mount - nbd-client Fsync error - Ask Ubuntu

i try insert usb memory , check device "/dev/sdb1"

root@ubuntu:~# lsblk

name maj:min rm size ro type mountpoint

sda 8:0 0 64g 0 disk

├─sda1 8:1 0 63g 0 part /

├─sda2 8:2 0 1k 0 part

└─sda5 8:5 0 1022m 0 part [swap]

sdb 8:16 1 3.8g 0 disk

└─sdb1 8:17 1 3.8g 0 part /media/fd74eeb0-2bf8-49b0-872a- 4a283f124c10

sr0 11:0 1 1024m 0 rom

sr1 11:1 1 1024m 0 rom

and create network device

nbd-server -r 2000 /dev/sdb

** (process:2778): warning **: specifying export on command line deprecated.

** (process:2778): warning **: please use configuration file instead.

and client side( same machine )

nbd-client 172.20.10.3 2000 /dev/nbd0

negotiation: ..size = 3850mb

bs=1024, sz=4037017600 bytes

and mount nbd device

mount -o loop /dev/nbd0p1 point/

but mount follows problem occurs

root@ubuntu# mount /dev/nbd0p1 point/

mount: block device /dev/nbd0p1 write-protected, mounting read-only

when tried modify files in device error occurrs

vi point/test.c

add lines

and :wq

point/test.c" e212: can't open file writing

why ??

i don't understand this

root@ubuntu:~# dmesg | tail

[ 371.280809] loop: write error @ byte offset 3035136, length 4096.

[ 371.280810] buffer i/o error on device loop0, logical block 741

[ 371.280812] lost page write due i/o error on loop0

[ 371.280815] loop: write error @ byte offset 4096, length 4096.

[ 371.280816] buffer i/o error on device loop0, logical block 1

[ 371.280818] lost page write due i/o error on loop0

[ 389.039901] loop: write error @ byte offset 8396800, length 4096.

[ 389.039909] ext4-fs warning (device loop0): ext4_end_bio:317: i/o error -1 writing inode 12 (offset 0 size 0 starting block 2050)

[ 389.039913] buffer i/o error on device loop0, logical block 2050

[ 391.266099] hrtimer: interrupt took 8643276 ns

solved.

my mistake

nbc-server "-r" option read-only. ..

remove "-r" , mount -o loop correctly operates