linux-kernel - Re: [PATCH 3.6 1/2] target: remove pscsi_clear_cdb

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Date:	Thu, 06 Sep 2012 11:58:05 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, target-devel@...r.kernel.org
Subject: Re: [PATCH 3.6 1/2] target: remove pscsi_clear_cdb_lun

On Thu, 2012-09-06 at 17:13 +0200, Paolo Bonzini wrote:
> The purpose of this function is to clear a LUN set in the CDB, in case
> the initiator talking to us is speaking an old standards version.
> However, as things stand, pscsi_clear_cdb_lun has two problems.  It
> will "deceive" the guest by clearing the LUN bits on initial
> commands (INQUIRY, TEST UNIT READY, etc.); but then it will let the
> LUN bits through on reads, which will likely fail due to protection not
> being enabled.  Second, not all commands are properly filtered, in
> particular WRITE's WRPROTECT bits are cleared.
> 
> This should be done by the fabric module rather than by PSCSI, if it
> knows such initiators may be lying around _and_ it can assume that its
> initiators do not really care about protection information.  Nuke it
> from PSCSI.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---

NAK.  This code was originally added to prevent certain pSCSI HBAs from
going bonkers when they got a legacy SCSI LUN ID encoded within the CDB
(eg: the fabric LUN ID) that's different from the physical SCSI LUN ID
on an Parallel SCSI bus.

If there are more special cases where the legacy SCSI LUN ID bit-range
needs to be cleared than please add those missing bits, but I don't
think it's yet safe to remove this completely for pSCSI w/ older LLDs.

>  drivers/target/target_core_pscsi.c |   26 --------------------------
>  1 files changed, 0 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
> index 5f7151d..a0fb2c3 100644
> --- a/drivers/target/target_core_pscsi.c
> +++ b/drivers/target/target_core_pscsi.c
> @@ -1031,30 +1031,6 @@ fail:
>  	return -ENOMEM;
>  }
>  
> -/*
> - * Clear a lun set in the cdb if the initiator talking to use spoke
> - * and old standards version, as we can't assume the underlying device
> - * won't choke up on it.
> - */
> -static inline void pscsi_clear_cdb_lun(unsigned char *cdb)
> -{
> -	switch (cdb[0]) {
> -	case READ_10: /* SBC - RDProtect */
> -	case READ_12: /* SBC - RDProtect */
> -	case READ_16: /* SBC - RDProtect */
> -	case SEND_DIAGNOSTIC: /* SPC - SELF-TEST Code */
> -	case VERIFY: /* SBC - VRProtect */
> -	case VERIFY_16: /* SBC - VRProtect */
> -	case WRITE_VERIFY: /* SBC - VRProtect */
> -	case WRITE_VERIFY_12: /* SBC - VRProtect */
> -	case MAINTENANCE_IN: /* SPC - Parameter Data Format for SA RTPG */
> -		break;
> -	default:
> -		cdb[1] &= 0x1f; /* clear logical unit number */
> -		break;
> -	}
> -}
> -
>  static int pscsi_parse_cdb(struct se_cmd *cmd)
>  {
>  	unsigned char *cdb = cmd->t_task_cdb;
> @@ -1067,8 +1043,6 @@ static int pscsi_parse_cdb(struct se_cmd *cmd)
>  		return -EINVAL;
>  	}
>  
> -	pscsi_clear_cdb_lun(cdb);
> -
>  	/*
>  	 * For REPORT LUNS we always need to emulate the response, for everything
>  	 * else the default for pSCSI is to pass the command to the underlying


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