[PATCH v3 00/19] Use block pr_ops in LIO

[Mike Christie <michael.christie@oracle.com>]

The following patches were built over Linus's tree and this patchset

https://lore.kernel.org/all/20221023030403.33845-24-michael.christie@oracle.com/t/

which allows the SCSI layer passthrough users to control retries for
commands like PRs used in this patchset.

The patches in this thread allow us to use the block pr_ops with LIO's
target_core_iblock module to support cluster applications in VMs.
Currently, to use windows clustering or linux clustering (pacemaker +
cluster labs scsi fence agents) in VMs with LIO and vhost-scsi, you have
to use tcmu or pscsi or use a cluster aware FS/framework for the LIO pr
file. Setting up a cluster FS/framework is pain and waste when your real
backend device is already a distributed device, and pscsi and tcmu are
nice for specific use cases, but iblock gives you the best performance and
allows you to use stacked devices like dm-multipath. So these patches
allow iblock to work like pscsi/tcmu where they can pass a PR command to
the backend module. And then iblock will use the pr_ops to pass the PR
command to the real devices similar to what we do for unmap today.

The patches are separated in the following groups:

patches 1 - 11
- Add callouts to read a reservation and it's keys.

patches 12 - 15
- Have pr_ops return a blk_status_t.

patches 16 - 19
- Support for target_core_iblock to bypass the emulate PR code and call
the pr_ops.

This patchset has been tested with the libiscsi PGR ops and with window's
failover cluster verification test.

v3:
- Fix patch subject formatting.
- Fix coding style.
- Rearrange patches so helpers are added with users to avoid compilation
errors.
- Move pr type conversion to array and add nvme_pr_type.
- Add Extended Data Structure control flag enum and use in code for checks.
- Move nvme pr code to new file.
- Add more info to patch subjects about why we need to add blk_status
to pr_ops.
- Use generic SCSI passthrough error handling interface.
- Fix checkpatch --strict errors. Note that I kept the existing coding
style that it complained about because it looked like it was the preferred
style for the code and I didn't want a mix and match.

v2:
- Drop BLK_STS_NEXUS rename changes. Will do separately.
- Add NVMe support.
- Fixed bug in target_core_iblock where a variable was not initialized
mentioned by Christoph.
- Fixed sd pr_ops UA handling issue found when running libiscsi PGR tests.
- Added patches to allow pr_ops to pass up a BLK_STS so we could return
a RESERVATION_CONFLICT status when a pr_ops callout fails.