Serialize msgbuf access with a mutex.

This introduces a system-wide mutex that serializes msgbuf operations.
The mutex controls access to all modifiable fields of struct msgbuf.
It also covers logsoftc.sc_state.

To avoid adding extra lock order constraints that would affect use of
printf(9), the code does not take new locks when the log mutex is held.

The code assumes that there is at most one thread using logread(). This
keeps the logic simple. If there was more than one reader, logread()
might return the same data to different readers. Also, log wakeup might
not be reliable with multiple threads.

Tested in snaps for two weeks.

OK mpi@

Remove an unnecessary field from struct msgbuf.

OK mvs@

It is annoying that the dmesg buffer can overflow and loose messages
undetected during debugging. To make clear what happens, count the
dropped bytes and write message buffer full to syslogd. This also
helps to have a reliable log system.
OK deraadt@ millert@ tedu@

Many architectures call initmsgbuf() really really early, before uvm is
initialized. Calling malloc(9) at that point is not a good idea. So
initialize consbuf later.

Fixes dmesg -s on sparc64 (and probably a few other architectures).

ok miod@, deraadt@

Add dmesg -s support, to view the output of rc(8) system startup messages.
Help and feedback by Theo and Miod.
OK deraadt@, manpage-ok jmc@

Try to start log message buffer on a new line. Helps install scripts avoid
detecting phantom devices when scanning dmesg output.

Suggested by miod@, ok deraadt@.

Remove the advertising clause in the UCB license which Berkeley
rescinded 22 July 1999. Proofed by myself and Theo.

Change all variables definitions (int foo) in sys/sys/*.h to variable
declarations (extern int foo), and compensate in the appropriate locations.

First round of __P removal in sys

branches: 1.4.10;
Get rid of leading NULs in /kern/msgbuf. If the msgbuf modified in between
reads at just the right time is is possible to get duplicate output but
in practice this is extremely rare. Joint effort with Theo.

enlarge msgbuf, somewhat line netbsd did

branches: 1.2.16;
From NetBSD: 960217 merge

branches: 1.1.1;
Initial revision

Remove an unnecessary field from struct msgbuf.

OK mvs@

It is annoying that the dmesg buffer can overflow and loose messages
undetected during debugging. To make clear what happens, count the
dropped bytes and write message buffer full to syslogd. This also
helps to have a reliable log system.
OK deraadt@ millert@ tedu@

Many architectures call initmsgbuf() really really early, before uvm is
initialized. Calling malloc(9) at that point is not a good idea. So
initialize consbuf later.

Fixes dmesg -s on sparc64 (and probably a few other architectures).

ok miod@, deraadt@

Add dmesg -s support, to view the output of rc(8) system startup messages.
Help and feedback by Theo and Miod.
OK deraadt@, manpage-ok jmc@

Try to start log message buffer on a new line. Helps install scripts avoid
detecting phantom devices when scanning dmesg output.

Suggested by miod@, ok deraadt@.

Remove the advertising clause in the UCB license which Berkeley
rescinded 22 July 1999. Proofed by myself and Theo.

Change all variables definitions (int foo) in sys/sys/*.h to variable
declarations (extern int foo), and compensate in the appropriate locations.

First round of __P removal in sys

branches: 1.4.10;
Get rid of leading NULs in /kern/msgbuf. If the msgbuf modified in between
reads at just the right time is is possible to get duplicate output but
in practice this is extremely rare. Joint effort with Theo.

enlarge msgbuf, somewhat line netbsd did

branches: 1.2.16;
From NetBSD: 960217 merge

branches: 1.1.1;
Initial revision

It is annoying that the dmesg buffer can overflow and loose messages
undetected during debugging. To make clear what happens, count the
dropped bytes and write message buffer full to syslogd. This also
helps to have a reliable log system.
OK deraadt@ millert@ tedu@

Many architectures call initmsgbuf() really really early, before uvm is
initialized. Calling malloc(9) at that point is not a good idea. So
initialize consbuf later.

Fixes dmesg -s on sparc64 (and probably a few other architectures).

ok miod@, deraadt@

Add dmesg -s support, to view the output of rc(8) system startup messages.
Help and feedback by Theo and Miod.
OK deraadt@, manpage-ok jmc@

Try to start log message buffer on a new line. Helps install scripts avoid
detecting phantom devices when scanning dmesg output.

Suggested by miod@, ok deraadt@.

Remove the advertising clause in the UCB license which Berkeley
rescinded 22 July 1999. Proofed by myself and Theo.

Change all variables definitions (int foo) in sys/sys/*.h to variable
declarations (extern int foo), and compensate in the appropriate locations.

First round of __P removal in sys

branches: 1.4.10;
Get rid of leading NULs in /kern/msgbuf. If the msgbuf modified in between
reads at just the right time is is possible to get duplicate output but
in practice this is extremely rare. Joint effort with Theo.

enlarge msgbuf, somewhat line netbsd did

branches: 1.2.16;
From NetBSD: 960217 merge

branches: 1.1.1;
Initial revision