Re: [PATCH/RFC] Add node 'states' sysfs class attribute - V2

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 27 Aug 2007 18:29:26 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:

> On Mon, 27 Aug 2007, Andrew Morton wrote:
> 
> > > online: 0-1, 3
> > 
> > really?  with commas and spaces and minus signs and colons?  ug, what next?
> > animated ascii art?  This is sysfs, not procfs ;)
> 
> The masks can get quite ugly to read if you have lots of nodes. F.e. with 
> 1024 nodes you get a line that wraps around more than 10 times.

So don't read them - use a program to turn them into your preferred
human-readable representation.

One could argue that with sufficient effort, all formats are
machine-digestible, but a simple, robust and maintainable format like a
bitmap makes sense for a kernel->userspace interface, IMO.

We see this often, btw.  People want nice and easy-to-read kernel->human
interfaces because the tool of choice for displaying these things to humans
is "cat".  How lame is that?

I do think that a sysfs interface like this should be optimised for
kernel->program communication, not for kernel->human.


> > OK, well if the meminfo file is the only one in there which broke the
> > golden rule, I don't think we have sufficient excuse to break it again.
> > 
> > $ cat  /sys/devices/system/node/possible
> > 0-4
> > $
> > 
> > I think a bitmap would be better, personally.
> > 
> > That in fact makes "possible" unneeded, doesn't it?  It would always be
> > all-ones?
> 
> There could be the case that nodes 1-9 and 20-29 are possible but 
> the ones in between are not available.

OK.

How do we communicate to userspace what is the maximum number of nodes
which this kernel supports?  That would be (1<<CONFIG_NODES_SHIFT), I
guess.  Or maybe we don't care?

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