Re: [ndctl RFC PATCH] ndctl/namespace: create namespaces greedily

From: "Verma, Vishal L" <vishal.l.verma@intel.com>
To: "Scargall, Steve" <steve.scargall@intel.com>,
	"jmoyer@redhat.com" <jmoyer@redhat.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Subject: Re: [ndctl RFC PATCH] ndctl/namespace: create namespaces greedily
Date: Wed, 28 Aug 2019 21:22:22 +0000	[thread overview]
Message-ID: <ce15fdbdee2135a1b1d698f46d3cc7c9856bb381.camel@intel.com> (raw)
In-Reply-To: <1ac1bafeaf3253fb9396c22db334b51deb653f0a.camel@intel.com>

On Wed, 2019-08-28 at 21:16 +0000, Verma, Vishal L wrote:
> On Wed, 2019-08-28 at 13:47 -0700, Scargall, Steve wrote:
> > Hi Jeff,
> > 
> > The issue is more of repetition.   On an 8-socket system,  should a
> > user really be expected to type 'ndctl create-namespace' eight times
> > vs. running 'ndctl create-namespace --region=all' once?   SAP HANA is
> > an example app the requires one namespace per region.  Scripting is a
> > viable solution, but that requires somebody to write the script and do
> > all the error checking & handling.  Each OEM/ISV/SysAdmin would have
> > their own script.  Pushing the logic to ndctl seems to be a reasonable
> > approach and let the user handle any errors returned by ndctl.
> 
> A scripted solution can indeed be really simple - e.g.:
> 
> # while read -r region; do  ndctl create-namespace --region="$region";
> done < <(ndctl list --bus=nfit_test.0 -R  | jq -r '.[].dev')
> 
> {
>   "dev":"namespace5.0",
>   "mode":"fsdax",
>   "map":"dev",
>   "size":"62.00 MiB (65.01 MB)",
>   "uuid":"c8014457-c268-4f22-8eae-6386fbf08ceb",
>   "sector_size":512,
>   "align":2097152,
>   "blockdev":"pmem5"
> }
> {
>   "dev":"namespace4.0",
>   "mode":"fsdax",
>   "map":"dev",
>   "size":"30.00 MiB (31.46 MB)",
>   "uuid":"f9498ef6-cdd6-46c7-95f1-86469546ecb9",
>   "sector_size":512,
>   "align":2097152,
>   "blockdev":"pmem4"
> }
> 
> > The ndctl-man-page implies the 'ndctl create-namespace --region=all'
> > feature exists today:
> > 
> >        -r, --region=
> > 
> >            A regionX device name, or a region id number. The keyword
> > all can be specified to carry out the operation on every region in the
> > system, optionally filtered by bus id (see --bus=  option).
> > 
> 
> This is true, but unfortunately, the implementation has treated create-
> namespace as an exception to this since the start, and I agree with Jeff
> that changing its behavior now can cause other Hyrum's law-esqe [1]
> breakage.
> 
> I think however it should be easy to make a compromise, and retain the
> legacy behavior of create-namespace, while creating a new create-
> namespace-greedy command with the new semantics.
> 
.. And it doesn't even need to be a new command, a simple --greedy
option to create-namespace should be sufficient.
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