Ceph » rbd

rbd-nbd can map and mount rbd image to /dev/nbdX successfully.
But can not write any files. The error message is "Read-only file system".

Test enviorment：
With Ubuntu kernel 3.14、3.16、4.4.0.
ceph version： 10.2.0 (3a9fba20ec743699b69bd0181dd6c54dc01c64b9)/ceph version 10.1.2 (4a2a6f72640d6b74a3bbd92798bb913ed380dcd4)

Test steps：
1.$rbd create testdisk -s 1G
2.$sudo rbd-nbd map testdisk
3.$sudo mkfs.ext4 -m 0 /dev/nbd0
4.$sudo mount /dev/nbd0 /mnt/mydisk
5.$echo 'Hello! ceph'|sudo tee /mnt/mydisk/he.txt
6.dmesg：
[71493.643241] block nbd0: Other side returned error (5)
[71493.643395] blk_update_request: I/O error, dev nbd0, sector 100224
[71493.643581] block nbd0: Other side returned error (5)
[71493.643780] blk_update_request: I/O error, dev nbd0, sector 100352
[71493.643954] block nbd0: Other side returned error (5)
[71493.644114] blk_update_request: I/O error, dev nbd0, sector 100480
[71493.644313] block nbd0: Other side returned error (5)
[71493.644498] block nbd0: Other side returned error (5)
[71493.644682] block nbd0: Other side returned error (5)
[71493.708647] block nbd0: Other side returned error (5)