On Sun, Mar 31, 2019 at 05:18:10PM -0700, Linus Torvalds wrote: > On Sun, Mar 31, 2019 at 5:09 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > Ugh... Which vfsmount would you have to go with it? > > I'd literally just do a lookup of "/proc" in the current root > directory in the lookup() function for that special pseudo-dentry. > > If it's not mounted, or not a /proc filesystem, screw it. > > > Except that we never let unattached _directory_ dentries out - if > > we can't reattach them to the tree, open-by-handle will tell you to > > take a hike. > > Absolutely. Which is why I said it's _conceptually_ similar to the alias lookup. > > And I suspect we can even use some of the same practical logic, but > it's definitely not _exactly_ the same. This thing very much involves > magic hooking into the lookup() function (but we then have to look up > the alias not for the path we're looking up, but for the _parent_ > we're looking that path up in, which is very different from the normal > case). > > > It's more than a tiny bit too clever for mine... > > Fair enough. The whole "just do the whole lookup at pidfd creation > time" is certainly a whole lot simpler. Even just from a pure maintenance perspective this sounds a better to me.
