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From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: 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
Date: Wed, 11 Aug 2021 22:18:43 +0300	[thread overview]
Message-ID: <YRQik5OnRyYQAm4o@smile.fi.intel.com> (raw)
In-Reply-To: <CAPcyv4jOEfi=RJTeOFTbvkBB+Khfzi5QirrhPxeM4J2bQXRYiQ@mail.gmail.com>

On Wed, Aug 11, 2021 at 10:11:56AM -0700, Dan Williams wrote:
> On Wed, Aug 11, 2021 at 9:59 AM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Wed, Aug 11, 2021 at 11:05:55AM +0300, Andy Shevchenko wrote:
> > > On Mon, Aug 09, 2021 at 03:28:40PM -0700, Dan Williams wrote:
> > > > In preparation for CXL labels that move the uuid to a different offset
> > > > in the label, add nsl_{ref,get,validate}_uuid(). These helpers use the
> > > > proper uuid_t type. That type definition predated the libnvdimm
> > > > subsystem, so now is as a good a time as any to convert all the uuid
> > > > handling in the subsystem to uuid_t to match the helpers.
> > > >
> > > > As for the whitespace changes, all new code is clang-format compliant.
> > >
> > > Thanks, looks good to me!
> > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> >
> > Sorry, I'm in doubt this Rb stays. See below.
> >
> > ...
> >
> > > >  struct btt_sb {
> > > >     u8 signature[BTT_SIG_LEN];
> > > > -   u8 uuid[16];
> > > > -   u8 parent_uuid[16];
> > > > +   uuid_t uuid;
> > > > +   uuid_t parent_uuid;
> >
> > uuid_t type is internal to the kernel. This seems to be an ABI?
> 
> No, it's not a user ABI, this is an on-disk metadata structure. uuid_t
> is approprirate.

So, changing size of the structure is forbidden after this change, right?
I don't like this. It means we always stuck with this type to be like this and
no change will be allowed.

> > > >     __le32 flags;
> > > >     __le16 version_major;
> > > >     __le16 version_minor;
> >
> > ...
> >
> > > >  struct nd_namespace_label {
> > > > -   u8 uuid[NSLABEL_UUID_LEN];
> > > > +   uuid_t uuid;
> >
> > So seems this.
> >
> > > >     u8 name[NSLABEL_NAME_LEN];
> > > >     __le32 flags;
> > > >     __le16 nlabel;
> >
> > ...
> >
> > I'm not familiar with FS stuff, but looks to me like unwanted changes.
> > In such cases you have to use export/import APIs. otherwise you make the type
> > carved in stone without even knowing that it's part of an ABI or some hardware
> > / firmware interfaces.
> 
> Can you clarify the concern? Carving the intent that these 16-bytes
> are meant to be treated as UUID in stone is deliberate.

It's a bit surprise to me. Do we have any documentation on that?
How do we handle such types in kernel that covers a lot of code?

-- 
With Best Regards,
Andy Shevchenko



  reply	other threads:[~2021-08-11 19:19 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09 22:27 [PATCH 00/23] cxl_test: Enable CXL Topology and UAPI regression tests Dan Williams
2021-08-09 22:27 ` [PATCH 01/23] libnvdimm/labels: Introduce getters for namespace label fields Dan Williams
2021-08-10 20:48   ` Ben Widawsky
2021-08-10 21:58     ` Dan Williams
2021-08-11 18:44   ` Jonathan Cameron
2021-08-09 22:27 ` [PATCH 02/23] libnvdimm/labels: Add isetcookie validation helper Dan Williams
2021-08-11 18:44   ` Jonathan Cameron
2021-08-09 22:28 ` [PATCH 03/23] libnvdimm/labels: Introduce label setter helpers Dan Williams
2021-08-11 17:27   ` Jonathan Cameron
2021-08-11 17:42     ` Dan Williams
2021-08-09 22:28 ` [PATCH 04/23] libnvdimm/labels: Add a checksum calculation helper Dan Williams
2021-08-11 18:44   ` Jonathan Cameron
2021-08-09 22:28 ` [PATCH 05/23] libnvdimm/labels: Add blk isetcookie set / validation helpers Dan Williams
2021-08-11 18:45   ` Jonathan Cameron
2021-08-09 22:28 ` [PATCH 06/23] libnvdimm/labels: Add blk special cases for nlabel and position helpers Dan Williams
2021-08-11 18:45   ` Jonathan Cameron
2021-08-09 22:28 ` [PATCH 07/23] libnvdimm/labels: Add type-guid helpers Dan Williams
2021-08-11 18:46   ` Jonathan Cameron
2021-08-09 22:28 ` [PATCH 08/23] libnvdimm/labels: Add claim class helpers Dan Williams
2021-08-11 18:46   ` Jonathan Cameron
2021-08-09 22:28 ` [PATCH 09/23] libnvdimm/labels: Add address-abstraction uuid definitions Dan Williams
2021-08-11 18:49   ` Jonathan Cameron
2021-08-11 22:47     ` Dan Williams
2021-08-09 22:28 ` [PATCH 10/23] libnvdimm/labels: Add uuid helpers Dan Williams
2021-08-11  8:05   ` Andy Shevchenko
2021-08-11 16:59     ` Andy Shevchenko
2021-08-11 17:11       ` Dan Williams
2021-08-11 19:18         ` Andy Shevchenko [this message]
2021-08-11 19:26           ` Dan Williams
2021-08-12 22:34           ` Dan Williams
2021-08-13 10:14             ` Andy Shevchenko
2021-08-14  7:35               ` Christoph Hellwig
2021-08-11 18:13   ` Jonathan Cameron
2021-08-12 21:17     ` Dan Williams
2021-08-09 22:28 ` [PATCH 11/23] libnvdimm/labels: Introduce CXL labels Dan Williams
2021-08-11 18:41   ` Jonathan Cameron
2021-08-11 23:01     ` Dan Williams
2021-08-09 22:28 ` [PATCH 12/23] cxl/pci: Make 'struct cxl_mem' device type generic Dan Williams
2021-08-09 22:28 ` [PATCH 13/23] cxl/mbox: Introduce the mbox_send operation Dan Williams
2021-08-09 22:29 ` [PATCH 14/23] cxl/mbox: Move mailbox and other non-PCI specific infrastructure to the core Dan Williams
2021-08-11  6:11   ` [PATCH v2 " Dan Williams
2021-08-09 22:29 ` [PATCH 15/23] cxl/pci: Use module_pci_driver Dan Williams
2021-08-09 22:29 ` [PATCH 16/23] cxl/mbox: Convert 'enabled_cmds' to DECLARE_BITMAP Dan Williams
2021-08-09 22:29 ` [PATCH 17/23] cxl/mbox: Add exclusive kernel command support Dan Williams
2021-08-10 21:34   ` Ben Widawsky
2021-08-10 21:52     ` Dan Williams
2021-08-10 22:06       ` Ben Widawsky
2021-08-11  1:22         ` Dan Williams
2021-08-11  2:14           ` Dan Williams
2021-08-09 22:29 ` [PATCH 18/23] cxl/pmem: Translate NVDIMM label commands to CXL label commands Dan Williams
2021-08-09 22:29 ` [PATCH 19/23] cxl/pmem: Add support for multiple nvdimm-bridge objects Dan Williams
2021-08-09 22:29 ` [PATCH 20/23] tools/testing/cxl: Introduce a mocked-up CXL port hierarchy Dan Williams
2021-08-10 21:57   ` Ben Widawsky
2021-08-10 22:40     ` Dan Williams
2021-08-11 15:18       ` Ben Widawsky
     [not found]       ` <xp0k4.l2r85dw1p7do@intel.com>
2021-08-11 21:03         ` Dan Williams
2021-08-09 22:29 ` [PATCH 21/23] cxl/bus: Populate the target list at decoder create Dan Williams
2021-08-09 22:29 ` [PATCH 22/23] cxl/mbox: Move command definitions to common location Dan Williams
2021-08-09 22:29 ` [PATCH 23/23] tools/testing/cxl: Introduce a mock memory device + driver Dan Williams
2021-08-10 22:10 ` [PATCH 00/23] cxl_test: Enable CXL Topology and UAPI regression tests Ben Widawsky
2021-08-10 22:58   ` Dan Williams

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