On Mon, Jul 07, 2025 at 04:18:34PM +0200, Christoph Hellwig wrote: > Hi all, > > I'm a bit lost on what to do about the sad state of NVMe atomic writes. > > As a short reminder the main issues are: > > 1) there is no flag on a command to request atomic (aka non-torn) > behavior, instead writes adhering to the atomicy requirements will > never be torn, and writes not adhering them can be torn any time. > This differs from SCSI where atomic writes have to be be explicitly > requested and fail when they can't be satisfied > 2) the original way to indicate the main atomicy limit is the AWUPF > field, which is in Identify Controller, but specified in logical > blocks which only exist at a namespace layer. This a) lead to If controller-wide AWUPF is a must property, the length has to be aligned with block size. > various problems because the limit is a mess when namespace have > different logical block sizes, and it b) also causes additional > issues because NVMe allows it to be different for different > controllers in the same subsystem. The spec mentioned clearly that controller AWUPF should be supported by any namespace format: ``` Atomic Write Unit Power Fail (AWUPF): This field indicates the size of the write operation guaranteed to be written atomically to the NVM across all namespaces with any supported namespace format during a power fail or error condition. ``` So I am wondering why nvme driver can't validate NAWUN against AWUPF? Thanks, Ming
