io_u->numberio is used to keep track of the sequence number of writes
and verify reads. It is entirely feasible to issue millions or even
billions of IOs in a singe load, so let's use enough bits to handle
that.

numberio is copied into io_piece and verify_header, so update those
structs accordingly.

Signed-off-by: Riley Thomasson <[email protected]>

Currently, fio keeps track of a finite number of recent write
completions for each file in fio_file->last_write_comp. This information
is saved/loaded as part of the "verify state." The verify code
(verify_state_should_stop(), specifically) assumes that any write issued
before these recorded writes must have been successfully completed. This
is not generally true for iodepth > 1 and if writes are completed
out-of-order.

Consider this example: a single write stalls while all other writes
complete normally. This condition can persist for an arbitrarily long
time, and the stalled write will fall out of the range "covered" by
last_write_comp. Saving state at this point (e.g. via a trigger) and
halting the workload (e.g. via power-cycling the machine) will result in
that stalled write being verified when the state is loaded despite the
fact that the write may have never completed.

Instead of tracking the last N write completions, we can instead track
(1) the maximum issued sequence number, and (2) the sequence numbers for
all in-flight writes. The "sequence number" here is a monotonically
increasing value assigned to each write and verifying read (this is
already implemented as io_u->numberio). An "in-flight" write is a write
which has been issued but not yet completed. Furthermore, the number of
in-flight writes is bounded by the iodepth.

We can accomplish this by using a simple array of sequence numbers,
which are initialized to an invalid value. Before issuing a write, its
sequence number is written to a "free" slot, and then the maximum issued
sequence number is incremented. After completing a write, its slot is
changed back to the invalid value. On the verify side, we are allowed to
verify as long as the current sequence number is <= the maximum issued
sequence number AND it is not present in the inflight list.

Saving/loading this information in the verify state and using it in
verify_state_should_stop() is covered in a subsequent patch.

Fixes: Issue axboe#1950

Signed-off-by: Riley Thomasson <[email protected]>