On Tue, 10 May 2022 at 13:53, Christian Brauner <brauner@xxxxxxxxxx> wrote: > > What exactly are the attributes that systemd requires? > > We keep a repo with ideas for (kernel) extensions - we should probably > publish that somewhere - but the list we used for a prototype roughly > contains: > > * mount flags MOUNT_ATTR_RDONLY etc. > * time flags MOUNT_ATTR_RELATIME etc. (could probably be combined with > mount flags. We missed the opportunity to make them proper enums > separate from other mount flags imho.) > * propagation "flags" (MS_SHARED) > * peer group > * mnt_id of the mount > * mnt_id of the mount's parent > * owning userns Sounds good thus far. And hey, we don't even need a new syscall: statx(2) could handle these fine. > There's a bit more advanced stuff systemd would really want but which I > think is misplaced in a mountinfo system call including: > * list of primary and auxiliary block device major/minor It's when you need to return variable size arrays or list of strings that the statx kind of interface falls down. For that a hierarchical namespace is a much better choice, as it can represent arbitrary levels of arrays, while doing that with a specialized syscall is going to be cumbersome. > I just have a really hard time understanding how this belongs into the > (f)getxattr() system call family and why it would be a big deal to just > make this a separate system call. Fragmenting syntactically equivalent interfaces is bad, unifying them is good. Dave's example of adding a new syscall for retrieving multiple xattrs is a prime example. Thanks, Miklos
