add option to interleave blktraces

Hi everyone,

Updates with v2:
- Added documentation for all patches in fio.1 and HOWTO
- Added to thread_options_pack and cconv.c
- Bumped the FIO_SERVER_VER number accordingly

From v1:
---
Understanding how a workload performs on different devices has been nice and easy given the infrastructure around blktrace, blkparse, and fio. Given a blktrace, fio can rerun that workload on a different drive.

Exploring colocation is a little tricker, but doable via adding multiple jobs in fio. An issue here is that the scheduler can influence the performance of each run as each job is async.

This patchset adds the ability to pass multiple blktrace binary dumps to "--read_iolog" as colon separated paths and then performs simple timestamp merging between the traces. Two additional parameters are added, "--merge_blktrace_scalars" and "--merge_blktrace_iters", to allow for scaling a particular trace and adjusting the number of iterations respectively.

In an example, given two 60s blktraces, A and B. Imagine we want to see how trace A would perform if we slowed it down by 50%. We can experiment here with --merge_blktrace_scalars="200:100" and --merge_blktrace_iters="1:2". This says to run the first blktrace over 200% of the time and the second at 100% running the first for a single iteration and the second for 2 iterations. This puts the overall runtime at 120s for each trace.

This patchset includes the following 4 patches:
0001-options-rename-name-string-operations-for-more-gener.patch 0002-blktrace-add-support-to-interleave-blktrace-files.patch 0003-blktrace-add-option-to-scale-a-trace.patch 0004-blktrace-add-option-to-iterate-over-a-trace-multiple.patch

0001 renames some string parsing functions to be more generic. 0002 adds basic merging support. 0003 adds merge_blktrace_scalars. 0004 adds merge_blktrace_iters.

diffstats below:

Dennis Zhou (4):
options: rename name string operations for more general use
blktrace: add support to interleave blktrace files
blktrace: add option to scale a trace
blktrace: add option to iterate over a trace multiple times

 HOWTO            |  71 ++++++++++++++++
 blktrace.c       | 210 +++++++++++++++++++++++++++++++++++++++++++++++
 blktrace.h       |  17 ++++
 cconv.c          |  15 ++++
 fio.1            |  66 +++++++++++++++
 init.c           |  21 +++++
 options.c        |  47 +++++++++--
 options.h        |   2 +
 server.h         |   2 +-
 thread_options.h |   6 ++
 10 files changed, 447 insertions(+), 10 deletions(-)

Thanks,
Dennis