cvs-src summary for July 19-26

I haven't had a chance to convert this summary to HTML yet (web page to be 
updated tomorrow), so it may change slightly when I find my markup typoes.  
Anyway, here it is.

FreeBSD cvs-src summary for 19/07/04 to 26/07/04
++++++++++++++++++++++++++++++++++++++++++++++++
This is a regular weekly summary of FreeBSD's cutting-edge development.
It is intended to help the FreeBSD community keep up with the fast-paced
work going on in FreeBSD-CURRENT by distilling the deluge of data from
the CVS mailing list into a (hopefully) easy-to-read newsletter.  This
newsletter is marked up in reStructuredText_, so any odd punctuation
that you see is likely intended for the reST parser.

.. _reStructuredText: http://docutils.sourceforge.net/rst.html

You can get old summaries, and an HTML version of this one, at
http://www.xl0.org/FreeBSD/.  Please send any comments to Mark Johnston
(mark at xl0.org).

For Lukasz Dudek and Szymon Roczniak's Polish translations of these
summaries, which may lag the English ones slightly, please see
http://mocart.pinco.pl/FreeBSD/.

.. contents::

============
New features
============
Support for kernel debugging with kgdb
--------------------------------------
Marcel Moolenaar (marcel) committed kgdb, which is a shell on top of
libgdb that adds basic support for kernel threads, modules, and VM.  Not
all of the desired features are present yet, but it is useful as is.

http://www.freebsd.org/cgi/mid.cgi?200407250529.i6P5TFag021812

NTP updated to 4.2.0
--------------------
Ollivier Robert (roberto) updated NTP, the network time protocol server
and client, to version 4.2.0.  The new version adds IPv6 support and
updated drivers and renames ntp-genkeys to ntp-keygen.

http://www.freebsd.org/cgi/mid.cgi?200407201544.i6KFiWWr001296

ACPI Panasonic extras driver added
----------------------------------
Takahashi Yoshihiro (nyan) added an ACPI "extras" driver for Panasonic
hardware.  This allows for special features of Panasonic ACPI-supporting
hardware to be used.  The driver was submitted by OGAWA Takaya.

http://www.freebsd.org/cgi/mid.cgi?200407211447.i6LElsVH050875

===============
Notable changes
===============
GEOM concat and stripe device naming scheme changed
---------------------------------------------------
Pawel Jakub Dawidek (pjd) changed the naming scheme for GEOM concatenated
and striped disks from /dev/<name>.concat to /dev/concat/<name> and from
/dev/<name>.stripe to /dev/stripe/<name>.

http://www.freebsd.org/cgi/mid.cgi?200407261714.i6QHElNr091950

=================
Discussion topics
=================
Syncing on panic and journaling filesystems
-------------------------------------------
Robert Watson (rwatson) changed the shutdown code so that when the system
panics, it will not attempt to write out data in the memory buffer to
disk.  He noted, "This seems to basically work very infrequently, and often
results in a compound panic which confuses debugging [ . . . ]."

Roman Kurakin (rik) responded, asking, "How to change behavior?"

Robert replied, "When we're in a "panic" state, we will no long attempt
to call out to all file systems to synchronize their on-disk data with
in-memory data. [ . . . ] For an example of what happens as a result of
syncing in panic(), take a look at `PR kern/69369`_." (hyperlink added)

.. _`PR kern/69369`: http://www.freebsd.org/cgi/query-pr.cgi?pr=69369

Roman clarified his original post, asking, "Is it possible to give a choice
to user?"

Nate Lawson (njl) also replied, saying, "I think the answer Rik is looking
for is 'sysctl kern.sync_on_panic'."

Scott Long (scottl) joined the discussion, asking, "Do you really want to
trust [the panic'ing system] to spam your drive with buffers that are in
an unknown state via a set of codepaths that are in an unknown state?"  He
also noted, "I can't remember a single time in the last 4 years when a
panic actually successfuly synced out all of the buffers and shutdown the
filesystem, so it's not likely that you'll avoid a fsck on reboot with
this."

Alfred Perlstein (alfred) answered, "It's not about avoiding a fsck, it's
about recovering the last 30+ seconds of disk activity."

Stephan Uphoff responded to Alfred, pointing out, "Locking is disabled
during a sync on panic. ( all lockmgr requests succeed)".  If other
threads are active in the filesystem, he said, "A sync requests trampling
through the file systems with total disregard for any locks can do
interesting things to a filesystem on disk."

Julian Elischer (julian) joked, "If you have no sync then you are more
likely to have a successful core-dump.. so write a utility that extracts
the missing data from the corefile !"

Scott replied, "Implementing a journalling filesystem would be a much more
beneficial use of time here."

Peter Jeremy asked, "How much effort would be required to add journalling
to UFS or UFS2?  How big a gain does journalling give you over
soft-updates?"

Scott gave some examples of commercial companies that had added
journalling, estimating that it would take "about 4-5 months to get it
going, and then at least 8-12 months to ensure that there are no bugs and
to tune performance."

Johan Pettersson asked, "Isn't there ongoing work to port XFS to FreeBSD?"

Scott answered, "There was, but it seems to have stalled due to lack of
time by the person who was doing it."

Nate also answered Peter's post, saying "Kirk pointed out something to me
the other day which many people don't think about.  None of the journaling
systems has had its recovery mode fully tested, especially on very large
systems (dozen TB)."

Scott replied, "[G]iven the enterprise nature of Sun, I'd say it's a bit
of a stretch to think that they haven't tested their f/s on multi-terabyte
arrays.  Even Apple advertises multi-terabyte storage with their XServe,
so I'd be surprised if they hadn't done at least some testing there."

Sam Leffler (sam) also answered Nate, saying, "I can assure you that XFS
has been well-tested with TB systems."

Nate then clarified, "I was referring to the herd of Linux journaling
systems."

http://www.freebsd.org/cgi/mid.cgi?200407211604.i6LG4kFK052991

=================
Committer changes
=================
Suleiman Souhlal (ssouhlal) has joined as a new src committer, helping
with the PowerPC port.

===============
Other bug fixes
===============
Hartmut Brandt (harti) fixed comment handling in make on lines using the
.elif command.  This closes `PR 25627`_, originally submitted by Seth
Kingsley.

.. _`PR 25627`: http://www.freebsd.org/cgi/query-pr.cgi?pr=25627

http://www.freebsd.org/cgi/mid.cgi?200407221112.i6MBC2OI098242