serial is required for -device nvme

Bug #1529449 reported by Tom Yan on 2015-12-27
8
This bug affects 1 person
Affects Status Importance Assigned to Milestone
QEMU
Undecided
Unassigned

Bug Description

I am not exactly sure if this is a bug, but I don't see why the option "serial" should be required for -device nvme like the option "drive". Truth is it seem to accept random string as its value anyway, if that's the case, couldn't qemu just generate one for it when it's not specified?

Tom Yan (tom-ty89) on 2015-12-27
description: updated

On Mon, Jan 11, 2016 at 05:35:50PM +0100, Markus Armbruster wrote:
> Tom Yan <email address hidden> writes:
> > Public bug reported:
> >
> > I am not exactly sure if this is a bug, but I don't see why the option
> > "serial" should be required for -device nvme like the option "drive".
> > Truth is it seem to accept random string as its value anyway, if that's
> > the case, couldn't qemu just generate one for it when it's not
> > specified?
>
> You should've included a reproducer. Here are mine:
>
> 1. Bad error reporting on missing drive:
>
> $ upstream-qemu -nodefaults -device nvme
> upstream-qemu: -device nvme: Device initialization failed
>
> Expected: error reported like for other devices, e.g.
>
> $ upstream-qemu -nodefaults -device virtio-blk
> upstream-qemu: -device virtio-blk: drive property not set
>
> 2. Bad error reporting on empty drive:
>
> $ upstream-qemu -nodefaults -drive if=none,id=foo -device nvme,drive=foo
> upstream-qemu: -device nvme,drive=foo: Device initialization failed
>
> Expected: error is reported like for other devices, e.g.
>
> $ upstream-qemu -nodefaults -drive if=none,id=foo -device virtio-blk,drive=foo
> upstream-qemu: -device virtio-blk,drive=foo: Device needs media, but drive is empty
>
> 3. Bad handling of missing serial:
>
> $ upstream-qemu -nodefaults -drive if=none,id=foo,file=tmp.qcow2 -device nvme,drive=foo
> upstream-qemu: -device nvme,drive=foo: Device initialization failed
>
> Expected: either default the serial number, like some other devices
> do, or a decent error message.
>
> I recommend to convert the device to realize(), and add the missing
> error_setg(). Keith?

Requiring a serial was a concious choice to push that responsibility
on the user, but I don't see a problem having the code provide default
serial string if the user does not over ride it.

If you've multiple nvme devices in your guest, creating the same serial
could cause problems with multipathing if they're basing end device
uniqueness on the serial (some do). If we have the code provide the
serial, perhaps it would be best to make each unique. That's easy enough
to append an incrementing number to the end of the serial.

Tom Yan (tom-ty89) wrote :

Instead of requiring a serial of arbitrary length/format, I think a WWN/EUI-64 is more useful/important, not to mention that the WWN/EUI-64 can pretty much always be used as the serial at the same time.

Unlike Linux, Windows consider the WWN/EUI-64 as the "serial":

"C:\Windows\system32>sg_vpd -i PD1
Device Identification VPD page:
  Addressed logical unit:
    designator type: SCSI name string, code set: UTF-8
      SCSI name string:
      8086QEMU NVMe Ctrl 00012BDAC262CF831698

C:\Windows\system32>sg_vpd -p sn PD1
Unit serial number VPD page:
  Unit serial number: 0000_0000_0000_0000."

(https://bugs.launchpad.net/qemu/+bug/1576347/+attachment/4650553/+files/02.PNG)

UEFI also makes use of the WWN/EUI-64 to generate boot entries for NVMe devices:
https://bugs.launchpad.net/qemu/+bug/1576347/+attachment/4650554/+files/03.png
https://bugs.launchpad.net/qemu/+bug/1576347/+attachment/4650555/+files/04.png

Download full text (4.5 KiB)

On 04/28/16 20:07, Tom Yan wrote:
> Instead of requiring a serial of arbitrary length/format, I think a
> WWN/EUI-64 is more useful/important,

WWN/EUI-64 is not "more important". Section "7.9 Unique Identifier" in
the NVMe spec (Revision 1.2a, October 23, 2015) says that the serial
number is mandatory, while implementing an EUI-64 is optional. Let me
quote it all (emphases mine):

> 7.9 Unique Identifier
>
> Information is returned in the Identify Controller data structure that
> may be used to construct a unique identifier. Specifically, the PCI
> Vendor ID, *Serial Number*, and Model Number fields when combined
> shall form a globally unique value that identifies the NVM subsystem.
> The mechanism used by the vendor to assign Serial Number and Model
> Number values to ensure uniqueness is *outside the scope* of this
> specification.
>
> An NVM subsystem may contain multiple controllers. All of the
> controllers that make up an NVM subsystem share the same NVM subsystem
> identifier (i.e., PCI Vendor ID, Serial Number, and Model Number). The
> Controller ID (CNTLID) value returned in the Identify Controller data
> structure may be used to uniquely identify a controller within an NVM
> subsystem. The Controller ID value when combined with the NVM
> subsystem identifier forms a globally unique value that identifies the
> controller. The mechanism used by the vendor to assign Controller ID
> values is outside the scope of this specification.
>
> The Identify Namespace data structure contains the IEEE Extended
> Unique Identifier (EUI64) and the Namespace Globally Unique Identifier
> (NGUID) fields. EUI64 is an 8-byte EUI-64 identifier and NGUID is a
> 16-byte identifier based on EUI-64. When creating a namespace, the
> controller specifies a globally unique value in the EUI64 or NGUID
> field (the controller may optionally specify a globally unique value
> in both fields). In cases where the 64-bit EUI64 field is unable to
> ensure a globally unique namespace identifier, the EUI64 field shall
> be cleared to 0h. *When not implemented*, these fields contain a value
> of 0h.

The QEMU device model conforms to this:

- The serial number is mandatory, and its generation is unspecified.
(First paragraph quoted.) Accordingly, QEMU forces the user to generate
and provide a serial number.

- The EUI64 is optional (third paragraph); it shall be zero-filled when
not implemented. QEMU conforms.

> not to mention that the WWN/EUI-64
> can pretty much always be used as the serial at the same time.
>
> Unlike Linux, Windows consider the WWN/EUI-64 as the "serial":

That's Windows's problem. Not the first (and not the last) occasion
where Microsoft interpret a specification creatively.

> "C:\Windows\system32>sg_vpd -i PD1
> Device Identification VPD page:
> Addressed logical unit:
> designator type: SCSI name string, code set: UTF-8
> SCSI name string:
> 8086QEMU NVMe Ctrl 00012BDAC262CF831698
>
> C:\Windows\system32>sg_vpd -p sn PD1
> Unit serial number VPD page:
> Unit serial number: 0000_0000_0000_0000."
>
> (https://bugs.launchpad.net/qemu/+bug/1576347/+attachment/4650553/+files/02.PNG)
>
> UEFI also mak...

Read more...

Tom Yan (tom-ty89) wrote :

Since both "drive=" and "serial=" expects an arbitrary string (while the value for "drive=" must be unique since it's the "id=" of a "-drive"), why not use the same string from "drive=" as the value of "serial=" when it's not specified explicitly?

Apparently "-device scsi-hd" has already been doing that (although it does not create the "sn" VPD when a serial is not explicitly specified).

Tom Yan (tom-ty89) wrote :
Tom Yan (tom-ty89) wrote :
To post a comment you must log in.
This report contains Public information  Edit
Everyone can see this information.

Other bug subscribers

Bug attachments