On Wed, 2019-07-03 at 09:24 +0800, Ian Kent wrote:
> On Wed, 2019-07-03 at 09:09 +0800, Ian Kent wrote:
> > Hi Christian,
> >
> > About the propagation attributes you mentioned ...
>
> Umm ... how did you work out if a mount is unbindable from proc
> mountinfo?
>
> I didn't notice anything that could be used for that when I was
> looking at this.
Oh wait, fs/proc_namespace.c:show_mountinfo() has:
if (IS_MNT_UNBINDABLE(r))
seq_puts(m, " unbindable");
I missed that, probably because I didn't have any unbindable mounts
at the time I was looking at it, oops!
That's missing and probably should be added too.
>
> > On Fri, 2019-06-28 at 16:47 +0100, David Howells wrote:
> >
> > snip ...
> >
> > > +
> > > +#ifdef CONFIG_FSINFO
> > > +int fsinfo_generic_mount_info(struct path *path, struct fsinfo_kparams
> > > *params)
> > > +{
> > > + struct fsinfo_mount_info *p = params->buffer;
> > > + struct super_block *sb;
> > > + struct mount *m;
> > > + struct path root;
> > > + unsigned int flags;
> > > +
> > > + if (!path->mnt)
> > > + return -ENODATA;
> > > +
> > > + m = real_mount(path->mnt);
> > > + sb = m->mnt.mnt_sb;
> > > +
> > > + p->f_sb_id = sb->s_unique_id;
> > > + p->mnt_id = m->mnt_id;
> > > + p->parent_id = m->mnt_parent->mnt_id;
> > > + p->change_counter = atomic_read(&m->mnt_change_counter);
> > > +
> > > + get_fs_root(current->fs, &root);
> > > + if (path->mnt == root.mnt) {
> > > + p->parent_id = p->mnt_id;
> > > + } else {
> > > + rcu_read_lock();
> > > + if (!are_paths_connected(&root, path))
> > > + p->parent_id = p->mnt_id;
> > > + rcu_read_unlock();
> > > + }
> > > + if (IS_MNT_SHARED(m))
> > > + p->group_id = m->mnt_group_id;
> > > + if (IS_MNT_SLAVE(m)) {
> > > + int master = m->mnt_master->mnt_group_id;
> > > + int dom = get_dominating_id(m, &root);
> > > + p->master_id = master;
> > > + if (dom && dom != master)
> > > + p->from_id = dom;
> >
> > This provides information about mount propagation (well mostly).
> >
> > My understanding of this was that:
> > "If a mount is propagation private (or slave) the group_id will
> > be zero otherwise it's propagation shared and it's group id will
> > be non-zero.
> >
> > If a mount is propagation slave and propagation peers exist then
> > the mount field mnt_master will be non-NULL. Then mnt_master
> > (slave's master) can be used to set master_id. If the group id
> > of the propagation source is not that of the master then set
> > the from_id group as well."
> >
> > This parallels the way in which these values are reported in
> > the proc pseudo file system.
> >
> > Perhaps adding flags as well as setting the fields would be
> > useful too, since interpreting the meaning of the structure
> > fields isn't obvious, ;)
> >
> > David, Al, thoughts?
> >
> > Ian
