On Wed, Sep 14, 2011 at 8:22 PM, Anthony Liguori <aligu...@us.ibm.com> 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
This set only contains the framework. Converting a few real life devices would be helpful to see the framework in action. Also, I didn't find anything about backlinks, did I miss something? >> >> 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. > > Regards, > > Anthony Liguori > > >> >> Cheers > > >
