MFC r298819:

sys/kern: spelling fixes in comments.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Clean up timestamps in msgbuf code. The timestamps should now be
inserted after the priority token thus cleaning up the output.
- Remove the needless double internal do_add_char function.
- Resolve a possible deadlock if interrupts are
disabled and getnanotime is called

Reviewed by: bde kmacy, avg, sbruno (various versions)
Approved by: cperciva
MFC after: 2 weeks

Add a timestamp to the msgbuf output in order to determine when when
messages were printed.

This can be enabled with the kern.msgbuf_show_timestamp sysctl

PR: kern/161553
Reviewed by: avg
Submitted by: Arnaud Lacombe <lacombar@gmail.com>
Approved by: cperciva
MFC after: 1 month

Fix a bug introduced in revision 222537.

In msgbuf_reinit() and msgbuf_init(), we weren't initializing the mutex.
Depending on the contents of memory, the LO_INITIALIZED flag might be
set on the mutex (either due to a warm reboot, and the message buffer
remaining in place, or due to garbage in memory) and in that case, with
INVARIANTS turned on, we would trigger an assertion that the mutex had
already been initialized.

Fix this by bzeroing the message buffer mutex for the _init() and _reinit()
paths.

Reported by: mdf

Fix apparent garbage in the message buffer.

While we have had a fix in place (options PRINTF_BUFR_SIZE=128) to fix
scrambled console output, the message buffer and syslog were still getting
log messages one character at a time. While all of the characters still
made it into the log (courtesy of atomic operations), they were often
interleaved when there were multiple threads writing to the buffer at the
same time.

This fixes message buffer accesses to use buffering logic as well, so that
strings that are less than PRINTF_BUFR_SIZE will be put into the message
buffer atomically. So now dmesg output should look the same as console
output.

subr_msgbuf.c: Convert most message buffer calls to use a new spin
lock instead of atomic variables in some places.

Add a new routine, msgbuf_addstr(), that adds a
NUL-terminated string to a message buffer. This
takes a priority argument, which allows us to
eliminate some races (at least in the the string
at a time case) that are present in the
implementation of msglogchar(). (dangling and
lastpri are static variables, and are subject to
races when multiple callers are present.)

msgbuf_addstr() also allows the caller to request
that carriage returns be stripped out of the
string. This matches the behavior of msglogchar(),
but in testing so far it doesn't appear that any
newlines are being stripped out. So the carriage
return removal functionality may be a candidate
for removal later on if further analysis shows
that it isn't necessary.

subr_prf.c: Add a new msglogstr() routine that calls
msgbuf_logstr().

Rename putcons() to putbuf(). This now handles
buffered output to the message log as well as
the console. Also, remove the logic in putcons()
(now putbuf()) that added a carriage return before
a newline. The console path was the only path that
needed it, and cnputc() (called by cnputs())
already adds a carriage return. So this
duplication resulted in kernel-generated console
output lines ending in '\r''\r''\n'.

Refactor putchar() to handle the new buffering
scheme.

Add buffering to log().

Change log_console() to use msglogstr() instead of
msglogchar(). Don't add extra newlines by default
in log_console(). Hide that behavior behind a
tunable/sysctl (kern.log_console_add_linefeed) for
those who would like the old behavior. The old
behavior led to the insertion of extra newlines
for log output for programs that print out a
string, and then a trailing newline on a separate
write. (This is visible with dmesg -a.)

msgbuf.h: Add a prototype for msgbuf_addstr().

Add three new fields to struct msgbuf, msg_needsnl,
msg_lastpri and msg_lock. The first two are needed
for log message functionality previously handled
by msglogchar(). (Which is still active if
buffering isn't enabled.)

Include sys/lock.h and sys/mutex.h for the new
mutex.

Reviewed by: gibbs

/* -> /*- for copyright notices, minor format tweaks as necessary

Put the message about msgbuf cksum mismatch under bootverbose and tell
people what the consequence is.

Replace the code for reading and writing the kernel message buffer
with a new implementation that has a mostly reentrant "addchar"
routine, supports multiple message buffers in the kernel, and hides
the implementation details from callers.

The new code uses a kind of sequence number to represend the current
read and write positions in the buffer. This approach (suggested
mainly by bde) permits the read and write pointers to be maintained
separately, which reduces the number of atomic operations that are
required. The "mostly reentrant" above refers to the way that while
it is now always safe to have any number of concurrent writers,
readers could see the message buffer after a writer has advanced
the pointers but before it has witten the new character.

Discussed on: freebsd-arch