hw/block/nvme: add the dataset management command
Add support for the Dataset Management command and the Deallocate attribute. Deallocation results in discards being sent to the underlying block device. Whether of not the blocks are actually deallocated is affected by the same factors as Write Zeroes (see previous commit). format | discard | dsm (512B) dsm (4KiB) dsm (64KiB) -------------------------------------------------------- qcow2 ignore n n n qcow2 unmap n n y raw ignore n n n raw unmap n y y Again, a raw format and 4KiB LBAs are preferable. In order to set the Namespace Preferred Deallocate Granularity and Alignment fields (NPDG and NPDA), choose a sane minimum discard granularity of 4KiB. If we are using a passthru device supporting discard at a 512B granularity, user should set the discard_granularity property explicitly. NPDG and NPDA will also account for the cluster_size of the block driver if required (i.e. for QCOW2). See NVM Express 1.3d, Section 6.7 ("Dataset Management command"). Signed-off-by: NKlaus Jensen <k.jensen@samsung.com> Reviewed-by: NKeith Busch <kbusch@kernel.org>
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