NVMe: Retry failed commands with non-fatal errors

For commands returned with failed status, queue these for resubmission and continue retrying them until success or for a limited amount of time. The final timeout was arbitrarily chosen so requests can't be retried indefinitely. Since these are requeued on the nvmeq that submitted the command, the callbacks have to take an nvmeq instead of an nvme_dev as a parameter so that we can use the locked queue to append the iod to retry later. The nvme_iod conviently can be used to track how long we've been trying to successfully complete an iod request. The nvme_iod also provides the nvme prp dma mappings, so I had to move a few things around so we can keep those mappings.

KBKeith Busch committed 12 years ago