Re: [libvirt] [PATCH] fix vol-create when target allocation=0

Regression is introduced by commit e30297b0. After that, it will report "Cannot fill file" error with following xml file: <volume> <name>virtinst-vmlinuz-xen.tP1NHh</name> <capacity>4343792</capacity> <allocation>0</allocation> <target> <format type="raw"/> <nocow/> </target> </volume> Because of this, installing xen pv guest with virt-manager fails. Reason is: posix_fallocate(int fd, off_t offset, off_t len) will return EINVAL when len is equal to 0. So, this patch adds a check before calling safezero().