linux/fs/nfs/namespace.c

/*
 * linux/fs/nfs/namespace.c
 *
 * Copyright (C) 2005 Trond Myklebust <Trond.Myklebust@netapp.com>
 *
 * NFS namespace
 */

#include <linux/config.h>

#include <linux/dcache.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/nfs_fs.h>
#include <linux/string.h>
#include <linux/sunrpc/clnt.h>
#include <linux/vfs.h>

#define NFSDBG_FACILITY		NFSDBG_VFS

/*
 * nfs_follow_mountpoint - handle crossing a mountpoint on the server
 * @dentry - dentry of mountpoint
 * @nd - nameidata info
 *
 * When we encounter a mountpoint on the server, we want to set up
 * a mountpoint on the client too, to prevent inode numbers from
 * colliding, and to allow "df" to work properly.
 * On NFSv4, we also want to allow for the fact that different
 * filesystems may be migrated to different servers in a failover
 * situation, and that different filesystems may want to use
 * different security flavours.
 */
static void * nfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
{
	struct vfsmount *mnt;
	struct nfs_server *server = NFS_SERVER(dentry->d_inode);
	struct dentry *parent;
	struct nfs_fh fh;
	struct nfs_fattr fattr;
	int err;

	BUG_ON(IS_ROOT(dentry));
	dprintk("%s: enter\n", __FUNCTION__);
	dput(nd->dentry);
	nd->dentry = dget(dentry);
	if (d_mountpoint(nd->dentry))
		goto out_follow;
	/* Look it up again */
	parent = dget_parent(nd->dentry);
	err = server->rpc_ops->lookup(parent->d_inode, &nd->dentry->d_name, &fh, &fattr);
	dput(parent);
	if (err != 0)
		goto out_err;

	mnt = nfs_do_submount(nd->mnt, nd->dentry, &fh, &fattr);
	err = PTR_ERR(mnt);
	if (IS_ERR(mnt))
		goto out_err;

	mntget(mnt);
	err = do_add_mount(mnt, nd, nd->mnt->mnt_flags, NULL);
	if (err < 0) {
		mntput(mnt);
		if (err == -EBUSY)
			goto out_follow;
		goto out_err;
	}
	mntput(nd->mnt);
	dput(nd->dentry);
	nd->mnt = mnt;
	nd->dentry = dget(mnt->mnt_root);
out:
	dprintk("%s: done, returned %d\n", __FUNCTION__, err);
	return ERR_PTR(err);
out_err:
	path_release(nd);
	goto out;
out_follow:
	while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
		;
	err = 0;
	goto out;
}

struct inode_operations nfs_mountpoint_inode_operations = {
	.follow_link	= nfs_follow_mountpoint,
	.getattr	= nfs_getattr,
};