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

[Milan Broz]

On 13/11/2018 01:23, Andy Grover wrote:
> 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.

Yes, I think Mikulas added this for this reason. We still read
superblock in integritysetup to be compatible with the older targets,
but you should not need it with 4.19+.

> So please disregard this patch, although some different documentation 
> changes are probably now needed.
Actually, meta_device option is not documented at all, and new status
line is undocumented as well (I can send patch for this later).

Anyway,  I have another page that describes dm-integrity options
(maintaining this while adding options to integritysetup, similar page
exists for DMcrypt and DMverity)
https://gitlab.com/cryptsetup/cryptsetup/wikis/DMIntegrity

m.