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https://bugzilla.redhat.com/show_bug.cgi?id=836710 https://bugzilla.redhat.com/show_bug.cgi?id=836913 There are at least two related bugs going on: (1) Linux sync(2) system call doesn't send a write barrier to the disk, so in effect it doesn't force the hard disk to flush its cache. libguestfs used sync(2) to force changes to disk. We didn't expect that qemu was caching anything

This rather complex set of patches allow non-optargs functions to gain optional arguments, while preserving source and binary backwards compatibility. The problem is that we cannot add an optional argument to an existing function. For example, we might want to add flags to the 'lvresize' API which currently has no optional arguments.