[Qemu-block] [PATCH 3/4] qdev-properties-system: Improve error message for drive assignment conflict

[Peter Maydell]

If the user forgot if=none on their drive specification they're likely
to get an error message because the drive is assigned once automatically
by QEMU and once by the manual id=/drive= user command line specification.
Improve the error message produced in this case to explicitly guide the
user towards if=none.

Signed-off-by: Peter Maydell <address@hidden>
---
 hw/core/qdev-properties-system.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 56954b4..bde9e12 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -78,8 +78,20 @@ static void parse_drive(DeviceState *dev, const char *str, 
void **ptr,
         return;
     }
     if (blk_attach_dev(blk, dev) < 0) {
-        error_setg(errp, "Property '%s.%s' can't take value '%s', it's in use",
-                  object_get_typename(OBJECT(dev)), propname, str);
+        DriveInfo *dinfo = blk_legacy_dinfo(blk);
+
+        if (dinfo->auto_claimed) {
+            error_setg(errp, "Property '%s.%s' can't be set to drive ID '%s'; "
+                       "that drive has been automatically connected to another 
"
+                       "device. Use if=none if you do not want that automatic "
+                       "connection.",
+                       object_get_typename(OBJECT(dev)), propname, str);
+        } else {
+            error_setg(errp, "Property '%s.%s' can't be set to drive ID '%s'; "
+                       "that drive has already been connected to another "
+                       "device.",
+                       object_get_typename(OBJECT(dev)), propname, str);
+        }
         return;
     }
     *ptr = blk;
-- 
1.9.1