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diff --git a/Documentation/networking/openvswitch.txt b/Documentation/networking/openvswitch.txt deleted file mode 100644 index b3b9ac61d29d..000000000000 --- a/Documentation/networking/openvswitch.txt +++ /dev/null @@ -1,248 +0,0 @@ -Open vSwitch datapath developer documentation -============================================= - -The Open vSwitch kernel module allows flexible userspace control over -flow-level packet processing on selected network devices. It can be -used to implement a plain Ethernet switch, network device bonding, -VLAN processing, network access control, flow-based network control, -and so on. - -The kernel module implements multiple "datapaths" (analogous to -bridges), each of which can have multiple "vports" (analogous to ports -within a bridge). Each datapath also has associated with it a "flow -table" that userspace populates with "flows" that map from keys based -on packet headers and metadata to sets of actions. The most common -action forwards the packet to another vport; other actions are also -implemented. - -When a packet arrives on a vport, the kernel module processes it by -extracting its flow key and looking it up in the flow table. If there -is a matching flow, it executes the associated actions. If there is -no match, it queues the packet to userspace for processing (as part of -its processing, userspace will likely set up a flow to handle further -packets of the same type entirely in-kernel). - - -Flow key compatibility ----------------------- - -Network protocols evolve over time. New protocols become important -and existing protocols lose their prominence. For the Open vSwitch -kernel module to remain relevant, it must be possible for newer -versions to parse additional protocols as part of the flow key. It -might even be desirable, someday, to drop support for parsing -protocols that have become obsolete. Therefore, the Netlink interface -to Open vSwitch is designed to allow carefully written userspace -applications to work with any version of the flow key, past or future. - -To support this forward and backward compatibility, whenever the -kernel module passes a packet to userspace, it also passes along the -flow key that it parsed from the packet. Userspace then extracts its -own notion of a flow key from the packet and compares it against the -kernel-provided version: - - - If userspace's notion of the flow key for the packet matches the - kernel's, then nothing special is necessary. - - - If the kernel's flow key includes more fields than the userspace - version of the flow key, for example if the kernel decoded IPv6 - headers but userspace stopped at the Ethernet type (because it - does not understand IPv6), then again nothing special is - necessary. Userspace can still set up a flow in the usual way, - as long as it uses the kernel-provided flow key to do it. - - - If the userspace flow key includes more fields than the - kernel's, for example if userspace decoded an IPv6 header but - the kernel stopped at the Ethernet type, then userspace can - forward the packet manually, without setting up a flow in the - kernel. This case is bad for performance because every packet - that the kernel considers part of the flow must go to userspace, - but the forwarding behavior is correct. (If userspace can - determine that the values of the extra fields would not affect - forwarding behavior, then it could set up a flow anyway.) - -How flow keys evolve over time is important to making this work, so -the following sections go into detail. - - -Flow key format ---------------- - -A flow key is passed over a Netlink socket as a sequence of Netlink -attributes. Some attributes represent packet metadata, defined as any -information about a packet that cannot be extracted from the packet -itself, e.g. the vport on which the packet was received. Most -attributes, however, are extracted from headers within the packet, -e.g. source and destination addresses from Ethernet, IP, or TCP -headers. - -The <linux/openvswitch.h> header file defines the exact format of the -flow key attributes. For informal explanatory purposes here, we write -them as comma-separated strings, with parentheses indicating arguments -and nesting. For example, the following could represent a flow key -corresponding to a TCP packet that arrived on vport 1: - - in_port(1), eth(src=e0:91:f5:21:d0:b2, dst=00:02:e3:0f:80:a4), - eth_type(0x0800), ipv4(src=172.16.0.20, dst=172.18.0.52, proto=17, tos=0, - frag=no), tcp(src=49163, dst=80) - -Often we ellipsize arguments not important to the discussion, e.g.: - - in_port(1), eth(...), eth_type(0x0800), ipv4(...), tcp(...) - - -Wildcarded flow key format --------------------------- - -A wildcarded flow is described with two sequences of Netlink attributes -passed over the Netlink socket. A flow key, exactly as described above, and an -optional corresponding flow mask. - -A wildcarded flow can represent a group of exact match flows. Each '1' bit -in the mask specifies a exact match with the corresponding bit in the flow key. -A '0' bit specifies a don't care bit, which will match either a '1' or '0' bit -of a incoming packet. Using wildcarded flow can improve the flow set up rate -by reduce the number of new flows need to be processed by the user space program. - -Support for the mask Netlink attribute is optional for both the kernel and user -space program. The kernel can ignore the mask attribute, installing an exact -match flow, or reduce the number of don't care bits in the kernel to less than -what was specified by the user space program. In this case, variations in bits -that the kernel does not implement will simply result in additional flow setups. -The kernel module will also work with user space programs that neither support -nor supply flow mask attributes. - -Since the kernel may ignore or modify wildcard bits, it can be difficult for -the userspace program to know exactly what matches are installed. There are -two possible approaches: reactively install flows as they miss the kernel -flow table (and therefore not attempt to determine wildcard changes at all) -or use the kernel's response messages to determine the installed wildcards. - -When interacting with userspace, the kernel should maintain the match portion -of the key exactly as originally installed. This will provides a handle to -identify the flow for all future operations. However, when reporting the -mask of an installed flow, the mask should include any restrictions imposed -by the kernel. - -The behavior when using overlapping wildcarded flows is undefined. It is the -responsibility of the user space program to ensure that any incoming packet -can match at most one flow, wildcarded or not. The current implementation -performs best-effort detection of overlapping wildcarded flows and may reject -some but not all of them. However, this behavior may change in future versions. - - -Unique flow identifiers ------------------------ - -An alternative to using the original match portion of a key as the handle for -flow identification is a unique flow identifier, or "UFID". UFIDs are optional -for both the kernel and user space program. - -User space programs that support UFID are expected to provide it during flow -setup in addition to the flow, then refer to the flow using the UFID for all -future operations. The kernel is not required to index flows by the original -flow key if a UFID is specified. - - -Basic rule for evolving flow keys ---------------------------------- - -Some care is needed to really maintain forward and backward -compatibility for applications that follow the rules listed under -"Flow key compatibility" above. - -The basic rule is obvious: - - ------------------------------------------------------------------ - New network protocol support must only supplement existing flow - key attributes. It must not change the meaning of already defined - flow key attributes. - ------------------------------------------------------------------ - -This rule does have less-obvious consequences so it is worth working -through a few examples. Suppose, for example, that the kernel module -did not already implement VLAN parsing. Instead, it just interpreted -the 802.1Q TPID (0x8100) as the Ethertype then stopped parsing the -packet. The flow key for any packet with an 802.1Q header would look -essentially like this, ignoring metadata: - - eth(...), eth_type(0x8100) - -Naively, to add VLAN support, it makes sense to add a new "vlan" flow -key attribute to contain the VLAN tag, then continue to decode the -encapsulated headers beyond the VLAN tag using the existing field -definitions. With this change, a TCP packet in VLAN 10 would have a -flow key much like this: - - eth(...), vlan(vid=10, pcp=0), eth_type(0x0800), ip(proto=6, ...), tcp(...) - -But this change would negatively affect a userspace application that -has not been updated to understand the new "vlan" flow key attribute. -The application could, following the flow compatibility rules above, -ignore the "vlan" attribute that it does not understand and therefore -assume that the flow contained IP packets. This is a bad assumption -(the flow only contains IP packets if one parses and skips over the -802.1Q header) and it could cause the application's behavior to change -across kernel versions even though it follows the compatibility rules. - -The solution is to use a set of nested attributes. This is, for -example, why 802.1Q support uses nested attributes. A TCP packet in -VLAN 10 is actually expressed as: - - eth(...), eth_type(0x8100), vlan(vid=10, pcp=0), encap(eth_type(0x0800), - ip(proto=6, ...), tcp(...))) - -Notice how the "eth_type", "ip", and "tcp" flow key attributes are -nested inside the "encap" attribute. Thus, an application that does -not understand the "vlan" key will not see either of those attributes -and therefore will not misinterpret them. (Also, the outer eth_type -is still 0x8100, not changed to 0x0800.) - -Handling malformed packets --------------------------- - -Don't drop packets in the kernel for malformed protocol headers, bad -checksums, etc. This would prevent userspace from implementing a -simple Ethernet switch that forwards every packet. - -Instead, in such a case, include an attribute with "empty" content. -It doesn't matter if the empty content could be valid protocol values, -as long as those values are rarely seen in practice, because userspace -can always forward all packets with those values to userspace and -handle them individually. - -For example, consider a packet that contains an IP header that -indicates protocol 6 for TCP, but which is truncated just after the IP -header, so that the TCP header is missing. The flow key for this -packet would include a tcp attribute with all-zero src and dst, like -this: - - eth(...), eth_type(0x0800), ip(proto=6, ...), tcp(src=0, dst=0) - -As another example, consider a packet with an Ethernet type of 0x8100, -indicating that a VLAN TCI should follow, but which is truncated just -after the Ethernet type. The flow key for this packet would include -an all-zero-bits vlan and an empty encap attribute, like this: - - eth(...), eth_type(0x8100), vlan(0), encap() - -Unlike a TCP packet with source and destination ports 0, an -all-zero-bits VLAN TCI is not that rare, so the CFI bit (aka -VLAN_TAG_PRESENT inside the kernel) is ordinarily set in a vlan -attribute expressly to allow this situation to be distinguished. -Thus, the flow key in this second example unambiguously indicates a -missing or malformed VLAN TCI. - -Other rules ------------ - -The other rules for flow keys are much less subtle: - - - Duplicate attributes are not allowed at a given nesting level. - - - Ordering of attributes is not significant. - - - When the kernel sends a given flow key to userspace, it always - composes it the same way. This allows userspace to hash and - compare entire flow keys that it may not be able to fully - interpret. |