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nvs: Check if an item is modified before writing out an identical copy

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This prevents wear and tear on the flash, and it also is faster in some
cases since the read-out of flash is a cheaper operation than the erasure
of flash.  Some library modules (such as the esp_wifi) write out to NVS
upon every initialization without checking first that the existing value
is the same, and this speeds up initialization of modules that make
these design choices and moves it into a centralized place.

The comparison functions are based on the read-out functions of the same
name, and changes out the memcpy(...) operations for memcmp(...)
operations.

Signed-off-by: Tim Nordell <tim.nordell@nimbelink.com>
This commit is contained in:
Tim Nordell
2019-04-15 14:06:57 -05:00
parent ba1ff1692b
commit c3fa2497b9
6 changed files with 176 additions and 5 deletions
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56
components/nvs_flash/src/nvs_storage.cpp
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@@ -269,6 +269,13 @@ esp_err_t Storage::writeItem(uint8_t nsIndex, ItemType datatype, const char* key
VerOffset prevStart, nextStart;
prevStart = nextStart = VerOffset::VER_0_OFFSET;
if (findPage) {
// Do a sanity check that the item in question is actually being modified.
// If it isn't, it is cheaper to purposefully not write out new data.
// since it may invoke an erasure of flash.
if (cmpMultiPageBlob(nsIndex, key, data, dataSize) == ESP_OK) {
return ESP_OK;
}
if (findPage->state() == Page::PageState::UNINITIALIZED ||
findPage->state() == Page::PageState::INVALID) {
ESP_ERROR_CHECK(findItem(nsIndex, datatype, key, findPage, item));
@@ -311,6 +318,13 @@ esp_err_t Storage::writeItem(uint8_t nsIndex, ItemType datatype, const char* key
}
}
} else {
// Do a sanity check that the item in question is actually being modified.
// If it isn't, it is cheaper to purposefully not write out new data.
// since it may invoke an erasure of flash.
if (findPage != nullptr &&
findPage->cmpItem(nsIndex, datatype, key, data, dataSize) == ESP_OK) {
return ESP_OK;
}
Page& page = getCurrentPage();
err = page.writeItem(nsIndex, datatype, key, data, dataSize);
@@ -443,6 +457,48 @@ esp_err_t Storage::readMultiPageBlob(uint8_t nsIndex, const char* key, void* dat
return err;
}
esp_err_t Storage::cmpMultiPageBlob(uint8_t nsIndex, const char* key, const void* data, size_t dataSize)
{
Item item;
Page* findPage = nullptr;
/* First read the blob index */
auto err = findItem(nsIndex, ItemType::BLOB_IDX, key, findPage, item);
if (err != ESP_OK) {
return err;
}
uint8_t chunkCount = item.blobIndex.chunkCount;
VerOffset chunkStart = item.blobIndex.chunkStart;
size_t readSize = item.blobIndex.dataSize;
size_t offset = 0;
if (dataSize != readSize) {
return ESP_ERR_NVS_CONTENT_DIFFERS;
}
/* Now read corresponding chunks */
for (uint8_t chunkNum = 0; chunkNum < chunkCount; chunkNum++) {
err = findItem(nsIndex, ItemType::BLOB_DATA, key, findPage, item, static_cast<uint8_t> (chunkStart) + chunkNum);
if (err != ESP_OK) {
if (err == ESP_ERR_NVS_NOT_FOUND) {
break;
}
return err;
}
err = findPage->cmpItem(nsIndex, ItemType::BLOB_DATA, key, static_cast<const uint8_t*>(data) + offset, item.varLength.dataSize, static_cast<uint8_t> (chunkStart) + chunkNum);
if (err != ESP_OK) {
return err;
}
assert(static_cast<uint8_t> (chunkStart) + chunkNum == item.chunkIndex);
offset += item.varLength.dataSize;
}
if (err == ESP_OK) {
assert(offset == dataSize);
}
return err;
}
esp_err_t Storage::readItem(uint8_t nsIndex, ItemType datatype, const char* key, void* data, size_t dataSize)
{
if (mState != StorageState::ACTIVE) {