diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg
index bb820be48179000dd85472ca5d02286778880aeb..fff817efa508f529559ac199bc3b5507dfd7a325 100644
--- a/Documentation/ABI/testing/dev-kmsg
+++ b/Documentation/ABI/testing/dev-kmsg
@@ -98,4 +98,13 @@ Description: The /dev/kmsg character device node provides userspace access
logic is used internally when messages are printed to the
console, /proc/kmsg or the syslog() syscall.
+ By default, kernel tries to avoid fragments by concatenating
+ when it can and fragments are rare; however, when extended
+ console support is enabled, the in-kernel concatenation is
+ disabled and /dev/kmsg output will contain more fragments. If
+ the log consumer performs concatenation, the end result
+ should be the same. In the future, the in-kernel concatenation
+ may be removed entirely and /dev/kmsg users are recommended to
+ implement fragment handling.
+
Users: dmesg(1), userspace kernel log consumers
diff --git a/include/linux/console.h b/include/linux/console.h
index 9f50fb413c11cbfab760acf79fe76e10062f4c6f..bd194343c3460d85730e53ef340ca8337e5827a1 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -115,6 +115,7 @@ static inline int con_debug_leave(void)
#define CON_BOOT (8)
#define CON_ANYTIME (16) /* Safe to call when cpu is offline */
#define CON_BRL (32) /* Used for a braille device */
+#define CON_EXTENDED (64) /* Use the extended output format a la /dev/kmsg */
struct console {
char name[16];
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 51ce4f1838b34808a8776550d11b9c7cb42db9af..ae980dc3ac1eab4da9772f568f9f9f57776b609d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -84,6 +84,18 @@ static struct lockdep_map console_lock_dep_map = {
};
#endif
+/*
+ * Number of registered extended console drivers.
+ *
+ * If extended consoles are present, in-kernel cont reassembly is disabled
+ * and each fragment is stored as a separate log entry with proper
+ * continuation flag so that every emitted message has full metadata. This
+ * doesn't change the result for regular consoles or /proc/kmsg. For
+ * /dev/kmsg, as long as the reader concatenates messages according to
+ * consecutive continuation flags, the end result should be the same too.
+ */
+static int nr_ext_console_drivers;
+
/*
* Helper macros to handle lockdep when locking/unlocking console_sem. We use
* macros instead of functions so that _RET_IP_ contains useful information.
@@ -195,7 +207,7 @@ static int console_may_schedule;
* need to be changed in the future, when the requirements change.
*
* /dev/kmsg exports the structured data in the following line format:
- * "level,sequnum,timestamp;<message text>\n"
+ * "<level>,<sequnum>,<timestamp>,<contflag>;<message text>\n"
*
* The optional key/value pairs are attached as continuation lines starting
* with a space character and terminated by a newline. All possible
@@ -1417,7 +1429,9 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
* log_buf[start] to log_buf[end - 1].
* The console_lock must be held.
*/
-static void call_console_drivers(int level, const char *text, size_t len)
+static void call_console_drivers(int level,
+ const char *ext_text, size_t ext_len,
+ const char *text, size_t len)
{
struct console *con;
@@ -1438,7 +1452,10 @@ static void call_console_drivers(int level, const char *text, size_t len)
if (!cpu_online(smp_processor_id()) &&
!(con->flags & CON_ANYTIME))
continue;
- con->write(con, text, len);
+ if (con->flags & CON_EXTENDED)
+ con->write(con, ext_text, ext_len);
+ else
+ con->write(con, text, len);
}
}
@@ -1581,8 +1598,12 @@ static bool cont_add(int facility, int level, const char *text, size_t len)
if (cont.len && cont.flushed)
return false;
- if (cont.len + len > sizeof(cont.buf)) {
- /* the line gets too long, split it up in separate records */
+ /*
+ * If ext consoles are present, flush and skip in-kernel
+ * continuation. See nr_ext_console_drivers definition. Also, if
+ * the line gets too long, split it up in separate records.
+ */
+ if (nr_ext_console_drivers || cont.len + len > sizeof(cont.buf)) {
cont_flush(LOG_CONT);
return false;
}
@@ -1917,9 +1938,19 @@ static struct cont {
u8 level;
bool flushed:1;
} cont;
+static char *log_text(const struct printk_log *msg) { return NULL; }
+static char *log_dict(const struct printk_log *msg) { return NULL; }
static struct printk_log *log_from_idx(u32 idx) { return NULL; }
static u32 log_next(u32 idx) { return 0; }
-static void call_console_drivers(int level, const char *text, size_t len) {}
+static ssize_t msg_print_ext_header(char *buf, size_t size,
+ struct printk_log *msg, u64 seq,
+ enum log_flags prev_flags) { return 0; }
+static ssize_t msg_print_ext_body(char *buf, size_t size,
+ char *dict, size_t dict_len,
+ char *text, size_t text_len) { return 0; }
+static void call_console_drivers(int level,
+ const char *ext_text, size_t ext_len,
+ const char *text, size_t len) {}
static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
bool syslog, char *buf, size_t size) { return 0; }
static size_t cont_print_text(char *text, size_t size) { return 0; }
@@ -2172,7 +2203,7 @@ static void console_cont_flush(char *text, size_t size)
len = cont_print_text(text, size);
raw_spin_unlock(&logbuf_lock);
stop_critical_timings();
- call_console_drivers(cont.level, text, len);
+ call_console_drivers(cont.level, NULL, 0, text, len);
start_critical_timings();
local_irq_restore(flags);
return;
@@ -2196,6 +2227,7 @@ static void console_cont_flush(char *text, size_t size)
*/
void console_unlock(void)
{
+ static char ext_text[CONSOLE_EXT_LOG_MAX];
static char text[LOG_LINE_MAX + PREFIX_MAX];
static u64 seen_seq;
unsigned long flags;
@@ -2214,6 +2246,7 @@ void console_unlock(void)
again:
for (;;) {
struct printk_log *msg;
+ size_t ext_len = 0;
size_t len;
int level;
@@ -2259,13 +2292,22 @@ void console_unlock(void)
level = msg->level;
len += msg_print_text(msg, console_prev, false,
text + len, sizeof(text) - len);
+ if (nr_ext_console_drivers) {
+ ext_len = msg_print_ext_header(ext_text,
+ sizeof(ext_text),
+ msg, console_seq, console_prev);
+ ext_len += msg_print_ext_body(ext_text + ext_len,
+ sizeof(ext_text) - ext_len,
+ log_dict(msg), msg->dict_len,
+ log_text(msg), msg->text_len);
+ }
console_idx = log_next(console_idx);
console_seq++;
console_prev = msg->flags;
raw_spin_unlock(&logbuf_lock);
stop_critical_timings(); /* don't trace print latency */
- call_console_drivers(level, text, len);
+ call_console_drivers(level, ext_text, ext_len, text, len);
start_critical_timings();
local_irq_restore(flags);
}
@@ -2521,6 +2563,11 @@ void register_console(struct console *newcon)
newcon->next = console_drivers->next;
console_drivers->next = newcon;
}
+
+ if (newcon->flags & CON_EXTENDED)
+ if (!nr_ext_console_drivers++)
+ pr_info("printk: continuation disabled due to ext consoles, expect more fragments in /dev/kmsg\n");
+
if (newcon->flags & CON_PRINTBUFFER) {
/*
* console_unlock(); will print out the buffered messages
@@ -2593,6 +2640,9 @@ int unregister_console(struct console *console)
}
}
+ if (!res && (console->flags & CON_EXTENDED))
+ nr_ext_console_drivers--;
+
/*
* If this isn't the last console and it has CON_CONSDEV set, we
* need to set it on the next preferred console.