On Wed, Sep 14, 2011 at 03:22:29PM -0500, Anthony Liguori wrote: > On 09/14/2011 03:00 PM, Edgar E. Iglesias wrote: > >On Wed, Sep 14, 2011 at 01:04:00PM -0500, Anthony Liguori wrote: > >>Hi, > >> > >>I spent a couple hours today writing up some comparisons and an > >>initial task list for converting qdev to QOM. The main location of > >>this is the wiki[1] but I thought I would inline it here for easier > >>commenting. > >> > >>I decided to do this because I wanted to avoid a massively long 00 > >>patch explaining the rationale for the first batch of changes that > >>I'm going to send out. > >> > >>There is so much complexity in qdev and the device model in general > >>that it's hard to come up with a concise document. I'd really > >>appreciate suggestions for topics to write up more rationale as that > >>would help me avoid writing a book on the topic :-) > > > >Thanks Anthony, > > > >I'd appreciate if you could elaborate more on the backlinks. Also, > >tiny code examples would help. Maybe you've got a git repo with > >more code to link to? > > Message-Id: <1311558293-5855-1-git-send-email-aligu...@us.ibm.com> > > Or > > http://repo.or.cz/w/qemu/aliguori.git/shortlog/refs/heads/qom > > > > >Regarding the composition, a problem I face (which I mostly just > >hack my way around) is that inter device connections may exist > >at various layers at the same time. For example, a device that is > >burried under a couple of busses/bridges may somehow be tighly > >connected to another device at a very different location in > >the bus hierarchy by means of another overlayed interconnect (e.g > >data channels, timing generation, IRQs etc). Maybe you could > >clarify a bit more on how QOM handles these topics. > > Links are meant to handle this. You can have something like: > > + PlatformDevice1 > + PlatformDevice2 > + PciBus > | > +- PciDevice1 > +- PciDevice2 > | > + I2CBus > | > +- I2CDevice1 > |- pd2: link<PlatformDevice2> > > So you have I2CDevice that sites behind multiple levels of > hierarchy, but has a direct relationship (via a link) to a platform > device much higher in the hierarchy. This is an simple > demonstration of how you can create a graph in QOM. > > qdev doesn't allow graphs in the object model which is the problem > that you're having today. That's because its a tree with > alternating levels. The top level is always a bus, the next level > is always devices, the next level are always busses, etc. > > With QOM, there are only devices, and devices can link to 0 or more other > devices.
Great, thanks for clarifying! Maybe you can copy+paste this into your book :p Cheers
