Errors in write don't reach the other end

[viric]

I tried to implement a block device that fails on some write operations, and userspace does not seem to care much. I don't know why.

At most I get a message in the kernel log saying:

[ 8557.506812] Buffer I/O error on device nbd0, logical block 83210
[ 8557.507071] block nbd0: Other side returned error (-5)
[ 8557.507074] blk_update_request: I/O error, dev nbd0, sector 167938

So, I run something like this:
mkfs.ext4 /dev/nbd0

And mkfs.ext4 isn't notified of any error.

I'm returning "htonl(-EIO)" from the write callback.