configurable block error injection

Hi all,

this series adds a new configurable block error injection facility.
We already have a few to inject block errors, but unfortunately most
of them are either not very useful or hard to use, or both:

 - The fail_make_request failure injection point can't distinguish
   different commands, different ranges in the file and can only injection
   plain I/O errors.
 - the should_fail_bio 'dynamic' failure injection has all the same issues
   as fail_make_request
 - dm-error can only fail all command in the table using BLK_STS_IOERR
   and requires setting up a new block device
 - dm-flakey and dm-dust allow all kinds of configurability, but still
   don't have good error selection, no good support for non-read/write
   commands and are limited to the dm table alignment requirements,
   which for zoned devices enforces setting them up for an entire zone.
   They also once again require setting up a stacked block device,
   which is really annoying in harnesses like xfstests

This series adds a new debugfs-based block layer error injection
that allows to configure what operations and ranges the injection
applied to, and what status to return.  It also allows to configure a
failure ratio similar to the xfs errortag injection.

As part of this the should_fail_bio is removed, as the should_fail_bio
function really gets in the way in it's current form, and the injection
of an errno which always gets turned into BLK_STS_IOERR doesn't make
much sense.  This required adjusting the bpf test suite as it attached
to this function as it assumed it to be present.

Diffstat:
 Documentation/block/error-injection.rst                    |   59 ++
 Documentation/block/index.rst                              |    1 
 block/Kconfig                                              |    6 
 block/Makefile                                             |    1 
 block/blk-core.c                                           |  128 ++---
 block/blk-merge.c                                          |    5 
 block/blk-mq.c                                             |    3 
 block/blk-sysfs.c                                          |    4 
 block/blk.h                                                |   24 
 block/error-injection.c                                    |  329 +++++++++++++
 block/genhd.c                                              |    4 
 include/linux/blk_types.h                                  |    2 
 include/linux/blkdev.h                                     |    5 
 lib/Kconfig.debug                                          |    6 
 tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c |    7 
 15 files changed, 507 insertions(+), 77 deletions(-)