Comment 1 for bug 1681688

blk->root->perm is 1 when blk_new_open.

the blk->root->perm is update to 3 during virtio_blk_device_realize.

but after this commit, the blk->root->perm is still 1. and cause bdrv_aligned_pwritev failed.

Breakpoint 1, blk_set_perm (blk=0x14c32b0, perm=3, shared_perm=29, errp=0x7fffffffd380) at block/block-backend.c:579
579 {
(gdb) bt
#0 blk_set_perm (blk=0x14c32b0, perm=3, shared_perm=29, errp=0x7fffffffd380) at block/block-backend.c:579
#1 0x000000000063484b in blkconf_apply_backend_options (conf=0x2de7fd0, readonly=false, resizable=true, errp=0x7fffffffd380) at hw/block/block.c:77
#2 0x00000000004a57bd in virtio_blk_device_realize (dev=0x2de7e30, errp=0x7fffffffd3e0) at /data/qemu/hw/block/virtio-blk.c:931
#3 0x00000000004f688e in virtio_device_realize (dev=0x2de7e30, errp=0x7fffffffd468) at /data/qemu/hw/virtio/virtio.c:2485
#4 0x000000000065806f in device_set_realized (obj=0x2de7e30, value=true, errp=0x7fffffffd6d8) at hw/core/qdev.c:939
#5 0x000000000083aaf5 in property_set_bool (obj=0x2de7e30, v=0x2e67a90, name=0xaf4b53 "realized", opaque=0x2de9660, errp=0x7fffffffd6d8) at qom/object.c:1860
#6 0x0000000000838c46 in object_property_set (obj=0x2de7e30, v=0x2e67a90, name=0xaf4b53 "realized", errp=0x7fffffffd6d8) at qom/object.c:1094
#7 0x000000000083c23f in object_property_set_qobject (obj=0x2de7e30, value=0x2e679e0, name=0xaf4b53 "realized", errp=0x7fffffffd6d8) at qom/qom-qobject.c:27
#8 0x0000000000838f9a in object_property_set_bool (obj=0x2de7e30, value=true, name=0xaf4b53 "realized", errp=0x7fffffffd6d8) at qom/object.c:1163
#9 0x00000000007bafac in virtio_blk_pci_realize (vpci_dev=0x2ddf920, errp=0x7fffffffd6d8) at hw/virtio/virtio-pci.c:1975
#10 0x00000000007ba966 in virtio_pci_realize (pci_dev=0x2ddf920, errp=0x7fffffffd6d8) at hw/virtio/virtio-pci.c:1853
#11 0x000000000071e439 in pci_qdev_realize (qdev=0x2ddf920, errp=0x7fffffffd7b8) at hw/pci/pci.c:2001
#12 0x00000000007badaa in virtio_pci_dc_realize (qdev=0x2ddf920, errp=0x7fffffffd7b8) at hw/virtio/virtio-pci.c:1930
#13 0x000000000065806f in device_set_realized (obj=0x2ddf920, value=true, errp=0x7fffffffd9a8) at hw/core/qdev.c:939
#14 0x000000000083aaf5 in property_set_bool (obj=0x2ddf920, v=0x2decfd0, name=0x9b2c0e "realized", opaque=0x2ddf5d0, errp=0x7fffffffd9a8) at qom/object.c:1860
#15 0x0000000000838c46 in object_property_set (obj=0x2ddf920, v=0x2decfd0, name=0x9b2c0e "realized", errp=0x7fffffffd9a8) at qom/object.c:1094
#16 0x000000000083c23f in object_property_set_qobject (obj=0x2ddf920, value=0x2dece90, name=0x9b2c0e "realized", errp=0x7fffffffd9a8) at qom/qom-qobject.c:27
#17 0x0000000000838f9a in object_property_set_bool (obj=0x2ddf920, value=true, name=0x9b2c0e "realized", errp=0x7fffffffd9a8) at qom/object.c:1163
#18 0x00000000005bfcea in qdev_device_add (opts=0x1451320, errp=0x7fffffffda30) at qdev-monitor.c:624
#19 0x00000000005c9662 in device_init_func (opaque=0x0, opts=0x1451320, errp=0x0) at vl.c:2305
#20 0x000000000095f491 in qemu_opts_foreach (list=0xe5bd80, func=0x5c9624 <device_init_func>, opaque=0x0, errp=0x0) at util/qemu-option.c:1114
#21 0x00000000005ce9be in main (argc=46, argv=0x7fffffffdeb8, envp=0x7fffffffe030) at vl.c:4583