The following patches were built over Linus's tree and this patchset https://lore.kernel.org/all/20221023030403.33845-24-michael.christie@xxxxxxxxxx/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.
