From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from verein.lst.de (verein.lst.de [213.95.11.211])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2CB5A2FAD
	for <nvdimm@lists.linux.dev>; Sat, 14 Aug 2021 07:35:15 +0000 (UTC)
Received: by verein.lst.de (Postfix, from userid 2407)
	id 645AA67373; Sat, 14 Aug 2021 09:35:06 +0200 (CEST)
Date: Sat, 14 Aug 2021 09:35:06 +0200
From: Christoph Hellwig <hch@lst.de>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>, Christoph Hellwig <hch@lst.de>,
	linux-cxl@vger.kernel.org, Linux NVDIMM <nvdimm@lists.linux.dev>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Ben Widawsky <ben.widawsky@intel.com>,
	Vishal L Verma <vishal.l.verma@intel.com>,
	"Schofield, Alison" <alison.schofield@intel.com>,
	"Weiny, Ira" <ira.weiny@intel.com>
Subject: Re: [PATCH 10/23] libnvdimm/labels: Add uuid helpers
Message-ID: <20210814073506.GA21463@lst.de>
References: <162854806653.1980150.3354618413963083778.stgit@dwillia2-desk3.amr.corp.intel.com> <162854812073.1980150.8157116233571368158.stgit@dwillia2-desk3.amr.corp.intel.com> <YROE48iCZNFaDcSo@smile.fi.intel.com> <YRQB9Yvh3tmT9An4@smile.fi.intel.com> <CAPcyv4jOEfi=RJTeOFTbvkBB+Khfzi5QirrhPxeM4J2bQXRYiQ@mail.gmail.com> <YRQik5OnRyYQAm4o@smile.fi.intel.com> <CAPcyv4hY9YL7MhkeSu4GYBNo6hbeMRgqnKf8YuLuQ3khSbhn9A@mail.gmail.com> <YRZGInO3vguWR4IA@smile.fi.intel.com>
Precedence: bulk
X-Mailing-List: nvdimm@lists.linux.dev
List-Id: <nvdimm.lists.linux.dev>
List-Subscribe: <mailto:nvdimm+subscribe@lists.linux.dev>
List-Unsubscribe: <mailto:nvdimm+unsubscribe@lists.linux.dev>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <YRZGInO3vguWR4IA@smile.fi.intel.com>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Aug 13, 2021 at 01:14:58PM +0300, Andy Shevchenko wrote:
> > Andy, does this incremental diff restore your reviewed-by? The awkward
> > piece of this for me is that it introduces a handful of unnecessary
> > memory copies. See some of the new nsl_get_uuid() additions and the
> > extra copy in nsl_uuid_equal()
> 
> It does, thanks! As for the deeper discussion I think you need to talk to
> Christoph. It was his idea to move uuid_t from UAPI to internal kernel type.
> And I think it made and still makes sense to be that way.
> 
> But if we have already users of uuid_t like you are doing here (without this
> patch) then it will be fine I guess. Not my area to advise or decide.

I'm missing a lot of context here.  But that whole uuid/guid thing is
a little complex:

 - for userspace APIs and on-disk formats a uuid is nothing but a blob
 - userspace historically has its own library to deal with this (libuuid),
   which defines a uuid_t itself.

So instead of trying to build abstractions that somehow word in diferent
software ecosystems I think just treating it as the blob that it is for
exchange makes life easіer for everyone.  It also really makes definitions
of on-disk structures more clear when using the raw bytes instead of a
semi-opaque typedef.