On Apr 20 07:30, Christoph Hellwig wrote: > On Tue, Apr 19, 2022 at 02:10:36PM +0200, Klaus Jensen wrote: > > From: Klaus Jensen <k.jen...@samsung.com> > > > > Unconditionally set an EUI64 for namespaces. The nvme-ns device defaults > > to auto-generating a persistent EUI64 if not specified, but for single > > namespace setups (-device nvme,drive=...), this does not happen. > > > > Since the EUI64 has previously been zeroed it is not considered valid, > > so it should be safe to add this now. > > > > The generated EUI64 is of the form 52:54:00:<namespace counter>. Note, > > this is NOT the namespace identifier since that is not unique across > > subsystems; it is a global namespace counter. This has the effect that > > the value of this auto-generated EUI64 is dependent on the order with > > which the namespaces are created. If a more flexible setup is required, > > the eui64 namespace parameter should be explicitly set. Update the > > documentation to make this clear. > > How is this actually globally unique given that it uses a start value > that is incremented for each created namespace?
I think it is as good as we can do when we cannot store the EUI64 persistently anywhere. The EUI64s will be unique to a single QEMU instance. If someone wants to simulate a fabrics setup or something like that, then, as per the documentation, set the EUI explicitly. > Also EUI64 values are based on a OUI, while NVME_EUI64_DEFAULT seems > to have the OUI values cleared to all zero as far as I can tell. > It really should be a u8 array, yes, but won't the integer approach work? The "template" is byte swapped to big endian, or am I off here? > I would strongly advise againt autogenerating eui64 values. They are > small and have little entropy, and require at least three bytes (for > new allocations more) to be set to a IEEE assigned OUI. 52:54:00 is a "private" OUI if I am not mistaken (something about some bit being 1 or 0, cant remember the specifics) and is what QEMU uses when an IEEE OUI is needed (MAC-addresses etc.). This is also what the device uses in the IEEE field.
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