[Qemu-devel] [PATCH] virtio-blk: set correct config size for the host driver

[Changpeng Liu]

Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features support"
introduced extra fields to existing struct virtio_blk_config, when
migration was executed from older QEMU version to current head, it
will break the migration.  While here, set the correct config size
when initializing the host driver, for now, discard/write zeroes
are not supported by virtio-blk host driver, so set the config
size as before, users can change config size when adding the new
feature bits support.

Signed-off-by: Changpeng Liu <address@hidden>
---
 hw/block/virtio-blk.c          | 15 +++++++++++----
 include/hw/virtio/virtio-blk.h |  1 +
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 9a87b3b..fac5d33 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -761,7 +761,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev, 
uint8_t *config)
     blkcfg.alignment_offset = 0;
     blkcfg.wce = blk_enable_write_cache(s->blk);
     virtio_stw_p(vdev, &blkcfg.num_queues, s->conf.num_queues);
-    memcpy(config, &blkcfg, sizeof(struct virtio_blk_config));
+    memcpy(config, &blkcfg, s->config_size);
 }
 
 static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
@@ -769,7 +769,7 @@ static void virtio_blk_set_config(VirtIODevice *vdev, const 
uint8_t *config)
     VirtIOBlock *s = VIRTIO_BLK(vdev);
     struct virtio_blk_config blkcfg;
 
-    memcpy(&blkcfg, config, sizeof(blkcfg));
+    memcpy(&blkcfg, config, s->config_size);
 
     aio_context_acquire(blk_get_aio_context(s->blk));
     blk_set_enable_write_cache(s->blk, blkcfg.wce != 0);
@@ -847,6 +847,13 @@ static void virtio_blk_set_status(VirtIODevice *vdev, 
uint8_t status)
     }
 }
 
+static void virtio_blk_set_config_size(VirtIOBlock *s)
+{
+    /* VIRTIO_BLK_F_MQ is supported by host driver */
+    s->config_size = offsetof(struct virtio_blk_config, num_queues) +
+                     sizeof_field(struct virtio_blk_config, num_queues);
+}
+
 static void virtio_blk_save_device(VirtIODevice *vdev, QEMUFile *f)
 {
     VirtIOBlock *s = VIRTIO_BLK(vdev);
@@ -952,8 +959,8 @@ static void virtio_blk_device_realize(DeviceState *dev, 
Error **errp)
         return;
     }
 
-    virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK,
-                sizeof(struct virtio_blk_config));
+    virtio_blk_set_config_size(s);
+    virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, s->config_size);
 
     s->blk = conf->conf.blk;
     s->rq = NULL;
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 5117431..9181a93 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -51,6 +51,7 @@ typedef struct VirtIOBlock {
     void *rq;
     QEMUBH *bh;
     VirtIOBlkConf conf;
+    size_t config_size;
     unsigned short sector_mask;
     bool original_wce;
     VMChangeStateEntry *change;
-- 
1.9.3