[dm-devel] [PATCH] dm integrity: Document size and format of superblock fields

[Andy Grover]

On 11/9/18 12:21 PM, Andy Grover wrote:
> As mentioned elsewhere in dm-integrity.txt, creating a new integrity
> device requires creating a small integrity device on top of the base
> device that formats the base device, reading the provided data sectors
> out of the superblock, and then recreating the integrity device with the
> correct size. For this, userspace must know the offset, length, and
> endianness of the provided_data_sectors field in the superblock.
> 
> Document all fields mentioned in the txt to include this, based on struct
> superblock in dm-integrity.c. Extra fields in struct superblock not
> already mentioned in the txt remain undocumented.

In 4.19 I just noticed provided_data_sectors is now included in dm 
status. I'm assuming that is now the preferred way for userspace to 
discover this value? Thus making reading it from the on-disk superblock 
unnecessary, and thus *documenting* the superblock format unnecessary. 
Sounds good.

So please disregard this patch, although some different documentation 
changes are probably now needed.

Thanks -- Regards -- Andy

p.s. I'd just run across an issue where creating an integrity device on 
a loopback device would result in the superblock still reading as all 
zeroes. Another reason to do it the new way :)