linux-kernel - Re: [patch] cpusets: allow empty {cpus,mems}_allowed to be set for unpopulated cpuset

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Date:	Tue, 1 May 2007 20:36:29 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Paul Jackson" <pj@....com>
Cc:	"David Rientjes" <rientjes@...gle.com>,
	torvalds@...ux-foundation.org, clameter@...ulhu.engr.sgi.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] cpusets: allow empty {cpus,mems}_allowed to be set for unpopulated cpuset

On 5/1/07, Paul Jackson <pj@....com> wrote:
> Why do you need this?  It adds a little more code, and changes
> semantics a little bit, so I'd think it should have at least a
> little bit of justfication.

We have cases where we'd like to be able to clear the memory nodes
away from a (temporarily) empty cpuset without actually deleting the
directory - there's really no reason for the interface to stop people
from doing that as far as I can see. Otherwise the only way to reclaim
the node for a different sibling is to delete the cpuset.

>
>
> +       if (!*buf) {
> +               cpus_clear(trialcs.cpus_allowed);
>
> Won't the above code fail if someone does:
>
>         echo > /dev/cpuset/foobar/mems
>
> Just guessing, but I'd expect buf[] to contain a newline char,
> not just a zero length string, at this point.

Yes, but that's arguably an artefact of the user using the wrong tool
to update the cpu/node set. Doing "echo -n > /dev/cpuset/foobar/mems"
has the expected effect.

Paul
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