[NEW]Update the module args during runtime and save the new args value into the conf file

[hwware]

The problem/use-case that the feature addresses
Before Redis OSS 7, if we load a module with some args during runtime,
and run the command "config rewrite", the module information will not be saved into the
conf file.

Since Redis OSS 7 and Valkey 7.2, if we load a module with some args during runtime,
the module information (path, args number, and args value) can be saved into the conf file after config rewrite command is called.
Thus the module will be loaded automatically when the server startup next time.

Following is one example:

bind 172.25.0.58
port 7000
protected-mode no
enable-module-command yes

Generated by CONFIG REWRITE
latency-tracking-info-percentiles 50 99 99.9
dir "/home/ubuntu/valkey"
save 3600 1 300 100 60 10000
user default on nopass sanitize-payload ~* &* +@ALL
loadmodule tests/modules/datatype.so 10 20

However there is one problem.
If developers write a module, and update the running args by someway, the updated args can not be saved into the conf file even "config rewrite" is called.
The reason comes from the following function
rewriteConfigLoadmoduleOption (src/config.c)

void rewriteConfigLoadmoduleOption(struct rewriteConfigState *state) {
..........
struct ValkeyModule *module = dictGetVal(de);
line = sdsnew("loadmodule ");
line = sdscatsds(line, module->loadmod->path);
for (int i = 0; i < module->loadmod->argc; i++) {
line = sdscatlen(line, " ", 1);
line = sdscatsds(line, module->loadmod->argv[i]->ptr);
}
rewriteConfigRewriteLine(state, "loadmodule", line, 1);
.......
}

The function only save the initial args information (module->loadmod) into the conf file.

Description of the feature

There are 2 ways to solve the problem:

Solution 1: It needs to take 2 steps. (This option is not what we choose)

step 1: client calls command: MODULE SET-ARGUMENT <module_name> [args...] to update the args (module->loadmod) during runtime
step 2: client gets the updated args (module->loadmod) in the module through the new API ValkeyModule_GetRunTimeArgs(ctx);
Reference: #1041

Solution 2: it only takes 1 step

Call int VM_UpdateRunTimeArgs(ValkeyModuleCtx *ctx, int index, char *value) API in the module and update the specific args according to the index (module->loadmod).
Reference: hwware#8

Thus, I think the best way is to add a Module API to implement the above 2 features.

Alternatives you've considered

Administrators or developer could update the module args by the following way:

MODULE UNLOAD
Update module args in the conf file
MODULE LOAD

But I think there are following disadvantages:

1. some modules can not be unloaded. Such as the example module datatype.so, which is tests/modules/datatype.so
2. it is not atomic operation for MODULE UNLOAD + MODULE LOAD
3. sometimes, if we just run the module unload, the client business could be interrupted

Additional information

Any additional information that is relevant to the feature request.

[hwware]

https://github.com/valkey-io/valkey/issues/1079

[wuranxx]

In Redis7, a new module configuration mode is added. This mode seems to be more readable and elegant than adding parameters after loadmodule. In addition, this mode can control module configuration like the native Redis configuration.redis/redis#10285

Can this feature replace the way that add parameters after loadmodules? Do we recommend adding module parameters in a new way in valkey?

[hwware]

one of solutions is to add a module API to allow module developer to update the args as below:

ValkeyModule_UpdateRunTimeArgs(ValkeyModuleCtx *ctx, int index, char *value)
index is the arg index, and value is new args value

The example is here hwware#8

[madolson]

Core meeting notes:
We all agree about solution 2, letting the module update it's arguments, making the most sense. There was a discussion about the API, whether or not implement get APIs as well as have a single API to replace all of them.

Original proposal:

int VM_UpdateRunTimeArgs(ValkeyModuleCtx *ctx, int index, char *value);

Updated proposal:

RedisModuleString **values VM_GetRuntimeArgs(ValkeyModuleCtx *ctx);
int VM_UpdateRuntimeArgs(ValkeyModuleCtx *ctx, int argc, RedisModuleString **values);

Either option is OK. We'll decide in the PR which one to take.