2 FreeBSD as a set of building blocks
FreeBSD makes an excellent foundation on which to build products:
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FreeBSD source code is distributed under a liberal BSD license facilitating its adoption in commercial products [Mon2005] with minimum hassle.
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The FreeBSD project has excellent engineering practices that can be leveraged.
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The project offers exceptional transparency into its workings, allowing organizations using its code to plan effectively for the future.
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The culture of the FreeBSD project, carried over from the Computer Science Research Group at The University of California, Berkeley [McKu1999-1], fosters high-quality work. Some features in FreeBSD define the state of the art.
[GoldGab2005] examines the business reasons for using open-source in greater detail. For organizations, the benefits of using FreeBSD components in their products include a shorter time to market, lower development costs and lower development risks.
2.1 Building with FreeBSD
Here are a few ways organizations have used FreeBSD:
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As an upstream source for tested code for libraries and utilities.
By being “downstream” of the project, organizations leverage the new features, bug fixes and testing that the upstream code receives.
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As an embedded OS (for example, for an OEM router and firewall device). In this model, organizations use a customized FreeBSD kernel and application program set along with a proprietary management layer for their device. OEMs benefit from new hardware support being added by the FreeBSD project upstream, and from the testing that the base system receives.
FreeBSD ships with a self-hosting development environment that allows easy creation of such configurations.
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As a Unix compatible environment for the management functions of high-end storage and networking devices, running on a separate processor “blade”.
FreeBSD provides the tools for creating dedicated OS and application program images. Its implementation of a BSD unix API is mature and tested. FreeBSD can also provide a stable cross-development environment for the other components of the high-end device.
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As a vehicle to get widespread testing and support from a worldwide team of developers for non-critical “intellectual property”.
In this model, organizations contribute useful infrastructural frameworks to the FreeBSD project (for example, see netgraph(3)). The widespread exposure that the code gets helps to quickly identify performance issues and bugs. The involvement of top-notch developers also leads to useful extensions to the infrastructure that the contributing organization also benefits from.
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As a development environment supporting cross-development for embedded OSes like RTEMS and eCOS.
There are many full-fledged development environments in the 20,000-strong collection of applications ported and packaged with FreeBSD.
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As a way to support a Unix-like API in an otherwise proprietary OS, increasing its palatability for application developers.
Here parts of FreeBSD's kernel and application programs are “ported” to run alongside other tasks in the proprietary OS. The availability of a stable and well tested Unix™ API implementation can reduce the effort needed to port popular applications to the proprietary OS. As FreeBSD ships with high-quality documentation for its internals and has effective vulnerability management and release engineering processes, the costs of keeping upto-date are kept low.
2.2 Technologies
There are a large number of technologies supported by the FreeBSD project. A selection of these are listed below:
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A complete system that can cross-host itself for the following architectures: alpha (up to FreeBSD version 6.X), amd64, ia64, i386, sparc64, powerpc (see build(7)).
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Support for the following technologies, protocols and standards: ATA, ATAPI, ATM, Bluetooth™, CAM, CardBus™, DHCP, DNS, EISA™, Ethernet™, FDDI, Fibre Channel, GPIB, IEEE 1394, IPv4, IPv6, IPSEC, IPX™, ISDN, MAC, NIS, NFS, OpenSSH, OPIE, PAM, PCI™, PCMCIA, POSIX™, PnP, RAID, RPC, SATA, SCSI, SMB, TCP, USB, VESA, VLAN, VLB, WebNFS™.
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A modular symmetric multiprocessing capable kernel, with loadable kernel modules and a flexible and easy to use configuration system.
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Support for emulation of Linux™ and SVR4 binaries at near machine speeds. Support for binary Windows™ (NDIS) network drivers.
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Libraries for many programming tasks: archivers, FTP and HTTP support, thread support, in addition to a full POSIX like programming environment.
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Advanced security features: Mandatory Access Control (mac(9)), jails (jail(2)), ACLs, and in-kernel cryptographic device support.
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Advanced networking features: firewall-ing, QoS management, high-performance TCP/IP networking with support for many advanced features.
FreeBSD's in-kernel Netgraph (netgraph(4)) framework allows kernel networking modules to be connected together in flexible ways.
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Support for advanced storage technologies: Fibre Channel, SCSI, software and hardware RAID, ATA and SATA.
FreeBSD supports a number of filesystems, and its native UFS2 filesystem supports soft updates, snapshots and very large filesystem sizes (16TB per filesystem) [McKu1999].
FreeBSD's in-kernel GEOM (geom(4)) framework allows kernel storage modules to be composed in flexible ways.
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Over 20,000 ported applications, both commercial and open-source, managed via the FreeBSD ports collection.
2.3 Organizational Structure
FreeBSD's organizational structure is non-hierarchical.
There are essentially two kinds of contributors to FreeBSD, general users of FreeBSD, and developers with write access (known as committers in the jargon) to the source base.
There are many thousands of contributors in the first group; the vast majority of contributions to FreeBSD come from individuals in this group. Commit rights (write access) to the repository are granted to individuals who contribute consistently to the project. Commit rights come with additional responsibilities, and new committers are assigned mentors to help them learn the ropes.
Conflict resolution is performed by a nine member “Core Team” that is elected from the group of committers.
FreeBSD does not have “corporate” committers. Individual committers are required to take responsibility for the changes they introduce to the code. The FreeBSD Committer's guide [ComGuide] documents the rules and responsibilities for committers.
FreeBSD's project model is examined in detail in [Nik2005].
2.4 FreeBSD Release Engineering Processes
FreeBSD's release engineering processes play a major role in ensuring that its released versions are of a high quality. At any point of time, FreeBSD's volunteers support multiple code lines (Figure 2):
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New features and disruptive code enters on the development branch, also known as the -CURRENT branch.
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-STABLE branches are code lines that are branched from HEAD at regular intervals. Only tested code is allowed onto a -STABLE branch. New features are allowed once they have been tested and stabilized in the -CURRENT branch.
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-RELEASE branches are maintained by the FreeBSD security team. Only bug fixes for critical issues are permitted onto -RELEASE branches.
Code lines are kept alive for as long as there is user and developer interest in them.
Machine architectures are grouped into “tiers”; Tier 1 architectures are fully supported by the project's release engineering and security teams, Tier 2 architectures are supported on a best effort basis, and experimental architectures comprise Tier 3. The list of supported architectures is part of the FreeBSD documentation collection.
The release engineering team publishes a road map for future releases of FreeBSD on the project's web site. The dates laid down in the road map are not deadlines; FreeBSD is released when its code and documentation are ready.
FreeBSD's release engineering processes are described in [RelEngDoc].