blockdev: Fix regression in -drive if=scsi,index=N

Before commit 622b520f, index=12 meant bus=1,unit=5.

Since the commit, it means bus=0,unit=12.  The drive is created, but
not the guest device.  That's because the controllers we use with
if=scsi drives (lsi53c895a and esp) support only 7 units, and
scsi_bus_legacy_handle_cmdline() ignores drives with unit numbers
exceeding that limit.

Changing the mapping of index to bus, unit is a regression.  Breaking
-drive invocations that used to work just makes it worse.

Revert the part of commit 622b520f that causes this, and clean up
some.

Note that the fix only affects if=scsi.  You can still put more than 7
units on a SCSI bus with -device & friends.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -32,8 +32,22 @@ static const char *const if_name[IF_COUNT] = {
 };
 
 static const int if_max_devs[IF_COUNT] = {
-    [IF_IDE] = MAX_IDE_DEVS,
+    /*
-    [IF_SCSI] = MAX_SCSI_DEVS,
+     * Do not change these numbers!  They govern how drive option
+     * index maps to unit and bus.  That mapping is ABI.
+     *
+     * All controllers used to imlement if=T drives need to support
+     * if_max_devs[T] units, for any T with if_max_devs[T] != 0.
+     * Otherwise, some index values map to "impossible" bus, unit
+     * values.
+     *
+     * For instance, if you change [IF_SCSI] to 255, -drive
+     * if=scsi,index=12 no longer means bus=1,unit=5, but
+     * bus=0,unit=12.  With an lsi53c895a controller (7 units max),
+     * the drive can't be set up.  Regression.
+     */
+    [IF_IDE] = 2,
+    [IF_SCSI] = 7,
 };
 
 /*

blockdev.h

@@ -37,9 +37,6 @@ struct DriveInfo {
     QTAILQ_ENTRY(DriveInfo) next;
 };
 
-#define MAX_IDE_DEVS	2
-#define MAX_SCSI_DEVS	255
-
 DriveInfo *drive_get(BlockInterfaceType type, int bus, int unit);
 int drive_get_max_bus(BlockInterfaceType type);
 DriveInfo *drive_get_next(BlockInterfaceType type);

hw/ide.h

@@ -4,6 +4,8 @@
 #include "isa.h"
 #include "pci.h"
 
+#define MAX_IDE_DEVS	2
+
 /* ide-isa.c */
 ISADevice *isa_ide_init(int iobase, int iobase2, int isairq,
                         DriveInfo *hd0, DriveInfo *hd1);

hw/ide/ahci.c

@@ -70,7 +70,6 @@
 #include "monitor.h"
 #include "dma.h"
 #include "cpu-common.h"
-#include "blockdev.h"
 #include "internal.h"
 #include <hw/ide/pci.h>
 

hw/qdev.c

@@ -29,7 +29,6 @@
 #include "qdev.h"
 #include "sysemu.h"
 #include "monitor.h"
-#include "blockdev.h"
 
 static int qdev_hotplug = 0;
 static bool qdev_hot_added = false;

hw/scsi.h

@@ -3,9 +3,10 @@
 
 #include "qdev.h"
 #include "block.h"
-#include "blockdev.h"
 #include "block_int.h"
 
+#define MAX_SCSI_DEVS	255
+
 #define SCSI_CMD_BUF_SIZE     16
 
 /* scsi-disk.c */

savevm.c

@@ -78,7 +78,6 @@
 #include "sysemu.h"
 #include "qemu-timer.h"
 #include "qemu-char.h"
-#include "blockdev.h"
 #include "audio/audio.h"
 #include "migration.h"
 #include "qemu_socket.h"