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settings: nvs: Fix first write issue with cache #69103

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merged 1 commit into from
Feb 26, 2024
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settings: nvs: Fix first write issue with cache #69103

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2 changes: 2 additions & 0 deletions subsys/settings/include/settings/settings_nvs.h
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,8 @@ struct settings_nvs {
} cache[CONFIG_SETTINGS_NVS_NAME_CACHE_SIZE];

uint16_t cache_next;
uint16_t cache_total;
bool loaded;
#endif
};

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23 changes: 23 additions & 0 deletions subsys/settings/src/settings_nvs.c
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Expand Up @@ -74,6 +74,8 @@ int settings_nvs_dst(struct settings_nvs *cf)
}

#if CONFIG_SETTINGS_NVS_NAME_CACHE
#define SETTINGS_NVS_CACHE_OVFL(cf) ((cf)->cache_total > ARRAY_SIZE((cf)->cache))

static void settings_nvs_cache_add(struct settings_nvs *cf, const char *name,
uint16_t name_id)
{
Expand Down Expand Up @@ -129,12 +131,22 @@ static int settings_nvs_load(struct settings_store *cs,
ssize_t rc1, rc2;
uint16_t name_id = NVS_NAMECNT_ID;

#if CONFIG_SETTINGS_NVS_NAME_CACHE
uint16_t cached = 0;

cf->loaded = false;
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This will disable the optimization if settings_load_subtree_direct with a handler that breaks the traversal before reaching NVS_NAMECNT_ID is used. It's still better than the existing behavior, so it's not a blocking comment, but just letting you know.

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Yeah, true. And also if an app loads a subtree (directly or not) several times, the cache will contain duplicated entries. The only way to make cache work correctly is to only use settings_load() unfortunately.

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Should we add info on that behavior to documentation?
Should we log an issue for that to be solved at some point?

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Regarding an issue I'm not certain. The cache kind of does what it is asked to do. An application should just be aware of this. I think documenting this behavior should be enough. I'll need to allocate a time to do this though.

#endif

name_id = cf->last_name_id + 1;

while (1) {

name_id--;
if (name_id == NVS_NAMECNT_ID) {
#if CONFIG_SETTINGS_NVS_NAME_CACHE
cf->loaded = true;
cf->cache_total = cached;
#endif
break;
}

Expand Down Expand Up @@ -186,6 +198,7 @@ static int settings_nvs_load(struct settings_store *cs,

#if CONFIG_SETTINGS_NVS_NAME_CACHE
settings_nvs_cache_add(cf, name, name_id);
cached++;
#endif

ret = settings_call_set_handler(
Expand Down Expand Up @@ -231,6 +244,13 @@ static int settings_nvs_save(struct settings_store *cs, const char *name,
write_name_id = cf->last_name_id + 1;
write_name = true;

#if CONFIG_SETTINGS_NVS_NAME_CACHE
/* We can skip reading NVS if we know that the cache wasn't overflowed. */
if (cf->loaded && !SETTINGS_NVS_CACHE_OVFL(cf)) {
goto found;
}
#endif

while (1) {
name_id--;
if (name_id == NVS_NAMECNT_ID) {
Expand Down Expand Up @@ -325,6 +345,9 @@ static int settings_nvs_save(struct settings_store *cs, const char *name,
#if CONFIG_SETTINGS_NVS_NAME_CACHE
if (!name_in_cache) {
settings_nvs_cache_add(cf, name, write_name_id);
if (cf->loaded && !SETTINGS_NVS_CACHE_OVFL(cf)) {
cf->cache_total++;
}
}
#endif

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