MFC 339620: Add a "live" mode to ktrdump.

Support a "live" mode in ktrdump enabled via the -l flag. In this
mode, ktrdump polls the kernel's trace buffer periodically (currently
hardcoded as a 50 millisecond interval) and dumps any newly added
entries. Fancier logic for the timeout (e.g. a command line option or
some kind of backoff based on the time since the last entry) can be
added later as the need arises.

Note that this does not include the capsicum fixes from the original
commit since ktrdump in stable/11 is not capsicum-ized.

MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

MFC r323439:
Provide an error message if KTR symbols in a vmcore cannot be resolved.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Change ktrdump to use the more standard -M/-N flags to specify the path
to a crash dump and kernel, respectively. The existing -m/-e flags are
still supported for backwards compatiblity but are no longer documented.

Requested by: np
MFC after: 2 weeks

Don't dump entries that were modified during the time the KTR buffer was being
copied to userspace. Failing to do this would result in entries at the bottom
of the ktrdump output to be more recent than entries at the top.

With this change the timestamps are monotonically decreasing going from the
top to the bottom of the ktrdump output.

Fix an issue with ktrdump(8) where it would not print all entries in the
KTR buffer.

This happens when 'i' tries to wrap around from 0 to 'entries - 1'. Since 'i'
is a signed integer the modulo operation actually returns a negative number.

Fix this by computing the next index to use "by hand" instead of relying
on the modulo operator.

Print the ktr(4) format line that caused a failure.

Sponsored by: Nginx, Inc.

- Implement run-time expansion of the KTR buffer via sysctl.
- Implement a function to ensure that all preempted threads have switched
back out at least once. Use this to make sure there are no stale
references to the old ktr_buf or the lock profiling buffers before
updating them.

Reviewed by: marius (sparc64 parts), attilio (earlier patch)
Sponsored by: EMC / Isilon Storage Division

Catch up with r238925. ktr_entries may not be a power of 2.

Add -H flag to print thread id.

Remove unnecessary opt* definations.

Skip format flags, when parsing ktr_desc.

Really fix the relative timestamp bug. It was only incorrect for the ALQ
case. It seems entries are in reverse order when read from the kernel
memory but in the right order when read from a file (i.e. ALQ). Handle
both cases.

MFC after: 1 day

Fix -r flag to actually work. "now" comes after "then", not vice versa.

MFC after: 1 day

Append a newline character to the usage string.

MFC after: 3 days

Sync program's usage() with manpage's SYNOPSIS.

Don't use an uninitialised variable when reading from a ktr alq file.

Add a "-r" flag to ktrdump(1) to print relative timestamps when used
with "-t" rather than absolute timestamps. This allows the reader
to get a better sense of latency between events, such as time to
schedule an interrupt thread from time the interrupt occurred. Assert
a copyright on ktrdump.c since I seem to be modifying it more than I
thought.

Add a quiet mode to ktrdump(1): if the "-q" flag is used, don't print
the pretty text header on top of the output. Simplifies feeding the
results of tracing into a script for mechanical processing.

When the 'f' flag is passed to ktrdump(1), use 40 characters for the
"file and line" field consistently; previously, a 32-character field
length was used for the table header, which resulted in the header
not lining up with the table.

Remove an unused variable.

Use strlcpy() instead of strcpy() to not overflow static buffers.

- Add the -i option to read in a saved ktr file output by KTR_ALQ.

1. Add missing include of stdint.h.
2. Fix reversed arguments to strcpy.

Noticed by: davidc (2)

ktrdump is a utility to dump the ktr trace buffer from userland. It can
also be run on a core dump.