NCS settings subsystem loading order

[db_lw]

Hello everyone,

I'm using the NCS/Zephyr settings subsystem to store some application data in non-volatile memory.

The settings structure looks something like this:

app/peripherals
app/config/0

I use the SETTINGS_STATIC_HANDLER_DEFINE to register two set-functions one for <app/peripherals> and one for <app/config>. I would like to have the <app/peripherals> settings before the other stuff but the set-function for <app/config> is always called before the other one.

I was wondering if I could affect the order in which the set-functions are called?

Thanks in advance!

[ovrebekk]

Hi 

Have you tried to change the order of your calls to settings_register() to see if it changes the order in which the set functions are called?

If this doesn't work I will check with the software developers if there is some way to influence this. 

Best regards
Torbjørn

[db_lw]

Hello Torbjørn,

at the moment I don't use the settings_register() function, instead I use the SETTINGS_STATIC_HANDLER_DEFINE() because I don't need the dynamic handler. If I change the order of this macro calls it doesn't influence the settings read order.

Best regards,
David

[ovrebekk]

Hi David

Apparently there is no API to set the order explicitly, but they are organized alphabetically by the handler name. 

In other words you can influence the order by adding a prefix to the handler name, something like this:

aa_first_handler
ab_second_handler

Best regards
Torbjørn

[db_lw]

I can't get it to work, that the settings are read in the order i want.

Here is a basic example that I tried:

static int alpha_handle_set(const char *key, size_t len_rd,
			settings_read_cb read_cb, void *cb_arg)
{
    LOG_INF("ALPHA");

    return 0;
}


SETTINGS_STATIC_HANDLER_DEFINE(alpha_handler, "alpha", NULL, alpha_handle_set,
			       NULL, NULL);

static int beta_handle_set(const char *key, size_t len_rd,
			settings_read_cb read_cb, void *cb_arg)
{
    LOG_INF("BETA");

    return 0;
}

SETTINGS_STATIC_HANDLER_DEFINE(beta_handler, "beta", NULL, beta_handle_set,
			       NULL, NULL);

static int store_settings(void)
{
    int err;
    static uint32_t value[] = {0xAAAAAAAA, 0xBBBBBBBB};
    const char alpha[] = "alpha";
    const char beta[] = "beta";
    const char *key[] = {alpha, beta};

    for (uint8_t i = 0; i < ARRAY_SIZE(value); i++) {       // VARIANT 1 (Save alpha first)
    //for (int8_t i = ARRAY_SIZE(value) - 1; i >= 0; i--) { // VARIANT 2 (Save beta first)
        err = settings_save_one(key[i], &value[i], sizeof(value[i]));
        if (err) {
            LOG_ERR("Couldn't save %s", key[i]);
            return err;
        }
    }

    return 0;
}

When I use this code it doesn't matter how I name the handlers but the order how I write the settings entries is relevant. If I write alpha and then beta the beta handler is always called first and if I write beta and then alpha the alpha handler is called first.

ovrebekk said:

In other words you can influence the order by adding a prefix to the handler name, something like this:

aa_first_handler
ab_second_handler

In my case the alpha_handler should always be called before the beta_handler am I right?

Best regards,
David

[ovrebekk]

Hi David

You mean to say the order at which you call the SETTINGS_STATIC_HANDLER_DEFINE macros decide which of the set functions is run first?

db_lw said:

In my case the alpha_handler should always be called before the beta_handler am I right?

That was my expectation, yes, but based on your findings this might not be the case. 

Best regards
Torbjørn

[db_lw]

ovrebekk said:

You mean to say the order at which you call the SETTINGS_STATIC_HANDLER_DEFINE macros decide which of the set functions is run first?

No, I mean the order in which I store the settings decides which of the set functions is run first.

It seems like it doesn't matter what I do with SETTINGS_STATIC_HANDLER_DEFINE macro. I tried the following things:

• Change the order of the SETTINGS_STATIC_HANDLER_DEFINE macro calls.
• Change the handler names to aa_handler and ab_handler.
• Change the key strings.

Nothing of those things changed the order in which the set functions are run.

Best regards,
David

[ovrebekk]

Hi David

Thanks for the input. 

Unfortunately it seems there is no way to reliably affect the order of the callbacks then. This would be influenced by how the underlying file system reads out the records, which is something that could change if you change the file system, or if the file system is updated later on. 

I would recommend that you modify your code to take this into account, and ensure that any 'order dependent' code is not run until all the set callbacks have been run (for instance by having all the set callbacks release (give) a semaphore that you can wait for somewhere else in the code). 

Best regards
Torbjørn