[libvirt] [PATCH 7/7] Remove global log buffer feature entirely

[Eric Blake]

On 03/10/2014 08:10 AM, Daniel P. Berrange wrote:
> 
> If we were to keep the global log buffer pretty much none of this
> patch series is worthwhile, because as long as the global log buffer
> exists the other performance improvements in this patch are dwarved
> by the printf. Just minimizing malloc/printf overhead might let you
> cut overhead in 1/2 or even in 1/4, but that still leaves massive
> overhead behind. This patch series is reducing the execution time
> in the test program from 1 minute 40 secs, to 3 secs.
> 
> I don't see any optimization of printf/malloc being able to get us
> anywhere near this kind of level of improvement.

I agree that killing the printfs into the ring buffer makes sense - just
waiting for anyone else to express an opinion.

>> We may not be dumping the ring buffer any more, but I _still_ think it's
>> worth keeping this signal handler and dumping a message that we detected
>> a fatal crash, as well as pointing the user to go read the contents of
>> the logging files (and/or rerun libvirtd with more logging enabled).  In
>> other words, delete the ring buffer, but DON'T delete this last-ditch
>> message to the user.
> 
> But if you don't install any SEGV signal handler, the kernel/glibc default
> will already print
> 
>   Segmentation fault (core dumped)
> 
> So what more would libvirt do ?

Print a nicer message, something like:

Fatal signal detected; please report this bug to libvir-list at redhat.com:
Segmentation fault

> 
> I'm open to suggestions of what else libvirt could usefully (& safely)
> add to this, but I couldn't think of anything worthwhile.

Bug reporting address is nice.  Backtrace would be useful, but hard to
prove that it would work safely, and may be non-portable outside of linux).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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