[PATCH 1/3] MdeModulePkg/ScsiBusDxe: don't produce ScsiIo for nonexistent LUNs, part 1

[Laszlo Ersek <lersek@redhat.com>]

The SPC-4 spec says about the INQUIRY data, in "Table 138 -- Peripheral
qualifier":

> Qualifier = 011b  The device server is not capable of supporting a
>                   peripheral device on this logical unit. For this
>                   peripheral qualifier the peripheral device type shall
>                   be set to 1Fh. All other peripheral device type values
>                   are reserved for this peripheral qualifier.

Accordingly, the DiscoverScsiDevice() function returns FALSE if
Peripheral_Qualifier is 3 decimal, but Peripheral_Type differs from 1Fh.
This is a valid sanity check -- such combinations are reserved.

When Peripheral_Qualifier is 3, and Peripheral_Type is 1Fh, then
DiscoverScsiDevice() returns TRUE. While this combination is not reserved,
returning TRUE for it is incorrect: Peripheral_Type 1Fh stands for
"Unknown or no device type", and this combination is returned in
particular when the INQUIRY command was directed to a nonexistent LUN.
Quoting the spec:

> In response to an INQUIRY command received by an incorrect logical unit,
> the SCSI target device shall return the INQUIRY data with the peripheral
> qualifier set to the value defined in 6.4.2. [...]
>
> [...]
>
> The PERIPHERAL QUALIFIER field and PERIPHERAL DEVICE TYPE field identify
> the peripheral device connected to the logical unit. If the SCSI target
> device is not capable of supporting a peripheral device connected to
> this logical unit, the device server shall set these fields to 7Fh
> (i.e., PERIPHERAL QUALIFIER field set to 011b and PERIPHERAL DEVICE TYPE
> field set to 1Fh).

The consequence of this bug is that for each nonexistent Target/LUN pair,
we produce a useless ScsiIo protocol interface. The internal
"ScsiIoDevice->ScsiDeviceType" field will be set to 0x1f, and it will be
returned to higher-level SCSI drivers when they call
ScsiIo->GetDeviceType().

Given that 0x1f means "Unknown or no device type", no higher-level driver
can ever support it, so these ScsiIo protocol interfaces are useless.

The fix is to return FALSE for the (Peripheral_Qualifier=3,
Peripheral_Type=0x1f) combination. With that however we reject the whole
Peripheral_Qualifier=3 space (justifiedly -- see the definition above),
which lets us simplify the code.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 MdeModulePkg/Bus/Scsi/ScsiBusDxe/ScsiBus.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/MdeModulePkg/Bus/Scsi/ScsiBusDxe/ScsiBus.c b/MdeModulePkg/Bus/Scsi/ScsiBusDxe/ScsiBus.c
index 0802b617268f..72e3da8967b2 100644
--- a/MdeModulePkg/Bus/Scsi/ScsiBusDxe/ScsiBus.c
+++ b/MdeModulePkg/Bus/Scsi/ScsiBusDxe/ScsiBus.c
@@ -1348,21 +1348,13 @@ DiscoverScsiDevice (
   
   //
   // Retrieved inquiry data successfully
   //
-  if ((InquiryData->Peripheral_Qualifier != 0) &&
-      (InquiryData->Peripheral_Qualifier != 3)) {
+  if (InquiryData->Peripheral_Qualifier != 0) {
     ScsiDeviceFound = FALSE;
     goto Done;
   }
 
-  if (InquiryData->Peripheral_Qualifier == 3) {
-    if (InquiryData->Peripheral_Type != 0x1f) {
-      ScsiDeviceFound = FALSE;
-      goto Done;
-    }
-  }
-
   if (0x1e >= InquiryData->Peripheral_Type && InquiryData->Peripheral_Type >= 0xa) {
     ScsiDeviceFound = FALSE;
     goto Done;
   }
-- 
2.14.1.3.gb7cf6e02401b