vfio/iommufd: Fix SIGSEV in iommufd_cdev_attach()

When iommufd_cdev_ram_block_discard_disable() fails for whatever reason,
errp should be set or else SIGSEV is triggered in vfio_realize() when
error_prepend() is called.

By this chance, use the same error message for both legacy and iommufd
backend.

Fixes: 5ee3dc7 ("vfio/iommufd: Implement the iommufd backend")
Signed-off-by: Zhenzhong Duan <[email protected]>
Reviewed-by: Eric Auger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Cédric Le Goater <[email protected]>
(cherry picked from commit 7b3d5b8)
Signed-off-by: Michael Tokarev <[email protected]>

Author: duanzhenzhong

hw/vfio/iommufd.c

@@ -515,8 +515,8 @@ static bool iommufd_cdev_attach(const char *name, VFIODevice *vbasedev,
         } else {
             ret = iommufd_cdev_ram_block_discard_disable(true);
             if (ret) {
-                error_setg(errp,
-                              "Cannot set discarding of RAM broken (%d)", ret);
+                error_setg_errno(errp, -ret,
+                                 "Cannot set discarding of RAM broken");
                 goto err_discard_disable;
             }
             goto found_container;
@@ -544,6 +544,7 @@ static bool iommufd_cdev_attach(const char *name, VFIODevice *vbasedev,
 
     ret = iommufd_cdev_ram_block_discard_disable(true);
     if (ret) {
+        error_setg_errno(errp, -ret, "Cannot set discarding of RAM broken");
         goto err_discard_disable;
     }