[Qemu-devel] Re: Commit 622b520f changed -drive if=scsi, index=N, intentional?

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/27/2011 01:10 PM, Markus Armbruster wrote:
> Consider -drive if=scsi,index=12,...
> 
> Before the commit, index=12 meant bus=1,unit=5.  Example:
> 
>      $ qemu-system-x86_64 -nodefaults -vnc :0 -S -monitor stdio -drive if=scsi,index=12,media=cdrom
>      QEMU 0.13.50 monitor - type 'help' for more information
>      (qemu) info block
>      scsi1-cd5: type=cdrom removable=1 locked=0 [not inserted]
>      (qemu) info qtree
>      [...]
>          bus: pci.0
>            type PCI
>            dev: lsi53c895a, id ""
>              bus-prop: addr = 03.0
>              bus-prop: romfile =<null>
>              bus-prop: rombar = 1
>              bus-prop: multifunction = off
>              class SCSI controller, addr 00:03.0, pci id 1000:0012 (sub 1af4:1000)
>              bar 0: i/o at 0xffffffffffffffff [0xfe]
>              bar 1: mem at 0xffffffffffffffff [0x3fe]
>              bar 2: mem at 0xffffffffffffffff [0x1ffe]
>              bus: scsi.0
>                type SCSI
>                dev: scsi-disk, id ""
>                  dev-prop: drive = scsi1-cd5
>                  dev-prop: logical_block_size = 512
>                  dev-prop: physical_block_size = 512
>                  dev-prop: min_io_size = 0
>                  dev-prop: opt_io_size = 0
>                  dev-prop: ver = "0.13.50"
>                  dev-prop: serial = "0"
>                  bus-prop: scsi-id = 5
>            dev: lsi53c895a, id ""
>              bus-prop: addr = 02.0
>              bus-prop: romfile =<null>
>              bus-prop: rombar = 1
>              bus-prop: multifunction = off
>              class SCSI controller, addr 00:02.0, pci id 1000:0012 (sub 1af4:1000)
>              bar 0: i/o at 0xffffffffffffffff [0xfe]
>              bar 1: mem at 0xffffffffffffffff [0x3fe]
>              bar 2: mem at 0xffffffffffffffff [0x1ffe]
>              bus: scsi.0
>                type SCSI
>      [...]
> 
>      Two scsi-buses, and scsi1-cd5 with scsi-id 5 is on the second one,
>      i.e. bus=1, unit=5.
> 
> After the commit, it means bus=0,unit=12.  The drive is created, but not
> the guest device.  That's because lsi53c895a supports only 7 units
> (LSI_MAX_DEVS), and scsi_bus_legacy_handle_cmdline() ignores drives with
> unit numbers exceeding that limit.

The culprit is

        type = IF_SCSI;
        max_devs = MAX_SCSI_DEVS;
        pstrcpy(devname, sizeof(devname), "scsi");

...

        } else if (!strcmp(buf, "scsi")) {
            type = IF_SCSI;
            max_devs = MAX_SCSI_DEVS;

Here is a patch, untested but trivial.


-------------- --8< ----------------
>From f64236fa1df4cfecaa2e5b91ce5eeb47ce97e97c Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu, 27 Jan 2011 13:45:16 +0100
Subject: [PATCH] change behavior of index=N to be the same as 0.13 and earlier

Even though we support theoretically more than 7 devices per target,
the controllers we have do not and they ignore LUNs above 6.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 blockdev.c |    4 ++--
 blockdev.h |    5 +++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index f7f591f..c5078f8 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -163,7 +163,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi, int *fatal_error)
 
     if (default_to_scsi) {
         type = IF_SCSI;
-        max_devs = MAX_SCSI_DEVS;
+        max_devs = DEFAULT_SCSI_DEVS_PER_BUS;
         pstrcpy(devname, sizeof(devname), "scsi");
     } else {
         type = IF_IDE;
@@ -194,7 +194,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi, int *fatal_error)
             max_devs = MAX_IDE_DEVS;
         } else if (!strcmp(buf, "scsi")) {
 	    type = IF_SCSI;
-            max_devs = MAX_SCSI_DEVS;
+            max_devs = DEFAULT_SCSI_DEVS_PER_BUS;
         } else if (!strcmp(buf, "floppy")) {
 	    type = IF_FLOPPY;
             max_devs = 0;
diff --git a/blockdev.h b/blockdev.h
index 4536b5c..1cfc013 100644
--- a/blockdev.h
+++ b/blockdev.h
@@ -31,8 +31,9 @@ struct DriveInfo {
     QTAILQ_ENTRY(DriveInfo) next;
 };
 
-#define MAX_IDE_DEVS	2
-#define MAX_SCSI_DEVS	255
+#define MAX_IDE_DEVS			2
+#define MAX_SCSI_DEVS			255
+#define DEFAULT_SCSI_DEVS_PER_BUS	7
 
 DriveInfo *drive_get(BlockInterfaceType type, int bus, int unit);
 int drive_get_max_bus(BlockInterfaceType type);
-- 
1.7.3.4

Paolo