Re: [PATCH] vhost-scsi: do not count PI bytes in the data length

[Jia Jia]

>
> On 10/6/26 3:21 AM, Jia Jia wrote:
> > vhost_scsi_handle_vq() moves pi_bytesout and pi_bytesin into the
> > protection sgl and subtracts them from exp_data_len.  The length passed
> > to TCM is still exp_data_len + prot_bytes.
> >
> > That sum matched an older target path which subtracted prot_length
> > again.  sbc_check_prot() now replaces data_length from the CDB only
>
> What patch changed this? Did all the drivers except vhost-scsi get fixed?
>

I had that wrong.  9f977ef7b671 says target would subtract prot_length
and points at 14ef9200.  That commit is not in the tree, and the target
code never subtracts prot_length.  The in-tree behavior is
e2a4f55c6498: if protect is non-zero, sbc_check_prot() sets
data_length from the CDB.  The vhost add has been there since
9f977ef7b671, in the same pull.  Nothing later changed it.

> > when the protect field is non-zero, and only for READ and WRITE.
> > target_cmd_size_check() leaves a write's data_length unchanged when the
> > CDB size is smaller.
> >
> > MODE SELECT, SET TARGET PORT GROUPS and UNMAP then use data_length as
> > the size of t_data_sg.  The PI bytes are not in that sgl.  A parameter
>
> Can you have prot_bytes > 0 with those commands?

I did not describe this clearly.  MODE SELECT is not where prot_bytes
comes from.
With VIRTIO_SCSI_F_T10_PI negotiated, pi_bytesout can be set in
virtio_scsi_cmd_req_pi, and vhost does not check that the CDB is a
READ or WRITE. .
A MODE SELECT sent with that field set hits this.  That is what I ran.