Hi! I just updated my developement systems to 6.5-rc6 (from 6.4) and now I can't start a VM with a disk which is mounted over the NFS. The VM has two qcow2 files, one depends on another and qemu opens both. This is the command line of qemu: -drive if=none,id=os_image,file=./disk_s1.qcow2,aio=native,discard=unmap,cache=none The disk_s1.qcow2 depends on disk_s0.qcow2 However this is what I get: qemu-system-x86_64: -drive if=none,id=os_image,file=./disk_s1.qcow2,aio=native,discard=unmap,cache=none: Could not open backing file: Could not open './QFI?': No such file or directory 'QFI?' is qcow2 file signature, which signals that there might be some nasty corruption happening. The program was supposed to read a field inside the disk_s1.qcow2 file which should read 'disk_s0.qcow2' but instead it seems to read the first 4 bytes of the file. Bisect leads to the above commit. Reverting it was not possible due to many changes. Both the client and the server were tested with the 6.5-rc6 kernel, but once rebooting the server into the 6.4, the bug disappeared, thus I did a bisect on the server. When I tested a version before the offending commit on the server, the 6.5-rc6 client was able to work with it, which increases the chances that the bug is in nfsd. Switching qemu to use write back paging also helps (aio=threads,discard=unmap,cache=writeback) The client and the server (both 6.5-rc6) work with this configuration. Running the VM on the same machine (also 6.5-rc6) where the VM disk is located (thus avoiding NFS) works as well. I tested several VMs that I have, all are affected in the same way. I run somewhat outdated qemu, but running the latest qemu doesn't make a difference. I use nfs4. I can test patches and provide more info if needed. Best regards, Maxim Levitsky
