Kevin Wolf <kw...@redhat.com> writes: > Am 01.08.2014 um 22:10 hat John Snow geschrieben: >> >> On 06/12/2014 05:03 AM, Markus Armbruster wrote: >> >Michael Tokarev <m...@tls.msk.ru> writes: >> > >> >>10.06.2014 10:34, Paolo Bonzini wrote: >> >>>Il 10/06/2014 08:30, Michael Tokarev ha scritto: >> >>>>Hello. >> >>>> >> >>>>The question is: are the drive shortcuts - -cdrom, -hda, -hdb etc - >> >>>>supposed to work in -machine q35 too? Or are they merely ignored? >> >>>> >> >>>> qemu-system-x86_64 -machine q35 -cdrom foo.img >> >>[] >> >>>It should work. I remember some complications due to AHCI not >> >>>having slaves, but it is a bug. >> >>It looks like the "short" -drive if=ide option does not connect the >> >>created drive to any bus at all. With the above command, or with >> >>-drive if=ide,index=*,bus=*, info qtree does not show the drive at >> >>all. While -drive if=none,id=X -device ide-cd,drive=X connects the >> >>drive to the right bus just fine. >> >-drive mixes up configuration of backend and frontend (a.k.a. device >> > model), as follows: >> > >> >1. It always defines a backend. "info block" shows them. >> > >> >2. It always defines a few frontend configuration bits for the device >> > models to pick up. >> > >> >3. Except with if=none, it posts a request to board code to create a >> > suitable frontend. It's up to the board code to honor, reject or >> > ignore the request. The i440FX boards honor it, the Q35 boards >> > ignore it. >> > >> > Nobody has gotten around to making the Q35 boards honor it, in part >> > because there has been some confusion on what if=ide is supposed to >> > mean on Q35. Should it connect an ide-hd / ide-cd in SATA mode or in >> > legacy PATA mode? >> > >> > I've always argued for SATA, because for me if=ide does *not* imply a >> > specific kind of HBA any more than if=scsi does, and the "natural" >> > HBA for Q35 is AHCI in SATA mode. >> > >> > Kevin (cc'ed) has argued for a way to make it connect in legacy PATA >> > mode. I'd be fine with that, as long as it's off by default. >> > >> > Patches welcome. >> > >> >> Kevin, (or anyone else with an opinion for that matter), what is the >> reasoning behind wanting -cdrom to use the old PATA interfaces? > > The assumption that makes it a problem is that sooner or later we'll > want to make Q35 the default. Most of the changes this brings in will > make the guest see different, but generally still compatible hardware. > AHCI however is not compatible with IDE in the sense that an OS that has > only an IDE driver won't work with AHCI. > > It wouldn't be reasonable to break things like '-hda winxp.qcow2'. And > in fact, if the internet is right, even newer Windows version give you > trouble when you suddenly change from IDE to AHCI. So after an upgrade > many users would find their existing guests to be broken.
I feel asking users of old guests to specify a machine type when the default one no longer works is better than having defaults stuck in the 90s forever. That said... >> For at least the immediate future, the AHCI device doesn't support >> the mixed-mode SATA/PATA access models, though I suppose we could, >> it seems like a more obvious and simple solution to just allow the >> shorthand syntactic sugar commands to use the native bus of the >> system until you specify otherwise. >> >> I think I will probably begin writing a patch under this assumption >> unless there is a better technical reason not to. > > I think the solution that was generally agreed on was to introduce a > machine option that decides whether to provide an IDE or AHCI interface > (similar to the BIOS option that commonly exists on real hardware). We > just need someone to implement it. ... if someone wants to implement legacy PATA for AHCI, I welcome patches :) However, I don't think we should keep if=ide broken on Q35 just to "motivate" such work.
