Re: netlink vs. debugfs (was Re: [Patch 0/6] statistics infrastructure)

[Balbir Singh <balbir@in.ibm.com>]

On Mon, May 22, 2006 at 11:09:22AM -0700, Tim Bird wrote:
> Andrew Morton wrote:
> > Martin Peschke <mp3@de.ibm.com> wrote:
> >> My patch series is a proposal for a generic implementation of statistics.
> > 
> > This uses debugfs for the user interface, but the
> > per-task-delay-accounting-*.patch series from Balbir creates an extensible
> > netlink-based system for passing instrumentation results back to userspace.
> > 
> > Can this code be converted to use those netlink interfaces, or is Balbir's
> > approach unsuitable, or hasn't it even been considered, or what?
> 
> Can someone give me the 20-second elevator pitch on why
> netlink is preferred over debugfs?  I've heard of a
> number of debugfs/procfs users requested to switch over.
> 
> Thanks,
>  -- Tim
> 
> =============================
> Tim Bird
> Architecture Group Chair, CE Linux Forum
> Senior Staff Engineer, Sony Electronics
> =============================

Hi, Tim,

I am no debugfs expert, I hope I can do justice to the comparison.

Debugfs						Netlink/Genetlink

1. Filesystem based - requires creating		Several types of data can
   files for each type of data passed		be multiplexed over one netlink
   down						socket.
2. Hard to determine record format/data		Contains metadata including
						type of data and length
						with each record
3. Notifications are hard			Notifications are very easy
   I think they can be done using inotify	good library support for
						notifications. Data can
						either be broadcast or
						selectively mulitcast
4. Requires several open/read/write/close	A single socket can be
   operations					opened, data from kernel
						space can be multiplexed
						over it.

I don't think I did any justice to the advantages of debugfs. The only
one I can think of is that it uses relayfs. Relayfs is efficient in the
sense that it uses per-cpu buffers.

Anybody else want to take a shot in comparing the two?

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs
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