On Mon, Apr 03, 2017 at 01:00:56AM -0500, Eric W. Biederman wrote:
> Refereshing my memory. d_automount mounts things and is what
> is used for nfs referrals. d_manage blocks waiting for
> an automounts to complete or expire. follow_down just calls d_manage,
> follow_manage calls both d_manage and d_automount as appropriate.
D'oh... Right. What's more, by that point getting back to original
state on error is needed.
> If the concern is nfs referral points calling follow_down is wrong and
> what is wanted is follow_managed.
... except that follow_managed() takes nameidata and there is no way in
hell we are letting that animal out of fs/namei.c ever again. Too low-level.
> The intent of the logic in mntns_install is to just pick a reasonable
> looking place somewhere in that mount namespace to use as a root
> directory. I arbitrarily picked the top of the mount stack on "/". Which
> is typically used as the root directory. If people really care where
> their root is they save a directory file descriptor off somewhere and
> call chroot. So there is a little wiggle room exactly what the code
> does.
Hmm... If anything, I'm tempted to add LOOKUP_DOWN that would have
path_lookupat() do
if (unlikely(flags & LOOKUP_DOWN)) {
struct path path = nd->path;
dget(nd->path.dentry);
err = follow_managed(&path, nd);
if (unlikely(err < 0))
terminate_walk(nd);
return err;
}
path_to_nameidate(&path, nd);
}
right after path_init(). Then your stuff would've turned into
get_mnt_ns(mnt_ns);
old_mnt_ns = nsproxy->mnt_ns;
nsproxy->mnt_ns = mnt_ns;
/* Find the root */
err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
"/", LOOKUP_DOWN, &root);
if (err) {
/* revert to old namespace */
nsproxy->mnt_ns = old_mnt_ns;
put_mnt_ns(mnt_ns);
return err;
}
/* Update the pwd and root */
set_fs_pwd(fs, &root);
set_fs_root(fs, &root);
path_put(&root);
put_mnt_ns(old_mnt_ns);
return 0;
This is absolutely untested, and I won't get around to testing it until
tomorrow, but something along those lines would IMO be better than
exposing a trimmed-down follow_managed(), not to mention struct nameidata
itself...
