On Fri, May 15, 2020 at 3:04 PM Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote: > > On Fri, May 15, 2020 at 1:40 PM Michael Kerrisk (man-pages) > <mtk.manpages@xxxxxxxxx> wrote: > > > > Hello David, Miklos, > > > > I've been looking at the new mount API (fsopen(), fsconfig(), > > fsmount(), move_mount(), etc.) and among the details that remain > > mysterious to me is this: how does one set the propagation type > > (private/shared/slave/unbindable) of a new mount and change the > > propagation type of an existing mount? > > Existing mount can be chaged with mount(NULL, path, NULL, MS_$(propflag), NULL). > > To do that with a detached mount created by fsmount(2) the > "/proc/self/fd/$fd" trick can be used. > > The plan was to introduce a mount_setattr(2) syscall, but that hasn't > happened yet... I'm not sure we should be adding propagation flags to > fsmount(2), since that is a less generic mechanism than > mount_setattr(2) or just plain mount(2) as shown above. Also note that only setting MS_SHARED makes sense on a new mount returned by fsmount(2) because - MS_PRIVATE is a no op, due to mount already being private - same for MS_SLAVE, since it's only different from MS_PRIVATE on mounts receiving propagation, which a new mount by definition isn't - MS_UNBINDABLE just prevents move_mount(2) from working so that's not really useful, though at least it does something A more interesting issue is whether we'd want to control the propagation of the target when moving into a shared tree. I.e. should there be a MOVE_MOUNT_DONTPROPAGATE flag for move_mount(20 that prevents the new mount from being propagated... Thanks, Miklos
