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take the targets of /proc/*/ns/* symlinks to separate fs

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New pseudo-filesystem: nsfs.  Targets of /proc/*/ns/* live there now.
It's not mountable (not even registered, so it's not in /proc/filesystems,
etc.).  Files on it *are* bindable - we explicitly permit that in do_loopback().

This stuff lives in fs/nsfs.c now; proc_ns_fget() moved there as well.
get_proc_ns() is a macro now (it's simply returning ->i_private; would
have been an inline, if not for header ordering headache).
proc_ns_inode() is an ex-parrot.  The interface used in procfs is
ns_get_path(path, task, ops) and ns_get_name(buf, size, task, ops).

Dentries and inodes are never hashed; a non-counting reference to dentry
is stashed in ns_common (removed by ->d_prune()) and reused by ns_get_path()
if present.  See ns_get_path()/ns_prune_dentry/nsfs_evict() for details
of that mechanism.

As the result, proc_ns_follow_link() has stopped poking in nd->path.mnt;
it does nd_jump_link() on a consistent <vfsmount,dentry> pair it gets
from ns_get_path().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2014-11-01 10:57:28 -04:00
parent f77c80142e
commit e149ed2b80
10 changed files with 208 additions and 161 deletions
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5
fs/proc/inode.c
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@@ -32,7 +32,6 @@ static void proc_evict_inode(struct inode *inode)
{
struct proc_dir_entry *de;
struct ctl_table_header *head;
struct ns_common *ns;
truncate_inode_pages_final(&inode->i_data);
clear_inode(inode);
@@ -49,10 +48,6 @@ static void proc_evict_inode(struct inode *inode)
RCU_INIT_POINTER(PROC_I(inode)->sysctl, NULL);
sysctl_head_put(head);
}
/* Release any associated namespace */
ns = PROC_I(inode)->ns.ns;
if (ns && ns->ops)
ns->ops->put(ns);
}
static struct kmem_cache * proc_inode_cachep;