deprecate-rpc

Deprecate SPDK RPC Parameters or Entire RPCs

Use this skill when asked to deprecate an RPC parameter, rename/replace a parameter, or deprecate an entire RPC method in SPDK.

Overview

SPDK requires at least one full release of deprecation notice before removal: announce in release N, remove no earlier than release N+1. Deprecating a parameter or RPC touches eight areas that must all stay in sync.

---

Phase 1 -- Deprecate (announce release)

Work through each file group in order. Every step is mandatory unless marked otherwise.

1. schema/schema.json -- mark the parameter deprecated

Add "deprecated": true to the parameter object in the schema.

{
  "name": "old_param_name",
  "type": "uint32",
  "deprecated": true,
  "description": "Old description. Default: 0"
}

If the parameter is being replaced by a new one, add the new parameter entry in the same params array (keep it near the deprecated one for readability).

2. lib/*/*.c -- register the deprecation and emit warnings

Use the SPDK_LOG_DEPRECATION_REGISTER / SPDK_LOG_DEPRECATED macros.

SPDK_LOG_DEPRECATION_REGISTER(tag_name,
                  "use new_param instead", "vXX.YY",
                  SPDK_LOG_DEPRECATION_EVERY_24H);

Pick the rate limit that fits:

If the old parameter still needs to work during the deprecation window, write a custom JSON decoder wrapper that (a) logs the deprecation and (b) delegates to the real decoder:

static int
decode_old_param(const struct spdk_json_val *val, void *out)
{
    SPDK_LOG_DEPRECATED(tag_name);
    return spdk_json_decode_uint32(val, out);
}

Then swap the decoder in the spdk_json_object_decoder table:

- {"old_param", offsetof(...), spdk_json_decode_uint32, true},
+ {"old_param", offsetof(...), decode_old_param, true},

If there is conversion logic (old units -> new units), keep it in the RPC handler with a sentinel check (e.g. UINT64_MAX means "not supplied") so the old parameter still works during the deprecation period.

3. Config writer / dump function -- emit the new parameter name

If the subsystem has a config-dump or state-save function (typically in *_tgt.c or similar, using spdk_json_write_* APIs), update it to emit the new parameter name. This ensures that any saved configuration written by a running instance already uses the replacement name, so reloading the config will not trigger deprecation warnings.

/* Before */
spdk_json_write_named_string(w, "old_param", value);

/* After */
spdk_json_write_named_string(w, "new_param", value);

If the type changed (e.g. comma-separated string to JSON array), rewrite the serialization logic to match the new schema type.

4. python/spdk/cli/*.py -- update argparse help text

The genrpc.py lint (lint_py_cli) requires the word Deprecated (capital D) in the help= string of any parameter whose schema has "deprecated": true.

# Before
p.add_argument('--old-param', help='Old description', type=int)

# After -- add deprecation notice pointing to the replacement
p.add_argument('--old-param',
               help='Old description. Deprecated, use --new-param instead.',
               type=int)

If the old param and new param are mutually exclusive, wrap them in a p.add_mutually_exclusive_group():

group = p.add_mutually_exclusive_group()
group.add_argument('--old-param', dest='old_param',
                   help='Old description. Deprecated, use --new-param instead.',
                   type=int)
group.add_argument('--new-param', help='New description', type=int)

5. Tests -- migrate all usages to the new parameter/RPC

Search the entire tree for every test that passes the deprecated parameter or calls the deprecated RPC and switch it to the replacement immediately. Do not leave tests using the old name -- the deprecation window is for external consumers, not for the project's own test suite.

# Find all references in tests (adjust the pattern to match your case)
grep -rn 'old_param\|old_rpc_name' test/

For each hit:

• Replace the old parameter/RPC with the new one in the test JSON payloads, Python RPC calls, and bash rpc_cmd invocations.
• If a test specifically validates that the deprecated path still works (compat test), keep it but add a comment noting the target removal release.
• Run the affected test suite to confirm nothing breaks.

6. deprecation.md -- add a notice section

Under the appropriate ### subsystem heading, add a #### entry whose title is the tag name used in SPDK_LOG_DEPRECATION_REGISTER:

#### `tag_name`

The `old_param` parameter of `rpc_method_name` RPC is deprecated and will be
removed in vXX.YY. Use `new_param` instead.

7. Verify

Run the genrpc lint to confirm schema, CLI, and deprecation annotations are consistent:

python3 scripts/genrpc.py --lint

This checks:

• Every schema param with "deprecated": true has Deprecated in CLI help
• Schema params and CLI args are in sync
• Type mappings are correct

---

Phase 2 -- Remove (target release)

Once the target release arrives, remove all compat/shim code.

1. schema/schema.json -- delete the deprecated parameter entry

Remove the entire parameter object from the params array. Clean up any descriptions on the replacement param that reference the old name.

2. lib/*/*.c -- remove deprecation machinery

Delete in this order:

1. SPDK_LOG_DEPRECATION_REGISTER(...) block
2. Custom decoder wrapper function (e.g. decode_old_param)
3. Decoder table entry {"old_param", ...}
4. Sentinel initialization (e.g. req.old_param = UINT64_MAX;)
5. Conversion / compat logic in the RPC handler
6. Any field in the RPC context struct that only existed for the old param

3. python/spdk/cli/*.py -- simplify CLI

• Remove the deprecated add_argument call
• If a mutually-exclusive group was used, dissolve it and keep only the replacement argument as a standalone add_argument
• Remove any dest= aliasing that was only needed for the old name

4. Tests -- remove any remaining compat test references

If any compat tests were kept during Phase 1, delete them now. Grep the test tree one more time to confirm zero references to the old parameter or RPC name remain:

grep -rn 'old_param\|old_rpc_name' test/

5. deprecation.md -- remove the notice section

Delete the #### block for this tag.

6. CHANGELOG.md -- document the removal

Under the upcoming release heading, add a removal note:

### subsystem_name

Removed the deprecated `old_param` parameter from the `rpc_method_name` RPC.
Use `new_param` instead.

7. Verify

python3 scripts/genrpc.py --lint

---

Deprecating an Entire RPC (not just a parameter)

The same two-phase approach applies, but with broader scope:

Phase 1 (deprecate):

1. SPDK_LOG_DEPRECATION_REGISTER at the top of the RPC handler.
2. Call SPDK_LOG_DEPRECATED(tag) at the start of the handler function.
3. Add "deprecated": true to the method object in schema/schema.json (at the method level, not param level).
4. Update the config writer/dump function to call the replacement RPC.
5. Add [Deprecated] to the CLI help= and/or subparser description.
6. Migrate all tests to the replacement RPC (same rules as parameter Phase 1 step 5).
7. Add a deprecation.md section.

Phase 2 (remove):

1. Delete the entire RPC handler, decoder table, and context struct.
2. Remove the SPDK_RPC_REGISTER(...) call.
3. Delete the CLI subparser (the add_parser block).
4. Remove from schema/schema.json.
5. Remove any remaining test references to the old RPC.
6. Remove deprecation.md entry; add CHANGELOG.md entry.

---

Quick Checklist

Deprecate:
  [ ] schema/schema.json    -- "deprecated": true (+ new param if replacing)
  [ ] lib/*/*.c              -- SPDK_LOG_DEPRECATION_REGISTER + custom decoder
  [ ] config writer          -- emit new param name in dump/save function
  [ ] python/spdk/cli/*.py   -- "Deprecated" in help text
  [ ] test/                  -- migrate all test usages to new param/RPC
  [ ] deprecation.md         -- #### tag_name section
  [ ] genrpc lint passes     -- python3 scripts/genrpc.py --lint

Remove:
  [ ] schema/schema.json    -- delete deprecated param entry
  [ ] lib/*/*.c              -- delete register, decoder, compat logic
  [ ] python/spdk/cli/*.py   -- delete old arg, dissolve exclusive groups
  [ ] test/                  -- remove remaining compat test references
  [ ] deprecation.md         -- delete section
  [ ] CHANGELOG.md           -- add removal note
  [ ] genrpc lint passes     -- python3 scripts/genrpc.py --lint

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