On Tue, Dec 04, 2018 at 02:12:39PM +0100, Christian Brauner wrote: > As discussed at Linux Plumbers Conference 2018 in Vancouver [1] this is the > implementation of binderfs. If you want to skip reading and just see how it > works, please go to [2]. First off, thanks for doing this so quickly. I think the overall idea and implementation is great, I just have some minor issues with the user api: > /* binder-control */ > Each new binderfs instance comes with a binder-control device. No other > devices will be present at first. The binder-control device can be used to > dynamically allocate binder devices. All requests operate on the binderfs > mount the binder-control device resides in: > - BINDER_CTL_ADD > Allocate a new binder device. > Assuming a new instance of binderfs has been mounted at /dev/binderfs via > mount -t binderfs binderfs /dev/binderfs. Then a request to create a new > binder device can be made via: > > struct binderfs_device device = {0}; > int fd = open("/dev/binderfs/binder-control", O_RDWR); > ioctl(fd, BINDER_CTL_ADD, &device); > > The struct binderfs_device will be used to return the major and minor > number, as well as the index used as the new name for the device. > Binderfs devices can simply be removed via unlink(). I think you should provide a name in the BINDER_CTL_ADD command. That way you can easily emulate the existing binder queues, and it saves you a create/rename sequence that you will be forced to do otherwise. Why not do it just in a single command? That way also you don't need to care about the major/minor number at all. Userspace should never need to worry about that, use a name, that's the best thing. Also, it allows you to drop the use of the idr, making the kernel code simpler overall. > /* Implementation details */ > - When binderfs is registered as a new filesystem it will dynamically > allocate a new major number. The allocated major number will be returned > in struct binderfs_device when a new binder device is allocated. Why does userspace care about major/minor numbers at all? You should just be able to deal with the binder "names", that's all that userspace uses normally as you are not calling mknod() yourself. > Minor numbers that have been given out are tracked in a global idr struct > that is capped at BINDERFS_MAX_MINOR. The minor number tracker is > protected by a global mutex. This is the only point of contention between > binderfs mounts. I doubt this will be any real contention given that setting up / tearing down binder mounts is going to be rare, right? Well, hopefully, who knows with some container systems... > - The naming scheme for binder devices is binder%d. Each binderfs mount > starts numbering of new binder devices at 0 up to n. The indeces used in > constructing the name are tracked in a struct idr that is per-binderfs > super block. Again, let userspace pick the name, as you will have to rename it anyway to get userspace to work properly with it. I'll stop repeating myself now :) thanks, greg k-h _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel