Re: [PATCH] ndctl: Use max_available_extent for creating namespaces

[Dan Williams <dan.j.williams@intel.com>]

On Tue, Jun 26, 2018 at 9:27 AM, Verma, Vishal L
<vishal.l.verma@intel.com> wrote:
> On Tue, 2018-06-26 at 10:29 -0600, Keith Busch wrote:
>> On Tue, Jun 26, 2018 at 09:19:28AM -0700, Verma, Vishal L wrote:
>> > On Tue, 2018-06-26 at 09:37 -0600, Keith Busch wrote:
>> > > The available_size attribute returns all the unused regions, but a
>> > > namespace has to use contiguous free regions. This patch uses the
>> > > attribute returning the largest capacity that can be created for
>> > > determining if the namespace can be created.
>> > >
>> > > Signed-off-by: Keith Busch <keith.busch@intel.com>
>> > > ---
>> > >  ndctl/lib/libndctl.c   | 30 ++++++++++++++++++++++++++++++
>> > >  ndctl/lib/libndctl.sym |  1 +
>> > >  ndctl/libndctl.h       |  2 ++
>> > >  ndctl/namespace.c      |  2 +-
>> > >  4 files changed, 34 insertions(+), 1 deletion(-)
>> >
>> > Hi Keith,
>> >
>> > The patch looks good, but just a couple of 'meta' comments.
>> > 1. We typically send ndctl patches separately from kernel patches (i.e.
>> > not
>> > thraded together).
>> > 2. for ndctl patches, an 'ndctl PATCH' prefix is recommended. You can
>> > set a
>> > repo local config parameter for doing this automatically on git format-
>> > patch.
>> >     git config format.subjectprefix "ndctl PATCH"
>> >
>> > I'm thinking the kernel changes will be queued for 4.19, which means
>> > the
>> > ndctl changes will go into v62.
>>
>> Thanks for the info. I'll make those changes for next time.
>>
>> I think I may need to send a v2 for this. Should we have this fall back
>> to
>> the available_size for the older kernels where the max_available_extents
>> attribute is not provided? I actually had that in my repo and used a
>> slightly older patch here, but I'm not sure if its okay to strongly
>> couple an ndctl release to a kernel version.
>
> I was thinking that too. Typically we don't guarantee ndctl to work with
> old kernels, but this does seem like a bit of an invasive change.
>
> Dan, thoughts?

It should fall back if the attribute is not available. Our *tests*
aren't guaranteed to pass on older kernels, but ndctl proper should
try it's best to accommodate old kernels.
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