Re: [libvirt] [PATCH v7 2/6] qapi: Introduce add-fd, remove-fd, query-fdsets

On 08/09/2012 03:04 AM, Stefan Hajnoczi wrote: Pretty much agreed - rather than listing 'removed', omitting the fd by default will match the monitors expectations ("why are you telling me about an fd I told you to remove?"). The only reason I could see for keeping it would be for debug purposes, but that would be debugging of qemu, not the application connected to the monitor, at which point gdb debugging is probably better. refcount _might_ be useful for knowing whether qemu is actively using the fdset. For example, in the sequence: add-fd nnn drive-add if libvirtd crashes after sending drive-add but before getting a response, then on restart it has to figure out if the drive-add took or failed. A non-zero refcount means it took. But then again, so does a query-block. I like the approach of being minimal until we prove we need it, and can't right now think of anything where having a refcount would tell libvirt anything new that it can't already learn from somewhere else. Very nice idea! In fact, even nicer than returning a markup of O_RDONLY - if the management app cares about knowing details on an fd, such as whether it is read-only, then an opaque string tied to the fd in the fdset becomes very useful. The string needs to be optional on add-fd. (Libvirt might even use an xml-like string like "<fd file='/path/to/file' mode='O_RDONLY'/>", but of course, being an opaque string, qemu doesn't have to care what the string contains.) -- Eric Blake eblake(a)redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org