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https://github.com/SCST-project/scst.git
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Gleb Chesnokov
e7ad7e093e
The scst_user specification copies ioctl structures and command payloads that predate several ABI extensions. Building a handler from those layouts can select the wrong union member, alignment or completion path. Commit3fc775c75a("EXTENDED COPY support") added remapping payloads. Commitdaee4dcb7e("WRITE SAME command improvements") added WRITE SAME descriptors. Commitd1bd22afd9("scst_user: avoid global locks") left the explicit unregister ioctl as an obsolete no-op. Use scst/include/scst_user.h and scst_user.c as the producer-side source of truth. Synchronize registration, command, reply and subcommand layouts, version checks, reserved fields and ioctl rules. Update the fileio_tgt, stpgd and event guides from current code. Make live-storage and event-consumption risks explicit.
62 lines
2.4 KiB
Plaintext
62 lines
2.4 KiB
Plaintext
stpgd explicit ALUA helper
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==========================
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stpgd is the user-space consumer for explicit ALUA state-transition events.
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It opens the SCST event device, subscribes to events issued by the SCST core,
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and handles SCST_EVENT_STPG_USER_INVOKE by executing an external helper once
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for each target-port-group descriptor. The helper's exit status is reported
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back to the kernel through SCST_EVENT_NOTIFY_DONE.
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The event payload and ioctl ABI are defined in scst/include/scst_event.h.
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The current event filtering, helper invocation, timeout handling, and
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command-line parsing are implemented in usr/stpgd/stpgd_main.c.
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Build and invocation
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--------------------
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From the repository root, "make usr" builds stpgd and fileio_tgt. To build
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only this daemon, run "make -C usr/stpgd". Installation is a separate,
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privileged operation.
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stpgd [OPTIONS]
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- -f, --foreground: do not daemonize
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- -p, --path=PATH: absolute path to the executable transition helper
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- -t, --timeout=SECONDS: helper timeout; the default is 17 seconds
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- -v, --version: print the program version
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- -h, --help: print usage information
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The -d/--debug option is present only when tracing or debugging is compiled
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in. Without -p, the daemon uses /usr/local/bin/scst/scst_on_stpg. If a
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different installation prefix is used, pass the installed helper path
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explicitly.
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Helper interface
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----------------
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The helper receives these five positional arguments, in order:
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1. SCST device name
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2. previous ALUA state
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3. requested ALUA state
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4. device-group name
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5. target-group name
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The same values are supplied as SCST_DEVICE_NAME, SCST_PREV_ALUA_STATE,
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SCST_ALUA_STATE, SCST_DEVICE_GROUP, and SCST_TARGET_GROUP in the helper's
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environment. The daemon supplies a restricted PATH containing /bin,
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/usr/bin, /sbin, and /usr/sbin.
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Safety
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------
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usr/stpgd/scst_on_stpg is only a minimal example. It writes the requested
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state directly to the target group's live SCST sysfs attribute; it does not
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coordinate replication, fencing, failover, or cluster-manager state. Do not
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run stpgd or deploy that helper until the transition workflow has been adapted
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and validated for the exact hosts, storage, target groups, and HA stack.
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SCST blocks the affected devices around the explicit transition event, as
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described in the explicit ALUA section of scst/README. The external helper is
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still responsible for performing every site-specific transition safely.
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