Add virtio disk identification support

This patch adds the final missing bits for support of
passing a serial/id string to a virtio-blk guest driver.

The guest-side component already exists in the virtio
driver, and has recently been reworked by Ryan to export
a /sys interface for retrieval of the id from guest userland.

Signed-off-by: john cooper <john.cooper@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/virtio-blk.c

@@ -26,6 +26,7 @@ typedef struct VirtIOBlock
     QEMUBH *bh;
     BlockConf *conf;
     unsigned short sector_mask;
+    char sn[BLOCK_SERIAL_STRLEN];
 } VirtIOBlock;
 
 static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
@@ -324,6 +325,12 @@ static void virtio_blk_handle_request(VirtIOBlockReq *req,
         virtio_blk_handle_flush(req, mrb);
     } else if (req->out->type & VIRTIO_BLK_T_SCSI_CMD) {
         virtio_blk_handle_scsi(req);
+    } else if (req->out->type & VIRTIO_BLK_T_GET_ID) {
+        VirtIOBlock *s = req->dev;
+
+        memcpy(req->elem.in_sg[0].iov_base, s->sn,
+               MIN(req->elem.in_sg[0].iov_len, sizeof(s->sn)));
+        virtio_blk_req_complete(req, VIRTIO_BLK_S_OK);
     } else if (req->out->type & VIRTIO_BLK_T_OUT) {
         qemu_iovec_init_external(&req->qiov, &req->elem.out_sg[1],
                                  req->elem.out_num - 1);
@@ -481,6 +488,7 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf)
     VirtIOBlock *s;
     int cylinders, heads, secs;
     static int virtio_blk_id;
+    DriveInfo *dinfo;
 
     s = (VirtIOBlock *)virtio_common_init("virtio-blk", VIRTIO_ID_BLOCK,
                                           sizeof(struct virtio_blk_config),
@@ -495,6 +503,12 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf)
     s->sector_mask = (s->conf->logical_block_size / BDRV_SECTOR_SIZE) - 1;
     bdrv_guess_geometry(s->bs, &cylinders, &heads, &secs);
 
+    /* NB: per existing s/n string convention the string is terminated
+     * by '\0' only when less than sizeof (s->sn)
+     */
+    dinfo = drive_get_by_blockdev(s->bs);
+    strncpy(s->sn, dinfo->serial, sizeof (s->sn));
+
     s->vq = virtio_add_queue(&s->vdev, 128, virtio_blk_handle_output);
 
     qemu_add_vm_change_state_handler(virtio_blk_dma_restart_cb, s);

hw/virtio-blk.h

@@ -59,6 +59,9 @@ struct virtio_blk_config
 /* Flush the volatile write cache */
 #define VIRTIO_BLK_T_FLUSH      4
 
+/* return the device ID string */
+#define VIRTIO_BLK_T_GET_ID     8
+
 /* Barrier before this op. */
 #define VIRTIO_BLK_T_BARRIER    0x80000000