Re: sysctl vs ifconfig vs other (was Re: sysctl-controlled key-value store ?)

On Sun, 07 Oct 2012 10:16:40 -0600
Ian Lepore <freebsd_at_damnhippie.dyndns.org> wrote:

> On Sun, 2012-10-07 at 17:53 +0200, Luigi Rizzo wrote:
> > Access through sysctl is incredibly easy from both userspace and
> > from a C application, because all the work is done in the kernel
> > side, whereas other mechanisms (ioctl, i'd rather leave kvm apart
> > as we really don't want that!) require the definition of a specific
> > API (ioctl, structs) _and_ some amount of wrapping code in
> > userspace.
> > 
> > cheers
> > luigi
> 
> A potential problem with sysctl is its "one thing at a time" nature.
> When you pack up a bunch of related data into a structure and hand it
> off to an implementation, that implementation can pretty easily make
> sure that all the data related to the config request is sane.  If you
> have to make a series of sysctl calls to achieve some complex config
> task, what happens when you're 2/3 of the way through the series and a
> call fails?  Who backs out the partial config that got accomplished?
> 
> If you go too far down this path you end up with something that looks
> a lot like the unmitigated mess which is the SNMP control API.
> 
> -- Ian

I agree with Ian here.  As messy as ioctl+structs are from a user
standpoint, they're the easiest way to guarantee atomic configuration
changes.

- Justin