When an io is rejected by nvmf_check_ready() due to validation of the
controller state, the nvmf_fail_nonready_command() will normally return
BLK_STS_RESOURCE to requeue and retry.  However, if the controller is
dying or the I/O is marked for NVMe multipath, the I/O is failed so that
the controller can terminate or so that the io can be issued on a
different path.  Unfortunately, as this reject point is before the
transport has accepted the command, blk-mq ends up completing the I/O
and never calls nvme_complete_rq(), which is where multipath may preserve
or re-route the I/O. The end result is, the device user ends up seeing an
EIO error.

Example: single path connectivity, controller is under load, and a reset
is induced.  An I/O is received:

  a) while the reset state has been set but the queues have yet to be
     stopped; or
  b) after queues are started (at end of reset) but before the reconnect
     has completed.

The I/O finishes with an EIO status.

This patch makes the following changes:

  - Adds the HOST_PATH_ERROR pathing status from TP4028
  - Modifies the reject point such that it appears to queue successfully,
    but actually completes the io with the new pathing status and calls
    nvme_complete_rq().
  - nvme_complete_rq() recognizes the new status, avoids resetting the
    controller (likely was already done in order to get this new status),
    and calls the multipather to clear the current path that errored.
    This allows the next command (retry or new command) to select a new
    path if there is one.
Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>