On Tue, 10 Sep 2013, Lucas De Marchi wrote: > >>> > The ordering is more of a recommendation than a necessity. Systems > >>> > should work oksy if the modules are loaded in the wrong order. > >>> > > >>> > The only issue if the drivers are loaded in the wrong order is that > >>> > full- and low-speed devices will end up being detected and enumerated > >>> > twice, with a disconnection in between. This can result in > >>> > disconcerting messages appearing in the system log. > >>> > > >>> > In theory, it is possible for a problem to arise. For example, suppose > >>> > a full-speed flash drive is plugged in when the system starts up. > >>> > When uhci-hcd or ohci-hcd gets loaded, the drive will be detected and > >>> > it may even be mounted. Then when ehci-hcd loads, the drive will get > >>> > disconnected and reconnected. Any open file references to the original > >>> > mount will be orphaned. > > Then IMO it should not only be advised to have this dependency, but > also require it. Requiring the ordering won't fix all the possible problems. For example, ehci-pci might be compiled into the kernel while ohci-pci is built as a module (although this probably could be prevented by tweaking the Kconfig file). > >> So this means that before installing ohci-hcd, modprobe would attempt > >> to install ehci-hcd? And if the attempt failed, it would go ahead and > >> load ohci-hcd anyway? > > > > Exactly. > > Not really. If we try to load the module, but then fail we fail the > operation altogether. Whereas if the module simply doesn't exist, then > we carry on. In reality what we do is to assume the indexes and > softdeps in configuration are correct) What if somebody really does want to load ohci-pci without loading ehci-pci? That is a perfectly valid thing to do (and I often want to do it for testing). It sounds like the only way to accomplish this would be to load both and then unload ehci-pci. Yes? Or would that unload ohci-pci as well? > >> What about during unloading? Would this mean that rmmod ohci-hcd would > >> automatically cause ehci-hcd to be unloaded also? Or would unloading > >> ehci-hcd cause ohci-hcd to be unloaded? > > > > No, unloading does not care about dependencies. > > modprobe -r will remove then as well, in the opposite order, i.e. post > softdep, module, pre softdep. However this applies only to modprobe, > not to the related function in libkmod since it would be weird to > other programs using this library function. Aside from testing, people hardly ever unload drivers. So this is a relatively minor concern. > Try playing with this in /etc/modprobe.d/bla.conf (and replace echo > with whatever unknown command to test a failure scenario): > install bla echo install bla > remove bla echo remove bla > softdep sr_mod pre: bla Good recommendation. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
