Re: [PATCH v3 10/15] block: Add fops atomic write support

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On 13/02/2024 11:08, Nilay Shroff wrote:
It's relied that atomic_write_unit_max is <= atomic_write_boundary and both are a power-of-2. Please see the NVMe patch, which this is checked. Indeed, it would not make sense if atomic_write_unit_max > atomic_write_boundary (when non-zero).

So if the write is naturally aligned and its size is <= atomic_write_unit_max, then it cannot be straddling a boundary.
Ok fine but in case the device doesn't support namespace atomic boundary size (i.e. NABSPF is zero) then still do we need
to restrict IO which crosses the atomic boundary?

Is there a boundary if NABSPF is zero?

I am quoting this from NVMe spec (Command Set Specification, revision 1.0a, Section :
"To ensure backwards compatibility, the values reported for AWUN, AWUPF, and ACWU shall be set such that
they  are  supported  even  if  a  write  crosses  an  atomic  boundary.  If  a  controller  does  not
guarantee atomicity across atomic boundaries, the controller shall set AWUN, AWUPF, and ACWU to 0h (1 LBA)."

How about respond to the NVMe patch in this series, asking this question?

I have my idea on how the boundary is determined, but I think that the spec could be made clearer.


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