Commit 8ed5eec9 authored by Amir Goldstein's avatar Amir Goldstein Committed by Miklos Szeredi
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ovl: encode pure upper file handles

Encode overlay file handles as struct ovl_fh containing the file handle
encoding of the real upper inode.

Signed-off-by: default avatarAmir Goldstein <>
Signed-off-by: default avatarMiklos Szeredi <>
parent a01f64b5
......@@ -4,4 +4,5 @@
obj-$(CONFIG_OVERLAY_FS) += overlay.o
overlay-objs := super.o namei.o util.o inode.o dir.o readdir.o copy_up.o
overlay-objs := super.o namei.o util.o inode.o dir.o readdir.o copy_up.o \
* Overlayfs NFS export support.
* Amir Goldstein <>
* Copyright (C) 2017-2018 CTERA Networks. All Rights Reserved.
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
#include <linux/fs.h>
#include <linux/cred.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/exportfs.h>
#include <linux/ratelimit.h>
#include "overlayfs.h"
static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
struct dentry *upper = ovl_dentry_upper(dentry);
struct dentry *origin = ovl_dentry_lower(dentry);
struct ovl_fh *fh = NULL;
int err;
* On overlay with an upper layer, overlay root inode is encoded as
* an upper file handle, because upper root dir is not indexed.
if (dentry == dentry->d_sb->s_root && upper)
origin = NULL;
err = -EACCES;
if (!upper || origin)
goto fail;
/* TODO: encode non pure-upper by origin */
fh = ovl_encode_fh(upper, true);
if (fh->len > buflen)
goto fail;
memcpy(buf, (char *)fh, fh->len);
err = fh->len;
return err;
pr_warn_ratelimited("overlayfs: failed to encode file handle (%pd2, err=%i, buflen=%d, len=%d, type=%d)\n",
dentry, err, buflen, fh ? (int)fh->len : 0,
fh ? fh->type : 0);
goto out;
static int ovl_dentry_to_fh(struct dentry *dentry, u32 *fid, int *max_len)
int res, len = *max_len << 2;
res = ovl_d_to_fh(dentry, (char *)fid, len);
if (res <= 0)
len = res;
/* Round up to dwords */
*max_len = (len + 3) >> 2;
return OVL_FILEID;
static int ovl_encode_inode_fh(struct inode *inode, u32 *fid, int *max_len,
struct inode *parent)
struct dentry *dentry;
int type;
/* TODO: encode connectable file handles */
if (parent)
dentry = d_find_any_alias(inode);
if (WARN_ON(!dentry))
type = ovl_dentry_to_fh(dentry, fid, max_len);
return type;
const struct export_operations ovl_export_operations = {
.encode_fh = ovl_encode_inode_fh,
......@@ -68,6 +68,9 @@ enum ovl_entry_flag {
#error Endianness not defined
/* The type returned by overlay exportfs ops when encoding an ovl_fh handle */
#define OVL_FILEID 0xfb
/* On-disk and in-memeory format for redirect by file handle */
struct ovl_fh {
u8 version; /* 0 */
......@@ -351,3 +354,6 @@ int ovl_set_attr(struct dentry *upper, struct kstat *stat);
struct ovl_fh *ovl_encode_fh(struct dentry *real, bool is_upper);
int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
struct dentry *upper);
/* export.c */
extern const struct export_operations ovl_export_operations;
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