nvs_write: Bad documented return value.

[Vladimirek]

Docs say:

zephyr/include/fs/nvs.h

Lines 105 to 106 in 1342d12

	* @return Number of bytes written. On success, it will be equal to the number
	* of bytes requested to be written. On error returns -ERRNO code.

But when the key is already in flash with the same value zero is returned:

zephyr/subsys/fs/nvs/nvs.c

Lines 842 to 846 in 6acc4a2

	/* compare the data and if equal return 0 */
	rc = nvs_flash_block_cmp(fs, rd_addr, data, len);
	if (rc <= 0) {
	return rc;
	}

Need update code or doc header.

[Laczen]

@Vladimirek, thanks for reporting this. I am unsure what the error is, when a rewrite of the same data is done, nothing is written to flash, so nvs reports 0 (as documented).

Wether this operation is succesful or not, this can be discussed.

[Vladimirek]

so nvs reports 0 (as documented).
That is exactly what I missing. Simple note about 0 will be describe the situation exactly.
Number of bytes written. On success, it will be equal to the number of bytes requested to be written. Zero if value already present. On error returns -ERRNO code.
Yes I know that there is documented on other place, but who have a time read it all :-)

[nvlsianpu]

I think from user perspective API should return the number of bytes requested to be written for this case as well.

[nvlsianpu]

Will response to this in a patch.

[Laczen]

@nvlsianpu, I don't think a patch is needed. It should be possible for a user to distinguish between a real write to flash and a trial to rewrite. If a documentation update is required i leave up to you.

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[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.

[jefffhaynes]

@nvlsianpu, I don't think a patch is needed. It should be possible for a user to distinguish between a real write to flash and a trial to rewrite. If a documentation update is required i leave up to you.

Decisions like this are why zephyr isn't as successful as it could be. The user doesn't care how the data was written, only that it was written. This just makes the API needlessly confusing.