kern/24882: ktrace not syncing .out file before panic

[rwatson at FreeBSD.org]

Synopsis: ktrace not syncing .out file before panic

State-Changed-From-To: open->closed
State-Changed-By: rwatson
State-Changed-When: Sat Mar 8 20:44:37 UTC 2008
State-Changed-Why: 
First off, apologies for the several years it has taken for someone to look
at this PR.  Unfortunately, I'm going to go ahead and close it, and point
you at the kern.sync_on_panic sysctl, which determines whether or not the
system tries to sync file systems on panic.  As you point out, it is a
constant trade-off between performance and stability of data, and ktrace is
not generally a tool that is intended to operate properly in the presence
of kernel data corruption/panic.  What we might want to consider doing is
allowing a bound on the amount of un-written ktrace data, sized by data or
time, but I'm not sure that will necessarily help the case of usin ktrace
to debug things leading up to a panic.  Recent FreeBSD versions include a
tool, KTR, to help trace those scenarios, and shortly DTrace will also be
available.


http://www.freebsd.org/cgi/query-pr.cgi?pr=24882