scsi-disk: respect the page control (PC) field in the MODE SENSE command

The page control (PC) field defines the type of mode parameter values
to be returned in the mode pages:

PC=0 : Current values
PC=1 : Changeable values
PC=2 : Default values
PC=3 : Saved values

The current implementation always returns the same type of parameters.
This is OK for Current and Default values as we don't support changes
to be done by the MODE SELECT command.

For Saved values the following applies (implemented by this patch):
"A PC field value of 3h requests that the target return the saved
values of the mode parameters. Implementation of saved page parameters
is optional. Mode parameters not supported by the target shall be set
to zero. If saved values are not implemented, the command shall be
terminated with CHECK CONDITION status, the sense key set to
ILLEGAL REQUEST and the additional sense code set to
SAVING PARAMETERS NOT SUPPORTED."

For Changeable values the following applies (implemented by this patch):
"A PC field value of 1h requests that the target return a mask denoting
those mode parameters that are changeable. In the mask, the fields of
the mode parameters that are changeable shall be set to all one bits and
the fields of the mode parameters that are non-changeable (i.e. defined
by the target) shall be set to all zero bits."

In newer versions of the SCSI-2 spec the following clause was added.
"If the logical unit does not implement changeable parameters mode pages
and the device server receives a MODE SENSE command with 01b in the PC
field, then the command shall be terminated with CHECK CONDITION status,
with the sense key set to ILLEGAL REQUEST, and the additional sense code
set to INVALID FIELD IN CDB."

This was not yet included in the SCSI-2 Working Drafts from 1986-1993.
I assume that the variant to return CHECK CONDITION for PC=1 is not
widely implemented by real devices. I have a legacy OS which fails,
if MODE_SENSE returns non GOOD for PC=1. So for highest compatibility I
implemented the former variant with this patch.

The last Working Draft X3T9.2 Rev. 10L 7-SEP-93 can be found here:
http://ldkelley.com/SCSI2/SCSI2/SCSI2-08.html#8.2.10

In mode_sense_page() this patch also avoids multiple hard coded
definitions of the same mode page length. Instead I use the varable
p[1]. In fact the returned length of the mode pages 4 and 5 were wrong
(2 bytes less).
Signed-off-by: NBernhard Kohl <bernhard.kohl@nsn.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

hw/scsi-disk.c

@@ -486,16 +486,26 @@ static int scsi_disk_emulate_inquiry(SCSIRequest *req, uint8_t *outbuf)
     return buflen;
 }
 
-static int mode_sense_page(SCSIRequest *req, int page, uint8_t *p)
+static int mode_sense_page(SCSIRequest *req, int page, uint8_t *p,
+                           int page_control)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, req->dev);
     BlockDriverState *bdrv = s->bs;
     int cylinders, heads, secs;
 
+    /*
+     * If Changeable Values are requested, a mask denoting those mode parameters
+     * that are changeable shall be returned. As we currently don't support
+     * parameter changes via MODE_SELECT all bits are returned set to zero.
+     * The buffer was already menset to zero by the caller of this function.
+     */
     switch (page) {
     case 4: /* Rigid disk device geometry page. */
         p[0] = 4;
         p[1] = 0x16;
+        if (page_control == 1) { /* Changeable Values */
+            return p[1] + 2;
+        }
         /* if a geometry hint is available, use it */
         bdrv_get_geometry_hint(bdrv, &cylinders, &heads, &secs);
         p[2] = (cylinders >> 16) & 0xff;
@@ -520,11 +530,14 @@ static int mode_sense_page(SCSIRequest *req, int page, uint8_t *p)
         /* Medium rotation rate [rpm], 5400 rpm */
         p[20] = (5400 >> 8) & 0xff;
         p[21] = 5400 & 0xff;
-        return 0x16;
+        return p[1] + 2;
 
     case 5: /* Flexible disk device geometry page. */
         p[0] = 5;
         p[1] = 0x1e;
+        if (page_control == 1) { /* Changeable Values */
+            return p[1] + 2;
+        }
         /* Transfer rate [kbit/s], 5Mbit/s */
         p[2] = 5000 >> 8;
         p[3] = 5000 & 0xff;
@@ -556,21 +569,27 @@ static int mode_sense_page(SCSIRequest *req, int page, uint8_t *p)
         /* Medium rotation rate [rpm], 5400 rpm */
         p[28] = (5400 >> 8) & 0xff;
         p[29] = 5400 & 0xff;
-        return 0x1e;
+        return p[1] + 2;
 
     case 8: /* Caching page.  */
         p[0] = 8;
         p[1] = 0x12;
+        if (page_control == 1) { /* Changeable Values */
+            return p[1] + 2;
+        }
         if (bdrv_enable_write_cache(s->bs)) {
             p[2] = 4; /* WCE */
         }
-        return 20;
+        return p[1] + 2;
 
     case 0x2a: /* CD Capabilities and Mechanical Status page. */
         if (bdrv_get_type_hint(bdrv) != BDRV_TYPE_CDROM)
             return 0;
         p[0] = 0x2a;
         p[1] = 0x14;
+        if (page_control == 1) { /* Changeable Values */
+            return p[1] + 2;
+        }
         p[2] = 3; // CD-R & CD-RW read
         p[3] = 0; // Writing not supported
         p[4] = 0x7f; /* Audio, composite, digital out,
@@ -594,7 +613,7 @@ static int mode_sense_page(SCSIRequest *req, int page, uint8_t *p)
         p[19] = (16 * 176) & 0xff;
         p[20] = (16 * 176) >> 8; // 16x write speed current
         p[21] = (16 * 176) & 0xff;
-        return 22;
+        return p[1] + 2;
 
     default:
         return 0;
@@ -605,13 +624,15 @@ static int scsi_disk_emulate_mode_sense(SCSIRequest *req, uint8_t *outbuf)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, req->dev);
     uint64_t nb_sectors;
-    int page, dbd, buflen;
+    int page, dbd, buflen, page_control;
     uint8_t *p;
     uint8_t dev_specific_param;
 
     dbd = req->cmd.buf[1]  & 0x8;
     page = req->cmd.buf[2] & 0x3f;
-    DPRINTF("Mode Sense (page %d, len %zd)\n", page, req->cmd.xfer);
+    page_control = (req->cmd.buf[2] & 0xc0) >> 6;
+    DPRINTF("Mode Sense(%d) (page %d, len %d, page_control %d)\n",
+        (req->cmd.buf[0] == MODE_SENSE) ? 6 : 10, page, len, page_control);
     memset(outbuf, 0, req->cmd.xfer);
     p = outbuf;
 
@@ -655,16 +676,20 @@ static int scsi_disk_emulate_mode_sense(SCSIRequest *req, uint8_t *outbuf)
         p += 8;
     }
 
+    if (page_control == 3) { /* Saved Values */
+        return -1; /* ILLEGAL_REQUEST */
+    }
+
     switch (page) {
     case 0x04:
     case 0x05:
     case 0x08:
     case 0x2a:
-        p += mode_sense_page(req, page, p);
+        p += mode_sense_page(req, page, p, page_control);
         break;
     case 0x3f:
-        p += mode_sense_page(req, 0x08, p);
-        p += mode_sense_page(req, 0x2a, p);
+        p += mode_sense_page(req, 0x08, p, page_control);
+        p += mode_sense_page(req, 0x2a, p, page_control);
         break;
     }