[v3 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 tests the code waiting above the block
layer, not the blk-mq timeout handler.

A delayed bio is marked with a new BIO_ERROR_INJECTED flag so the rules
are not applied to it again, even after a split.  Christoph asked on v2
to avoid the flag by allowing a delay only together with an error.  I kept
delay-only rules, as a slow device that succeeds is the more useful case,
so the flag question is still open.

Holding a bio back reorders it against bios submitted later, which breaks
sequential write ordering on zoned devices.

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.

v1: https://lore.kernel.org/linux-block/20260827000115.128093-1-haris.iqbal@xxxxxxxxx/
v2: https://lore.kernel.org/linux-block/20260830012002.80275-1-haris.iqbal@xxxxxxxxx/

Changes since v2:

 - Patch 1: return bool, rewrite the commit message.

 - Patch 2: drop __submit_bio_noacct_nocheck(); the flag alone stops the
   rules being applied again.  Log the error when a delayed bio is failed.

 - Patch 3: trim the documentation.

Changes since v1:

 - Add the BIO_ERROR_INJECTED bio flag.  v1 only resubmitted a delayed bio
   below the injection hook, which left the remainder of a split going
   through the hook and matching the same rule again, so a bio was held
   once per split instead of once.

 - Patch 1: tag_to_blk_status() returns an error and passes the status back
   through a pointer, instead of returning BLK_STS_OK for both the "OK" tag
   and an unknown one.  A delay-only rule has no status, so the two have to
   be told apart.

 - Documentation: a delayed bio is held once rather than once per split.

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 delay feature

 Documentation/block/error-injection.rst |  39 +++++-
 block/blk-core.c                        |  14 +-
 block/blk.h                             |   2 +-
 block/error-injection.c                 | 167 +++++++++++++++++++++---
 block/error-injection.h                 |   1 +
 include/linux/blk_types.h               |   1 +
 6 files changed, 192 insertions(+), 32 deletions(-)

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2.53.0