Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted

Pull networking updates from Jakub Kicinski:
 "Core:

   - Add dedicated kmem_cache for typical/small skb->head, avoid having
     to access struct page at kfree time, and improve memory use.

   - Introduce sysctl to set default RPS configuration for new netdevs.

   - Define Netlink protocol specification format which can be used to
     describe messages used by each family and auto-generate parsers.
     Add tools for generating kernel data structures and uAPI headers.

   - Expose all net/core sysctls inside netns.

   - Remove 4s sleep in netpoll if carrier is instantly detected on
     boot.

   - Add configurable limit of MDB entries per port, and port-vlan.

   - Continue populating drop reasons throughout the stack.

   - Retire a handful of legacy Qdiscs and classifiers.

  Protocols:

   - Support IPv4 big TCP (TSO frames larger than 64kB).

   - Add IP_LOCAL_PORT_RANGE socket option, to control local port range
     on socket by socket basis.

   - Track and report in procfs number of MPTCP sockets used.

   - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path
     manager.

   - IPv6: don't check net.ipv6.route.max_size and rely on garbage
     collection to free memory (similarly to IPv4).

   - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986).

   - ICMP: add per-rate limit counters.

   - Add support for user scanning requests in ieee802154.

   - Remove static WEP support.

   - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate
     reporting.

   - WiFi 7 EHT channel puncturing support (client & AP).

  BPF:

   - Add a rbtree data structure following the "next-gen data structure"
     precedent set by recently added linked list, that is, by using
     kfunc + kptr instead of adding a new BPF map type.

   - Expose XDP hints via kfuncs with initial support for RX hash and
     timestamp metadata.

   - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to
     better support decap on GRE tunnel devices not operating in collect
     metadata.

   - Improve x86 JIT's codegen for PROBE_MEM runtime error checks.

   - Remove the need for trace_printk_lock for bpf_trace_printk and
     bpf_trace_vprintk helpers.

   - Extend libbpf's bpf_tracing.h support for tracing arguments of
     kprobes/uprobes and syscall as a special case.

   - Significantly reduce the search time for module symbols by
     livepatch and BPF.

   - Enable cpumasks to be used as kptrs, which is useful for tracing
     programs tracking which tasks end up running on which CPUs in
     different time intervals.

   - Add support for BPF trampoline on s390x and riscv64.

   - Add capability to export the XDP features supported by the NIC.

   - Add __bpf_kfunc tag for marking kernel functions as kfuncs.

   - Add cgroup.memory=nobpf kernel parameter option to disable BPF
     memory accounting for container environments.

  Netfilter:

   - Remove the CLUSTERIP target. It has been marked as obsolete for
     years, and we still have WARN splats wrt races of the out-of-band
     /proc interface installed by this target.

   - Add 'destroy' commands to nf_tables. They are identical to the
     existing 'delete' commands, but do not return an error if the
     referenced object (set, chain, rule...) did not exist.

  Driver API:

   - Improve cpumask_local_spread() locality to help NICs set the right
     IRQ affinity on AMD platforms.

   - Separate C22 and C45 MDIO bus transactions more clearly.

   - Introduce new DCB table to control DSCP rewrite on egress.

   - Support configuration of Physical Layer Collision Avoidance (PLCA)
     Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of
     shared medium Ethernet.

   - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing
     preemption of low priority frames by high priority frames.

   - Add support for controlling MACSec offload using netlink SET.

   - Rework devlink instance refcounts to allow registration and
     de-registration under the instance lock. Split the code into
     multiple files, drop some of the unnecessarily granular locks and
     factor out common parts of netlink operation handling.

   - Add TX frame aggregation parameters (for USB drivers).

   - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning
     messages with notifications for debug.

   - Allow offloading of UDP NEW connections via act_ct.

   - Add support for per action HW stats in TC.

   - Support hardware miss to TC action (continue processing in SW from
     a specific point in the action chain).

   - Warn if old Wireless Extension user space interface is used with
     modern cfg80211/mac80211 drivers. Do not support Wireless
     Extensions for Wi-Fi 7 devices at all. Everyone should switch to
     using nl80211 interface instead.

   - Improve the CAN bit timing configuration. Use extack to return
     error messages directly to user space, update the SJW handling,
     including the definition of a new default value that will benefit
     CAN-FD controllers, by increasing their oscillator tolerance.

  New hardware / drivers:

   - Ethernet:
      - nVidia BlueField-3 support (control traffic driver)
      - Ethernet support for imx93 SoCs
      - Motorcomm yt8531 gigabit Ethernet PHY
      - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA)
      - Microchip LAN8841 PHY (incl. cable diagnostics and PTP)
      - Amlogic gxl MDIO mux

   - WiFi:
      - RealTek RTL8188EU (rtl8xxxu)
      - Qualcomm Wi-Fi 7 devices (ath12k)

   - CAN:
      - Renesas R-Car V4H

  Drivers:

   - Bluetooth:
      - Set Per Platform Antenna Gain (PPAG) for Intel controllers.

   - Ethernet NICs:
      - Intel (1G, igc):
         - support TSN / Qbv / packet scheduling features of i226 model
      - Intel (100G, ice):
         - use GNSS subsystem instead of TTY
         - multi-buffer XDP support
         - extend support for GPIO pins to E823 devices
      - nVidia/Mellanox:
         - update the shared buffer configuration on PFC commands
         - implement PTP adjphase function for HW offset control
         - TC support for Geneve and GRE with VF tunnel offload
         - more efficient crypto key management method
         - multi-port eswitch support
      - Netronome/Corigine:
         - add DCB IEEE support
         - support IPsec offloading for NFP3800
      - Freescale/NXP (enetc):
         - support XDP_REDIRECT for XDP non-linear buffers
         - improve reconfig, avoid link flap and waiting for idle
         - support MAC Merge layer
      - Other NICs:
         - sfc/ef100: add basic devlink support for ef100
         - ionic: rx_push mode operation (writing descriptors via MMIO)
         - bnxt: use the auxiliary bus abstraction for RDMA
         - r8169: disable ASPM and reset bus in case of tx timeout
         - cpsw: support QSGMII mode for J721e CPSW9G
         - cpts: support pulse-per-second output
         - ngbe: add an mdio bus driver
         - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing
         - r8152: handle devices with FW with NCM support
         - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation
         - virtio-net: support multi buffer XDP
         - virtio/vsock: replace virtio_vsock_pkt with sk_buff
         - tsnep: XDP support

   - Ethernet high-speed switches:
      - nVidia/Mellanox (mlxsw):
         - add support for latency TLV (in FW control messages)
      - Microchip (sparx5):
         - separate explicit and implicit traffic forwarding rules, make
           the implicit rules always active
         - add support for egress DSCP rewrite
         - IS0 VCAP support (Ingress Classification)
         - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS
           etc.)
         - ES2 VCAP support (Egress Access Control)
         - support for Per-Stream Filtering and Policing (802.1Q,
           8.6.5.1)

   - Ethernet embedded switches:
      - Marvell (mv88e6xxx):
         - add MAB (port auth) offload support
         - enable PTP receive for mv88e6390
      - NXP (ocelot):
         - support MAC Merge layer
         - support for the the vsc7512 internal copper phys
      - Microchip:
         - lan9303: convert to PHYLINK
         - lan966x: support TC flower filter statistics
         - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x
         - lan937x: support Credit Based Shaper configuration
         - ksz9477: support Energy Efficient Ethernet
      - other:
         - qca8k: convert to regmap read/write API, use bulk operations
         - rswitch: Improve TX timestamp accuracy

   - Intel WiFi (iwlwifi):
      - EHT (Wi-Fi 7) rate reporting
      - STEP equalizer support: transfer some STEP (connection to radio
        on platforms with integrated wifi) related parameters from the
        BIOS to the firmware.

   - Qualcomm 802.11ax WiFi (ath11k):
      - IPQ5018 support
      - Fine Timing Measurement (FTM) responder role support
      - channel 177 support

   - MediaTek WiFi (mt76):
      - per-PHY LED support
      - mt7996: EHT (Wi-Fi 7) support
      - Wireless Ethernet Dispatch (WED) reset support
      - switch to using page pool allocator

   - RealTek WiFi (rtw89):
      - support new version of Bluetooth co-existance

   - Mobile:
      - rmnet: support TX aggregation"

* tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits)
  page_pool: add a comment explaining the fragment counter usage
  net: ethtool: fix __ethtool_dev_mm_supported() implementation
  ethtool: pse-pd: Fix double word in comments
  xsk: add linux/vmalloc.h to xsk.c
  sefltests: netdevsim: wait for devlink instance after netns removal
  selftest: fib_tests: Always cleanup before exit
  net/mlx5e: Align IPsec ASO result memory to be as required by hardware
  net/mlx5e: TC, Set CT miss to the specific ct action instance
  net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
  net/mlx5: Refactor tc miss handling to a single function
  net/mlx5: Kconfig: Make tc offload depend on tc skb extension
  net/sched: flower: Support hardware miss to tc action
  net/sched: flower: Move filter handle initialization earlier
  net/sched: cls_api: Support hardware miss to tc action
  net/sched: Rename user cookie and act cookie
  sfc: fix builds without CONFIG_RTC_LIB
  sfc: clean up some inconsistent indentings
  net/mlx4_en: Introduce flexible array to silence overflow warning
  net: lan966x: Fix possible deadlock inside PTP
  net/ulp: Remove redundant ->clone() test in inet_clone_ulp().
  ...

1 files changed, 877 insertions, 0 deletions

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
new file mode 100644
index 000000000..defd4e231
--- /dev/null
+++ b/fs/overlayfs/export.c
@@ -0,0 +1,877 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Overlayfs NFS export support.
+ *
+ * Amir Goldstein <amir73il@gmail.com>
+ *
+ * Copyright (C) 2017-2018 CTERA Networks. All Rights Reserved.
+ */
+
+#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_encode_maybe_copy_up(struct dentry *dentry)
+{
+	int err;
+
+	if (ovl_dentry_upper(dentry))
+		return 0;
+
+	err = ovl_want_write(dentry);
+	if (!err) {
+		err = ovl_copy_up(dentry);
+		ovl_drop_write(dentry);
+	}
+
+	if (err) {
+		pr_warn_ratelimited("failed to copy up on encode (%pd2, err=%i)\n",
+				    dentry, err);
+	}
+
+	return err;
+}
+
+/*
+ * Before encoding a non-upper directory file handle from real layer N, we need
+ * to check if it will be possible to reconnect an overlay dentry from the real
+ * lower decoded dentry. This is done by following the overlay ancestry up to a
+ * "layer N connected" ancestor and verifying that all parents along the way are
+ * "layer N connectable". If an ancestor that is NOT "layer N connectable" is
+ * found, we need to copy up an ancestor, which is "layer N connectable", thus
+ * making that ancestor "layer N connected". For example:
+ *
+ * layer 1: /a
+ * layer 2: /a/b/c
+ *
+ * The overlay dentry /a is NOT "layer 2 connectable", because if dir /a is
+ * copied up and renamed, upper dir /a will be indexed by lower dir /a from
+ * layer 1. The dir /a from layer 2 will never be indexed, so the algorithm (*)
+ * in ovl_lookup_real_ancestor() will not be able to lookup a connected overlay
+ * dentry from the connected lower dentry /a/b/c.
+ *
+ * To avoid this problem on decode time, we need to copy up an ancestor of
+ * /a/b/c, which is "layer 2 connectable", on encode time. That ancestor is
+ * /a/b. After copy up (and index) of /a/b, it will become "layer 2 connected"
+ * and when the time comes to decode the file handle from lower dentry /a/b/c,
+ * ovl_lookup_real_ancestor() will find the indexed ancestor /a/b and decoding
+ * a connected overlay dentry will be accomplished.
+ *
+ * (*) the algorithm in ovl_lookup_real_ancestor() can be improved to lookup an
+ * entry /a in the lower layers above layer N and find the indexed dir /a from
+ * layer 1. If that improvement is made, then the check for "layer N connected"
+ * will need to verify there are no redirects in lower layers above N. In the
+ * example above, /a will be "layer 2 connectable". However, if layer 2 dir /a
+ * is a target of a layer 1 redirect, then /a will NOT be "layer 2 connectable":
+ *
+ * layer 1: /A (redirect = /a)
+ * layer 2: /a/b/c
+ */
+
+/* Return the lowest layer for encoding a connectable file handle */
+static int ovl_connectable_layer(struct dentry *dentry)
+{
+	struct ovl_entry *oe = OVL_E(dentry);
+
+	/* We can get overlay root from root of any layer */
+	if (dentry == dentry->d_sb->s_root)
+		return oe->numlower;
+
+	/*
+	 * If it's an unindexed merge dir, then it's not connectable with any
+	 * lower layer
+	 */
+	if (ovl_dentry_upper(dentry) &&
+	    !ovl_test_flag(OVL_INDEX, d_inode(dentry)))
+		return 0;
+
+	/* We can get upper/overlay path from indexed/lower dentry */
+	return oe->lowerstack[0].layer->idx;
+}
+
+/*
+ * @dentry is "connected" if all ancestors up to root or a "connected" ancestor
+ * have the same uppermost lower layer as the origin's layer. We may need to
+ * copy up a "connectable" ancestor to make it "connected". A "connected" dentry
+ * cannot become non "connected", so cache positive result in dentry flags.
+ *
+ * Return the connected origin layer or < 0 on error.
+ */
+static int ovl_connect_layer(struct dentry *dentry)
+{
+	struct dentry *next, *parent = NULL;
+	int origin_layer;
+	int err = 0;
+
+	if (WARN_ON(dentry == dentry->d_sb->s_root) ||
+	    WARN_ON(!ovl_dentry_lower(dentry)))
+		return -EIO;
+
+	origin_layer = OVL_E(dentry)->lowerstack[0].layer->idx;
+	if (ovl_dentry_test_flag(OVL_E_CONNECTED, dentry))
+		return origin_layer;
+
+	/* Find the topmost origin layer connectable ancestor of @dentry */
+	next = dget(dentry);
+	for (;;) {
+		parent = dget_parent(next);
+		if (WARN_ON(parent == next)) {
+			err = -EIO;
+			break;
+		}
+
+		/*
+		 * If @parent is not origin layer connectable, then copy up
+		 * @next which is origin layer connectable and we are done.
+		 */
+		if (ovl_connectable_layer(parent) < origin_layer) {
+			err = ovl_encode_maybe_copy_up(next);
+			break;
+		}
+
+		/* If @parent is connected or indexed we are done */
+		if (ovl_dentry_test_flag(OVL_E_CONNECTED, parent) ||
+		    ovl_test_flag(OVL_INDEX, d_inode(parent)))
+			break;
+
+		dput(next);
+		next = parent;
+	}
+
+	dput(parent);
+	dput(next);
+
+	if (!err)
+		ovl_dentry_set_flag(OVL_E_CONNECTED, dentry);
+
+	return err ?: origin_layer;
+}
+
+/*
+ * We only need to encode origin if there is a chance that the same object was
+ * encoded pre copy up and then we need to stay consistent with the same
+ * encoding also after copy up. If non-pure upper is not indexed, then it was
+ * copied up before NFS export was enabled. In that case we don't need to worry
+ * about staying consistent with pre copy up encoding and we encode an upper
+ * file handle. Overlay root dentry is a private case of non-indexed upper.
+ *
+ * The following table summarizes the different file handle encodings used for
+ * different overlay object types:
+ *
+ *  Object type		| Encoding
+ * --------------------------------
+ *  Pure upper		| U
+ *  Non-indexed upper	| U
+ *  Indexed upper	| L (*)
+ *  Non-upper		| L (*)
+ *
+ * U = upper file handle
+ * L = lower file handle
+ *
+ * (*) Connecting an overlay dir from real lower dentry is not always
+ * possible when there are redirects in lower layers and non-indexed merge dirs.
+ * To mitigate those case, we may copy up the lower dir ancestor before encode
+ * a lower dir file handle.
+ *
+ * Return 0 for upper file handle, > 0 for lower file handle or < 0 on error.
+ */
+static int ovl_check_encode_origin(struct dentry *dentry)
+{
+	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+
+	/* Upper file handle for pure upper */
+	if (!ovl_dentry_lower(dentry))
+		return 0;
+
+	/*
+	 * Upper file handle for non-indexed upper.
+	 *
+	 * Root is never indexed, so if there's an upper layer, encode upper for
+	 * root.
+	 */
+	if (ovl_dentry_upper(dentry) &&
+	    !ovl_test_flag(OVL_INDEX, d_inode(dentry)))
+		return 0;
+
+	/*
+	 * Decoding a merge dir, whose origin's ancestor is under a redirected
+	 * lower dir or under a non-indexed upper is not always possible.
+	 * ovl_connect_layer() will try to make origin's layer "connected" by
+	 * copying up a "connectable" ancestor.
+	 */
+	if (d_is_dir(dentry) && ovl_upper_mnt(ofs))
+		return ovl_connect_layer(dentry);
+
+	/* Lower file handle for indexed and non-upper dir/non-dir */
+	return 1;
+}
+
+static int ovl_dentry_to_fid(struct ovl_fs *ofs, struct dentry *dentry,
+			     u32 *fid, int buflen)
+{
+	struct ovl_fh *fh = NULL;
+	int err, enc_lower;
+	int len;
+
+	/*
+	 * Check if we should encode a lower or upper file handle and maybe
+	 * copy up an ancestor to make lower file handle connectable.
+	 */
+	err = enc_lower = ovl_check_encode_origin(dentry);
+	if (enc_lower < 0)
+		goto fail;
+
+	/* Encode an upper or lower file handle */
+	fh = ovl_encode_real_fh(ofs, enc_lower ? ovl_dentry_lower(dentry) :
+				ovl_dentry_upper(dentry), !enc_lower);
+	if (IS_ERR(fh))
+		return PTR_ERR(fh);
+
+	len = OVL_FH_LEN(fh);
+	if (len <= buflen)
+		memcpy(fid, fh, len);
+	err = len;
+
+out:
+	kfree(fh);
+	return err;
+
+fail:
+	pr_warn_ratelimited("failed to encode file handle (%pd2, err=%i)\n",
+			    dentry, err);
+	goto out;
+}
+
+static int ovl_encode_fh(struct inode *inode, u32 *fid, int *max_len,
+			 struct inode *parent)
+{
+	struct ovl_fs *ofs = OVL_FS(inode->i_sb);
+	struct dentry *dentry;
+	int bytes, buflen = *max_len << 2;
+
+	/* TODO: encode connectable file handles */
+	if (parent)
+		return FILEID_INVALID;
+
+	dentry = d_find_any_alias(inode);
+	if (!dentry)
+		return FILEID_INVALID;
+
+	bytes = ovl_dentry_to_fid(ofs, dentry, fid, buflen);
+	dput(dentry);
+	if (bytes <= 0)
+		return FILEID_INVALID;
+
+	*max_len = bytes >> 2;
+	if (bytes > buflen)
+		return FILEID_INVALID;
+
+	return OVL_FILEID_V1;
+}
+
+/*
+ * Find or instantiate an overlay dentry from real dentries and index.
+ */
+static struct dentry *ovl_obtain_alias(struct super_block *sb,
+				       struct dentry *upper_alias,
+				       struct ovl_path *lowerpath,
+				       struct dentry *index)
+{
+	struct dentry *lower = lowerpath ? lowerpath->dentry : NULL;
+	struct dentry *upper = upper_alias ?: index;
+	struct dentry *dentry;
+	struct inode *inode;
+	struct ovl_entry *oe;
+	struct ovl_inode_params oip = {
+		.lowerpath = lowerpath,
+		.index = index,
+		.numlower = !!lower
+	};
+
+	/* We get overlay directory dentries with ovl_lookup_real() */
+	if (d_is_dir(upper ?: lower))
+		return ERR_PTR(-EIO);
+
+	oip.upperdentry = dget(upper);
+	inode = ovl_get_inode(sb, &oip);
+	if (IS_ERR(inode)) {
+		dput(upper);
+		return ERR_CAST(inode);
+	}
+
+	if (upper)
+		ovl_set_flag(OVL_UPPERDATA, inode);
+
+	dentry = d_find_any_alias(inode);
+	if (dentry)
+		goto out_iput;
+
+	dentry = d_alloc_anon(inode->i_sb);
+	if (unlikely(!dentry))
+		goto nomem;
+	oe = ovl_alloc_entry(lower ? 1 : 0);
+	if (!oe)
+		goto nomem;
+
+	if (lower) {
+		oe->lowerstack->dentry = dget(lower);
+		oe->lowerstack->layer = lowerpath->layer;
+	}
+	dentry->d_fsdata = oe;
+	if (upper_alias)
+		ovl_dentry_set_upper_alias(dentry);
+
+	ovl_dentry_update_reval(dentry, upper,
+			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
+
+	return d_instantiate_anon(dentry, inode);
+
+nomem:
+	dput(dentry);
+	dentry = ERR_PTR(-ENOMEM);
+out_iput:
+	iput(inode);
+	return dentry;
+}
+
+/* Get the upper or lower dentry in stack whose on layer @idx */
+static struct dentry *ovl_dentry_real_at(struct dentry *dentry, int idx)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+	int i;
+
+	if (!idx)
+		return ovl_dentry_upper(dentry);
+
+	for (i = 0; i < oe->numlower; i++) {
+		if (oe->lowerstack[i].layer->idx == idx)
+			return oe->lowerstack[i].dentry;
+	}
+
+	return NULL;
+}
+
+/*
+ * Lookup a child overlay dentry to get a connected overlay dentry whose real
+ * dentry is @real. If @real is on upper layer, we lookup a child overlay
+ * dentry with the same name as the real dentry. Otherwise, we need to consult
+ * index for lookup.
+ */
+static struct dentry *ovl_lookup_real_one(struct dentry *connected,
+					  struct dentry *real,
+					  const struct ovl_layer *layer)
+{
+	struct inode *dir = d_inode(connected);
+	struct dentry *this, *parent = NULL;
+	struct name_snapshot name;
+	int err;
+
+	/*
+	 * Lookup child overlay dentry by real name. The dir mutex protects us
+	 * from racing with overlay rename. If the overlay dentry that is above
+	 * real has already been moved to a parent that is not under the
+	 * connected overlay dir, we return -ECHILD and restart the lookup of
+	 * connected real path from the top.
+	 */
+	inode_lock_nested(dir, I_MUTEX_PARENT);
+	err = -ECHILD;
+	parent = dget_parent(real);
+	if (ovl_dentry_real_at(connected, layer->idx) != parent)
+		goto fail;
+
+	/*
+	 * We also need to take a snapshot of real dentry name to protect us
+	 * from racing with underlying layer rename. In this case, we don't
+	 * care about returning ESTALE, only from dereferencing a free name
+	 * pointer because we hold no lock on the real dentry.
+	 */
+	take_dentry_name_snapshot(&name, real);
+	/*
+	 * No idmap handling here: it's an internal lookup.  Could skip
+	 * permission checking altogether, but for now just use non-idmap
+	 * transformed ids.
+	 */
+	this = lookup_one_len(name.name.name, connected, name.name.len);
+	release_dentry_name_snapshot(&name);
+	err = PTR_ERR(this);
+	if (IS_ERR(this)) {
+		goto fail;
+	} else if (!this || !this->d_inode) {
+		dput(this);
+		err = -ENOENT;
+		goto fail;
+	} else if (ovl_dentry_real_at(this, layer->idx) != real) {
+		dput(this);
+		err = -ESTALE;
+		goto fail;
+	}
+
+out:
+	dput(parent);
+	inode_unlock(dir);
+	return this;
+
+fail:
+	pr_warn_ratelimited("failed to lookup one by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
+			    real, layer->idx, connected, err);
+	this = ERR_PTR(err);
+	goto out;
+}
+
+static struct dentry *ovl_lookup_real(struct super_block *sb,
+				      struct dentry *real,
+				      const struct ovl_layer *layer);
+
+/*
+ * Lookup an indexed or hashed overlay dentry by real inode.
+ */
+static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
+					    struct dentry *real,
+					    const struct ovl_layer *layer)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct dentry *index = NULL;
+	struct dentry *this = NULL;
+	struct inode *inode;
+
+	/*
+	 * Decoding upper dir from index is expensive, so first try to lookup
+	 * overlay dentry in inode/dcache.
+	 */
+	inode = ovl_lookup_inode(sb, real, !layer->idx);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+	if (inode) {
+		this = d_find_any_alias(inode);
+		iput(inode);
+	}
+
+	/*
+	 * For decoded lower dir file handle, lookup index by origin to check
+	 * if lower dir was copied up and and/or removed.
+	 */
+	if (!this && layer->idx && ofs->indexdir && !WARN_ON(!d_is_dir(real))) {
+		index = ovl_lookup_index(ofs, NULL, real, false);
+		if (IS_ERR(index))
+			return index;
+	}
+
+	/* Get connected upper overlay dir from index */
+	if (index) {
+		struct dentry *upper = ovl_index_upper(ofs, index, true);
+
+		dput(index);
+		if (IS_ERR_OR_NULL(upper))
+			return upper;
+
+		/*
+		 * ovl_lookup_real() in lower layer may call recursively once to
+		 * ovl_lookup_real() in upper layer. The first level call walks
+		 * back lower parents to the topmost indexed parent. The second
+		 * recursive call walks back from indexed upper to the topmost
+		 * connected/hashed upper parent (or up to root).
+		 */
+		this = ovl_lookup_real(sb, upper, &ofs->layers[0]);
+		dput(upper);
+	}
+
+	if (IS_ERR_OR_NULL(this))
+		return this;
+
+	if (ovl_dentry_real_at(this, layer->idx) != real) {
+		dput(this);
+		this = ERR_PTR(-EIO);
+	}
+
+	return this;
+}
+
+/*
+ * Lookup an indexed or hashed overlay dentry, whose real dentry is an
+ * ancestor of @real.
+ */
+static struct dentry *ovl_lookup_real_ancestor(struct super_block *sb,
+					       struct dentry *real,
+					       const struct ovl_layer *layer)
+{
+	struct dentry *next, *parent = NULL;
+	struct dentry *ancestor = ERR_PTR(-EIO);
+
+	if (real == layer->mnt->mnt_root)
+		return dget(sb->s_root);
+
+	/* Find the topmost indexed or hashed ancestor */
+	next = dget(real);
+	for (;;) {
+		parent = dget_parent(next);
+
+		/*
+		 * Lookup a matching overlay dentry in inode/dentry
+		 * cache or in index by real inode.
+		 */
+		ancestor = ovl_lookup_real_inode(sb, next, layer);
+		if (ancestor)
+			break;
+
+		if (parent == layer->mnt->mnt_root) {
+			ancestor = dget(sb->s_root);
+			break;
+		}
+
+		/*
+		 * If @real has been moved out of the layer root directory,
+		 * we will eventully hit the real fs root. This cannot happen
+		 * by legit overlay rename, so we return error in that case.
+		 */
+		if (parent == next) {
+			ancestor = ERR_PTR(-EXDEV);
+			break;
+		}
+
+		dput(next);
+		next = parent;
+	}
+
+	dput(parent);
+	dput(next);
+
+	return ancestor;
+}
+
+/*
+ * Lookup a connected overlay dentry whose real dentry is @real.
+ * If @real is on upper layer, we lookup a child overlay dentry with the same
+ * path the real dentry. Otherwise, we need to consult index for lookup.
+ */
+static struct dentry *ovl_lookup_real(struct super_block *sb,
+				      struct dentry *real,
+				      const struct ovl_layer *layer)
+{
+	struct dentry *connected;
+	int err = 0;
+
+	connected = ovl_lookup_real_ancestor(sb, real, layer);
+	if (IS_ERR(connected))
+		return connected;
+
+	while (!err) {
+		struct dentry *next, *this;
+		struct dentry *parent = NULL;
+		struct dentry *real_connected = ovl_dentry_real_at(connected,
+								   layer->idx);
+
+		if (real_connected == real)
+			break;
+
+		/* Find the topmost dentry not yet connected */
+		next = dget(real);
+		for (;;) {
+			parent = dget_parent(next);
+
+			if (parent == real_connected)
+				break;
+
+			/*
+			 * If real has been moved out of 'real_connected',
+			 * we will not find 'real_connected' and hit the layer
+			 * root. In that case, we need to restart connecting.
+			 * This game can go on forever in the worst case. We
+			 * may want to consider taking s_vfs_rename_mutex if
+			 * this happens more than once.
+			 */
+			if (parent == layer->mnt->mnt_root) {
+				dput(connected);
+				connected = dget(sb->s_root);
+				break;
+			}
+
+			/*
+			 * If real file has been moved out of the layer root
+			 * directory, we will eventully hit the real fs root.
+			 * This cannot happen by legit overlay rename, so we
+			 * return error in that case.
+			 */
+			if (parent == next) {
+				err = -EXDEV;
+				break;
+			}
+
+			dput(next);
+			next = parent;
+		}
+
+		if (!err) {
+			this = ovl_lookup_real_one(connected, next, layer);
+			if (IS_ERR(this))
+				err = PTR_ERR(this);
+
+			/*
+			 * Lookup of child in overlay can fail when racing with
+			 * overlay rename of child away from 'connected' parent.
+			 * In this case, we need to restart the lookup from the
+			 * top, because we cannot trust that 'real_connected' is
+			 * still an ancestor of 'real'. There is a good chance
+			 * that the renamed overlay ancestor is now in cache, so
+			 * ovl_lookup_real_ancestor() will find it and we can
+			 * continue to connect exactly from where lookup failed.
+			 */
+			if (err == -ECHILD) {
+				this = ovl_lookup_real_ancestor(sb, real,
+								layer);
+				err = PTR_ERR_OR_ZERO(this);
+			}
+			if (!err) {
+				dput(connected);
+				connected = this;
+			}
+		}
+
+		dput(parent);
+		dput(next);
+	}
+
+	if (err)
+		goto fail;
+
+	return connected;
+
+fail:
+	pr_warn_ratelimited("failed to lookup by real (%pd2, layer=%d, connected=%pd2, err=%i)\n",
+			    real, layer->idx, connected, err);
+	dput(connected);
+	return ERR_PTR(err);
+}
+
+/*
+ * Get an overlay dentry from upper/lower real dentries and index.
+ */
+static struct dentry *ovl_get_dentry(struct super_block *sb,
+				     struct dentry *upper,
+				     struct ovl_path *lowerpath,
+				     struct dentry *index)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+	const struct ovl_layer *layer = upper ? &ofs->layers[0] : lowerpath->layer;
+	struct dentry *real = upper ?: (index ?: lowerpath->dentry);
+
+	/*
+	 * Obtain a disconnected overlay dentry from a non-dir real dentry
+	 * and index.
+	 */
+	if (!d_is_dir(real))
+		return ovl_obtain_alias(sb, upper, lowerpath, index);
+
+	/* Removed empty directory? */
+	if ((real->d_flags & DCACHE_DISCONNECTED) || d_unhashed(real))
+		return ERR_PTR(-ENOENT);
+
+	/*
+	 * If real dentry is connected and hashed, get a connected overlay
+	 * dentry whose real dentry is @real.
+	 */
+	return ovl_lookup_real(sb, real, layer);
+}
+
+static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
+					struct ovl_fh *fh)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct dentry *dentry;
+	struct dentry *upper;
+
+	if (!ovl_upper_mnt(ofs))
+		return ERR_PTR(-EACCES);
+
+	upper = ovl_decode_real_fh(ofs, fh, ovl_upper_mnt(ofs), true);
+	if (IS_ERR_OR_NULL(upper))
+		return upper;
+
+	dentry = ovl_get_dentry(sb, upper, NULL, NULL);
+	dput(upper);
+
+	return dentry;
+}
+
+static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
+					struct ovl_fh *fh)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+	struct ovl_path origin = { };
+	struct ovl_path *stack = &origin;
+	struct dentry *dentry = NULL;
+	struct dentry *index = NULL;
+	struct inode *inode;
+	int err;
+
+	/* First lookup overlay inode in inode cache by origin fh */
+	err = ovl_check_origin_fh(ofs, fh, false, NULL, &stack);
+	if (err)
+		return ERR_PTR(err);
+
+	if (!d_is_dir(origin.dentry) ||
+	    !(origin.dentry->d_flags & DCACHE_DISCONNECTED)) {
+		inode = ovl_lookup_inode(sb, origin.dentry, false);
+		err = PTR_ERR(inode);
+		if (IS_ERR(inode))
+			goto out_err;
+		if (inode) {
+			dentry = d_find_any_alias(inode);
+			iput(inode);
+			if (dentry)
+				goto out;
+		}
+	}
+
+	/* Then lookup indexed upper/whiteout by origin fh */
+	if (ofs->indexdir) {
+		index = ovl_get_index_fh(ofs, fh);
+		err = PTR_ERR(index);
+		if (IS_ERR(index)) {
+			index = NULL;
+			goto out_err;
+		}
+	}
+
+	/* Then try to get a connected upper dir by index */
+	if (index && d_is_dir(index)) {
+		struct dentry *upper = ovl_index_upper(ofs, index, true);
+
+		err = PTR_ERR(upper);
+		if (IS_ERR_OR_NULL(upper))
+			goto out_err;
+
+		dentry = ovl_get_dentry(sb, upper, NULL, NULL);
+		dput(upper);
+		goto out;
+	}
+
+	/* Find origin.dentry again with ovl_acceptable() layer check */
+	if (d_is_dir(origin.dentry)) {
+		dput(origin.dentry);
+		origin.dentry = NULL;
+		err = ovl_check_origin_fh(ofs, fh, true, NULL, &stack);
+		if (err)
+			goto out_err;
+	}
+	if (index) {
+		err = ovl_verify_origin(ofs, index, origin.dentry, false);
+		if (err)
+			goto out_err;
+	}
+
+	/* Get a connected non-upper dir or disconnected non-dir */
+	dentry = ovl_get_dentry(sb, NULL, &origin, index);
+
+out:
+	dput(origin.dentry);
+	dput(index);
+	return dentry;
+
+out_err:
+	dentry = ERR_PTR(err);
+	goto out;
+}
+
+static struct ovl_fh *ovl_fid_to_fh(struct fid *fid, int buflen, int fh_type)
+{
+	struct ovl_fh *fh;
+
+	/* If on-wire inner fid is aligned - nothing to do */
+	if (fh_type == OVL_FILEID_V1)
+		return (struct ovl_fh *)fid;
+
+	if (fh_type != OVL_FILEID_V0)
+		return ERR_PTR(-EINVAL);
+
+	if (buflen <= OVL_FH_WIRE_OFFSET)
+		return ERR_PTR(-EINVAL);
+
+	fh = kzalloc(buflen, GFP_KERNEL);
+	if (!fh)
+		return ERR_PTR(-ENOMEM);
+
+	/* Copy unaligned inner fh into aligned buffer */
+	memcpy(fh->buf, fid, buflen - OVL_FH_WIRE_OFFSET);
+	return fh;
+}
+
+static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid,
+				       int fh_len, int fh_type)
+{
+	struct dentry *dentry = NULL;
+	struct ovl_fh *fh = NULL;
+	int len = fh_len << 2;
+	unsigned int flags = 0;
+	int err;
+
+	fh = ovl_fid_to_fh(fid, len, fh_type);
+	err = PTR_ERR(fh);
+	if (IS_ERR(fh))
+		goto out_err;
+
+	err = ovl_check_fh_len(fh, len);
+	if (err)
+		goto out_err;
+
+	flags = fh->fb.flags;
+	dentry = (flags & OVL_FH_FLAG_PATH_UPPER) ?
+		 ovl_upper_fh_to_d(sb, fh) :
+		 ovl_lower_fh_to_d(sb, fh);
+	err = PTR_ERR(dentry);
+	if (IS_ERR(dentry) && err != -ESTALE)
+		goto out_err;
+
+out:
+	/* We may have needed to re-align OVL_FILEID_V0 */
+	if (!IS_ERR_OR_NULL(fh) && fh != (void *)fid)
+		kfree(fh);
+
+	return dentry;
+
+out_err:
+	pr_warn_ratelimited("failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n",
+			    fh_len, fh_type, flags, err);
+	dentry = ERR_PTR(err);
+	goto out;
+}
+
+static struct dentry *ovl_fh_to_parent(struct super_block *sb, struct fid *fid,
+				       int fh_len, int fh_type)
+{
+	pr_warn_ratelimited("connectable file handles not supported; use 'no_subtree_check' exportfs option.\n");
+	return ERR_PTR(-EACCES);
+}
+
+static int ovl_get_name(struct dentry *parent, char *name,
+			struct dentry *child)
+{
+	/*
+	 * ovl_fh_to_dentry() returns connected dir overlay dentries and
+	 * ovl_fh_to_parent() is not implemented, so we should not get here.
+	 */
+	WARN_ON_ONCE(1);
+	return -EIO;
+}
+
+static struct dentry *ovl_get_parent(struct dentry *dentry)
+{
+	/*
+	 * ovl_fh_to_dentry() returns connected dir overlay dentries, so we
+	 * should not get here.
+	 */
+	WARN_ON_ONCE(1);
+	return ERR_PTR(-EIO);
+}
+
+const struct export_operations ovl_export_operations = {
+	.encode_fh	= ovl_encode_fh,
+	.fh_to_dentry	= ovl_fh_to_dentry,
+	.fh_to_parent	= ovl_fh_to_parent,
+	.get_name	= ovl_get_name,
+	.get_parent	= ovl_get_parent,
+};