538919d3a6
The C standard allows compilers to do type-based alias analysis, which means that the compiler is allowed to assume that pointers to objects of different types are pointers to different objects. For example, a compiler may assume that "uint16_t *a" and "uint32_t *b" point to different and nonoverlapping locations because the pointed-to types are different. This can lead to surprising "optimizations" with compilers that by default do this kind of analysis, which includes GCC and Clang. The one escape clause that the C standard gives us is that character types must be assumed to alias any other object. We've always tried to use this escape clause to avoid problems with type-based alias analysis in the past. I think that we should continue to try to do this in the future. It's hard to tell what compiler we might want to use in the future, and one never knows what kind of control that compiler allows over alias analysis. However, recently I helped another developer debug a nasty and confusing issue, which turned out to be the result of a surprising compiler optimization due to alias analysis. I've seen enough of these that I don't think it's worthwhile to risk more problems than we have to. Thus, this commit turns off type-based alias analysis in GCC and Clang. Linus Torvalds thinks that type-base alias analysis is not sane, at least as GCC implements it: https://lkml.org/lkml/2003/2/26/158 The GCC manual says that -Wstrict-aliasing is only effective without -fno-strict-aliasing, otherwise I'd keep -Wstrict-aliasing also. Indications are that MSVC doesn't do type-based alias analysis by default. Signed-off-by: Ben Pfaff <blp@nicira.com> Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
Open vSwitch
Build Status:
What is Open vSwitch?
Open vSwitch is a multilayer software switch licensed under the open source Apache 2 license. Our goal is to implement a production quality switch platform that supports standard management interfaces and opens the forwarding functions to programmatic extension and control.
Open vSwitch is well suited to function as a virtual switch in VM environments. In addition to exposing standard control and visibility interfaces to the virtual networking layer, it was designed to support distribution across multiple physical servers. Open vSwitch supports multiple Linux-based virtualization technologies including Xen/XenServer, KVM, and VirtualBox.
The bulk of the code is written in platform-independent C and is easily ported to other environments. The current release of Open vSwitch supports the following features:
- Standard 802.1Q VLAN model with trunk and access ports
- NIC bonding with or without LACP on upstream switch
- NetFlow, sFlow(R), and mirroring for increased visibility
- QoS (Quality of Service) configuration, plus policing
- Geneve, GRE, GRE over IPSEC, VXLAN, and LISP tunneling
- 802.1ag connectivity fault management
- OpenFlow 1.0 plus numerous extensions
- Transactional configuration database with C and Python bindings
- High-performance forwarding using a Linux kernel module
The included Linux kernel module supports Linux 2.6.32 and up, with testing focused on 2.6.32 with Centos and Xen patches. Open vSwitch also has special support for Citrix XenServer and Red Hat Enterprise Linux hosts.
Open vSwitch can also operate, at a cost in performance, entirely in userspace, without assistance from a kernel module. This userspace implementation should be easier to port than the kernel-based switch. It is considered experimental.
What's here?
The main components of this distribution are:
- ovs-vswitchd, a daemon that implements the switch, along with a companion Linux kernel module for flow-based switching.
- ovsdb-server, a lightweight database server that ovs-vswitchd queries to obtain its configuration.
- ovs-dpctl, a tool for configuring the switch kernel module.
- Scripts and specs for building RPMs for Citrix XenServer and Red Hat Enterprise Linux. The XenServer RPMs allow Open vSwitch to be installed on a Citrix XenServer host as a drop-in replacement for its switch, with additional functionality.
- ovs-vsctl, a utility for querying and updating the configuration of ovs-vswitchd.
- ovs-appctl, a utility that sends commands to running Open vSwitch daemons.
Open vSwitch also provides some tools:
- ovs-ofctl, a utility for querying and controlling OpenFlow switches and controllers.
- ovs-pki, a utility for creating and managing the public-key infrastructure for OpenFlow switches.
- ovs-testcontroller, a simple OpenFlow controller that may be useful for testing (though not for production).
- A patch to tcpdump that enables it to parse OpenFlow messages.
What other documentation is available?
To install Open vSwitch on a regular Linux or FreeBSD host, please read INSTALL. For specifics around installation on a specific platform, please see one of these files:
- INSTALL.Debian
- INSTALL.Fedora
- INSTALL.RHEL
- INSTALL.XenServer
To use Open vSwitch...
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...with KVM on Linux, read INSTALL, read INSTALL.KVM.
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...with Libvirt, read INSTALL.Libvirt.
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...without using a kernel module, read INSTALL.userspace.
For answers to common questions, read FAQ.
To learn how to set up SSL support for Open vSwitch, read INSTALL.SSL.
To learn about some advanced features of the Open vSwitch software switch, read the tutorial in tutorial/Tutorial.
Each Open vSwitch userspace program is accompanied by a manpage. Many of the manpages are customized to your configuration as part of the build process, so we recommend building Open vSwitch before reading the manpages.