On Wed, Nov 04, 2020 at 04:48:53PM +0000, Daniel P. Berrangé wrote: > On Wed, Nov 04, 2020 at 11:35:56AM -0500, Masayoshi Mizuma wrote: > > Hello, > > > > It seems that locking option doesn't work as expected. > > When I run qemu as following options, then I got an error and failed to > > boot the guest: > > > > qemu-system-x86_64 \ > > -machine pc \ > > -enable-kvm \ > > -cpu host \ > > -smp 1 -m 4G \ > > -nographic \ > > -serial telnet::1235,server,nowait \ > > -blockdev > > driver=qcow2,node-name=disk,file.driver=file,file.filename=/mnt/guest.qcow2,file.locking=auto > > \ > > -device virtio-blk-pci,scsi=off,drive=disk,id=virtio-disk0,bootindex=1 > > > > qemu-system-x86_64: -blockdev > > driver=qcow2,node-name=disk,file.driver=file,file.filename=/mnt/guest.qcow2,file.locking=auto: > > Failed to lock byte 100 > > > > The error happens when the filesystem doesn't support OFD lock. > > qemu_probe_lock_ops() judges whether qemu can use OFD lock or not with doing > > fcntl(F_OFD_GETLK) to /dev/null, so the error happens if /dev/null supports > > OFD lock, > > but the filesystem doesn't support the lock. > > > > I'm thinking how to fix the error. My idea is to add locking=posix option > > to use posix > > lock to the file, but I'm not sure the idea is good way to fix the error... > > > > I would appreciate it if you could give me some advises to fix the error. > > Ideally we would not attempt to probe it on /dev/null at all. Instead just > attempt to lock the actual file using F_OFD_SETLK and if that fails, then > falback to F_SETLK. We can do similar when checking whether the lock > currently exists. AFAIK, the locking code isn't so performance critical > that the extra syscall would hurt us in the case where OFD doesn't exist > or isn't supported by the FS.
Thank you for your comments! I'll fix the error to lock the file using F_OFD_SETLK and if that fails, then falback to F_SETLK. Thanks! Masa > > > > > BTW, locking=off may be useful for the workaround so far, however, > > locking=off > > doesn't work on the splitting blockdev configs as followings... > > I split the blockdev option as libvirt doing. > > > > -blockdev > > driver=file,filename=/mnt/guest.qcow2,node-name=storage,auto-read-only=on,locking=off > > \ > > -blockdev node-name=format,read-only=off,driver=qcow2,file=storage \ > > > > Thanks, > > Masa > > > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >
