Re: [Lsf-pc] [LSF/MM/BPF ATTEND][LSF/MM/BPF TOPIC] Meta/Integrity/PI improvements

["Martin K. Petersen" <martin.petersen@oracle.com>]

Kanchan,

> Just to be clear, I was thinking of three new flags that userspace can
> pass: RWF_CHK_GUARD, RWF_CHK_APPTAG, RWF_CHK_REFTAG. And corresponding
> bip flags will need to be introduced (I don't see anything existing).
> Driver will see those and convert to protocol specific flags. Does
> this match with you what you have in mind.

See bip_flags in bio.h. We currently can't pick which tag to check or
not check because RDPROTECT/WRPROTECT in SCSI are a bit of a mess.
However, we do have separate flags to disabling checking at HBA and disk
level. That distinction doesn't really apply for NVMe but we do need it
for SCSI.

>>> Right. This can work for the case when host does not need to pass
>>> the buffer (meta-size is equal to pi-size). But when meta-size is
>>> greater than pi-size, the meta-buffer needs to be allocated. Some
>>> changes are required so that Block-integrity does that allocation,
>>> without having to do read_verify/write_generate.

The block layer should not allocate or mess with the bip when the
metadata originates in userland.

-- 
Martin K. Petersen	Oracle Linux Engineering