Re: [Qemu-devel] [PATCH v3 1/1] hw/scsi: support SCSI-2 passthrough without PI

From: Fam Zheng <famz@redhat.com>
To: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Cc: qemu-devel@nongnu.org, pbonzini@redhat.com
Subject: Re: [Qemu-devel] [PATCH v3 1/1] hw/scsi: support SCSI-2 passthrough without PI
Date: Wed, 28 Mar 2018 09:38:04 +0800	[thread overview]
Message-ID: <20180328013804.GM31422@lemon.usersys.redhat.com> (raw)
In-Reply-To: <20180327211451.14647-1-danielhb@linux.vnet.ibm.com>

On Tue, 03/27 18:14, Daniel Henrique Barboza wrote:
> QEMU SCSI code makes assumptions about how the PROTECT and BYTCHK
> works in the protocol, denying support for PI (Protection
> Information) in case the guest OS requests it. However, in SCSI versions 2
> and older, there is no PI concept in the protocol.
> 
> This means that when dealing with such devices:
> 
> - there is no PROTECT bit in byte 5 of the standard INQUIRY response. The
> whole byte is marked as "Reserved";
> 
> - there is no RDPROTECT in byte 2 of READ. We have 'Logical Unit Number'
> in this field instead;
> 
> - there is no VRPROTECT in byte 2 of VERIFY. We have 'Logical Unit Number'
> in this field instead. This also means that the BYTCHK bit in this case
> is not related to PI.
> 
> Since QEMU does not consider these changes, a SCSI passthrough using
> a SCSI-2 device will not work. It will mistake these fields with
> PI information and return Illegal Request SCSI SENSE thinking
> that the driver is asking for PI support.
> 
> This patch fixes it by adding a new attribute called 'scsi_version'
> that is read from the standard INQUIRY response of passthrough
> devices. This allows for a version verification before applying
> conditions related to PI that doesn't apply for older versions.
> 
> Reported-by: Dac Nguyen <dacng@us.ibm.com>
> Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
> ---
> 
> Changes in v3:
> - moved the scsi_version initialization from realize functions to
> reset functions, allowing the scsi_version to be redefined again after
> each reboot.

Reviewed-by: Fam Zheng <famz@redhat.com>