On Wed, Aug 12, 2020 at 02:43:32PM +0200, Miklos Szeredi wrote: > 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. The notification also reports new mount nodes, so we have no mount ID <-> mount path mapping in userspace yet. The another problem is that open(path) cannot be used if you have multiple filesystems on the same mount point -- in this case (at least in theory) you can get ID for by-path inaccessible filesystem. > 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); Yes, something like this is necessary. You do not want to depend on paths if you want to read information about mountpoints. Karel -- Karel Zak <kzak@xxxxxxxxxx> http://karelzak.blogspot.com
