FAQ: Add entry about different datapaths features.

This is an easy way to keep track of the features supported by the
different datapaths.

Nithin helped filling the list for the Hyper-V port.

CC: Nithin Raju <[email protected]>
Signed-off-by: Daniele Di Proietto <[email protected]>
Acked-by: Ben Pfaff <[email protected]>
Acked-by: Nithin Raju <[email protected]>
Acked-by: Justin Pettit <[email protected]>

FAQ.md

@@ -165,28 +165,72 @@ A: The following table lists the Linux kernel versions against which the
    It should build against almost any kernel, certainly against 2.6.32
    and later.
 
-### Q: Are all features available with all versions of the kernel module?
-
-A: Features are gradually introduced into the upstream kernel so unless
-   you are running the latest Linux release there may be some missing
-   features. ovs-vswitchd probes for kernel features during startup and
-   lists them in the ovs-vswitchd log file. If you need features that
-   are unsupported, you can upgrade the Linux version or use the kernel
-   module paired with the userspace distribution.
-
-   For a given Open vSwitch release, the vast majority of features are
-   supported when using the kernel module paired with the userspace
-   distribution, no matter which kernel you build it against. However,
-   from time to time, new features may be introduced which rely on
-   functionality not available in older kernels. The features below are
-   included in the kernel module distributed with OVS, but have more
-   stringent requirements for minimum kernel versions than the support
-   listed earlier.
-
-| Feature   | Open vSwitch | Linux kernel
-|:---------:|:------------:|:------------:
-|    STT    |     2.4+     |     3.5+
-| Conntrack |     2.5+     |     3.10+
+### Q: Are all features available with all datapaths?
+
+A: Open vSwitch supports different datapaths on different platforms.  Each
+   datapath has a different feature set: the following tables try to summarize
+   the status.
+
+   Supported datapaths:
+
+   * *Linux upstream*: The datapath implemented by the kernel module shipped
+                       with Linux upstream.  Since features have been gradually
+                       introduced into the kernel, the table mentions the first
+                       Linux release whose OVS module supports the feature.
+
+   * *Linux OVS tree*: The datapath implemented by the Linux kernel module
+                       distributed with the OVS source tree. Some features of
+                       this module rely on functionality not available in older
+                       kernels: in this case the minumum Linux version (against
+                       which the feature can be compiled) is listed.
+
+   * *Userspace*: Also known as DPDK, dpif-netdev or dummy datapath. It is the
+                  only datapath that works on NetBSD and FreeBSD.
+
+   * *Hyper-V*: Also known as the Windows datapath.
+
+   The following table lists the datapath supported features from
+   an Open vSwitch user's perspective.
+
+Feature               | Linux upstream | Linux OVS tree | Userspace | Hyper-V |
+----------------------|:--------------:|:--------------:|:---------:|:-------:|
+Connection tracking   |      4.3       |       3.10     |    NO     |   NO    |
+Tunnel - LISP         |      NO        |       YES      |    NO     |   NO    |
+Tunnel - STT          |      NO        |       3.5      |    NO     |   YES   |
+Tunnel - GRE          |      3.11      |       YES      |    YES    |   NO    |
+Tunnel - VXLAN        |      3.12      |       YES      |    YES    |   YES   |
+Tunnel - Geneve       |      3.18      |       YES      |    YES    |   NO    |
+QoS - Policing        |      YES       |       YES      |    NO     |   NO    |
+QoS - Shaping         |      YES       |       YES      |    NO     |   NO    |
+sFlow                 |      YES       |       YES      |    YES    |   NO    |
+Set action            |      YES       |       YES      |    YES    | PARTIAL |
+NIC Bonding           |      YES       |       YES      |    YES    |   NO    |
+Multiple VTEPs        |      YES       |       YES      |    YES    |   NO    |
+
+   **Notes:**
+   * Only a limited set of flow fields is modifiable via the set action by the
+     Hyper-V datapath.
+   * The Hyper-V datapath only supports one physical NIC per datapath. This is
+     why bonding is not supported.
+   * The Hyper-V datapath can have at most one IP address configured as a
+     tunnel endpoint.
+
+   The following table lists features that do not *directly* impact an
+   Open vSwitch user, e.g. because their absence can be hidden by the ofproto
+   layer (usually this comes with a performance penalty).
+
+Feature               | Linux upstream | Linux OVS tree | Userspace | Hyper-V |
+----------------------|:--------------:|:--------------:|:---------:|:-------:|
+SCTP flows            |      3.12      |       YES      |    YES    |   YES   |
+MPLS                  |      3.19      |       YES      |    YES    |   NO    |
+UFID                  |      4.0       |       YES      |    YES    |   NO    |
+Megaflows             |      3.12      |       YES      |    YES    |   NO    |
+Masked set action     |      4.0       |       YES      |    YES    |   NO    |
+Recirculation         |      3.19      |       YES      |    YES    |   NO    |
+TCP flags matching    |      3.13      |       YES      |    YES    |   NO    |
+Validate flow actions |      YES       |       YES      |    N/A    |   NO    |
+Multiple datapaths    |      YES       |       YES      |    YES    |   NO    |
+Tunnel TSO - STT      |      N/A       |       YES      |    NO     |   YES   |
 
 ### Q: I get an error like this when I configure Open vSwitch: