qemu-nbd trouble: UPD

[Oleg]

Hi.

mkfs.ext4 on nbd device cause:

Discarding device blocks: failed - Input/output error

message.

The actions:

~# qemu-img create -f raw test.img 10G
Formatting 'test.img', fmt=raw size=10737418240
~# qemu-nbd -f raw -c /dev/nbd0 test.img
~# fdisk /dev/nbd0
...[PARTITION A DISK]...
~# fdisk -l /dev/nbd0
Disk /dev/nbd0: 10 GiB, 10737418240 bytes, 20971520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xe75e6795

Device      Boot Start      End  Sectors Size Id Type
/dev/nbd0p1       2048 20971519 20969472  10G 83 Linux
~# mkfs.ext4 /dev/nbd0p1 
mke2fs 1.45.2 (27-May-2019)
Discarding device blocks: failed - Input/output error
Creating filesystem with 2621184 4k blocks and 655360 inodes
Filesystem UUID: 442620a3-0f00-432b-884e-0f14d76a993a
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done 
~# dmesg | tail
...[CUT]...
[64297.914937]  nbd0: p1
[64306.284714] block nbd0: Other side returned error (5)
[64306.284722] blk_update_request: I/O error, dev nbd0, sector 34816 op 
0x3:(DISCARD) flags 0x800 phys_seg 1 prio class 0


With qcow2 format i get the same problem. With losetup instead of qemu-nbd 
there is no errors.
Forgot to say:

kernel - 5.4.82(4.19.132 get the same error)
qemu - 5.0.0

-- 
Олег Неманов (Oleg Nemanov)