doc: update documentation

This patch adds info on kernel requirement for XDP and rework a few
things.

doc/userguide/capture-hardware/ebpf-xdp.rst

@@ -40,7 +40,7 @@ card that support XDP in the driver.
 Suricata XDP code has been tested with 4.13.10 but 4.15 or later is necessary to have all
 features like the CPU redirect map.
 
-If yu are using an Intel netword card, you will need to stay with in tree kernel NIC drivers.
+If you are using an Intel netword card, you will need to stay with in tree kernel NIC drivers.
 The out of tree drivers do not contain the XDP support.
 
 Having a network card with support for RSS symmetric hashing is a good point or you will have to
@@ -62,7 +62,7 @@ Disable irqbalance
 Kernel
 ~~~~~~
 
-Install kernel 4.13.+ and reboot.
+You need to run a kernel 4.13 or newer.
 
 Clang
 ~~~~~
@@ -96,7 +96,7 @@ Now, you can build and install the library ::
 Compile and install Suricata
 ----------------------------
 
-If ever you don't have the source ::
+To get Suricata source, you can use the usual ::
 
  git clone  https://github.com/OISF/suricata.git
  cd suricata && git clone https://github.com/OISF/libhtp.git -b 0.5.x
@@ -144,9 +144,13 @@ in the app-layer tls section ::
 Setup eBPF filter
 -----------------
 
-Copy the resulting ebpf fiter as needed ::
+The file `ebpf/vlan_filter.c` contains a list of vlan id in a switch
+that you need to edit to get something adapted to your network.
+
+Once modifications and build via `make` are done, you can copy the resulting
+eBPF filter as needed ::
 
- cp src/ebpf/vlan_filter.bpf /etc/suricata/ebpf/
+ cp ebpf/vlan_filter.bpf /etc/suricata/ebpf/
 
 Then setup the `ebpf-filter-file` variable in af-packet section ::
 
@@ -165,6 +169,9 @@ You can then run suricata normally ::
 
  /usr/bin/suricata --pidfile /var/run/suricata.pid  --af-packet=eth3 -vvv 
 
+Setup eBPF bypass
+-----------------
+
 You can also use eBPF bypass. To do that load the `bypass_filter.bpf` file and
 update af-packet configuration to set bypass to yes ::
 
@@ -173,9 +180,6 @@ update af-packet configuration to set bypass to yes ::
     cluster-id: 97
     cluster-type: cluster_qm # symmetric hashing is a must!
     defrag: yes
-    # eBPF file containing a 'loadbalancer' function that will be inserted into the
-    # kernel and used as load balancing function
-    #ebpf-lb-file:  /etc/suricata/ebpf/lb.bpf
     # eBPF file containing a 'filter' function that will be inserted into the
     # kernel and used as packet filter function
     # eBPF file containing a 'xdp' function that will be inserted into the
@@ -191,7 +195,7 @@ Setup eBPF load balancing
 
 Copy the resulting ebpf fiter as needed ::
 
- cp src/ebpf/lb.bpf /etc/suricata/
+ cp ebpf/lb.bpf /etc/suricata/
 
 We will use ``cluster_ebpf`` in the interface section of af-packet ::
 
@@ -206,12 +210,20 @@ We will use ``cluster_ebpf`` in the interface section of af-packet ::
     use-mmap: yes
     ring-size: 200000
 
-Setup XDP
+Setup XDP bypass
----------
+----------------
+
+XDP bypass will allow Suricata to tell the kernel that packets for some
+flows have to be dropped via the XDP mechanism. This is a really early
+drop that occurs before the datagram is reaching the Linux kernel
+network stack.
+
+Linux 4.15 or newer are recommended to use that feature. You can use it
+on older kernel if you set ``BUILD_CPUMAP`` to 0 in ``ebpf/xdp_filter.c``.
 
-Copy the resulting xdp fiter as needed::
+Copy the resulting xdp filter as needed::
 
- cp src/ebpf/xdp_filter.bpf /etc/suricata/ebpf/
+ cp ebpf/xdp_filter.bpf /etc/suricata/ebpf/
 
 Setup af-packet section/interface in ``suricata.yaml``.
 
@@ -223,14 +235,6 @@ also use the ``/etc/suricata/ebpf/xdp_filter.bpf`` (in our example TCP offloadin
     cluster-id: 97
     cluster-type: cluster_qm # symmetric hashing is a must!
     defrag: yes
-    # eBPF file containing a 'loadbalancer' function that will be inserted into the
-    # kernel and used as load balancing function
-    #ebpf-lb-file:  /etc/suricata/ebpf/lb.bpf
-    # eBPF file containing a 'filter' function that will be inserted into the
-    # kernel and used as packet filter function
-    # eBPF file containing a 'xdp' function that will be inserted into the
-    # kernel and used as XDP packet filter function
-    #ebpf-filter-file:  /etc/suricata/ebpf/filter.bpf
     # Xdp mode, "soft" for skb based version, "driver" for network card based
     # and "hw" for card supporting eBPF.
     xdp-mode: driver
@@ -257,10 +261,10 @@ Follow these instructions closely for desired result::
 
 Use in tree kernel drivers: XDP support is not available in Intel drivers available on Intel website.
 
-Enable symmetric hashing::
+Enable symmetric hashing ::
 
  ifconfig eth3 down 
- ethtool -L eth3 combined 16
+ ethtool -L eth3 combined 16 # if you have at least 16 cores
  ethtool -K eth3 rxhash on 
  ethtool -K eth3 ntuple on
  ifconfig eth3 up
@@ -300,6 +304,8 @@ can then use the CPU redirect map support available in the xdp_filter.bpf file.
 balancinf will be done by the XDP filter and each CPU will handle the whole packet treatment including
 the creation of the skb structure in kernel.
 
+You will need Linux 4.15 or newer to use that feature.
+
 To do so set the `xdp-cpu-redirect` variable in af-packet interface configuration to a set of CPUs.
 Then use the `cluster_cpu` as load balancing function. You will also need to set the affinity
 accordingly.