[RFC for-next 0/3] block: delay support for error injection

[Md Haris Iqbal]

Error injection can only fail a bio today.  This adds a delay_us option so
that a rule can hold a bio back first, to model a slow device.

The delay happens above the driver, so it is invisible to the I/O
statistics and never reaches the blk-mq timeout handler or SCSI error
handling.  What it does exercise is the code waiting above the block
layer: io_uring cancellation, hung task detection, and filesystem or
userspace timeouts.

Two things are worth a look.  A delayed bio is resubmitted below the
injection hook, so the rules are not applied to it again and it can never
pick up a status from another rule.  And holding a bio back reorders it
against bios submitted later, which breaks sequential write ordering on
zoned devices.  Both are documented in patch 3.

Patch 1 is a prep cleanup.  It moves the rejection of an unknown status
tag into the parser, because patch 2 makes a rule without a status valid.

Tested in a VM.

Md Haris Iqbal (3):
  block: reject unknown status tags in error injection rules
  block: allow error injection rules to delay bios
  Documentation: block: document error injection delays

 Documentation/block/error-injection.rst |  56 ++++++++-
 block/blk-core.c                        |  13 +-
 block/blk.h                             |   1 +
 block/error-injection.c                 | 154 +++++++++++++++++++++---
 4 files changed, 201 insertions(+), 23 deletions(-)

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2.53.0