Commit 73287a43 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge git://

Pull networking updates from David Miller:
 "Highlights (1721 non-merge commits, this has to be a record of some

   1) Add 'random' mode to team driver, from Jiri Pirko and Eric

   2) Make it so that any driver that supports configuration of multiple
      MAC addresses can provide the forwarding database add and del
      calls by providing a default implementation and hooking that up if
      the driver doesn't have an explicit set of handlers.  From Vlad

   3) Support GSO segmentation over tunnels and other encapsulating
      devices such as VXLAN, from Pravin B Shelar.

   4) Support L2 GRE tunnels in the flow dissector, from Michael Dalton.

   5) Implement Tail Loss Probe (TLP) detection in TCP, from Nandita

   6) In the PHY layer, allow supporting wake-on-lan in situations where
      the PHY registers have to be written for it to be configured.

      Use it to support wake-on-lan in mv643xx_eth.

      From Michael Stapelberg.

   7) Significantly improve firewire IPV6 support, from YOSHIFUJI

   8) Allow multiple packets to be sent in a single transmission using
      network coding in batman-adv, from Martin Hundebøll.

   9) Add support for T5 cxgb4 chips, from Santosh Rastapur.

  10) Generalize the VXLAN forwarding tables so that there is more
      flexibility in configurating various aspects of the endpoints.
      From David Stevens.

  11) Support RSS and TSO in hardware over GRE tunnels in bxn2x driver,
      from Dmitry Kravkov.

  12) Zero copy support in nfnelink_queue, from Eric Dumazet and Pablo
      Neira Ayuso.

  13) Start adding networking selftests.

  14) In situations of overload on the same AF_PACKET fanout socket, or
      per-cpu packet receive queue, minimize drop by distributing the
      load to other cpus/fanouts.  From Willem de Bruijn and Eric

  15) Add support for new payload offset BPF instruction, from Daniel

  16) Convert several drivers over to mdoule_platform_driver(), from
      Sachin Kamat.

  17) Provide a minimal BPF JIT image disassembler userspace tool, from
      Daniel Borkmann.

  18) Rewrite F-RTO implementation in TCP to match the final
      specification of it in RFC4138 and RFC5682.  From Yuchung Cheng.

  19) Provide netlink socket diag of netlink sockets ("Yo dawg, I hear
      you like netlink, so I implemented netlink dumping of netlink
      sockets.") From Andrey Vagin.

  20) Remove ugly passing of rtnetlink attributes into rtnl_doit
      functions, from Thomas Graf.

  21) Allow userspace to be able to see if a configuration change occurs
      in the middle of an address or device list dump, from Nicolas

  22) Support RFC3168 ECN protection for ipv6 fragments, from Hannes
      Frederic Sowa.

  23) Increase accuracy of packet length used by packet scheduler, from
      Jason Wang.

  24) Beginning set of changes to make ipv4/ipv6 fragment handling more
      scalable and less susceptible to overload and locking contention,
      from Jesper Dangaard Brouer.

  25) Get rid of using non-type-safe NLMSG_* macros and use nlmsg_*()
      instead.  From Hong Zhiguo.

  26) Optimize route usage in IPVS by avoiding reference counting where
      possible, from Julian Anastasov.

  27) Convert IPVS schedulers to RCU, also from Julian Anastasov.

  28) Support cpu fanouts in xt_NFQUEUE netfilter target, from Holger

  29) Network namespace support for nf_log, ebt_log, xt_LOG, ipt_ULOG,
      nfnetlink_log, and nfnetlink_queue.  From Gao feng.

  30) Implement RFC3168 ECN protection, from Hannes Frederic Sowa.

  31) Support several new r8169 chips, from Hayes Wang.

  32) Support tokenized interface identifiers in ipv6, from Daniel

  33) Use usbnet_link_change() helper in USB net driver, from Ming Lei.

  34) Add 802.1ad vlan offload support, from Patrick McHardy.

  35) Support mmap() based netlink communication, also from Patrick

  36) Support HW timestamping in mlx4 driver, from Amir Vadai.

  37) Rationalize AF_PACKET packet timestamping when transmitting, from
      Willem de Bruijn and Daniel Borkmann.

  38) Bring parity to what's provided by /proc/net/packet socket dumping
      and the info provided by netlink socket dumping of AF_PACKET
      sockets.  From Nicolas Dichtel.

  39) Fix peeking beyond zero sized SKBs in AF_UNIX, from Benjamin

* git:// (1722 commits)
  filter: fix va_list build error
  af_unix: fix a fatal race with bit fields
  bnx2x: Prevent memory leak when cnic is absent
  bnx2x: correct reading of speed capabilities
  net: sctp: attribute printl with __printf for gcc fmt checks
  netlink: kconfig: move mmap i/o into netlink kconfig
  netpoll: convert mutex into a semaphore
  netlink: Fix skb ref counting.
  net_sched: act_ipt forward compat with xtables
  mlx4_en: fix a build error on 32bit arches
  Revert "bnx2x: allow nvram test to run when device is down"
  bridge: avoid OOPS if root port not found
  drivers: net: cpsw: fix kernel warn on cpsw irq enable
  sh_eth: use random MAC address if no valid one supplied
  3c509.c: call SET_NETDEV_DEV for all device types (ISA/ISAPnP/EISA)
  tg3: fix to append hardware time stamping flags
  unix/stream: fix peeking with an offset larger than data in queue
  unix/dgram: fix peeking with an offset larger than data in queue
  unix/dgram: peek beyond 0-sized skbs
  openvswitch: Remove unneeded ovs_netdev_get_ifindex()
parents 251df49d 20074f35
......@@ -67,6 +67,14 @@ Description:
Defines the penalty which will be applied to an
originator message's tq-field on every hop.
What: /sys/class/net/<mesh_iface>/mesh/network_coding
Date: Nov 2012
Contact: Martin Hundeboll <>
Controls whether Network Coding (using some magic
to send fewer wifi packets but still the same
content) is enabled or not.
What: /sys/class/net/<mesh_iface>/mesh/orig_interval
Date: May 2010
Contact: Marek Lindner <>
......@@ -437,7 +437,7 @@
!Finclude/net/mac80211.h ieee80211_get_buffered_bc
!Finclude/net/mac80211.h ieee80211_beacon_get
!Finclude/net/mac80211.h ieee80211_sta_eosp_irqsafe
!Finclude/net/mac80211.h ieee80211_sta_eosp
!Finclude/net/mac80211.h ieee80211_frame_release_type
!Finclude/net/mac80211.h ieee80211_sta_ps_transition
!Finclude/net/mac80211.h ieee80211_sta_ps_transition_ni
......@@ -18,6 +18,8 @@ memcg_test.txt
- Memory Resource Controller; implementation details.
- Memory Resource Controller; design, accounting, interface, testing.
- Network classifier cgroups details and usages.
- Network priority cgroups details and usages.
Network classifier cgroup
The Network classifier cgroup provides an interface to
tag network packets with a class identifier (classid).
The Traffic Controller (tc) can be used to assign
different priorities to packets from different cgroups.
Creating a net_cls cgroups instance creates a net_cls.classid file.
This net_cls.classid value is initialized to 0.
You can write hexadecimal values to net_cls.classid; the format for these
values is 0xAAAABBBB; AAAA is the major handle number and BBBB
is the minor handle number.
Reading net_cls.classid yields a decimal result.
mkdir /sys/fs/cgroup/net_cls
mount -t cgroup -onet_cls net_cls /sys/fs/cgroup/net_cls
mkdir /sys/fs/cgroup/net_cls/0
echo 0x100001 > /sys/fs/cgroup/net_cls/0/net_cls.classid
- setting a 10:1 handle.
cat /sys/fs/cgroup/net_cls/0/net_cls.classid
configuring tc:
tc qdisc add dev eth0 root handle 10: htb
tc class add dev eth0 parent 10: classid 10:1 htb rate 40mbit
- creating traffic class 10:1
tc filter add dev eth0 parent 10: protocol ip prio 10 handle 1: cgroup
......@@ -115,6 +115,9 @@ prefixed with the string "marvell,", for Marvell Technology Group Ltd.
- compatible : "marvell,mv64360-eth-block"
- reg : Offset and length of the register set for this block
Optional properties:
- clocks : Phandle to the clock control device and gate bit
Example Discovery Ethernet block node:
ethernet-block@2000 {
#address-cells = <1>;
* AT91 CAN *
Required properties:
- compatible: Should be "atmel,at91sam9263-can" or "atmel,at91sam9x5-can"
- reg: Should contain CAN controller registers location and length
- interrupts: Should contain IRQ line for the CAN controller
can0: can@f000c000 {
compatbile = "atmel,at91sam9x5-can";
reg = <0xf000c000 0x300>;
interrupts = <40 4 5>
......@@ -15,16 +15,22 @@ Required properties:
- mac_control : Specifies Default MAC control register content
for the specific platform
- slaves : Specifies number for slaves
- cpts_active_slave : Specifies the slave to use for time stamping
- active_slave : Specifies the slave to use for time stamping,
ethtool and SIOCGMIIPHY
- cpts_clock_mult : Numerator to convert input clock ticks into nanoseconds
- cpts_clock_shift : Denominator to convert input clock ticks into nanoseconds
- phy_id : Specifies slave phy id
- mac-address : Specifies slave MAC address
Optional properties:
- ti,hwmods : Must be "cpgmac0"
- no_bd_ram : Must be 0 or 1
- dual_emac : Specifies Switch to act as Dual EMAC
Slave Properties:
Required properties:
- phy_id : Specifies slave phy id
- mac-address : Specifies slave MAC address
Optional properties:
- dual_emac_res_vlan : Specifies VID to be used to segregate the ports
Note: "ti,hwmods" field is used to fetch the base address and irq
......@@ -47,7 +53,7 @@ Examples:
rx_descs = <64>;
mac_control = <0x20>;
slaves = <2>;
cpts_active_slave = <0>;
active_slave = <0>;
cpts_clock_mult = <0x80000000>;
cpts_clock_shift = <29>;
cpsw_emac0: slave@0 {
......@@ -73,7 +79,7 @@ Examples:
rx_descs = <64>;
mac_control = <0x20>;
slaves = <2>;
cpts_active_slave = <0>;
active_slave = <0>;
cpts_clock_mult = <0x80000000>;
cpts_clock_shift = <29>;
cpsw_emac0: slave@0 {
Marvell Distributed Switch Architecture Device Tree Bindings
Required properties:
- compatible : Should be "marvell,dsa"
- #address-cells : Must be 2, first cell is the address on the MDIO bus
and second cell is the address in the switch tree.
Second cell is used only when cascading/chaining.
- #size-cells : Must be 0
- dsa,ethernet : Should be a phandle to a valid Ethernet device node
- dsa,mii-bus : Should be a phandle to a valid MDIO bus device node
Optionnal properties:
- interrupts : property with a value describing the switch
interrupt number (not supported by the driver)
A DSA node can contain multiple switch chips which are therefore child nodes of
the parent DSA node. The maximum number of allowed child nodes is 4
Each of these switch child nodes should have the following required properties:
- reg : Describes the switch address on the MII bus
- #address-cells : Must be 1
- #size-cells : Must be 0
A switch may have multiple "port" children nodes
Each port children node must have the following mandatory properties:
- reg : Describes the port address in the switch
- label : Describes the label associated with this port, special
labels are "cpu" to indicate a CPU port and "dsa" to
indicate an uplink/downlink port.
Note that a port labelled "dsa" will imply checking for the uplink phandle
described below.
Optionnal property:
- link : Should be a phandle to another switch's DSA port.
This property is only used when switches are being
chained/cascaded together.
dsa@0 {
compatible = "marvell,dsa";
#address-cells = <2>;
#size-cells = <0>;
interrupts = <10>;
dsa,ethernet = <&ethernet0>;
dsa,mii-bus = <&mii_bus0>;
switch@0 {
#address-cells = <1>;
#size-cells = <0>;
reg = <16 0>; /* MDIO address 16, switch 0 in tree */
port@0 {
reg = <0>;
label = "lan1";
port@1 {
reg = <1>;
label = "lan2";
port@5 {
reg = <5>;
label = "cpu";
switch0uplink: port@6 {
reg = <6>;
label = "dsa";
link = <&switch1uplink>;
switch@1 {
#address-cells = <1>;
#size-cells = <0>;
reg = <17 1>; /* MDIO address 17, switch 1 in tree */
switch1uplink: port@0 {
reg = <0>;
label = "dsa";
link = <&switch0uplink>;
......@@ -9,6 +9,10 @@ Required properties:
- compatible: "marvell,orion-mdio"
- reg: address and length of the SMI register
Optional properties:
- interrupts: interrupt line number for the SMI error/done interrupt
- clocks: Phandle to the clock control device and gate bit
The child nodes of the MDIO driver are the individual PHY devices
connected to this MDIO bus. They must have a "reg" property given the
PHY address on the MDIO bus.
......@@ -71,8 +71,9 @@ submits skb to qdisc), so if you need something from that cb later, you should
store info in the skb->data on your own.
To hook the MLME interface you have to populate the ml_priv field of your
net_device with a pointer to struct ieee802154_mlme_ops instance. All fields are
net_device with a pointer to struct ieee802154_mlme_ops instance. The fields
assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional.
All other fields are required.
We provide an example of simple HardMAC driver at drivers/ieee802154/fakehard.c
......@@ -29,7 +29,7 @@ route/max_size - INTEGER
neigh/default/gc_thresh1 - INTEGER
Minimum number of entries to keep. Garbage collector will not
purge entries if there are fewer than this number.
Default: 256
Default: 128
neigh/default/gc_thresh3 - INTEGER
Maximum number of neighbor entries allowed. Increase this
......@@ -175,14 +175,6 @@ tcp_congestion_control - STRING
is inherited.
[see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
tcp_cookie_size - INTEGER
Default size of TCP Cookie Transactions (TCPCT) option, that may be
overridden on a per socket basis by the TCPCT socket option.
Values greater than the maximum (16) are interpreted as the maximum.
Values greater than zero and less than the minimum (8) are interpreted
as the minimum. Odd values are interpreted as the next even value.
Default: 0 (off).
tcp_dsack - BOOLEAN
Allows TCP to send "duplicate" SACKs.
......@@ -190,7 +182,9 @@ tcp_early_retrans - INTEGER
Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
for triggering fast retransmit when the amount of outstanding data is
small and when no previously unsent data can be transmitted (such
that limited transmit could be used).
that limited transmit could be used). Also controls the use of
Tail loss probe (TLP) that converts RTOs occuring due to tail
losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
Possible values:
0 disables ER
1 enables ER
......@@ -198,7 +192,9 @@ tcp_early_retrans - INTEGER
by a fourth of RTT. This mitigates connection falsely
recovers when network has a small degree of reordering
(less than 3 packets).
Default: 2
3 enables delayed ER and TLP.
4 enables TLP only.
Default: 3
tcp_ecn - INTEGER
Control use of Explicit Congestion Notification (ECN) by TCP.
......@@ -229,36 +225,13 @@ tcp_fin_timeout - INTEGER
Default: 60 seconds
tcp_frto - INTEGER
Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
F-RTO is an enhanced recovery algorithm for TCP retransmission
timeouts. It is particularly beneficial in wireless environments
where packet loss is typically due to random radio interference
rather than intermediate router congestion. F-RTO is sender-side
only modification. Therefore it does not require any support from
the peer.
If set to 1, basic version is enabled. 2 enables SACK enhanced
F-RTO if flow uses SACK. The basic version can be used also when
SACK is in use though scenario(s) with it exists where F-RTO
interacts badly with the packet counting of the SACK enabled TCP
tcp_frto_response - INTEGER
When F-RTO has detected that a TCP retransmission timeout was
spurious (i.e, the timeout would have been avoided had TCP set a
longer retransmission timeout), TCP has several options what to do
next. Possible values are:
0 Rate halving based; a smooth and conservative response,
results in halved cwnd and ssthresh after one RTT
1 Very conservative response; not recommended because even
though being valid, it interacts poorly with the rest of
Linux TCP, halves cwnd and ssthresh immediately
2 Aggressive response; undoes congestion control measures
that are now known to be unnecessary (ignoring the
possibility of a lost retransmission that would require
TCP to be more cautious), cwnd and ssthresh are restored
to the values prior timeout
Default: 0 (rate halving based)
timeouts. It is particularly beneficial in networks where the
RTT fluctuates (e.g., wireless). F-RTO is sender-side only
modification. It does not require any support from the peer.
By default it's enabled with a non-zero value. 0 disables F-RTO.
tcp_keepalive_time - INTEGER
How often TCP sends out keepalive messages when keepalive is enabled.
This file documents how to use memory mapped I/O with netlink.
Author: Patrick McHardy <>
Memory mapped netlink I/O can be used to increase throughput and decrease
overhead of unicast receive and transmit operations. Some netlink subsystems
require high throughput, these are mainly the netfilter subsystems
nfnetlink_queue and nfnetlink_log, but it can also help speed up large
dump operations of f.i. the routing database.
Memory mapped netlink I/O used two circular ring buffers for RX and TX which
are mapped into the processes address space.
The RX ring is used by the kernel to directly construct netlink messages into
user-space memory without copying them as done with regular socket I/O,
additionally as long as the ring contains messages no recvmsg() or poll()
syscalls have to be issued by user-space to get more message.
The TX ring is used to process messages directly from user-space memory, the
kernel processes all messages contained in the ring using a single sendmsg()
Usage overview
In order to use memory mapped netlink I/O, user-space needs three main changes:
- ring setup
- conversion of the RX path to get messages from the ring instead of recvmsg()
- conversion of the TX path to construct messages into the ring
Ring setup is done using setsockopt() to provide the ring parameters to the
kernel, then a call to mmap() to map the ring into the processes address space:
- setsockopt(fd, SOL_NETLINK, NETLINK_RX_RING, &params, sizeof(params));
- setsockopt(fd, SOL_NETLINK, NETLINK_TX_RING, &params, sizeof(params));
- ring = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)
Usage of either ring is optional, but even if only the RX ring is used the
mapping still needs to be writable in order to update the frame status after
Conversion of the reception path involves calling poll() on the file
descriptor, once the socket is readable the frames from the ring are
processsed in order until no more messages are available, as indicated by
a status word in the frame header.
On kernel side, in order to make use of memory mapped I/O on receive, the
originating netlink subsystem needs to support memory mapped I/O, otherwise
it will use an allocated socket buffer as usual and the contents will be
copied to the ring on transmission, nullifying most of the performance gains.
Dumps of kernel databases automatically support memory mapped I/O.
Conversion of the transmit path involves changing message contruction to
use memory from the TX ring instead of (usually) a buffer declared on the
stack and setting up the frame header approriately. Optionally poll() can
be used to wait for free frames in the TX ring.
Structured and definitions for using memory mapped I/O are contained in
RX and TX rings
Each ring contains a number of continous memory blocks, containing frames of
fixed size dependant on the parameters used for ring setup.
Ring: [ block 0 ]
[ frame 0 ]
[ frame 1 ]
[ block 1 ]
[ frame 2 ]
[ frame 3 ]
[ block n ]
[ frame 2 * n ]
[ frame 2 * n + 1 ]
The blocks are only visible to the kernel, from the point of view of user-space
the ring just contains the frames in a continous memory zone.
The ring parameters used for setting up the ring are defined as follows:
struct nl_mmap_req {
unsigned int nm_block_size;
unsigned int nm_block_nr;
unsigned int nm_frame_size;
unsigned int nm_frame_nr;
Frames are grouped into blocks, where each block is a continous region of memory
and holds nm_block_size / nm_frame_size frames. The total number of frames in
the ring is nm_frame_nr. The following invariants hold:
- frames_per_block = nm_block_size / nm_frame_size
- nm_frame_nr = frames_per_block * nm_block_nr
Some parameters are constrained, specifically:
- nm_block_size must be a multiple of the architectures memory page size.
The getpagesize() function can be used to get the page size.
- nm_frame_size must be equal or larger to NL_MMAP_HDRLEN, IOW a frame must be
able to hold at least the frame header
- nm_frame_size must be smaller or equal to nm_block_size
- nm_frame_size must be a multiple of NL_MMAP_MSG_ALIGNMENT
- nm_frame_nr must equal the actual number of frames as specified above.
When the kernel can't allocate phsyically continous memory for a ring block,
it will fall back to use physically discontinous memory. This might affect
performance negatively, in order to avoid this the nm_frame_size parameter
should be chosen to be as small as possible for the required frame size and
the number of blocks should be increased instead.
Ring frames
Each frames contain a frame header, consisting of a synchronization word and some
meta-data, and the message itself.
Frame: [ header message ]
The frame header is defined as follows:
struct nl_mmap_hdr {
unsigned int nm_status;
unsigned int nm_len;
__u32 nm_group;
/* credentials */
__u32 nm_pid;
__u32 nm_uid;
__u32 nm_gid;
- nm_status is used for synchronizing processing between the kernel and user-
space and specifies ownership of the frame as well as the operation to perform
- nm_len contains the length of the message contained in the data area
- nm_group specified the destination multicast group of message
- nm_pid, nm_uid and nm_gid contain the netlink pid, UID and GID of the sending
process. These values correspond to the data available using SOCK_PASSCRED in
The possible values in the status word are:
RX ring: frame belongs to the kernel and contains no message
for user-space. Approriate action is to invoke poll()
to wait for new messages.
TX ring: frame belongs to user-space and can be used for
message construction.
RX ring only: frame is currently used by the kernel for message
construction and contains no valid message yet.
Appropriate action is to invoke poll() to wait for
new messages.
RX ring: frame contains a valid message. Approriate action is
to process the message and release the frame back to
the kernel by setting the status to
NL_MMAP_STATUS_UNUSED or queue the frame by setting the
TX ring: the frame contains a valid message from user-space to
be processed by the kernel. After completing processing
the kernel will release the frame back to user-space by
setting the status to NL_MMAP_STATUS_UNUSED.
RX ring only: a message is ready to be processed but could not be
stored in the ring, either because it exceeded the
frame size or because the originating subsystem does
not support memory mapped I/O. Appropriate action is
to invoke recvmsg() to receive the message and release
the frame back to the kernel by setting the status to
RX ring only: user-space queued the message for later processing, but
processed some messages following it in the ring. The
kernel should skip this frame when looking for unused
The data area of a frame begins at a offset of NL_MMAP_HDRLEN relative to the
frame header.
TX limitations
Kernel processing usually involves validation of the message received by
user-space, then processing its contents. The kernel must assure that
userspace is not able to modify the message contents after they have been
validated. In order to do so, the message is copied from the ring frame
to an allocated buffer if either of these conditions is false:
- only a single mapping of the ring exists
- the file descriptor is not shared between processes
This means that for threaded programs, the kernel will fall back to copying.
Ring setup:
unsigned int block_size = 16 * getpagesize();
struct nl_mmap_req req = {
.nm_block_size = block_size,
.nm_block_nr = 64,
.nm_frame_size = 16384,
.nm_frame_nr = 64 * block_size / 16384,
unsigned int ring_size;
void *rx_ring, *tx_ring;
/* Configure ring parameters */
if (setsockopt(fd, NETLINK_RX_RING, &req, sizeof(req)) < 0)
if (setsockopt(fd, NETLINK_TX_RING, &req, sizeof(req)) < 0)
/* Calculate size of each invididual ring */
ring_size = req.nm_block_nr * req.nm_block_size;
/* Map RX/TX rings. The TX ring is located after the RX ring */
rx_ring = mmap(NULL, 2 * ring_size, PROT_READ | PROT_WRITE,
MAP_SHARED, fd, 0);
if ((long)rx_ring == -1L)
tx_ring = rx_ring + ring_size:
Message reception:
This example assumes some ring parameters of the ring setup are available.
unsigned int frame_offset = 0;
struct nl_mmap_hdr *hdr;
struct nlmsghdr *nlh;
unsigned char buf[16384];
ssize_t len;
while (1) {
struct pollfd pfds[1];
pfds[0].fd = fd;
pfds[0].events = POLLIN | POLLERR;
pfds[0].revents = 0;
if (poll(pfds, 1, -1) < 0 && errno != -EINTR)
/* Check for errors. Error handling omitted */
if (pfds[0].revents & POLLERR)
<handle error>
/* If no new messages, poll again */
if (!(pfds[0].revents & POLLIN))
/* Process all frames */
while (1) {
/* Get next frame header */
hdr = rx_ring + frame_offset;
if (hdr->nm_status == NL_MMAP_STATUS_VALID)
/* Regular memory mapped frame */
nlh = (void *hdr) + NL_MMAP_HDRLEN;
len = hdr->nm_len;
/* Release empty message immediately. May happen