 DEVKMSG_LOG_MASK_OFF = BIT(__DEVKMSG_LOG_BIT_OFF),
110 DEVKMSG_LOG_MASK_LOCK = BIT(__DEVKMSG_LOG_BIT_LOCK),
113 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
114 #define DEVKMSG_LOG_MASK_DEFAULT 0
116 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
118 static int __control_devkmsg(char *str)
125 len = str_has_prefix(str, "on");
127 devkmsg_log = DEVKMSG_LOG_MASK_ON;
131 len = str_has_prefix(str, "off");
133 devkmsg_log = DEVKMSG_LOG_MASK_OFF;
137 len = str_has_prefix(str, "ratelimit");
139 devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
146 static int __init control_devkmsg(char *str)
148 if (__control_devkmsg(str) < 0)
152 * Set sysctl string accordingly:
154 if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
155 strcpy(devkmsg_log_str, "on");
156 else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
157 strcpy(devkmsg_log_str, "off");
158 /* else "ratelimit" which is set by default. */
161 * Sysctl cannot change it anymore. The kernel command line setting of
162 * this parameter is to force the setting to be permanent throughout the
163 * runtime of the system. This is a precation measure against userspace
164 * trying to be a smarta** and attempting to change it up on us.
166 devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
170 __setup("printk.devkmsg=", control_devkmsg);
172 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
174 int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
175 void *buffer, size_t *lenp, loff_t *ppos)
177 char old_str[DEVKMSG_STR_MAX_SIZE];
182 if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
186 strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
189 err = proc_dostring(table, write, buffer, lenp, ppos);
194 err = __control_devkmsg(devkmsg_log_str);
197 * Do not accept an unknown string OR a known string with
200 if (err < 0 || (err + 1 != *lenp)) {
202 /* ... and restore old setting. */
204 strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
213 /* Number of registered extended console drivers. */
214 static int nr_ext_console_drivers;
217 * Helper macros to handle lockdep when locking/unlocking console_sem. We use
218 * macros instead of functions so that _RET_IP_ contains useful information.
220 #define down_console_sem() do { \
222 mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
225 static int __down_trylock_console_sem(unsigned long ip)
231 * Here and in __up_console_sem() we need to be in safe mode,
232 * because spindump/WARN/etc from under console ->lock will
233 * deadlock in printk()->down_trylock_console_sem() otherwise.
235 printk_safe_enter_irqsave(flags);
236 lock_failed = down_trylock(&console_sem);
237 printk_safe_exit_irqrestore(flags);
241 mutex_acquire(&console_lock_dep_map, 0, 1, ip);
244 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
246 static void __up_console_sem(unsigned long ip)
250 mutex_release(&console_lock_dep_map, ip);
252 printk_safe_enter_irqsave(flags);
254 printk_safe_exit_irqrestore(flags);
256 #define up_console_sem() __up_console_sem(_RET_IP_)
259 * This is used for debugging the mess that is the VT code by
260 * keeping track if we have the console semaphore held. It's
261 * definitely not the perfect debug tool (we don't know if _WE_
262 * hold it and are racing, but it helps tracking those weird code
263 * paths in the console code where we end up in places I want
264 * locked without the console sempahore held).
266 static int console_locked, console_suspended;
269 * If exclusive_console is non-NULL then only this console is to be printed to.
271 static struct console *exclusive_console;
274 * Array of consoles built from command line options (console=)
277 #define MAX_CMDLINECONSOLES 8
279 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
281 static int preferred_console = -1;
282 static bool has_preferred_console;
283 int console_set_on_cmdline;
284 EXPORT_SYMBOL(console_set_on_cmdline);
286 /* Flag: console code may call schedule() */
287 static int console_may_schedule;
289 enum con_msg_format_flags {
290 MSG_FORMAT_DEFAULT = 0,
291 MSG_FORMAT_SYSLOG = (1 << 0),
294 static int console_msg_format = MSG_FORMAT_DEFAULT;
297 * The printk log buffer consists of a chain of concatenated variable
298 * length records. Every record starts with a record header, containing
299 * the overall length of the record.
301 * The heads to the first and last entry in the buffer, as well as the
302 * sequence numbers of these entries are maintained when messages are
305 * If the heads indicate available messages, the length in the header
306 * tells the start next message. A length == 0 for the next message
307 * indicates a wrap-around to the beginning of the buffer.
309 * Every record carries the monotonic timestamp in microseconds, as well as
310 * the standard userspace syslog level and syslog facility. The usual
311 * kernel messages use LOG_KERN; userspace-injected messages always carry
312 * a matching syslog facility, by default LOG_USER. The origin of every
313 * message can be reliably determined that way.
315 * The human readable log message directly follows the message header. The
316 * length of the message text is stored in the header, the stored message
319 * Optionally, a message can carry a dictionary of properties (key/value pairs),
320 * to provide userspace with a machine-readable message context.
322 * Examples for well-defined, commonly used property names are:
323 * DEVICE=b12:8 device identifier
327 * +sound:card0 subsystem:devname
328 * SUBSYSTEM=pci driver-core subsystem name
330 * Valid characters in property names are [a-zA-Z0-9.-_]. The plain text value
331 * follows directly after a '=' character. Every property is terminated by
332 * a '\0' character. The last property is not terminated.
334 * Example of a message structure:
335 * 0000 ff 8f 00 00 00 00 00 00 monotonic time in nsec
336 * 0008 34 00 record is 52 bytes long
337 * 000a 0b 00 text is 11 bytes long
338 * 000c 1f 00 dictionary is 23 bytes long
339 * 000e 03 00 LOG_KERN (facility) LOG_ERR (level)
340 * 0010 69 74 27 73 20 61 20 6c "it's a l"
342 * 001b 44 45 56 49 43 "DEVIC"
343 * 45 3d 62 38 3a 32 00 44 "E=b8:2\0D"
344 * 52 49 56 45 52 3d 62 75 "RIVER=bu"
346 * 0032 00 00 00 padding to next message header
348 * The 'struct printk_log' buffer header must never be directly exported to
349 * userspace, it is a kernel-private implementation detail that might
350 * need to be changed in the future, when the requirements change.
352 * /dev/kmsg exports the structured data in the following line format:
353 * "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
355 * Users of the export format should ignore possible additional values
356 * separated by ',', and find the message after the ';' character.
358 * The optional key/value pairs are attached as continuation lines starting
359 * with a space character and terminated by a newline. All possible
360 * non-prinatable characters are escaped in the "\xff" notation.
364 LOG_NEWLINE = 2, /* text ended with a newline */
365 LOG_CONT = 8, /* text is a fragment of a continuation line */
369 u64 ts_nsec; /* timestamp in nanoseconds */
370 u16 len; /* length of entire record */
371 u16 text_len; /* length of text buffer */
372 u16 dict_len; /* length of dictionary buffer */
373 u8 facility; /* syslog facility */
374 u8 flags:5; /* internal record flags */
375 u8 level:3; /* syslog level */
376 #ifdef CONFIG_PRINTK_CALLER
377 u32 caller_id; /* thread id or processor id */
380 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
381 __packed __aligned(4)
386 * The logbuf_lock protects kmsg buffer, indices, counters. This can be taken
387 * within the scheduler's rq lock. It must be released before calling
388 * console_unlock() or anything else that might wake up a process.
390 DEFINE_RAW_SPINLOCK(logbuf_lock);
393 * Helper macros to lock/unlock logbuf_lock and switch between
394 * printk-safe/unsafe modes.
396 #define logbuf_lock_irq() \
398 printk_safe_enter_irq(); \
399 raw_spin_lock(&logbuf_lock); \
402 #define logbuf_unlock_irq() \
404 raw_spin_unlock(&logbuf_lock); \
405 printk_safe_exit_irq(); \
408 #define logbuf_lock_irqsave(flags) \
410 printk_safe_enter_irqsave(flags); \
411 raw_spin_lock(&logbuf_lock); \
414 #define logbuf_unlock_irqrestore(flags) \
416 raw_spin_unlock(&logbuf_lock); \
417 printk_safe_exit_irqrestore(flags); \
421 DECLARE_WAIT_QUEUE_HEAD(log_wait);
422 /* the next printk record to read by syslog(READ) or /proc/kmsg */
423 static u64 syslog_seq;
424 static u32 syslog_idx;
425 static size_t syslog_partial;
426 static bool syslog_time;
428 /* index and sequence number of the first record stored in the buffer */
429 static u64 log_first_seq;
430 static u32 log_first_idx;
432 /* index and sequence number of the next record to store in the buffer */
433 static u64 log_next_seq;
434 static u32 log_next_idx;
436 /* the next printk record to write to the console */
437 static u64 console_seq;
438 static u32 console_idx;
439 static u64 exclusive_console_stop_seq;
441 /* the next printk record to read after the last 'clear' command */
442 static u64 clear_seq;
443 static u32 clear_idx;
445 #ifdef CONFIG_PRINTK_CALLER
446 #define PREFIX_MAX 48
448 #define PREFIX_MAX 32
450 #define LOG_LINE_MAX (1024 - PREFIX_MAX)
452 #define LOG_LEVEL(v) ((v) & 0x07)
453 #define LOG_FACILITY(v) ((v) >> 3 & 0xff)
456 #define LOG_ALIGN __alignof__(struct printk_log)
457 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
458 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
459 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
460 static char *log_buf = __log_buf;
461 static u32 log_buf_len = __LOG_BUF_LEN;
464 * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
465 * per_cpu_areas are initialised. This variable is set to true when
466 * it's safe to access per-CPU data.
468 static bool __printk_percpu_data_ready __read_mostly;
470 bool printk_percpu_data_ready(void)
472 return __printk_percpu_data_ready;
475 /* Return log buffer address */
476 char *log_buf_addr_get(void)
481 /* Return log buffer size */
482 u32 log_buf_len_get(void)
487 /* human readable text of the record */
488 static char *log_text(const struct printk_log *msg)
490 return (char *)msg + sizeof(struct printk_log);
493 /* optional key/value pair dictionary attached to the record */
494 static char *log_dict(const struct printk_log *msg)
496 return (char *)msg + sizeof(struct printk_log) + msg->text_len;
499 /* get record by index; idx must point to valid msg */
500 static struct printk_log *log_from_idx(u32 idx)
502 struct printk_log *msg = (struct printk_log *)(log_buf + idx);
505 * A length == 0 record is the end of buffer marker. Wrap around and
506 * read the message at the start of the buffer.
509 return (struct printk_log *)log_buf;
513 /* get next record; idx must point to valid msg */
514 static u32 log_next(u32 idx)
516 struct printk_log *msg = (struct printk_log *)(log_buf + idx);
518 /* length == 0 indicates the end of the buffer; wrap */
520 * A length == 0 record is the end of buffer marker. Wrap around and
521 * read the message at the start of the buffer as *this* one, and
522 * return the one after that.
525 msg = (struct printk_log *)log_buf;
528 return idx + msg->len;
532 * Check whether there is enough free space for the given message.
534 * The same values of first_idx and next_idx mean that the buffer
535 * is either empty or full.
537 * If the buffer is empty, we must respect the position of the indexes.
538 * They cannot be reset to the beginning of the buffer.
540 static int logbuf_has_space(u32 msg_size, bool empty)
544 if (log_next_idx > log_first_idx || empty)
545 free = max(log_buf_len - log_next_idx, log_first_idx);
547 free = log_first_idx - log_next_idx;
550 * We need space also for an empty header that signalizes wrapping
553 return free >= msg_size + sizeof(struct printk_log);
556 static int log_make_free_space(u32 msg_size)
558 while (log_first_seq < log_next_seq &&
559 !logbuf_has_space(msg_size, false)) {
560 /* drop old messages until we have enough contiguous space */
561 log_first_idx = log_next(log_first_idx);
565 if (clear_seq < log_first_seq) {
566 clear_seq = log_first_seq;
567 clear_idx = log_first_idx;
570 /* sequence numbers are equal, so the log buffer is empty */
571 if (logbuf_has_space(msg_size, log_first_seq == log_next_seq))
577 /* compute the message size including the padding bytes */
578 static u32 msg_used_size(u16 text_len, u16 dict_len, u32 *pad_len)
582 size = sizeof(struct printk_log) + text_len + dict_len;
583 *pad_len = (-size) & (LOG_ALIGN - 1);
590 * Define how much of the log buffer we could take at maximum. The value
591 * must be greater than two. Note that only half of the buffer is available
592 * when the index points to the middle.
594 #define MAX_LOG_TAKE_PART 4
595 static const char trunc_msg[] = "<truncated>";
597 static u32 truncate_msg(u16 *text_len, u16 *trunc_msg_len,
598 u16 *dict_len, u32 *pad_len)
601 * The message should not take the whole buffer. Otherwise, it might
602 * get removed too soon.
604 u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
605 if (*text_len > max_text_len)
606 *text_len = max_text_len;
607 /* enable the warning message */
608 *trunc_msg_len = strlen(trunc_msg);
609 /* disable the "dict" completely */
611 /* compute the size again, count also the warning message */
612 return msg_used_size(*text_len + *trunc_msg_len, 0, pad_len);
615 /* insert record into the buffer, discard old ones, update heads */
616 static int log_store(u32 caller_id, int facility, int level,
617 enum log_flags flags, u64 ts_nsec,
618 const char *dict, u16 dict_len,
619 const char *text, u16 text_len)
621 struct printk_log *msg;
623 u16 trunc_msg_len = 0;
625 /* number of '\0' padding bytes to next message */
626 size = msg_used_size(text_len, dict_len, &pad_len);
628 if (log_make_free_space(size)) {
629 /* truncate the message if it is too long for empty buffer */
630 size = truncate_msg(&text_len, &trunc_msg_len,
631 &dict_len, &pad_len);
632 /* survive when the log buffer is too small for trunc_msg */
633 if (log_make_free_space(size))
637 if (log_next_idx + size + sizeof(struct printk_log) > log_buf_len) {
639 * This message + an additional empty header does not fit
640 * at the end of the buffer. Add an empty header with len == 0
641 * to signify a wrap around.
643 memset(log_buf + log_next_idx, 0, sizeof(struct printk_log));
648 msg = (struct printk_log *)(log_buf + log_next_idx);
649 memcpy(log_text(msg), text, text_len);
650 msg->text_len = text_len;
652 memcpy(log_text(msg) + text_len, trunc_msg, trunc_msg_len);
653 msg->text_len += trunc_msg_len;
655 memcpy(log_dict(msg), dict, dict_len);
656 msg->dict_len = dict_len;
657 msg->facility = facility;
658 msg->level = level & 7;
659 msg->flags = flags & 0x1f;
661 msg->ts_nsec = ts_nsec;
663 msg->ts_nsec = local_clock();
664 #ifdef CONFIG_PRINTK_CALLER
665 msg->caller_id = caller_id;
667 memset(log_dict(msg) + dict_len, 0, pad_len);
671 log_next_idx += msg->len;
674 return msg->text_len;
677 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
679 static int syslog_action_restricted(int type)
684 * Unless restricted, we allow "read all" and "get buffer size"
687 return type != SYSLOG_ACTION_READ_ALL &&
688 type != SYSLOG_ACTION_SIZE_BUFFER;
691 static int check_syslog_permissions(int type, int source)
694 * If this is from /proc/kmsg and we've already opened it, then we've
695 * already done the capabilities checks at open time.
697 if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
700 if (syslog_action_restricted(type)) {
701 if (capable(CAP_SYSLOG))
704 * For historical reasons, accept CAP_SYS_ADMIN too, with
707 if (capable(CAP_SYS_ADMIN)) {
708 pr_warn_once("%s (%d): Attempt to access syslog with "
709 "CAP_SYS_ADMIN but no CAP_SYSLOG "
711 current->comm, task_pid_nr(current));
717 return security_syslog(type);
720 static void append_char(char **pp, char *e, char c)
726 static ssize_t msg_print_ext_header(char *buf, size_t size,
727 struct printk_log *msg, u64 seq)
729 u64 ts_usec = msg->ts_nsec;
731 #ifdef CONFIG_PRINTK_CALLER
732 u32 id = msg->caller_id;
734 snprintf(caller, sizeof(caller), ",caller=%c%u",
735 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
740 do_div(ts_usec, 1000);
742 return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
743 (msg->facility << 3) | msg->level, seq, ts_usec,
744 msg->flags & LOG_CONT ? 'c' : '-', caller);
747 static ssize_t msg_print_ext_body(char *buf, size_t size,
748 char *dict, size_t dict_len,
749 char *text, size_t text_len)
751 char *p = buf, *e = buf + size;
754 /* escape non-printable characters */
755 for (i = 0; i < text_len; i++) {
756 unsigned char c = text[i];
758 if (c < ' ' || c >= 127 || c == '\\')
759 p += scnprintf(p, e - p, "\\x%02x", c);
761 append_char(&p, e, c);
763 append_char(&p, e, '\n');
768 for (i = 0; i < dict_len; i++) {
769 unsigned char c = dict[i];
772 append_char(&p, e, ' ');
777 append_char(&p, e, '\n');
782 if (c < ' ' || c >= 127 || c == '\\') {
783 p += scnprintf(p, e - p, "\\x%02x", c);
787 append_char(&p, e, c);
789 append_char(&p, e, '\n');
795 /* /dev/kmsg - userspace message inject/listen interface */
796 struct devkmsg_user {
799 struct ratelimit_state rs;
801 char buf[CONSOLE_EXT_LOG_MAX];
804 static __printf(3, 4) __cold
805 int devkmsg_emit(int facility, int level, const char *fmt, ...)
811 r = vprintk_emit(facility, level, NULL, 0, fmt, args);
817 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
820 int level = default_message_loglevel;
821 int facility = 1; /* LOG_USER */
822 struct file *file = iocb->ki_filp;
823 struct devkmsg_user *user = file->private_data;
824 size_t len = iov_iter_count(from);
827 if (!user || len > LOG_LINE_MAX)
830 /* Ignore when user logging is disabled. */
831 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
834 /* Ratelimit when not explicitly enabled. */
835 if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
836 if (!___ratelimit(&user->rs, current->comm))
840 buf = kmalloc(len+1, GFP_KERNEL);
845 if (!copy_from_iter_full(buf, len, from)) {
851 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
852 * the decimal value represents 32bit, the lower 3 bit are the log
853 * level, the rest are the log facility.
855 * If no prefix or no userspace facility is specified, we
856 * enforce LOG_USER, to be able to reliably distinguish
857 * kernel-generated messages from userspace-injected ones.
860 if (line[0] == '<') {
864 u = simple_strtoul(line + 1, &endp, 10);
865 if (endp && endp[0] == '>') {
866 level = LOG_LEVEL(u);
867 if (LOG_FACILITY(u) != 0)
868 facility = LOG_FACILITY(u);
875 devkmsg_emit(facility, level, "%s", line);
880 static ssize_t devkmsg_read(struct file *file, char __user *buf,
881 size_t count, loff_t *ppos)
883 struct devkmsg_user *user = file->private_data;
884 struct printk_log *msg;
891 ret = mutex_lock_interruptible(&user->lock);
896 while (user->seq == log_next_seq) {
897 if (file->f_flags & O_NONBLOCK) {
904 ret = wait_event_interruptible(log_wait,
905 user->seq != log_next_seq);
911 if (user->seq < log_first_seq) {
912 /* our last seen message is gone, return error and reset */
913 user->idx = log_first_idx;
914 user->seq = log_first_seq;
920 msg = log_from_idx(user->idx);
921 len = msg_print_ext_header(user->buf, sizeof(user->buf),
923 len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
924 log_dict(msg), msg->dict_len,
925 log_text(msg), msg->text_len);
927 user->idx = log_next(user->idx);
936 if (copy_to_user(buf, user->buf, len)) {
942 mutex_unlock(&user->lock);
947 * Be careful when modifying this function!!!
949 * Only few operations are supported because the device works only with the
950 * entire variable length messages (records). Non-standard values are
951 * returned in the other cases and has been this way for quite some time.
952 * User space applications might depend on this behavior.
954 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
956 struct devkmsg_user *user = file->private_data;
967 /* the first record */
968 user->idx = log_first_idx;
969 user->seq = log_first_seq;
973 * The first record after the last SYSLOG_ACTION_CLEAR,
974 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
975 * changes no global state, and does not clear anything.
977 user->idx = clear_idx;
978 user->seq = clear_seq;
981 /* after the last record */
982 user->idx = log_next_idx;
983 user->seq = log_next_seq;
992 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
994 struct devkmsg_user *user = file->private_data;
998 return EPOLLERR|EPOLLNVAL;
1000 poll_wait(file, &log_wait, wait);
1003 if (user->seq < log_next_seq) {
1004 /* return error when data has vanished underneath us */
1005 if (user->seq < log_first_seq)
1006 ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
1008 ret = EPOLLIN|EPOLLRDNORM;
1010 logbuf_unlock_irq();
1015 static int devkmsg_open(struct inode *inode, struct file *file)
1017 struct devkmsg_user *user;
1020 if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
1023 /* write-only does not need any file context */
1024 if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
1025 err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
1026 SYSLOG_FROM_READER);
1031 user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
1035 ratelimit_default_init(&user->rs);
1036 ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
1038 mutex_init(&user->lock);
1041 user->idx = log_first_idx;
1042 user->seq = log_first_seq;
1043 logbuf_unlock_irq();
1045 file->private_data = user;
1049 static int devkmsg_release(struct inode *inode, struct file *file)
1051 struct devkmsg_user *user = file->private_data;
1056 ratelimit_state_exit(&user->rs);
1058 mutex_destroy(&user->lock);
1063 const struct file_operations kmsg_fops = {
1064 .open = devkmsg_open,
1065 .read = devkmsg_read,
1066 .write_iter = devkmsg_write,
1067 .llseek = devkmsg_llseek,
1068 .poll = devkmsg_poll,
1069 .release = devkmsg_release,
1072 #ifdef CONFIG_CRASH_CORE
1074 * This appends the listed symbols to /proc/vmcore
1076 * /proc/vmcore is used by various utilities, like crash and makedumpfile to
1077 * obtain access to symbols that are otherwise very difficult to locate. These
1078 * symbols are specifically used so that utilities can access and extract the
1079 * dmesg log from a vmcore file after a crash.
1081 void log_buf_vmcoreinfo_setup(void)
1083 VMCOREINFO_SYMBOL(log_buf);
1084 VMCOREINFO_SYMBOL(log_buf_len);
1085 VMCOREINFO_SYMBOL(log_first_idx);
1086 VMCOREINFO_SYMBOL(clear_idx);
1087 VMCOREINFO_SYMBOL(log_next_idx);
1089 * Export struct printk_log size and field offsets. User space tools can
1090 * parse it and detect any changes to structure down the line.
1092 VMCOREINFO_STRUCT_SIZE(printk_log);
1093 VMCOREINFO_OFFSET(printk_log, ts_nsec);
1094 VMCOREINFO_OFFSET(printk_log, len);
1095 VMCOREINFO_OFFSET(printk_log, text_len);
1096 VMCOREINFO_OFFSET(printk_log, dict_len);
1097 #ifdef CONFIG_PRINTK_CALLER
1098 VMCOREINFO_OFFSET(printk_log, caller_id);
1103 /* requested log_buf_len from kernel cmdline */
1104 static unsigned long __initdata new_log_buf_len;
1106 /* we practice scaling the ring buffer by powers of 2 */
1107 static void __init log_buf_len_update(u64 size)
1109 if (size > (u64)LOG_BUF_LEN_MAX) {
1110 size = (u64)LOG_BUF_LEN_MAX;
1111 pr_err("log_buf over 2G is not supported.\n");
1115 size = roundup_pow_of_two(size);
1116 if (size > log_buf_len)
1117 new_log_buf_len = (unsigned long)size;
1120 /* save requested log_buf_len since it's too early to process it */
1121 static int __init log_buf_len_setup(char *str)
1128 size = memparse(str, &str);
1130 log_buf_len_update(size);
1134 early_param("log_buf_len", log_buf_len_setup);
1137 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1139 static void __init log_buf_add_cpu(void)
1141 unsigned int cpu_extra;
1144 * archs should set up cpu_possible_bits properly with
1145 * set_cpu_possible() after setup_arch() but just in
1146 * case lets ensure this is valid.
1148 if (num_possible_cpus() == 1)
1151 cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1153 /* by default this will only continue through for large > 64 CPUs */
1154 if (cpu_extra <= __LOG_BUF_LEN / 2)
1157 pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1158 __LOG_CPU_MAX_BUF_LEN);
1159 pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1161 pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1163 log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1165 #else /* !CONFIG_SMP */
1166 static inline void log_buf_add_cpu(void) {}
1167 #endif /* CONFIG_SMP */
1169 static void __init set_percpu_data_ready(void)
1172 /* Make sure we set this flag only after printk_safe() init is done */
1174 __printk_percpu_data_ready = true;
1177 void __init setup_log_buf(int early)
1179 unsigned long flags;
1184 * Some archs call setup_log_buf() multiple times - first is very
1185 * early, e.g. from setup_arch(), and second - when percpu_areas
1189 set_percpu_data_ready();
1191 if (log_buf != __log_buf)
1194 if (!early && !new_log_buf_len)
1197 if (!new_log_buf_len)
1200 new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
1201 if (unlikely(!new_log_buf)) {
1202 pr_err("log_buf_len: %lu bytes not available\n",
1207 logbuf_lock_irqsave(flags);
1208 log_buf_len = new_log_buf_len;
1209 log_buf = new_log_buf;
1210 new_log_buf_len = 0;
1211 free = __LOG_BUF_LEN - log_next_idx;
1212 memcpy(log_buf, __log_buf, __LOG_BUF_LEN);
1213 logbuf_unlock_irqrestore(flags);
1215 pr_info("log_buf_len: %u bytes\n", log_buf_len);
1216 pr_info("early log buf free: %u(%u%%)\n",
1217 free, (free * 100) / __LOG_BUF_LEN);
1220 static bool __read_mostly ignore_loglevel;
1222 static int __init ignore_loglevel_setup(char *str)
1224 ignore_loglevel = true;
1225 pr_info("debug: ignoring loglevel setting.\n");
1230 early_param("ignore_loglevel", ignore_loglevel_setup);
1231 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1232 MODULE_PARM_DESC(ignore_loglevel,
1233 "ignore loglevel setting (prints all kernel messages to the console)");
1235 static bool suppress_message_printing(int level)
1237 return (level >= console_loglevel && !ignore_loglevel);
1240 #ifdef CONFIG_BOOT_PRINTK_DELAY
1242 static int boot_delay; /* msecs delay after each printk during bootup */
1243 static unsigned long long loops_per_msec; /* based on boot_delay */
1245 static int __init boot_delay_setup(char *str)
1249 lpj = preset_lpj ? preset_lpj : 1000000; /* some guess */
1250 loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1252 get_option(&str, &boot_delay);
1253 if (boot_delay > 10 * 1000)
1256 pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1257 "HZ: %d, loops_per_msec: %llu\n",
1258 boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1261 early_param("boot_delay", boot_delay_setup);
1263 static void boot_delay_msec(int level)
1265 unsigned long long k;
1266 unsigned long timeout;
1268 if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1269 || suppress_message_printing(level)) {
1273 k = (unsigned long long)loops_per_msec * boot_delay;
1275 timeout = jiffies + msecs_to_jiffies(boot_delay);
1280 * use (volatile) jiffies to prevent
1281 * compiler reduction; loop termination via jiffies
1282 * is secondary and may or may not happen.
1284 if (time_after(jiffies, timeout))
1286 touch_nmi_watchdog();
1290 static inline void boot_delay_msec(int level)
1295 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1296 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1298 static size_t print_syslog(unsigned int level, char *buf)
1300 return sprintf(buf, "<%u>", level);
1303 static size_t print_time(u64 ts, char *buf)
1305 unsigned long rem_nsec = do_div(ts, 1000000000);
1307 return sprintf(buf, "[%5lu.%06lu]",
1308 (unsigned long)ts, rem_nsec / 1000);
1311 #ifdef CONFIG_PRINTK_CALLER
1312 static size_t print_caller(u32 id, char *buf)
1316 snprintf(caller, sizeof(caller), "%c%u",
1317 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
1318 return sprintf(buf, "[%6s]", caller);
1321 #define print_caller(id, buf) 0
1324 static size_t print_prefix(const struct printk_log *msg, bool syslog,
1325 bool time, char *buf)
1330 len = print_syslog((msg->facility << 3) | msg->level, buf);
1333 len += print_time(msg->ts_nsec, buf + len);
1335 len += print_caller(msg->caller_id, buf + len);
1337 if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
1345 static size_t msg_print_text(const struct printk_log *msg, bool syslog,
1346 bool time, char *buf, size_t size)
1348 const char *text = log_text(msg);
1349 size_t text_size = msg->text_len;
1351 char prefix[PREFIX_MAX];
1352 const size_t prefix_len = print_prefix(msg, syslog, time, prefix);
1355 const char *next = memchr(text, '\n', text_size);
1359 text_len = next - text;
1361 text_size -= next - text;
1363 text_len = text_size;
1367 if (prefix_len + text_len + 1 >= size - len)
1370 memcpy(buf + len, prefix, prefix_len);
1372 memcpy(buf + len, text, text_len);
1376 /* SYSLOG_ACTION_* buffer size only calculation */
1377 len += prefix_len + text_len + 1;
1386 static int syslog_print(char __user *buf, int size)
1389 struct printk_log *msg;
1392 text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
1401 if (syslog_seq < log_first_seq) {
1402 /* messages are gone, move to first one */
1403 syslog_seq = log_first_seq;
1404 syslog_idx = log_first_idx;
1407 if (syslog_seq == log_next_seq) {
1408 logbuf_unlock_irq();
1413 * To keep reading/counting partial line consistent,
1414 * use printk_time value as of the beginning of a line.
1416 if (!syslog_partial)
1417 syslog_time = printk_time;
1419 skip = syslog_partial;
1420 msg = log_from_idx(syslog_idx);
1421 n = msg_print_text(msg, true, syslog_time, text,
1422 LOG_LINE_MAX + PREFIX_MAX);
1423 if (n - syslog_partial <= size) {
1424 /* message fits into buffer, move forward */
1425 syslog_idx = log_next(syslog_idx);
1427 n -= syslog_partial;
1430 /* partial read(), remember position */
1432 syslog_partial += n;
1435 logbuf_unlock_irq();
1440 if (copy_to_user(buf, text + skip, n)) {
1455 static int syslog_print_all(char __user *buf, int size, bool clear)
1464 text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
1471 * Find first record that fits, including all following records,
1472 * into the user-provided buffer for this dump.
1476 while (seq < log_next_seq) {
1477 struct printk_log *msg = log_from_idx(idx);
1479 len += msg_print_text(msg, true, time, NULL, 0);
1480 idx = log_next(idx);
1484 /* move first record forward until length fits into the buffer */
1487 while (len > size && seq < log_next_seq) {
1488 struct printk_log *msg = log_from_idx(idx);
1490 len -= msg_print_text(msg, true, time, NULL, 0);
1491 idx = log_next(idx);
1495 /* last message fitting into this dump */
1496 next_seq = log_next_seq;
1499 while (len >= 0 && seq < next_seq) {
1500 struct printk_log *msg = log_from_idx(idx);
1501 int textlen = msg_print_text(msg, true, time, text,
1502 LOG_LINE_MAX + PREFIX_MAX);
1504 idx = log_next(idx);
1507 logbuf_unlock_irq();
1508 if (copy_to_user(buf + len, text, textlen))
1514 if (seq < log_first_seq) {
1515 /* messages are gone, move to next one */
1516 seq = log_first_seq;
1517 idx = log_first_idx;
1522 clear_seq = log_next_seq;
1523 clear_idx = log_next_idx;
1525 logbuf_unlock_irq();
1531 static void syslog_clear(void)
1534 clear_seq = log_next_seq;
1535 clear_idx = log_next_idx;
1536 logbuf_unlock_irq();
1539 int do_syslog(int type, char __user *buf, int len, int source)
1542 static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1545 error = check_syslog_permissions(type, source);
1550 case SYSLOG_ACTION_CLOSE: /* Close log */
1552 case SYSLOG_ACTION_OPEN: /* Open log */
1554 case SYSLOG_ACTION_READ: /* Read from log */
1555 if (!buf || len < 0)
1559 if (!access_ok(buf, len))
1561 error = wait_event_interruptible(log_wait,
1562 syslog_seq != log_next_seq);
1565 error = syslog_print(buf, len);
1567 /* Read/clear last kernel messages */
1568 case SYSLOG_ACTION_READ_CLEAR:
1571 /* Read last kernel messages */
1572 case SYSLOG_ACTION_READ_ALL:
1573 if (!buf || len < 0)
1577 if (!access_ok(buf, len))
1579 error = syslog_print_all(buf, len, clear);
1581 /* Clear ring buffer */
1582 case SYSLOG_ACTION_CLEAR:
1585 /* Disable logging to console */
1586 case SYSLOG_ACTION_CONSOLE_OFF:
1587 if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1588 saved_console_loglevel = console_loglevel;
1589 console_loglevel = minimum_console_loglevel;
1591 /* Enable logging to console */
1592 case SYSLOG_ACTION_CONSOLE_ON:
1593 if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1594 console_loglevel = saved_console_loglevel;
1595 saved_console_loglevel = LOGLEVEL_DEFAULT;
1598 /* Set level of messages printed to console */
1599 case SYSLOG_ACTION_CONSOLE_LEVEL:
1600 if (len < 1 || len > 8)
1602 if (len < minimum_console_loglevel)
1603 len = minimum_console_loglevel;
1604 console_loglevel = len;
1605 /* Implicitly re-enable logging to console */
1606 saved_console_loglevel = LOGLEVEL_DEFAULT;
1608 /* Number of chars in the log buffer */
1609 case SYSLOG_ACTION_SIZE_UNREAD:
1611 if (syslog_seq < log_first_seq) {
1612 /* messages are gone, move to first one */
1613 syslog_seq = log_first_seq;
1614 syslog_idx = log_first_idx;
1617 if (source == SYSLOG_FROM_PROC) {
1619 * Short-cut for poll(/"proc/kmsg") which simply checks
1620 * for pending data, not the size; return the count of
1621 * records, not the length.
1623 error = log_next_seq - syslog_seq;
1625 u64 seq = syslog_seq;
1626 u32 idx = syslog_idx;
1627 bool time = syslog_partial ? syslog_time : printk_time;
1629 while (seq < log_next_seq) {
1630 struct printk_log *msg = log_from_idx(idx);
1632 error += msg_print_text(msg, true, time, NULL,
1635 idx = log_next(idx);
1638 error -= syslog_partial;
1640 logbuf_unlock_irq();
1642 /* Size of the log buffer */
1643 case SYSLOG_ACTION_SIZE_BUFFER:
1644 error = log_buf_len;
1654 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1656 return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1660 * Special console_lock variants that help to reduce the risk of soft-lockups.
1661 * They allow to pass console_lock to another printk() call using a busy wait.
1664 #ifdef CONFIG_LOCKDEP
1665 static struct lockdep_map console_owner_dep_map = {
1666 .name = "console_owner"
1670 static DEFINE_RAW_SPINLOCK(console_owner_lock);
1671 static struct task_struct *console_owner;
1672 static bool console_waiter;
1675 * console_lock_spinning_enable - mark beginning of code where another
1676 * thread might safely busy wait
1678 * This basically converts console_lock into a spinlock. This marks
1679 * the section where the console_lock owner can not sleep, because
1680 * there may be a waiter spinning (like a spinlock). Also it must be
1681 * ready to hand over the lock at the end of the section.
1683 static void console_lock_spinning_enable(void)
1685 raw_spin_lock(&console_owner_lock);
1686 console_owner = current;
1687 raw_spin_unlock(&console_owner_lock);
1689 /* The waiter may spin on us after setting console_owner */
1690 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1694 * console_lock_spinning_disable_and_check - mark end of code where another
1695 * thread was able to busy wait and check if there is a waiter
1697 * This is called at the end of the section where spinning is allowed.
1698 * It has two functions. First, it is a signal that it is no longer
1699 * safe to start busy waiting for the lock. Second, it checks if
1700 * there is a busy waiter and passes the lock rights to her.
1702 * Important: Callers lose the lock if there was a busy waiter.
1703 * They must not touch items synchronized by console_lock
1706 * Return: 1 if the lock rights were passed, 0 otherwise.
1708 static int console_lock_spinning_disable_and_check(void)
1712 raw_spin_lock(&console_owner_lock);
1713 waiter = READ_ONCE(console_waiter);
1714 console_owner = NULL;
1715 raw_spin_unlock(&console_owner_lock);
1718 spin_release(&console_owner_dep_map, _THIS_IP_);
1722 /* The waiter is now free to continue */
1723 WRITE_ONCE(console_waiter, false);
1725 spin_release(&console_owner_dep_map, _THIS_IP_);
1728 * Hand off console_lock to waiter. The waiter will perform
1729 * the up(). After this, the waiter is the console_lock owner.
1731 mutex_release(&console_lock_dep_map, _THIS_IP_);
1736 * console_trylock_spinning - try to get console_lock by busy waiting
1738 * This allows to busy wait for the console_lock when the current
1739 * owner is running in specially marked sections. It means that
1740 * the current owner is running and cannot reschedule until it
1741 * is ready to lose the lock.
1743 * Return: 1 if we got the lock, 0 othrewise
1745 static int console_trylock_spinning(void)
1747 struct task_struct *owner = NULL;
1750 unsigned long flags;
1752 if (console_trylock())
1755 printk_safe_enter_irqsave(flags);
1757 raw_spin_lock(&console_owner_lock);
1758 owner = READ_ONCE(console_owner);
1759 waiter = READ_ONCE(console_waiter);
1760 if (!waiter && owner && owner != current) {
1761 WRITE_ONCE(console_waiter, true);
1764 raw_spin_unlock(&console_owner_lock);
1767 * If there is an active printk() writing to the
1768 * consoles, instead of having it write our data too,
1769 * see if we can offload that load from the active
1770 * printer, and do some printing ourselves.
1771 * Go into a spin only if there isn't already a waiter
1772 * spinning, and there is an active printer, and
1773 * that active printer isn't us (recursive printk?).
1776 printk_safe_exit_irqrestore(flags);
1780 /* We spin waiting for the owner to release us */
1781 spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1782 /* Owner will clear console_waiter on hand off */
1783 while (READ_ONCE(console_waiter))
1785 spin_release(&console_owner_dep_map, _THIS_IP_);
1787 printk_safe_exit_irqrestore(flags);
1789 * The owner passed the console lock to us.
1790 * Since we did not spin on console lock, annotate
1791 * this as a trylock. Otherwise lockdep will
1794 mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
1800 * Call the console drivers, asking them to write out
1801 * log_buf[start] to log_buf[end - 1].
1802 * The console_lock must be held.
1804 static void call_console_drivers(const char *ext_text, size_t ext_len,
1805 const char *text, size_t len)
1807 struct console *con;
1809 trace_console_rcuidle(text, len);
1811 for_each_console(con) {
1812 if (exclusive_console && con != exclusive_console)
1814 if (!(con->flags & CON_ENABLED))
1818 if (!cpu_online(smp_processor_id()) &&
1819 !(con->flags & CON_ANYTIME))
1821 if (con->flags & CON_EXTENDED)
1822 con->write(con, ext_text, ext_len);
1824 con->write(con, text, len);
1828 int printk_delay_msec __read_mostly;
1830 static inline void printk_delay(void)
1832 if (unlikely(printk_delay_msec)) {
1833 int m = printk_delay_msec;
1837 touch_nmi_watchdog();
1842 static inline u32 printk_caller_id(void)
1844 return in_task() ? task_pid_nr(current) :
1845 0x80000000 + raw_smp_processor_id();
1849 * Continuation lines are buffered, and not committed to the record buffer
1850 * until the line is complete, or a race forces it. The line fragments
1851 * though, are printed immediately to the consoles to ensure everything has
1852 * reached the console in case of a kernel crash.
1854 static struct cont {
1855 char buf[LOG_LINE_MAX];
1856 size_t len; /* length == 0 means unused buffer */
1857 u32 caller_id; /* printk_caller_id() of first print */
1858 u64 ts_nsec; /* time of first print */
1859 u8 level; /* log level of first message */
1860 u8 facility; /* log facility of first message */
1861 enum log_flags flags; /* prefix, newline flags */
1864 static void cont_flush(void)
1869 log_store(cont.caller_id, cont.facility, cont.level, cont.flags,
1870 cont.ts_nsec, NULL, 0, cont.buf, cont.len);
1874 static bool cont_add(u32 caller_id, int facility, int level,
1875 enum log_flags flags, const char *text, size_t len)
1877 /* If the line gets too long, split it up in separate records. */
1878 if (cont.len + len > sizeof(cont.buf)) {
1884 cont.facility = facility;
1886 cont.caller_id = caller_id;
1887 cont.ts_nsec = local_clock();
1891 memcpy(cont.buf + cont.len, text, len);
1894 // The original flags come from the first line,
1895 // but later continuations can add a newline.
1896 if (flags & LOG_NEWLINE) {
1897 cont.flags |= LOG_NEWLINE;
1904 static size_t log_output(int facility, int level, enum log_flags lflags, const char *dict, size_t dictlen, char *text, size_t text_len)
1906 const u32 caller_id = printk_caller_id();
1909 * If an earlier line was buffered, and we're a continuation
1910 * write from the same context, try to add it to the buffer.
1913 if (cont.caller_id == caller_id && (lflags & LOG_CONT)) {
1914 if (cont_add(caller_id, facility, level, lflags, text, text_len))
1917 /* Otherwise, make sure it's flushed */
1921 /* Skip empty continuation lines that couldn't be added - they just flush */
1922 if (!text_len && (lflags & LOG_CONT))
1925 /* If it doesn't end in a newline, try to buffer the current line */
1926 if (!(lflags & LOG_NEWLINE)) {
1927 if (cont_add(caller_id, facility, level, lflags, text, text_len))
1931 /* Store it in the record log */
1932 return log_store(caller_id, facility, level, lflags, 0,
1933 dict, dictlen, text, text_len);
1936 /* Must be called under logbuf_lock. */
1937 int vprintk_store(int facility, int level,
1938 const char *dict, size_t dictlen,
1939 const char *fmt, va_list args)
1941 static char textbuf[LOG_LINE_MAX];
1942 char *text = textbuf;
1944 enum log_flags lflags = 0;
1947 * The printf needs to come first; we need the syslog
1948 * prefix which might be passed-in as a parameter.
1950 text_len = vscnprintf(text, sizeof(textbuf), fmt, args);
1952 /* mark and strip a trailing newline */
1953 if (text_len && text[text_len-1] == '\n') {
1955 lflags |= LOG_NEWLINE;
1958 /* strip kernel syslog prefix and extract log level or control flags */
1959 if (facility == 0) {
1962 while ((kern_level = printk_get_level(text)) != 0) {
1963 switch (kern_level) {
1965 if (level == LOGLEVEL_DEFAULT)
1966 level = kern_level - '0';
1968 case 'c': /* KERN_CONT */
1977 if (level == LOGLEVEL_DEFAULT)
1978 level = default_message_loglevel;
1981 lflags |= LOG_NEWLINE;
1983 return log_output(facility, level, lflags,
1984 dict, dictlen, text, text_len);
1987 asmlinkage int vprintk_emit(int facility, int level,
1988 const char *dict, size_t dictlen,
1989 const char *fmt, va_list args)
1992 bool in_sched = false, pending_output;
1993 unsigned long flags;
1996 /* Suppress unimportant messages after panic happens */
1997 if (unlikely(suppress_printk))
2000 if (level == LOGLEVEL_SCHED) {
2001 level = LOGLEVEL_DEFAULT;
2005 boot_delay_msec(level);
2008 /* This stops the holder of console_sem just where we want him */
2009 logbuf_lock_irqsave(flags);
2010 curr_log_seq = log_next_seq;
2011 printed_len = vprintk_store(facility, level, dict, dictlen, fmt, args);
2012 pending_output = (curr_log_seq != log_next_seq);
2013 logbuf_unlock_irqrestore(flags);
2015 /* If called from the scheduler, we can not call up(). */
2016 if (!in_sched && pending_output) {
2018 * Disable preemption to avoid being preempted while holding
2019 * console_sem which would prevent anyone from printing to
2024 * Try to acquire and then immediately release the console
2025 * semaphore. The release will print out buffers and wake up
2026 * /dev/kmsg and syslog() users.
2028 if (console_trylock_spinning())
2037 EXPORT_SYMBOL(vprintk_emit);
2039 asmlinkage int vprintk(const char *fmt, va_list args)
2041 return vprintk_func(fmt, args);
2043 EXPORT_SYMBOL(vprintk);
2045 int vprintk_default(const char *fmt, va_list args)
2047 return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
2049 EXPORT_SYMBOL_GPL(vprintk_default);
2052 * printk - print a kernel message
2053 * @fmt: format string
2055 * This is printk(). It can be called from any context. We want it to work.
2057 * We try to grab the console_lock. If we succeed, it's easy - we log the
2058 * output and call the console drivers. If we fail to get the semaphore, we
2059 * place the output into the log buffer and return. The current holder of
2060 * the console_sem will notice the new output in console_unlock(); and will
2061 * send it to the consoles before releasing the lock.
2063 * One effect of this deferred printing is that code which calls printk() and
2064 * then changes console_loglevel may break. This is because console_loglevel
2065 * is inspected when the actual printing occurs.
2070 * See the vsnprintf() documentation for format string extensions over C99.
2072 asmlinkage __visible int printk(const char *fmt, ...)
2077 va_start(args, fmt);
2078 r = vprintk_func(fmt, args);
2083 EXPORT_SYMBOL(printk);
2085 #else /* CONFIG_PRINTK */
2087 #define LOG_LINE_MAX 0
2088 #define PREFIX_MAX 0
2089 #define printk_time false
2091 static u64 syslog_seq;
2092 static u32 syslog_idx;
2093 static u64 console_seq;
2094 static u32 console_idx;
2095 static u64 exclusive_console_stop_seq;
2096 static u64 log_first_seq;
2097 static u32 log_first_idx;
2098 static u64 log_next_seq;
2099 static char *log_text(const struct printk_log *msg) { return NULL; }
2100 static char *log_dict(const struct printk_log *msg) { return NULL; }
2101 static struct printk_log *log_from_idx(u32 idx) { return NULL; }
2102 static u32 log_next(u32 idx) { return 0; }
2103 static ssize_t msg_print_ext_header(char *buf, size_t size,
2104 struct printk_log *msg,
2105 u64 seq) { return 0; }
2106 static ssize_t msg_print_ext_body(char *buf, size_t size,
2107 char *dict, size_t dict_len,
2108 char *text, size_t text_len) { return 0; }
2109 static void console_lock_spinning_enable(void) { }
2110 static int console_lock_spinning_disable_and_check(void) { return 0; }
2111 static void call_console_drivers(const char *ext_text, size_t ext_len,
2112 const char *text, size_t len) {}
2113 static size_t msg_print_text(const struct printk_log *msg, bool syslog,
2114 bool time, char *buf, size_t size) { return 0; }
2115 static bool suppress_message_printing(int level) { return false; }
2117 #endif /* CONFIG_PRINTK */
2119 #ifdef CONFIG_EARLY_PRINTK
2120 struct console *early_console;
2122 asmlinkage __visible void early_printk(const char *fmt, ...)
2132 n = vscnprintf(buf, sizeof(buf), fmt, ap);
2135 early_console->write(early_console, buf, n);
2139 static int __add_preferred_console(char *name, int idx, char *options,
2140 char *brl_options, bool user_specified)
2142 struct console_cmdline *c;
2146 * See if this tty is not yet registered, and
2147 * if we have a slot free.
2149 for (i = 0, c = console_cmdline;
2150 i < MAX_CMDLINECONSOLES && c->name[0];
2152 if (strcmp(c->name, name) == 0 && c->index == idx) {
2154 preferred_console = i;
2156 c->user_specified = true;
2160 if (i == MAX_CMDLINECONSOLES)
2163 preferred_console = i;
2164 strlcpy(c->name, name, sizeof(c->name));
2165 c->options = options;
2166 c->user_specified = user_specified;
2167 braille_set_options(c, brl_options);
2173 static int __init console_msg_format_setup(char *str)
2175 if (!strcmp(str, "syslog"))
2176 console_msg_format = MSG_FORMAT_SYSLOG;
2177 if (!strcmp(str, "default"))
2178 console_msg_format = MSG_FORMAT_DEFAULT;
2181 __setup("console_msg_format=", console_msg_format_setup);
2184 * Set up a console. Called via do_early_param() in init/main.c
2185 * for each "console=" parameter in the boot command line.
2187 static int __init console_setup(char *str)
2189 char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
2190 char *s, *options, *brl_options = NULL;
2196 if (_braille_console_setup(&str, &brl_options))
2200 * Decode str into name, index, options.
2202 if (str[0] >= '0' && str[0] <= '9') {
2203 strcpy(buf, "ttyS");
2204 strncpy(buf + 4, str, sizeof(buf) - 5);
2206 strncpy(buf, str, sizeof(buf) - 1);
2208 buf[sizeof(buf) - 1] = 0;
2209 options = strchr(str, ',');
2213 if (!strcmp(str, "ttya"))
2214 strcpy(buf, "ttyS0");
2215 if (!strcmp(str, "ttyb"))
2216 strcpy(buf, "ttyS1");
2218 for (s = buf; *s; s++)
2219 if (isdigit(*s) || *s == ',')
2221 idx = simple_strtoul(s, NULL, 10);
2224 __add_preferred_console(buf, idx, options, brl_options, true);
2225 console_set_on_cmdline = 1;
2228 __setup("console=", console_setup);
2231 * add_preferred_console - add a device to the list of preferred consoles.
2232 * @name: device name
2233 * @idx: device index
2234 * @options: options for this console
2236 * The last preferred console added will be used for kernel messages
2237 * and stdin/out/err for init. Normally this is used by console_setup
2238 * above to handle user-supplied console arguments; however it can also
2239 * be used by arch-specific code either to override the user or more
2240 * commonly to provide a default console (ie from PROM variables) when
2241 * the user has not supplied one.
2243 int add_preferred_console(char *name, int idx, char *options)
2245 return __add_preferred_console(name, idx, options, NULL, false);
2248 bool console_suspend_enabled = true;
2249 EXPORT_SYMBOL(console_suspend_enabled);
2251 static int __init console_suspend_disable(char *str)
2253 console_suspend_enabled = false;
2256 __setup("no_console_suspend", console_suspend_disable);
2257 module_param_named(console_suspend, console_suspend_enabled,
2258 bool, S_IRUGO | S_IWUSR);
2259 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2260 " and hibernate operations");
2263 * suspend_console - suspend the console subsystem
2265 * This disables printk() while we go into suspend states
2267 void suspend_console(void)
2269 if (!console_suspend_enabled)
2271 pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2273 console_suspended = 1;
2277 void resume_console(void)
2279 if (!console_suspend_enabled)
2282 console_suspended = 0;
2287 * console_cpu_notify - print deferred console messages after CPU hotplug
2290 * If printk() is called from a CPU that is not online yet, the messages
2291 * will be printed on the console only if there are CON_ANYTIME consoles.
2292 * This function is called when a new CPU comes online (or fails to come
2293 * up) or goes offline.
2295 static int console_cpu_notify(unsigned int cpu)
2297 if (!cpuhp_tasks_frozen) {
2298 /* If trylock fails, someone else is doing the printing */
2299 if (console_trylock())
2306 * console_lock - lock the console system for exclusive use.
2308 * Acquires a lock which guarantees that the caller has
2309 * exclusive access to the console system and the console_drivers list.
2311 * Can sleep, returns nothing.
2313 void console_lock(void)
2318 if (console_suspended)
2321 console_may_schedule = 1;
2323 EXPORT_SYMBOL(console_lock);
2326 * console_trylock - try to lock the console system for exclusive use.
2328 * Try to acquire a lock which guarantees that the caller has exclusive
2329 * access to the console system and the console_drivers list.
2331 * returns 1 on success, and 0 on failure to acquire the lock.
2333 int console_trylock(void)
2335 if (down_trylock_console_sem())
2337 if (console_suspended) {
2342 console_may_schedule = 0;
2345 EXPORT_SYMBOL(console_trylock);
2347 int is_console_locked(void)
2349 return console_locked;
2351 EXPORT_SYMBOL(is_console_locked);
2354 * Check if we have any console that is capable of printing while cpu is
2355 * booting or shutting down. Requires console_sem.
2357 static int have_callable_console(void)
2359 struct console *con;
2361 for_each_console(con)
2362 if ((con->flags & CON_ENABLED) &&
2363 (con->flags & CON_ANYTIME))
2370 * Can we actually use the console at this time on this cpu?
2372 * Console drivers may assume that per-cpu resources have been allocated. So
2373 * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
2374 * call them until this CPU is officially up.
2376 static inline int can_use_console(void)
2378 return cpu_online(raw_smp_processor_id()) || have_callable_console();
2382 * console_unlock - unlock the console system
2384 * Releases the console_lock which the caller holds on the console system
2385 * and the console driver list.
2387 * While the console_lock was held, console output may have been buffered
2388 * by printk(). If this is the case, console_unlock(); emits
2389 * the output prior to releasing the lock.
2391 * If there is output waiting, we wake /dev/kmsg and syslog() users.
2393 * console_unlock(); may be called from any context.
2395 void console_unlock(void)
2397 static char ext_text[CONSOLE_EXT_LOG_MAX];
2398 static char text[LOG_LINE_MAX + PREFIX_MAX];
2399 unsigned long flags;
2400 bool do_cond_resched, retry;
2402 if (console_suspended) {
2408 * Console drivers are called with interrupts disabled, so
2409 * @console_may_schedule should be cleared before; however, we may
2410 * end up dumping a lot of lines, for example, if called from
2411 * console registration path, and should invoke cond_resched()
2412 * between lines if allowable. Not doing so can cause a very long
2413 * scheduling stall on a slow console leading to RCU stall and
2414 * softlockup warnings which exacerbate the issue with more
2415 * messages practically incapacitating the system.
2417 * console_trylock() is not able to detect the preemptive
2418 * context reliably. Therefore the value must be stored before
2419 * and cleared after the the "again" goto label.
2421 do_cond_resched = console_may_schedule;
2423 console_may_schedule = 0;
2426 * We released the console_sem lock, so we need to recheck if
2427 * cpu is online and (if not) is there at least one CON_ANYTIME
2430 if (!can_use_console()) {
2437 struct printk_log *msg;
2441 printk_safe_enter_irqsave(flags);
2442 raw_spin_lock(&logbuf_lock);
2443 if (console_seq < log_first_seq) {
2444 len = snprintf(text, sizeof(text),
2445 "** %llu printk messages dropped **\n",
2446 log_first_seq - console_seq);
2448 /* messages are gone, move to first one */
2449 console_seq = log_first_seq;
2450 console_idx = log_first_idx;
2455 if (console_seq == log_next_seq)
2458 msg = log_from_idx(console_idx);
2459 if (suppress_message_printing(msg->level)) {
2461 * Skip record we have buffered and already printed
2462 * directly to the console when we received it, and
2463 * record that has level above the console loglevel.
2465 console_idx = log_next(console_idx);
2470 /* Output to all consoles once old messages replayed. */
2471 if (unlikely(exclusive_console &&
2472 console_seq >= exclusive_console_stop_seq)) {
2473 exclusive_console = NULL;
2476 len += msg_print_text(msg,
2477 console_msg_format & MSG_FORMAT_SYSLOG,
2478 printk_time, text + len, sizeof(text) - len);
2479 if (nr_ext_console_drivers) {
2480 ext_len = msg_print_ext_header(ext_text,
2483 ext_len += msg_print_ext_body(ext_text + ext_len,
2484 sizeof(ext_text) - ext_len,
2485 log_dict(msg), msg->dict_len,
2486 log_text(msg), msg->text_len);
2488 console_idx = log_next(console_idx);
2490 raw_spin_unlock(&logbuf_lock);
2493 * While actively printing out messages, if another printk()
2494 * were to occur on another CPU, it may wait for this one to
2495 * finish. This task can not be preempted if there is a
2496 * waiter waiting to take over.
2498 console_lock_spinning_enable();
2500 stop_critical_timings(); /* don't trace print latency */
2501 call_console_drivers(ext_text, ext_len, text, len);
2502 start_critical_timings();
2504 if (console_lock_spinning_disable_and_check()) {
2505 printk_safe_exit_irqrestore(flags);
2509 printk_safe_exit_irqrestore(flags);
2511 if (do_cond_resched)
2517 raw_spin_unlock(&logbuf_lock);
2522 * Someone could have filled up the buffer again, so re-check if there's
2523 * something to flush. In case we cannot trylock the console_sem again,
2524 * there's a new owner and the console_unlock() from them will do the
2525 * flush, no worries.
2527 raw_spin_lock(&logbuf_lock);
2528 retry = console_seq != log_next_seq;
2529 raw_spin_unlock(&logbuf_lock);
2530 printk_safe_exit_irqrestore(flags);
2532 if (retry && console_trylock())
2535 EXPORT_SYMBOL(console_unlock);
2538 * console_conditional_schedule - yield the CPU if required
2540 * If the console code is currently allowed to sleep, and
2541 * if this CPU should yield the CPU to another task, do
2544 * Must be called within console_lock();.
2546 void __sched console_conditional_schedule(void)
2548 if (console_may_schedule)
2551 EXPORT_SYMBOL(console_conditional_schedule);
2553 void console_unblank(void)
2558 * console_unblank can no longer be called in interrupt context unless
2559 * oops_in_progress is set to 1..
2561 if (oops_in_progress) {
2562 if (down_trylock_console_sem() != 0)
2568 console_may_schedule = 0;
2570 if ((c->flags & CON_ENABLED) && c->unblank)
2576 * console_flush_on_panic - flush console content on panic
2577 * @mode: flush all messages in buffer or just the pending ones
2579 * Immediately output all pending messages no matter what.
2581 void console_flush_on_panic(enum con_flush_mode mode)
2584 * If someone else is holding the console lock, trylock will fail
2585 * and may_schedule may be set. Ignore and proceed to unlock so
2586 * that messages are flushed out. As this can be called from any
2587 * context and we don't want to get preempted while flushing,
2588 * ensure may_schedule is cleared.
2591 console_may_schedule = 0;
2593 if (mode == CONSOLE_REPLAY_ALL) {
2594 unsigned long flags;
2596 logbuf_lock_irqsave(flags);
2597 console_seq = log_first_seq;
2598 console_idx = log_first_idx;
2599 logbuf_unlock_irqrestore(flags);
2605 * Return the console tty driver structure and its associated index
2607 struct tty_driver *console_device(int *index)
2610 struct tty_driver *driver = NULL;
2613 for_each_console(c) {
2616 driver = c->device(c, index);
2625 * Prevent further output on the passed console device so that (for example)
2626 * serial drivers can disable console output before suspending a port, and can
2627 * re-enable output afterwards.
2629 void console_stop(struct console *console)
2632 console->flags &= ~CON_ENABLED;
2635 EXPORT_SYMBOL(console_stop);
2637 void console_start(struct console *console)
2640 console->flags |= CON_ENABLED;
2643 EXPORT_SYMBOL(console_start);
2645 static int __read_mostly keep_bootcon;
2647 static int __init keep_bootcon_setup(char *str)
2650 pr_info("debug: skip boot console de-registration.\n");
2655 early_param("keep_bootcon", keep_bootcon_setup);
2658 * This is called by register_console() to try to match
2659 * the newly registered console with any of the ones selected
2660 * by either the command line or add_preferred_console() and
2663 * Care need to be taken with consoles that are statically
2664 * enabled such as netconsole
2666 static int try_enable_new_console(struct console *newcon, bool user_specified)
2668 struct console_cmdline *c;
2671 for (i = 0, c = console_cmdline;
2672 i < MAX_CMDLINECONSOLES && c->name[0];
2674 if (c->user_specified != user_specified)
2676 if (!newcon->match ||
2677 newcon->match(newcon, c->name, c->index, c->options) != 0) {
2678 /* default matching */
2679 BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
2680 if (strcmp(c->name, newcon->name) != 0)
2682 if (newcon->index >= 0 &&
2683 newcon->index != c->index)
2685 if (newcon->index < 0)
2686 newcon->index = c->index;
2688 if (_braille_register_console(newcon, c))
2691 if (newcon->setup &&
2692 (err = newcon->setup(newcon, c->options)) != 0)
2695 newcon->flags |= CON_ENABLED;
2696 if (i == preferred_console) {
2697 newcon->flags |= CON_CONSDEV;
2698 has_preferred_console = true;
2704 * Some consoles, such as pstore and netconsole, can be enabled even
2705 * without matching. Accept the pre-enabled consoles only when match()
2706 * and setup() had a chance to be called.
2708 if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
2715 * The console driver calls this routine during kernel initialization
2716 * to register the console printing procedure with printk() and to
2717 * print any messages that were printed by the kernel before the
2718 * console driver was initialized.
2720 * This can happen pretty early during the boot process (because of
2721 * early_printk) - sometimes before setup_arch() completes - be careful
2722 * of what kernel features are used - they may not be initialised yet.
2724 * There are two types of consoles - bootconsoles (early_printk) and
2725 * "real" consoles (everything which is not a bootconsole) which are
2726 * handled differently.
2727 * - Any number of bootconsoles can be registered at any time.
2728 * - As soon as a "real" console is registered, all bootconsoles
2729 * will be unregistered automatically.
2730 * - Once a "real" console is registered, any attempt to register a
2731 * bootconsoles will be rejected
2733 void register_console(struct console *newcon)
2735 unsigned long flags;
2736 struct console *bcon = NULL;
2739 for_each_console(bcon) {
2740 if (WARN(bcon == newcon, "console '%s%d' already registered\n",
2741 bcon->name, bcon->index))
2746 * before we register a new CON_BOOT console, make sure we don't
2747 * already have a valid console
2749 if (newcon->flags & CON_BOOT) {
2750 for_each_console(bcon) {
2751 if (!(bcon->flags & CON_BOOT)) {
2752 pr_info("Too late to register bootconsole %s%d\n",
2753 newcon->name, newcon->index);
2759 if (console_drivers && console_drivers->flags & CON_BOOT)
2760 bcon = console_drivers;
2762 if (!has_preferred_console || bcon || !console_drivers)
2763 has_preferred_console = preferred_console >= 0;
2766 * See if we want to use this console driver. If we
2767 * didn't select a console we take the first one
2768 * that registers here.
2770 if (!has_preferred_console) {
2771 if (newcon->index < 0)
2773 if (newcon->setup == NULL ||
2774 newcon->setup(newcon, NULL) == 0) {
2775 newcon->flags |= CON_ENABLED;
2776 if (newcon->device) {
2777 newcon->flags |= CON_CONSDEV;
2778 has_preferred_console = true;
2783 /* See if this console matches one we selected on the command line */
2784 err = try_enable_new_console(newcon, true);
2786 /* If not, try to match against the platform default(s) */
2788 err = try_enable_new_console(newcon, false);
2790 /* printk() messages are not printed to the Braille console. */
2791 if (err || newcon->flags & CON_BRL)
2795 * If we have a bootconsole, and are switching to a real console,
2796 * don't print everything out again, since when the boot console, and
2797 * the real console are the same physical device, it's annoying to
2798 * see the beginning boot messages twice
2800 if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
2801 newcon->flags &= ~CON_PRINTBUFFER;
2804 * Put this console in the list - keep the
2805 * preferred driver at the head of the list.
2808 if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
2809 newcon->next = console_drivers;
2810 console_drivers = newcon;
2812 newcon->next->flags &= ~CON_CONSDEV;
2813 /* Ensure this flag is always set for the head of the list */
2814 newcon->flags |= CON_CONSDEV;
2816 newcon->next = console_drivers->next;
2817 console_drivers->next = newcon;
2820 if (newcon->flags & CON_EXTENDED)
2821 nr_ext_console_drivers++;
2823 if (newcon->flags & CON_PRINTBUFFER) {
2825 * console_unlock(); will print out the buffered messages
2828 logbuf_lock_irqsave(flags);
2830 * We're about to replay the log buffer. Only do this to the
2831 * just-registered console to avoid excessive message spam to
2832 * the already-registered consoles.
2834 * Set exclusive_console with disabled interrupts to reduce
2835 * race window with eventual console_flush_on_panic() that
2836 * ignores console_lock.
2838 exclusive_console = newcon;
2839 exclusive_console_stop_seq = console_seq;
2840 console_seq = syslog_seq;
2841 console_idx = syslog_idx;
2842 logbuf_unlock_irqrestore(flags);
2845 console_sysfs_notify();
2848 * By unregistering the bootconsoles after we enable the real console
2849 * we get the "console xxx enabled" message on all the consoles -
2850 * boot consoles, real consoles, etc - this is to ensure that end
2851 * users know there might be something in the kernel's log buffer that
2852 * went to the bootconsole (that they do not see on the real console)
2854 pr_info("%sconsole [%s%d] enabled\n",
2855 (newcon->flags & CON_BOOT) ? "boot" : "" ,
2856 newcon->name, newcon->index);
2858 ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
2860 /* We need to iterate through all boot consoles, to make
2861 * sure we print everything out, before we unregister them.
2863 for_each_console(bcon)
2864 if (bcon->flags & CON_BOOT)
2865 unregister_console(bcon);
2868 EXPORT_SYMBOL(register_console);
2870 int unregister_console(struct console *console)
2872 struct console *con;
2875 pr_info("%sconsole [%s%d] disabled\n",
2876 (console->flags & CON_BOOT) ? "boot" : "" ,
2877 console->name, console->index);
2879 res = _braille_unregister_console(console);
2887 if (console_drivers == console) {
2888 console_drivers=console->next;
2891 for_each_console(con) {
2892 if (con->next == console) {
2893 con->next = console->next;
2901 goto out_disable_unlock;
2903 if (console->flags & CON_EXTENDED)
2904 nr_ext_console_drivers--;
2907 * If this isn't the last console and it has CON_CONSDEV set, we
2908 * need to set it on the next preferred console.
2910 if (console_drivers != NULL && console->flags & CON_CONSDEV)
2911 console_drivers->flags |= CON_CONSDEV;
2913 console->flags &= ~CON_ENABLED;
2915 console_sysfs_notify();
2918 res = console->exit(console);
2923 console->flags &= ~CON_ENABLED;
2928 EXPORT_SYMBOL(unregister_console);
2931 * Initialize the console device. This is called *early*, so
2932 * we can't necessarily depend on lots of kernel help here.
2933 * Just do some early initializations, and do the complex setup
2936 void __init console_init(void)
2940 initcall_entry_t *ce;
2942 /* Setup the default TTY line discipline. */
2946 * set up the console device so that later boot sequences can
2947 * inform about problems etc..
2949 ce = __con_initcall_start;
2950 trace_initcall_level("console");
2951 while (ce < __con_initcall_end) {
2952 call = initcall_from_entry(ce);
2953 trace_initcall_start(call);
2955 trace_initcall_finish(call, ret);
2961 * Some boot consoles access data that is in the init section and which will
2962 * be discarded after the initcalls have been run. To make sure that no code
2963 * will access this data, unregister the boot consoles in a late initcall.
2965 * If for some reason, such as deferred probe or the driver being a loadable
2966 * module, the real console hasn't registered yet at this point, there will
2967 * be a brief interval in which no messages are logged to the console, which
2968 * makes it difficult to diagnose problems that occur during this time.
2970 * To mitigate this problem somewhat, only unregister consoles whose memory
2971 * intersects with the init section. Note that all other boot consoles will
2972 * get unregistred when the real preferred console is registered.
2974 static int __init printk_late_init(void)
2976 struct console *con;
2979 for_each_console(con) {
2980 if (!(con->flags & CON_BOOT))
2983 /* Check addresses that might be used for enabled consoles. */
2984 if (init_section_intersects(con, sizeof(*con)) ||
2985 init_section_contains(con->write, 0) ||
2986 init_section_contains(con->read, 0) ||
2987 init_section_contains(con->device, 0) ||
2988 init_section_contains(con->unblank, 0) ||
2989 init_section_contains(con->data, 0)) {
2991 * Please, consider moving the reported consoles out
2992 * of the init section.
2994 pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
2995 con->name, con->index);
2996 unregister_console(con);
2999 ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
3000 console_cpu_notify);
3002 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
3003 console_cpu_notify, NULL);
3007 late_initcall(printk_late_init);
3009 #if defined CONFIG_PRINTK
3011 * Delayed printk version, for scheduler-internal messages:
3013 #define PRINTK_PENDING_WAKEUP 0x01
3014 #define PRINTK_PENDING_OUTPUT 0x02
3016 static DEFINE_PER_CPU(int, printk_pending);
3018 static void wake_up_klogd_work_func(struct irq_work *irq_work)
3020 int pending = __this_cpu_xchg(printk_pending, 0);
3022 if (pending & PRINTK_PENDING_OUTPUT) {
3023 /* If trylock fails, someone else is doing the printing */
3024 if (console_trylock())
3028 if (pending & PRINTK_PENDING_WAKEUP)
3029 wake_up_interruptible(&log_wait);
3032 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = {
3033 .func = wake_up_klogd_work_func,
3034 .flags = ATOMIC_INIT(IRQ_WORK_LAZY),
3037 void wake_up_klogd(void)
3039 if (!printk_percpu_data_ready())
3043 if (waitqueue_active(&log_wait)) {
3044 this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
3045 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3050 void defer_console_output(void)
3052 if (!printk_percpu_data_ready())
3056 __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
3057 irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3061 int vprintk_deferred(const char *fmt, va_list args)
3065 r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
3066 defer_console_output();
3071 int printk_deferred(const char *fmt, ...)
3076 va_start(args, fmt);
3077 r = vprintk_deferred(fmt, args);
3084 * printk rate limiting, lifted from the networking subsystem.
3086 * This enforces a rate limit: not more than 10 kernel messages
3087 * every 5s to make a denial-of-service attack impossible.
3089 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
3091 int __printk_ratelimit(const char *func)
3093 return ___ratelimit(&printk_ratelimit_state, func);
3095 EXPORT_SYMBOL(__printk_ratelimit);
3098 * printk_timed_ratelimit - caller-controlled printk ratelimiting
3099 * @caller_jiffies: pointer to caller's state
3100 * @interval_msecs: minimum interval between prints
3102 * printk_timed_ratelimit() returns true if more than @interval_msecs
3103 * milliseconds have elapsed since the last time printk_timed_ratelimit()
3106 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
3107 unsigned int interval_msecs)
3109 unsigned long elapsed = jiffies - *caller_jiffies;
3111 if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
3114 *caller_jiffies = jiffies;
3117 EXPORT_SYMBOL(printk_timed_ratelimit);
3119 static DEFINE_SPINLOCK(dump_list_lock);
3120 static LIST_HEAD(dump_list);
3123 * kmsg_dump_register - register a kernel log dumper.
3124 * @dumper: pointer to the kmsg_dumper structure
3126 * Adds a kernel log dumper to the system. The dump callback in the
3127 * structure will be called when the kernel oopses or panics and must be
3128 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
3130 int kmsg_dump_register(struct kmsg_dumper *dumper)
3132 unsigned long flags;
3135 /* The dump callback needs to be set */
3139 spin_lock_irqsave(&dump_list_lock, flags);
3140 /* Don't allow registering multiple times */
3141 if (!dumper->registered) {
3142 dumper->registered = 1;
3143 list_add_tail_rcu(&dumper->list, &dump_list);
3146 spin_unlock_irqrestore(&dump_list_lock, flags);
3150 EXPORT_SYMBOL_GPL(kmsg_dump_register);
3153 * kmsg_dump_unregister - unregister a kmsg dumper.
3154 * @dumper: pointer to the kmsg_dumper structure
3156 * Removes a dump device from the system. Returns zero on success and
3157 * %-EINVAL otherwise.
3159 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
3161 unsigned long flags;
3164 spin_lock_irqsave(&dump_list_lock, flags);
3165 if (dumper->registered) {
3166 dumper->registered = 0;
3167 list_del_rcu(&dumper->list);
3170 spin_unlock_irqrestore(&dump_list_lock, flags);
3175 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
3177 static bool always_kmsg_dump;
3178 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
3180 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
3183 case KMSG_DUMP_PANIC:
3185 case KMSG_DUMP_OOPS:
3187 case KMSG_DUMP_EMERG:
3189 case KMSG_DUMP_SHUTDOWN:
3195 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
3198 * kmsg_dump - dump kernel log to kernel message dumpers.
3199 * @reason: the reason (oops, panic etc) for dumping
3201 * Call each of the registered dumper's dump() callback, which can
3202 * retrieve the kmsg records with kmsg_dump_get_line() or
3203 * kmsg_dump_get_buffer().
3205 void kmsg_dump(enum kmsg_dump_reason reason)
3207 struct kmsg_dumper *dumper;
3208 unsigned long flags;
3211 list_for_each_entry_rcu(dumper, &dump_list, list) {
3212 enum kmsg_dump_reason max_reason = dumper->max_reason;
3215 * If client has not provided a specific max_reason, default
3216 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
3218 if (max_reason == KMSG_DUMP_UNDEF) {
3219 max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
3222 if (reason > max_reason)
3225 /* initialize iterator with data about the stored records */
3226 dumper->active = true;
3228 logbuf_lock_irqsave(flags);
3229 dumper->cur_seq = clear_seq;
3230 dumper->cur_idx = clear_idx;
3231 dumper->next_seq = log_next_seq;
3232 dumper->next_idx = log_next_idx;
3233 logbuf_unlock_irqrestore(flags);
3235 /* invoke dumper which will iterate over records */
3236 dumper->dump(dumper, reason);
3238 /* reset iterator */
3239 dumper->active = false;
3245 * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
3246 * @dumper: registered kmsg dumper
3247 * @syslog: include the "<4>" prefixes
3248 * @line: buffer to copy the line to
3249 * @size: maximum size of the buffer
3250 * @len: length of line placed into buffer
3252 * Start at the beginning of the kmsg buffer, with the oldest kmsg
3253 * record, and copy one record into the provided buffer.
3255 * Consecutive calls will return the next available record moving
3256 * towards the end of the buffer with the youngest messages.
3258 * A return value of FALSE indicates that there are no more records to
3261 * The function is similar to kmsg_dump_get_line(), but grabs no locks.
3263 bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
3264 char *line, size_t size, size_t *len)
3266 struct printk_log *msg;
3270 if (!dumper->active)
3273 if (dumper->cur_seq < log_first_seq) {
3274 /* messages are gone, move to first available one */
3275 dumper->cur_seq = log_first_seq;
3276 dumper->cur_idx = log_first_idx;
3280 if (dumper->cur_seq >= log_next_seq)
3283 msg = log_from_idx(dumper->cur_idx);
3284 l = msg_print_text(msg, syslog, printk_time, line, size);
3286 dumper->cur_idx = log_next(dumper->cur_idx);
3296 * kmsg_dump_get_line - retrieve one kmsg log line
3297 * @dumper: registered kmsg dumper
3298 * @syslog: include the "<4>" prefixes
3299 * @line: buffer to copy the line to
3300 * @size: maximum size of the buffer
3301 * @len: length of line placed into buffer
3303 * Start at the beginning of the kmsg buffer, with the oldest kmsg
3304 * record, and copy one record into the provided buffer.
3306 * Consecutive calls will return the next available record moving
3307 * towards the end of the buffer with the youngest messages.
3309 * A return value of FALSE indicates that there are no more records to
3312 bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
3313 char *line, size_t size, size_t *len)
3315 unsigned long flags;
3318 logbuf_lock_irqsave(flags);
3319 ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
3320 logbuf_unlock_irqrestore(flags);
3324 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
3327 * kmsg_dump_get_buffer - copy kmsg log lines
3328 * @dumper: registered kmsg dumper
3329 * @syslog: include the "<4>" prefixes
3330 * @buf: buffer to copy the line to
3331 * @size: maximum size of the buffer
3332 * @len: length of line placed into buffer
3334 * Start at the end of the kmsg buffer and fill the provided buffer
3335 * with as many of the the *youngest* kmsg records that fit into it.
3336 * If the buffer is large enough, all available kmsg records will be
3337 * copied with a single call.
3339 * Consecutive calls will fill the buffer with the next block of
3340 * available older records, not including the earlier retrieved ones.
3342 * A return value of FALSE indicates that there are no more records to
3345 bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
3346 char *buf, size_t size, size_t *len)
3348 unsigned long flags;
3355 bool time = printk_time;
3357 if (!dumper->active)
3360 logbuf_lock_irqsave(flags);
3361 if (dumper->cur_seq < log_first_seq) {
3362 /* messages are gone, move to first available one */
3363 dumper->cur_seq = log_first_seq;
3364 dumper->cur_idx = log_first_idx;
3368 if (dumper->cur_seq >= dumper->next_seq) {
3369 logbuf_unlock_irqrestore(flags);
3373 /* calculate length of entire buffer */
3374 seq = dumper->cur_seq;
3375 idx = dumper->cur_idx;
3376 while (seq < dumper->next_seq) {
3377 struct printk_log *msg = log_from_idx(idx);
3379 l += msg_print_text(msg, true, time, NULL, 0);
3380 idx = log_next(idx);
3384 /* move first record forward until length fits into the buffer */
3385 seq = dumper->cur_seq;
3386 idx = dumper->cur_idx;
3387 while (l >= size && seq < dumper->next_seq) {
3388 struct printk_log *msg = log_from_idx(idx);
3390 l -= msg_print_text(msg, true, time, NULL, 0);
3391 idx = log_next(idx);
3395 /* last message in next interation */
3400 while (seq < dumper->next_seq) {
3401 struct printk_log *msg = log_from_idx(idx);
3403 l += msg_print_text(msg, syslog, time, buf + l, size - l);
3404 idx = log_next(idx);
3408 dumper->next_seq = next_seq;
3409 dumper->next_idx = next_idx;
3411 logbuf_unlock_irqrestore(flags);
3417 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
3420 * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
3421 * @dumper: registered kmsg dumper
3423 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3424 * kmsg_dump_get_buffer() can be called again and used multiple
3425 * times within the same dumper.dump() callback.
3427 * The function is similar to kmsg_dump_rewind(), but grabs no locks.
3429 void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
3431 dumper->cur_seq = clear_seq;
3432 dumper->cur_idx = clear_idx;
3433 dumper->next_seq = log_next_seq;
3434 dumper->next_idx = log_next_idx;
3438 * kmsg_dump_rewind - reset the iterator
3439 * @dumper: registered kmsg dumper
3441 * Reset the dumper's iterator so that kmsg_dump_get_line() and
3442 * kmsg_dump_get_buffer() can be called again and used multiple
3443 * times within the same dumper.dump() callback.
3445 void kmsg_dump_rewind(struct kmsg_dumper *dumper)
3447 unsigned long flags;
3449 logbuf_lock_irqsave(flags);
3450 kmsg_dump_rewind_nolock(dumper);
3451 logbuf_unlock_irqrestore(flags);
3453 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);