Re: [RFC PATCH v4 03/12] vfs - move mnt_namespace definition to linux/mount.h

Al Viro
2015-03-19T19:47:16Z

On Tue, Mar 17, 2015 at 10:45:09AM +0800, Ian Kent wrote:
> From: Ian Kent <ikent@redhat.com>
>
> The mnt_namespace definition will be needed by the usermode helper
> contained execution implementation, move it to include/linux/mount.h.

I really don't like that. AFAICS, the root of the evil is that fscking
nsproxy keeps a pointer to mnt_namespace while all it really needs to
know about is the address of ns_common field embedded into it. Let's see...

fs/namespace.c:697: struct mnt_namespace *ns = current->nsproxy->mnt_ns;
fs/namespace.c:770: return mnt->mnt_ns == current->nsproxy->mnt_ns;
fs/namespace.c:1502: return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
fs/namespace.c:1587: return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
fs/namespace.c:2293: struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
fs/namespace.c:2961: touch_mnt_namespace(current->nsproxy->mnt_ns);
fs/namespace.c:3003: init_task.nsproxy->mnt_ns = ns;
fs/namespace.c:3101: ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
fs/namespace.c:3119: struct mnt_namespace *ns = current->nsproxy->mnt_ns;
fs/namespace.c:3159: ns = &nsproxy->mnt_ns->ns;
fs/namespace.c:3187: put_mnt_ns(nsproxy->mnt_ns);
fs/namespace.c:3188: nsproxy->mnt_ns = mnt_ns;
fs/pnode.c:282: user_ns = current->nsproxy->mnt_ns->user_ns;
fs/proc_namespace.c:246: if (!nsp || !nsp->mnt_ns) {
fs/proc_namespace.c:251: ns = nsp->mnt_ns;
include/linux/nsproxy.h:33: struct mnt_namespace *mnt_ns;
kernel/nsproxy.c:37: .mnt_ns = NULL,
kernel/nsproxy.c:70: new_nsp->mnt_ns = copy_mnt_ns(flags, tsk->nsproxy->mnt_ns, user_ns, new_fs);
kernel/nsproxy.c:71: if (IS_ERR(new_nsp->mnt_ns)) {
kernel/nsproxy.c:72: err = PTR_ERR(new_nsp->mnt_ns);
kernel/nsproxy.c:113: if (new_nsp->mnt_ns)
kernel/nsproxy.c:114: put_mnt_ns(new_nsp->mnt_ns);
kernel/nsproxy.c:160: if (ns->mnt_ns)
kernel/nsproxy.c:161: put_mnt_ns(ns->mnt_ns);

OK, so we need

a) add in fs/mount.h
static inline struct mnt_namespace *current_mnt_ns(void)
{
return current->nsproxy->mnt_ns;
}

and replace a lot of open-coded instances.

b) lift to_mnt_ns() into fs/mount.h (as static inline)

c) switch put_mnt_ns() to struct ns_common *, replacing put_mnt_ns(ns)
with put_mnt_ns(&ns->ns) and using to_mnt_ns() in the body to recover
the original.

d) make copy_mnt_ns() take and return struct ns_common * (same treatment as for
put_mnt_ns() in (c); replace
new_nsp->mnt_ns = copy_mnt_ns(flags, tsk->nsproxy->mnt_ns, user_ns, new_fs);
if (IS_ERR(new_nsp->mnt_ns)) {
err = PTR_ERR(new_nsp->mnt_ns);
goto out_ns;
}
with
ns = copy_mnt_ns(flags, &tsk->nsproxy->mnt_ns->ns, user_ns, new_fs);
if (IS_ERR(ns)) {
err = PTR_ERR(ns);
goto out_ns;
}
new_nsp->mnt_ns = to_mnt_ns(ns);

e) replace struct mnt_namespace *mnt_ns with struct ns_common *__mnt_ns in
nsproxy.h, deal with users of mnt_ns by
* everywhere in the tree replace put_mnt_ns(&...->mnt_ns->ns) with
put_mnt_ns(...->__mnt_ns) (i.e. modify the lines modified by (c) again).
* in fs/namespace.c replace
init_task.nsproxy->mnt_ns = ns;
with
init_task.nsproxy->__mnt_ns = &ns->ns;
replace
ns = &nsproxy->mnt_ns->ns;
with
ns = nsproxy->__mnt_ns;
replace
nsproxy->mnt_ns = mnt_ns;
with
nsproxy>__mnt_ns = &mnt_ns->ns;
* in fs/proc_namespace.c replace
ns = nsp->mnt_ns;
with
ns = to_mnt_ns(nsp->__mnt_ns);
and
if (!nsp || !nsp->mnt_ns) {
with
if (!nsp || !nsp->__mnt_ns) {
* in kernel/nsproxy.c: replace
ns = copy_mnt_ns(flags, &tsk->nsproxy->mnt_ns->ns, user_ns, new_fs);
added in (d) with
ns = copy_mnt_ns(flags, tsk->nsproxy->__mnt_ns, user_ns, new_fs);
and
new_nsp->mnt_ns = to_mnt_ns(ns);
with
new_nsp->__mnt_ns = ns;
The rest of mnt_ns in that file get replaced by __mnt_ns.
* in current_mnt_ns() replace ...->mnt_ns with to_mnt_ns(...->__mnt_ns)

Do you want me to push such a series in vfs.git? After such 5 commits we have
no pointers to struct mnt_namespace in nsproxy.h *and* no need for your patches
to dig into ->mnt_ns->ns - we already have that as ->__mnt_ns.