[libvirt] NFS over RDMA small block DIRECT_IO bug

Hello. # Avi Kivity avi(a)redhat recommended I copy kvm in on this. It would also seem relevent to libvirt. # I have a Centos 6.2 server and Centos 6.2 client. [root@store ~]# cat /etc/exports /dev/shm 10.149.0.0/16(rw,fsid=1,no_root_squash,insecure) (I have tried with non tempfs targets also) [root@node001 ~]# cat /etc/fstab store.ibnet:/dev/shm /mnt nfs rdma,port=2050,defaults 0 0 I wrote a little for loop one liner that dd'd the centos net install image to a file called 'hello' then checksummed that file. Each iteration uses a different block size. Non DIRECT_IO seems to work fine. DIRECT_IO with 512byte, 1K and 2K block sizes get corrupted. I want to run my KVM guests on top of NFS over RDMA. My guests cannot create filesystems. Thanks, Andrew. bug report: https://bugzilla.linux-nfs.org/show_bug.cgi?id=228 [root@node001 mnt]# for f in 512 1024 2048 4096 8192 16384 32768 65536 131072; do dd bs="$f" if=CentOS-6.3-x86_64-netinstall.iso of=hello iflag=direct oflag=direct && md5sum hello && rm -f hello; done 409600+0 records in 409600+0 records out 209715200 bytes (210 MB) copied, 62.3649 s, 3.4 MB/s aadd0ffe3c9dfa35d8354e99ecac9276 hello -- 512 byte block 204800+0 records in 204800+0 records out 209715200 bytes (210 MB) copied, 41.3876 s, 5.1 MB/s 336f6da78f93dab591edc18da81f002e hello -- 1K block 102400+0 records in 102400+0 records out 209715200 bytes (210 MB) copied, 21.1712 s, 9.9 MB/s f4cefe0a05c9b47ba68effdb17dc95d6 hello -- 2k block 51200+0 records in 51200+0 records out 209715200 bytes (210 MB) copied, 10.9631 s, 19.1 MB/s 690138908de516b6e5d7d180d085c3f3 hello -- 4k block 25600+0 records in 25600+0 records out 209715200 bytes (210 MB) copied, 5.4136 s, 38.7 MB/s 690138908de516b6e5d7d180d085c3f3 hello 12800+0 records in 12800+0 records out 209715200 bytes (210 MB) copied, 3.1448 s, 66.7 MB/s 690138908de516b6e5d7d180d085c3f3 hello 6400+0 records in 6400+0 records out 209715200 bytes (210 MB) copied, 1.77304 s, 118 MB/s 690138908de516b6e5d7d180d085c3f3 hello 3200+0 records in 3200+0 records out 209715200 bytes (210 MB) copied, 1.4331 s, 146 MB/s 690138908de516b6e5d7d180d085c3f3 hello 1600+0 records in 1600+0 records out 209715200 bytes (210 MB) copied, 0.922167 s, 227 MB/s 690138908de516b6e5d7d180d085c3f3 hello