file locking.

Robert Watson rwatson at
Sun Sep 2 04:28:38 PDT 2007

On Fri, 31 Aug 2007, David O'Brien wrote:

> On Thu, Aug 16, 2007 at 04:35:20PM -0400, John Baldwin wrote:
>> On Thursday 16 August 2007 04:18:51 pm Jeff Roberson wrote:
>>> Do we have an official stance on libkvm?  Now that we have sysctl for 
>>> run-time it's only useful for crashdump debugging.  Really in most cases 
>>> it could be replaced with a reasonable set of gcc scripts.
>> s/gcc/gdb/.  At work we do mostly post-mortem analysis, so having working 
>> libkvm is still very important for us.  xref the way I just fixed netstat 
>> to work again on coredumps recently.  Breaking fstat on coredumps would 
>> probably be very annoying.
> This applies at Juniper as well.  I think post-mortem analysis is a Big 
> Deal(tm) to those developing commercial products based on FreeBSD.

I think it's a given that post-mortem analysis will be more fragile than live 
analysis due to weaker ABI requirements for in-kernel data structures -- on 
the other hand, it's also a critical feature.  I think keeping libkvm 
functioning on core dumps is really important -- the ability to run ps, 
netstat, etc, etc, all on core dumps is remarkably useful in debugging.

What I occasionally wish is that all the magic in DDB could also be used on 
coredumps -- i.e., that we could compile the kernel DDB bits into a user 
binary to run on matching core dumps in order to more easily extract things 
like WITNESS data, etc.  No doubt a moderate amount of evil would be required 
to do this...

Robert N M Watson
Computer Laboratory
University of Cambridge

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