On Wed, Aug 12, 2020 at 1:28 PM Karel Zak <kzak@xxxxxxxxxx> wrote: > The proposal is based on paths and open(), how do you plan to deal > with mount IDs? David's fsinfo() allows to ask for mount info by mount > ID and it works well with mount notification where you get the ID. The > collaboration with notification interface is critical for our use-cases. One would use the notification to keep an up to date set of attributes for each watched mount, right? That presumably means the mount ID <-> mount path mapping already exists, which means it's just possible to use the open(mount_path, O_PATH) to obtain the base fd. If that assumption is not true, we could add a new interface for opening the root of the mount by ID. Fsinfo uses the dfd as a root for checking connectivity and the filename as the mount ID + a special flag indicating that it's not "dfd + path" we are dealing with but "rootfd + mntid". That sort of semantic multiplexing is quite ugly and I wouldn't suggest doing that with openat(2). A new syscall that returns an fd pointing to the root of the mount might be the best solution: int open_mount(int root_fd, u64 mntid, int flags); Yeah, yeah this is adding just another syscall interface, but notice how: a) it does one simple thing, no multiplexing at all b) is general purpose, and could be used for example in conjunction with open_by_handle_at(2), that also requires an fd pointing to a mount. Thanks, Miklos
