[Qemu-devel] [PATCH 1/3] virtio-blk: report non-zero status when failing SG_IO requests

[Paolo Bonzini <pbonzini@redhat.com>]

Linux really looks only at scsi->errors.  Arguably it is their bug,
but we can make it safe for older guests now.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/virtio-blk.c |   48 +++++++++++++++++++++++-------------------------
 1 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 49990f8..b7e510d 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -145,20 +145,12 @@ static VirtIOBlockReq *virtio_blk_get_request(VirtIOBlock *s)
     return req;
 }
 
-#ifdef __linux__
 static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
 {
-    struct sg_io_hdr hdr;
-    int ret;
+    int ret = -1;
     int status;
     int i;
 
-    if ((req->dev->vdev.guest_features & (1 << VIRTIO_BLK_F_SCSI)) == 0) {
-        virtio_blk_req_complete(req, VIRTIO_BLK_S_UNSUPP);
-        g_free(req);
-        return;
-    }
-
     /*
      * We require at least one output segment each for the virtio_blk_outhdr
      * and the SCSI command block.
@@ -173,20 +165,26 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
     }
 
     /*
-     * No support for bidirection commands yet.
+     * The scsi inhdr is placed in the second-to-last input segment, just
+     * before the regular inhdr.
      */
-    if (req->elem.out_num > 2 && req->elem.in_num > 3) {
-        virtio_blk_req_complete(req, VIRTIO_BLK_S_UNSUPP);
-        g_free(req);
-        return;
+    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) {
+        status = VIRTIO_BLK_S_UNSUPP;
+        goto fail;
     }
 
     /*
-     * The scsi inhdr is placed in the second-to-last input segment, just
-     * before the regular inhdr.
+     * No support for bidirection commands yet.
      */
-    req->scsi = (void *)req->elem.in_sg[req->elem.in_num - 2].iov_base;
+    if (req->elem.out_num > 2 && req->elem.in_num > 3) {
+        status = VIRTIO_BLK_S_UNSUPP;
+        goto fail;
+    }
 
+#ifdef __linux__
+    struct sg_io_hdr hdr;
     memset(&hdr, 0, sizeof(struct sg_io_hdr));
     hdr.interface_id = 'S';
     hdr.cmd_len = req->elem.out_sg[1].iov_len;
@@ -229,9 +227,7 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
 
     ret = bdrv_ioctl(req->dev->bs, SG_IO, &hdr);
     if (ret) {
-        status = VIRTIO_BLK_S_UNSUPP;
-        hdr.status = ret;
-        hdr.resid = hdr.dxfer_len;
+        goto fail;
     } else if (hdr.status) {
         status = VIRTIO_BLK_S_IOERR;
     } else {
@@ -258,14 +254,16 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
 
     virtio_blk_req_complete(req, status);
     g_free(req);
-}
 #else
-static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
-{
-    virtio_blk_req_complete(req, VIRTIO_BLK_S_UNSUPP);
+    abort();
+#endif
+
+fail:
+    /* Just put anything nonzero so that the ioctl fails in the guest.  */
+    stl_p(&req->scsi->errors, 255);
+    virtio_blk_req_complete(req, status);
     g_free(req);
 }
-#endif /* __linux__ */
 
 typedef struct MultiReqBuffer {
     BlockRequest        blkreq[32];
-- 
1.7.7.6