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References: <20191101202713.5111-1-vishal.l.verma@intel.com>
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From: Dan Williams <dan.j.williams@intel.com>
Date: Mon, 4 Nov 2019 10:58:26 -0800
Message-ID: <CAPcyv4i5cqOrO6LLPZ2z5xx1xApbHaSvMiNk5CCQQ0ZxOr2hCQ@mail.gmail.com>
Subject: Re: [ndctl PATCH 2/2] ndctl/namespace: introduce ndctl_namespace_is_configurable()
To: "Verma, Vishal L" <vishal.l.verma@intel.com>
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On Mon, Nov 4, 2019 at 10:48 AM Verma, Vishal L
<vishal.l.verma@intel.com> wrote:
>
> On Mon, 2019-11-04 at 08:35 -0800, Dan Williams wrote:
> > On Fri, Nov 1, 2019 at 1:27 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
> > > The motivation for this change is that we want to refrain from
> > > (re)configuring what appear to be partially configured namespaces.
> > > Namespaces may end up in a state that looks partially configured when
> > > the kernel isn't able to enable a namespace due to mismatched
> > > PAGE_SIZE expectations. In such cases, ndctl should not treat those
> > > as unconfigured 'seed' namespaces, and reuse them.
> > >
> > > Add a new ndctl_namespace_is_configurable API, whish tests whether a
> > > namespaces is active, and whether it is partially configured. If neither
> > > are true, then it can be used for (re)configuration. Additionally, deal
> > > with the corner case of ND_DEVICE_NAMESPACE_IO (legacy PMEM) namespaces
> > > by testing whether the size attribute is read-only (which indicates such
> > > a namespace). Legacy namespaces always appear as configured, since their
> > > size cannot be changed, but they are also always re-configurable.
> > >
> > > Use this API in namespace_reconfig() and namespace_create() to enable
> > > this partial configuration detection.
> >
> > A couple comments.... I think it's probably sufficient to just check
> > for ND_DEVICE_NAMESPACE_IO as I don't anticipate we'll ever have more
> > than one namespace type with a read-only size attribute.
>
> Yep I did notice I could do that, but I decided to go to the source of
> it instead of adding another ND_DEVICE_NAMESPACE_IO assumption. Also I
> had already written sysfs_attr_writable() before I noticed that :)
> But there are already assumptions around ND_DEVICE_NAMESPACE_IO, so
> adding another one here is fine.
>
> > Also, how about s/ndctl_namespace_is_configurable/ndctl_namespace_is_configuration_idle/?
> > Because to me all namespaces are always "configurable", but some may
> > have active non-default properties set.
>
> Sounds reasonable, but how about ndctl_namespace_has_partial_config(),
> which I think describes the situation better, and makes it
> straightforward for a potential future --really-force (or -ff) option
> where we might still want to blow away anything on this namespace and
> reclaim it.

Does "_has_partial_config()" imply "_has_full_config()"? In other
words, what ndctl cares about are namespaces that can effectively be
used as seeds with no existing configuration parameters having been
set. So "_is_configuration_idle()" seems unambiguous where
"_has_partial_config()" does not.
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