Le 15/04/2014 17:06, One Thousand Gnomes a écrit : >> In order to associate devices to their files, the Linux kernel uses >> their major and minor numbers. However, mine doesn't; instead, I've >> attributed myself a single group of values (major=0, minor=0, for both >> character-mode and block-mode special files), with the meaning (for the >> userspace) "you cannot identify the content of this file based on its >> major and minor numbers". > > If you are using the Linux ABI then you'll hit cases (in particular tty > cases) where the ABI/API knows about major/minor numbers.
Well, in fact, my kernel *can* handle major and minor numbers. That is, if you tell it "mknod /dev/efjkb c 8 6" , you'll actually get a device file with major/minor numbers 8/6. But then, the kernel simply disregards these values and waits for userspace to specify it what this device means. So it's completely possible to emulate Linux's behaviour with it. > In addition the > standards and common sense together pretty much imply that you need each > device to at least have a unique identifier. > Why is it? I mean, as far as userspace is concerned, they do have a unique identifier : their name. How would it be problematic that the software is unable to confirm that /dev/null is actually connected to the usual /dev/null kernel driver? I mean, it's supposed to trust the OS and its admin to have done their job properly, not second-guess them! (My idea behind this is to allow lying, for example by allowing the sysadmin to fake the content of, say, /dev/random, to an application he wants to test, or even deliberately sabotage. So, in my OS's logic, there's nothing wrong with emulating Linux's major/minor device identifiers, but of course, their reliability will be in the sysadmin's hands, so I thought I could simply make this clear by using explicitely unreliable identifiers.) > Finally you need major/minor numbers to NFS serve to a diskless client. Not a problem, but of course, the distant client will have the ability to connect anything it wants to any device it wants. > > Most Linux device numbering beyond that is basically dynamic so it > probably does't matter that much for things you concoct - providing in > som cases your /proc table of major numbers is right. > Ah... Uhhh... I've not implemented any such table, so I guess it's currently not. Whoops... Emmanuel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
