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.
>
> 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
