Re: [PATCH 06/19] target: Fix data buffer size for VERIFY and WRITE AND VERIFY commands

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

On Sun, 2017-05-07 at 15:49 -0700, Nicholas A. Bellinger wrote:
> On Thu, 2017-05-04 at 15:50 -0700, Bart Van Assche wrote:
> > For VERIFY and WRITE AND VERIFY commands the size of the SCSI
> > Data-Out buffer can differ from the size of the data area on
> > the storage medium that is affected by the command. Make sure
> > that the Data-Out buffer size is computed correctly. Apparently
> > this part got dropped from my previous VERIFY / WRITE AND VERIFY
> > patch before I posted it due to rebasing.
> > 
> > Fixes: commit 0e2eb7d12eaa ("target: Fix VERIFY and WRITE VERIFY command parsing")
> > Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
> > Cc: Hannes Reinecke <hare@suse.com>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Andy Grover <agrover@redhat.com>
> > Cc: David Disseldorp <ddiss@suse.de>
> > Cc: <stable@vger.kernel.org>
> > ---
> >  drivers/target/target_core_sbc.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
> > index a0ad618f1b1a..51489d96cb31 100644
> > --- a/drivers/target/target_core_sbc.c
> > +++ b/drivers/target/target_core_sbc.c
> > @@ -888,9 +888,10 @@ static sense_reason_t sbc_parse_verify(struct se_cmd *cmd, int *sectors,
> >  sense_reason_t
> >  sbc_parse_cdb(struct se_cmd *cmd, struct sbc_ops *ops)
> >  {
> > +	enum { INVALID_SIZE = 1 };
> >  	struct se_device *dev = cmd->se_dev;
> >  	unsigned char *cdb = cmd->t_task_cdb;
> > -	unsigned int size;
> > +	unsigned int size = INVALID_SIZE;
> >  	u32 sectors = 0;
> >  	sense_reason_t ret;
> >  
> > @@ -1212,7 +1213,7 @@ sbc_parse_cdb(struct se_cmd *cmd, struct sbc_ops *ops)
> >  			return TCM_ADDRESS_OUT_OF_RANGE;
> >  		}
> >  
> > -		if (!(cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE))
> > +		if (size == INVALID_SIZE)
> >  			size = sbc_get_size(cmd, sectors);
> >  	}
> >  
> 
> This patch has no effect.

Hello Nic,

That's a misinterpretation of your side. What this patch does is to ensure
that 'size' remains zero if a VERIFY or WRITE AND VERIFY command is submitted
with BYTCHK == 0. SBC mentions clearly that BYTCHK == 0 means that there is
no Data-Out buffer, or in other words, that the size of the Data-Out buffer
is zero.

>From the sg_verify man page:

       When --ndo=NDO is not given then the verify starts at the logical block
       address given by the --lba=LBA option and continues for --count=COUNT
       blocks.

In other words, sg_verify is able to submit a VERIFY command without Data-Out
buffer (NDO is the size of the Data-Out buffer in bytes).

> Anyways, I've fixed both cases and will post the proper fix inline
> against patch #19.

Do you perhaps mean patch "target: Fix sbc_parse_verify bytchk = 0 handling"?
(https://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending.git/commit/?h=for-next&id=d7d40280f868463d01a82186fd61cdc0e590381f)

If you want to know my opinion about that patch: it doesn't fix anything but
breaks the sbc_parse_verify() function and definitely doesn't make the
behavior of VERIFY nor WRITE AND VERIFY more compliant with the SCSI specs.

Bart.