Re: sysfs integrity fields use

[Milan Broz <gmazyland@gmail.com>]

On 2/25/25 11:10 AM, Kanchan Joshi wrote:
> On 2/25/2025 2:53 PM, Milan Broz wrote:
>> Hi,
>>
>> I tried to add some support for using devices with PI/DIF metadata
>> and checked (through sysfs) how large metadata space per sector
>> is available.
>>
>> The problem is that some values behave differently than I expected.
>>
>> For an NVMe drive, reformatted to 4096 + 64 profile, I see this:
>>
>> - /sys/block/<disk>/integrity/device_is_integrity_capable
>>     Contains 0 (?)
>>     According to docs, this field
>>    "Indicates whether a storage device is capable of storing integrity
>> metadata.
>>    Set if the device is T10 PI-capable."
>>
>> - /sys/block/<disk>/integrity/format
>>    Contains expected "nop" (not "none")
>>
>> - /sys/block/<disk>/integrity/tag_size
>>     Contains 0 (?)
> 
> This and "nop" indicates that pi-type was configured to be 0?
> Maybe you can share the nvme format command as well.

Sure, it is formatted to 4k data + 64 bytes metadata profile:

# nvme id-ns -H /dev/nvme0n1
...

LBA Format  0 : Metadata Size: 0   bytes - Data Size: 512 bytes - Relative Performance: 0 Best
LBA Format  1 : Metadata Size: 8   bytes - Data Size: 512 bytes - Relative Performance: 0 Best
LBA Format  2 : Metadata Size: 0   bytes - Data Size: 4096 bytes - Relative Performance: 0 Best
LBA Format  3 : Metadata Size: 64  bytes - Data Size: 4096 bytes - Relative Performance: 0 Best (in use)

formatted with
# nvme format --lbaf=3 --force /dev/nvme0n1

>>     According to docs, this is "Number of bytes of integrity tag space
>>     available per 512 bytes of data."
>>     (I think 512 bytes is incorrect; it should be sector size, or perhaps
>>      value in protection_interval_bytes, though.)
>>
>> Then we have new (undocumented) value for NVMe in
>> - /sys/block/<nvme>/integrity/metadata_bytes
>>     This contains the correct 64.
> 
> Maybe you mean "/sys/block/>/metadata_bytes"?

Yes, it is not under integrity subdir, just copy& paste error, sorry.

Just to add - I would like to add these integrity fields also to lsblk, but there we need exact
specification where to get integrity info.

Milan