Messages in this thread | | | Date | Wed, 10 Dec 2008 13:02:06 +0100 | From | "Kay Sievers" <> | Subject | Re: [PATCH] virtio: make PCI devices take a virtio_pci module ref |
| |
On Wed, Dec 10, 2008 at 10:49, Mark McLoughlin <markmc@redhat.com> wrote: > On Tue, 2008-12-09 at 19:16 +0100, Kay Sievers wrote: >> On Tue, Dec 9, 2008 at 17:41, Mark McLoughlin <markmc@redhat.com> wrote: >> > On Mon, 2008-12-08 at 08:46 -0600, Anthony Liguori wrote: >> >> Mark McLoughlin wrote: >> >> > On Sun, 2008-12-07 at 18:52 +1030, Rusty Russell wrote: >> >> >> On Saturday 06 December 2008 01:37:06 Mark McLoughlin wrote: >> >> >> >> >> >>> Another example of a lack of an explicit dependency causing problems is >> >> >>> Fedora's mkinitrd having this hack: >> >> >>> >> >> >>> if echo $PWD | grep -q /virtio-pci/ ; then >> >> >>> findmodule virtio_pci >> >> >>> fi >> >> >>> >> >> >>> which basically says "if this is a virtio device, don't forget to >> >> >>> include virtio_pci in the initrd too!". Now, mkinitrd is full of hacks, >> >> >>> but this is a particularly unusual one. >> >> >>> >> >> >> Um, I don't know what this does, sorry. >> >> >> >> >> >> I have no idea how Fedora chooses what to put in an initrd; I can't think >> >> >> of a sensible way of deciding what goes in and what doesn't other than >> >> >> lists and heuristics. >> >> >> >> >> > >> >> > Fedora's mkinitrd creates an initrd suitable to boot the machine you run >> >> > mkinitrd on, rather than creating an initrd suitable to boot any >> >> > machine. >> >> > >> >> > So, it goes "ah, / is mounted from /dev/vda, we need to include >> >> > virtio_blk and it's dependencies". It does that in a generic way that >> >> > works well for most setups: >> >> > >> >> > 1) Find the device name (e.g. vda) below /sys/block >> >> > >> >> > 2) Follow the 'device' link to e.g. /sys/devices/virtio-pci/virtio1 >> >> > >> >> > 3) Find the module need for this through either 'modalias' or the >> >> > 'driver/module' symlink >> >> > >> >> > 4) Use modprobe to list any dependencies of that module >> >> > >> >> > Clearly, virtio-pci won't be pulled in by any of this so we've added a >> >> > hack to say "oh, it's a virtio device, let's include virtio_pci just in >> >> > case". >> >> > >> >> > It's not even the case that mkinitrd needs to know how to include the >> >> > the module for the bus, because in our case that's virtio.ko ... we've >> >> > pretty effectively hidden the the bus *implementation* from userspace. >> >> > >> >> > I don't think this is worth wasting too much time fixing, that's why I'm >> >> > thinking we should just make virtio_pci built-in by default with >> >> > CONFIG_KVM_GUEST. >> >> > >> >> >> >> What if we have multiple virtio transports? >> > >> > I don't think that's so much an an issue (just build in any transport >> > supported by KVM), but rather that you might build a non-pv_ops kernel >> > to run on QEMU which would benefit from using virtio drivers ... >> > >> >> Is there a way that we can >> >> expose the relationship with virtio-blk and virtio-pci in sysfs? We >> >> have a struct device for the PCI device, it's just a matter of making >> >> the link visible. >> > >> > It feels a bit like busy work to generalise this since only virtio_pci >> > can be built as a module, but here's a patch. >> > >> > The mkinitrd hack turns into: >> > >> > # Handle finding virtio bus implementations >> > if [ -L ./virtio_module ] ; then >> > findmodule $(basename $(readlink ./virtio_module)) >> > else if echo $PWD | grep -q /virtio-pci/ ; then >> > findmodule virtio_pci >> > fi; fi >> > >> > [PATCH] virtio: add a 'virtio_module' sysfs symlink >> >> Doesn't the device have a "driver" link already? If yes, the driver it >> points to should have a "module" link. > > The virtio bus is an abstraction that has several different backend > implementations - currently virtio-pci, lguest and kvm-s390. > > So yes, the driver/module link gives us the device driver, but the > virtio_module link is to the virtio bus driver (aka implementation, > transport, backend, ...): > > $> basename $(readlink virtio_module) > virtio_pci > $> basename $(readlink driver/module) > virtio_net
I see. But why not just call it "module", like we do in all other places, when it points to /sys/module/.
To find dependent modules, you would walk up the chain of parents, and include everything that is found by looking for "driver/module" and "module" links?
Wouldn't that make it completely generic, without any virtio specific hacks?
Kay
| |