Re: [libvirt] [PATCH 0/2] Two simple sparse streams fixes

On Tue, May 30, 2017 at 12:44:21PM +0200, Michal Privoznik wrote: > I've been experimenting with sparse streams and found a bug. If you > try to > download a volume which doesn't support sparseness here's what happens: > > # virsh vol-download --sparse > /dev/disk/by-path/ip-XX.XX.XX.XX:3260-iscsi-iqn.2017-03.com.blah:server-lun-0 > /mnt/floppy/blah.raw > > # echo $? > 0 > # ls -lhs /mnt/floppy/bla.raw > 0 -rw-r--r-- 1 root root 0 May 30 12:40 /mnt/floppy/bla.raw > > That's not good. iSCSI doesn't know anything about sparseness so an > error is > expected here. Fortunately, the fix is fairly simple: > > # virsh vol-download --sparse > /dev/disk/by-path/ip-XX.XX.XX.XX:3260-iscsi-iqn.2017-03.com.blah:server-lun-0 > /mnt/floppy/bla.raw > error: cannot close volume > /dev/disk/by-path/ip-XX.XX.XX.XX:3260-iscsi-iqn.2017-03.com.blah:server-lun-0 > > error: Unable to seek to data: Invalid argument > I'm also getting confusing errors when there is no space on the destination: error: cannot receive data from volume fedora.img error: An error occurred, but the cause is unknown

But that's not related to the sparse streams (unless it was caused by making the iohelper a thread). ... few moments later after /me tries just a thing or two ... Well, this made me try out few more things and I've found out few things. I'm not sure what's related to your patches and what's not, so here's the rundown, and I'll let you decide: - vol-download --sparse --offset $source_file_size --length 1 /path/to/source.file destination.file - Every now and then (not always) it gets stuck waiting for the daemon to receive data (see backtrace below), but the daemon is not waiting for anything, it's just some weird race. We can try debugging it with wireshark later. That file ends with a hole.