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proc: Usable inode numbers for the namespace file descriptors.

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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 <[email protected]>
This commit is contained in:
Eric W. Biederman 2011-06-15 10:21:48 -07:00
commit 98f842e675
18 changed files with 132 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

24
fs/proc/namespaces.c
View file

@ -82,7 +82,7 @@ static struct dentry *proc_ns_get_dentry(struct super_block *sb,
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 @@ static struct dentry *proc_ns_get_dentry(struct super_block *sb,
}
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 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl
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);