proc: Usable inode numbers for the namespace file descriptors.
Assign a unique proc inode to each namespace, and use that
inode number to ensure we only allocate at most one proc
inode for every namespace in proc.
A single proc inode per namespace allows userspace to test
to see if two processes are in the same namespace.
This has been a long requested feature and only blocked because
a naive implementation would put the id in a global space and
would ultimately require having a namespace for the names of
namespaces, making migration and certain virtualization tricks
impossible.
We still don't have per superblock inode numbers for proc, which
appears necessary for application unaware checkpoint/restart and
migrations (if the application is using namespace file descriptors)
but that is now allowd by the design if it becomes important.
I have preallocated the ipc and uts initial proc inode numbers so
their structures can be statically initialized.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 7a6d8d6..b7a4719 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -82,7 +82,7 @@
return ERR_PTR(-ENOMEM);
}
- inode = new_inode(sb);
+ inode = iget_locked(sb, ns_ops->inum(ns));
if (!inode) {
dput(dentry);
ns_ops->put(ns);
@@ -90,13 +90,17 @@
}
ei = PROC_I(inode);
- inode->i_ino = get_next_ino();
- inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
- inode->i_op = &ns_inode_operations;
- inode->i_mode = S_IFREG | S_IRUGO;
- inode->i_fop = &ns_file_operations;
- ei->ns_ops = ns_ops;
- ei->ns = ns;
+ if (inode->i_state & I_NEW) {
+ inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+ inode->i_op = &ns_inode_operations;
+ inode->i_mode = S_IFREG | S_IRUGO;
+ inode->i_fop = &ns_file_operations;
+ ei->ns_ops = ns_ops;
+ ei->ns = ns;
+ unlock_new_inode(inode);
+ } else {
+ ns_ops->put(ns);
+ }
d_set_d_op(dentry, &ns_dentry_operations);
result = d_instantiate_unique(dentry, inode);
@@ -162,12 +166,12 @@
if (!ns)
goto out_put_task;
- snprintf(name, sizeof(name), "%s", ns_ops->name);
+ snprintf(name, sizeof(name), "%s:[%u]", ns_ops->name, ns_ops->inum(ns));
len = strlen(name);
if (len > buflen)
len = buflen;
- if (copy_to_user(buffer, ns_ops->name, len))
+ if (copy_to_user(buffer, name, len))
len = -EFAULT;
ns_ops->put(ns);