This update is mainly motivated by an attempt to make the discard_zeroes_data reporting more accurate. As we have discussed several times in the past we are stuck with pretty weak guarantees from the T10/T13 standards. And as a result we feel compelled to tighten up the scenarios under which we advertise discard_zeroes_data since several applications and subsystems depend on it being accurate. The first patch is the most controversial. It disables discard_zeroes_data for libata devices unless they explicitly have been whitelisted. I had hoped to have a more comprehensive list of drives but I didn't have much luck in procuring the identify strings that would allow me to generate the whitelist matching patterns. I could use some help here. The second patch tweaks the SCSI disk driver to prefer WRITE SAME w/ UNMAP instead of the UNMAP command since the former has deterministic behavior. The lack of a hard discard_zeroes_data guarantees has also prevented us from having a variant of blkdev_issue_zeroout() that discards if possible. The last patch in this series will add such a call that the filesystems and virt block drivers can use to clear and deprovision block ranges. -- Martin K. Petersen Oracle Linux Engineering -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
