sd: disable discard_zeroes_data for UNMAP
The T10 SBC UNMAP command does not provide any hard guarantees that blocks will return zeroes on a subsequent READ. This is due to the fact that the device server is free to silently ignore all or parts of the request. The only way to ensure that a block consistently returns zeroes after being unmapped is to use WRITE SAME with the UNMAP bit set. Should the device be unable to unmap one or more blocks described by the command it is required to manually write zeroes to them. Until now we have preferred UNMAP over the WRITE SAME variants to accommodate thinly provisioned devices that predated the final SBC-3 spec. This patch changes the heuristic so that we favor WRITE SAME(16) or (10) over UNMAP if these commands are marked as supported in the Logical Block Provisioning VPD page. The patch also disables discard_zeroes_data for devices operating in UNMAP mode. Signed-off-by:Martin K. Petersen <martin.petersen@oracle.com> Reviewed-by:
Paolo Bonzini <pbonzini@redhat.com> Signed-off-by:
Christoph Hellwig <hch@lst.de>
parent
e9afccc5
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