[Qemu-devel] [PATCH 3/3] virtio-blk: always enable VIRTIO_BLK_F_SCSI

[Paolo Bonzini]

VIRTIO_BLK_F_SCSI is supposed to mean whether the host can *parse* SCSI
requests, not *execute* them.  We need to change this to fix a migration
compatibility problem related to the version of *management* (hence
unrelated to the QEMU machine type), so we must do this unconditionally
even on older machine types.

This more or less assumes that no one ever invoked QEMU with scsi=off.
Here is how migration works/fails with various combinations:

- old QEMU, scsi=on -> new QEMU, scsi=on
- new QEMU, scsi=on -> old QEMU, scsi=on
- old QEMU, scsi=off -> new QEMU, scsi=on
- new QEMU, scsi=off -> old QEMU, scsi=on
        ok (new QEMU has VIRTIO_BLK_F_SCSI, adding host features is fine)

- old QEMU, scsi=off -> new QEMU, scsi=off
        ok (new QEMU has VIRTIO_BLK_F_SCSI, adding host features is fine)

- old QEMU, scsi=on -> new QEMU, scsi=off
        ok, bug fixed

- new QEMU, scsi=on -> old QEMU, scsi=off
        doesn't work (same as: old QEMU, scsi=on -> old QEMU, scsi=off)

- new QEMU, scsi=off -> old QEMU, scsi=off
        broken by the patch (new->old not supported upstream)

If any downstream cares about new->old migration, they can apply v1 of
the patches instead of this (since the problem is in the destination,
applying both series would not help), and carry those until they can
break downward-compatibility.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 hw/s390-virtio-bus.c |    3 +++
 hw/virtio-blk.c      |    3 ++-
 hw/virtio-blk.h      |    7 +------
 hw/virtio-pci.c      |    3 +++
 4 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/hw/s390-virtio-bus.c b/hw/s390-virtio-bus.c
index 300454b..a7f0a95 100644
--- a/hw/s390-virtio-bus.c
+++ b/hw/s390-virtio-bus.c
@@ -377,6 +377,9 @@ static TypeInfo s390_virtio_net = {
 static Property s390_virtio_blk_properties[] = {
     DEFINE_BLOCK_PROPERTIES(VirtIOS390Device, blk.conf),
     DEFINE_PROP_STRING("serial", VirtIOS390Device, blk.serial),
+#ifdef __linux__
+    DEFINE_PROP_BIT("scsi", VirtIOS390Device, blk.scsi, 0, true),
+#endif
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 10d84d5..4735ded 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -170,7 +170,7 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
      */
     req->scsi = (void *)req->elem.in_sg[req->elem.in_num - 2].iov_base;
 
-    if ((req->dev->vdev.guest_features & (1 << VIRTIO_BLK_F_SCSI)) == 0) {
+    if (!req->dev->blk->scsi) {
         status = VIRTIO_BLK_S_UNSUPP;
         goto fail;
     }
@@ -507,6 +507,7 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev, 
uint32_t features)
     features |= (1 << VIRTIO_BLK_F_GEOMETRY);
     features |= (1 << VIRTIO_BLK_F_TOPOLOGY);
     features |= (1 << VIRTIO_BLK_F_BLK_SIZE);
+    features |= (1 << VIRTIO_BLK_F_SCSI);
 
     if (bdrv_enable_write_cache(s->bs))
         features |= (1 << VIRTIO_BLK_F_WCACHE);
diff --git a/hw/virtio-blk.h b/hw/virtio-blk.h
index 70564a1..d785001 100644
--- a/hw/virtio-blk.h
+++ b/hw/virtio-blk.h
@@ -101,15 +101,10 @@ struct VirtIOBlkConf
 {
     BlockConf conf;
     char *serial;
+    uint32_t scsi;
 };
 
-#ifdef __linux__
-#define DEFINE_VIRTIO_BLK_FEATURES(_state, _field) \
-        DEFINE_VIRTIO_COMMON_FEATURES(_state, _field), \
-        DEFINE_PROP_BIT("scsi", _state, _field, VIRTIO_BLK_F_SCSI, true)
-#else
 #define DEFINE_VIRTIO_BLK_FEATURES(_state, _field) \
         DEFINE_VIRTIO_COMMON_FEATURES(_state, _field)
-#endif
 
 #endif
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 956926b..6169d99 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -809,6 +809,9 @@ static Property virtio_blk_properties[] = {
     DEFINE_PROP_HEX32("class", VirtIOPCIProxy, class_code, 0),
     DEFINE_BLOCK_PROPERTIES(VirtIOPCIProxy, blk.conf),
     DEFINE_PROP_STRING("serial", VirtIOPCIProxy, blk.serial),
+#ifdef __linux__
+    DEFINE_PROP_BIT("scsi", VirtIOPCIProxy, blk.scsi, 0, true),
+#endif
     DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags, 
VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
     DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
     DEFINE_VIRTIO_BLK_FEATURES(VirtIOPCIProxy, host_features),
-- 
1.7.7.6