DragonFly BSD
Encyclopedia
DragonFly BSD is a free
Unix-like
operating system created as a fork of FreeBSD
4.8. Matthew Dillon, an Amiga
developer in the late 1980s and early 1990s and a FreeBSD developer between 1994 and 2003, began work on DragonFly BSD in June 2003 and announced it on the FreeBSD mailing lists on July 16, 2003.
Dillon started DragonFly in the belief that the methods and techniques being adopted for threading and symmetric multiprocessing
in FreeBSD 5 would lead to poor system performance and would cause maintenance difficulties. He sought to correct these suspected problems within the FreeBSD project. Due to ongoing conflicts with other FreeBSD developers over the implementation of his ideas, and other reasons, his ability to directly change the FreeBSD code was eventually revoked. Despite this, the DragonFly BSD and FreeBSD projects still work together contributing bug fixes, driver updates and other system improvements to each other.
Intended to be the logical continuation of the FreeBSD 4.x series, DragonFly's development has diverged significantly from FreeBSD's, including a new Light Weight Kernel Threads
implementation (LWKT) and a light weight ports/messaging system. Many concepts planned for DragonFly were inspired by AmigaOS
.
, containing features of both monolithic and microkernels, such as the message passing capability of microkernels enabling larger portions of the OS to benefit from protected memory, as well as retaining the speed of monolithic kernels for certain critical tasks. The messaging subsystem being developed is similar to those found in microkernels such as Mach, though it is less complex by design. DragonFly's messaging subsystem has the ability to act in either a synchronous or asynchronous fashion, and attempts to use this capability to achieve the best performance possible in any given situation.
There is progress being made to provide both device input/output
(I/O) and virtual file system
(VFS) messaging capabilities that will allow the remainder of the project goals to be met. The new infrastructure will allow many parts of the kernel to be migrated out into userland, whereby they will be more easily debugged as they will be smaller, isolated programs, instead of being small parts entwined in a larger chunk of code. The migration of select kernel code into userspace has the additional benefit of making the system more robust; if a userspace driver crashes, it will not crash the kernel.
System call
s are being split into userland and kernel versions, as well as being encapsulated into messages. This will help reduce the size and complexity of the kernel by moving variants of standard system calls into a userland compatibility layer
, as well as help maintain forwards and backwards compatibility between DragonFly versions. Linux
and other Unix-like
OS compatibility code is being migrated out similarly. Multiple instances of the native userland compatibility layer created in jails
could give DragonFly functionality similar to that found in UML
. Unlike UML (which is essentially a port of Linux to itself as if the host kernel was a different hardware platform), DragonFly's virtualization doesn't require special drivers to communicate with the real hardware on the computer.
by design, and each processor has its own LWKT scheduler. Threads are never preemptively switched from one processor to another; they are only migrated by the passing of an IPI
message between the CPUs involved. Inter-processor thread scheduling is also accomplished by sending asynchronous IPI messages. One advantage to this clean compartmentalization of the threading subsystem is that the processors' on-board caches
in SMP systems do not contain duplicated data, allowing for higher performance by giving each processor in the system the ability to use its own cache to store different things to work on.
The LWKT subsystem is being employed to partition work among multiple kernel threads (for example in the networking code; one thread per protocol per processor), reducing contention by removing the need to share certain resources among various kernel tasks. This thread partitioning implementation of CPU localization algorithms is arguably the key differentiating feature of DragonFly's design.
so that threads or processes do not attempt to modify the same resource at the same time. In order to prevent multiple threads from accessing or modifying a shared resource simultaneously, DragonFly employs critical sections, and serializing tokens to prevent concurrent access. Whereas both Linux and FreeBSD 5 employ fine-grained mutex models to achieve higher performance on multiprocessor
systems, DragonFly does not. Until recently, DragonFly also employed SPLs, but these were replaced with critical sections.
Much of the system's core, including the LWKT subsystem, the IPI messaging subsystem and the new kernel memory allocator, are lockless, meaning that they work without using mutexes, and operate on a per-CPU basis. Critical sections are used to protect against local interrupts and operate on a per-CPU basis, guaranteeing that a thread currently being executed will not be preempted.
Serializing tokens
are used to prevent concurrent accesses from other CPUs and may be held simultaneously by multiple threads, ensuring that only one of those threads is running at any given time. Blocked or sleeping threads therefore do not prevent other threads from accessing the shared resource unlike a thread that is holding a mutex. Among other things, the use of serializing tokens prevents many of the situations that could result in deadlock
s and priority inversion
s when using mutexes, as well as greatly simplifying the design and implementation of a many-step procedure that would require a resource to be shared among multiple threads. The serializing token code is evolving into something quite similar to the "Read-copy-update
" feature now available in Linux. Unlike Linux's current RCU implementation, DragonFly's is being implemented such that only processors competing for the same token are affected rather than all processors in the computer.
support, DragonFly BSD limits its supported platforms to x86 and x86-64
, with both single processor and SMP
models. Since version 1.10, DragonFly supports 1:1 userland threading (one kernel thread for every userland thread), which is seen as a relatively simple and easy to maintain solution. Inherited from FreeBSD, DragonFly also supports SMP multi-threading imported.
DragonFly uses SFBUFs (Super-Fast BUFfers) and MSFBUFs (Multi-SFBUFs). A SFBUF is used to manage ephemeral single-page mappings and cache them when appropriate. They are used for retrieving a reference to data that is held by a single VM page. This simple, yet powerful, abstraction gives a broad number of abilities, such as zero-copy
achieved in the sendfile(2) system call.
SFBUFs are used in numerous parts of the kernel, such as the Vnode Object Pager and the PIPE
subsystems (indirectly via XIOs) for supporting high-bandwidth transfers. An SFBUF can only be used for a single VM page; MSFBUFs are used for managing ephemeral mappings of multiple-pages.
The SFBUF concept was devised by David Greenman of the FreeBSD Project when he wrote the sendfile(2) system call; it was later revised by Dr. Alan L. Cox and Matthew Dillon. MSFBUFs were designed by Hiten Pandya and Matthew Dillon.
system for third party software, but since the 1.4 release, NetBSD's pkgsrc
is the official package management system
. With
Still
-based package management system capable of dealing with multiple packages versions.
(commonly referred as CARP) to was finished in March 2007. As of 2011, CARP support is integrated into DragonFly BSD.
, which is typically the default file system
on BSDs, DragonFly BSD supports HAMMER file system. It was developed specifically for DragonFly BSD to provide a feature-rich yet better designed analogue of then increasingly popular ZFS
.
HAMMER supports configurable file system history, snapshot
s, checksum
ming, data deduplication
and other features typical for file systems of its kind. Though its performance is currently beyond the similar file systems like ZFS or btrfs
, it is recognised as an interesting and perspective option.
, which dynamically adds and removed device nodes, allows accessing devices by connection paths, recognises drives by serial number
s and removes the need for pre-populated
'2009 project.
-style resident applications feature: it takes a snapshot of a large, dynamically linked program's virtual memory space after loading, allowing future instances of the program to start much more quickly than it otherwise would have. This replaces the prelinking capability that was being worked on earlier in the project's history, as the resident support is much more efficient. Large programs like those found in KDE
with many shared libraries
will benefit the most from this support.
and a new ATA driver framework from FreeBSD 4. As the number of DragonFly developers is currently small, with most of them focused on implementing basic functionality, device driver
s are being kept mostly in sync with FreeBSD 5.x, the branch of FreeBSD where all new drivers are being written. The DragonFly developers are slowly moving toward using the "busdma
" APIs, which will help to make the system easier to port to new architectures, but it is not a major focus at this time.
As with FreeBSD
and OpenBSD
, the developers of DragonFly BSD are slowly replacing K&R style C
code with more modern, ANSI
equivalents. Similar to other operating systems, DragonFly's version of the GNU Compiler Collection
has an enhancement called the Stack-Smashing Protector (ProPolice) enabled by default, providing some additional protection against buffer overflow
based attacks. It should be noted that , the kernel is no longer built with this protection by default.
Being a derivative of FreeBSD, DragonFly has inherited an easy-to-use integrated build system that can rebuild the entire base system from source with only a few commands. The DragonFly developers use the Git
version control system to manage changes to the DragonFly source code
. Unlike its parent FreeBSD, DragonFly has both stable and unstable releases in a single source tree, due to a smaller developer base.
Like the other BSD kernels (and those of most modern operating systems), DragonFly employs a built-in kernel debugger
to help the developers find kernel bugs. Furthermore, , a debug kernel, which makes bug reports more useful for tracking down kernel-related problems, is installed by default, at the expense of a relatively small quantity of disk space. When a new kernel is installed, the backup copy of the previous kernel and its modules are stripped of their debugging symbols to further minimize disk space usage.
and Live USB
(full X11
flavour available) that boots into a complete DragonFly system. It includes the base system and a complete set of manual pages, and may include source code and useful packages in future versions. The advantage of this is that with a single CD you can install the software onto a computer, use a full set of tools to repair a damaged installation, or demonstrate the capabilities of the system without installing it. Daily snapshots for both i386 and x86-64 architectures are available from the master site for those who want to install the most recent versions of DragonFly without building from source.
Like the other free open source BSDs, DragonFly is distributed under the terms of the modern version of the BSD license.
The userland VFS system is a prerequisite of a number of desired features to be incorporated into DragonFly. Dillon envisions a new package management system based at least in part, on VFS environments which give the packages the environment they expect to be in, independent of the larger filesystem environment and its quirks. In addition to system call message filtering, VFS environments are also to play a role in future security mechanisms, by restricting users or processes to their own isolated environments.
A new journaling layer is being developed for DragonFly for the purpose of transparently backing up entire filesystems in real-time, securely over a network. What remains to be done is the ability to restore a filesystem to a previous state, as well as general stability enhancements. This differs from traditional meta-data journaling filesystems in two ways: (1) it will work with all supported filesystems, as it is implemented in the VFS layer instead of in the individual filesystem drivers, and (2) it will back up all of the data contained on a disk or partition, instead of just meta-data, allowing for the recovery of even the most damaged of installations.
While working on the journaling code, Dillon realized that the userland VFS he envisioned may be closer than he initially thought, though it is still some ways off.
, and the light weight ports/messaging system will help to provide this capability. Security settings aside, there is technically no difference between messages created locally or on another computer over a network. Achieving this single-system image
capability transparently will be a big job, and will take quite some time to properly implement, even with the new foundation fully in place. While some of the short term goals of the project will be completed in months, other features may take years to complete. SSI clustering will have applications in scientific computing.
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating system created as a fork of FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
4.8. Matthew Dillon, an Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
developer in the late 1980s and early 1990s and a FreeBSD developer between 1994 and 2003, began work on DragonFly BSD in June 2003 and announced it on the FreeBSD mailing lists on July 16, 2003.
Dillon started DragonFly in the belief that the methods and techniques being adopted for threading and symmetric multiprocessing
Symmetric multiprocessing
In computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
in FreeBSD 5 would lead to poor system performance and would cause maintenance difficulties. He sought to correct these suspected problems within the FreeBSD project. Due to ongoing conflicts with other FreeBSD developers over the implementation of his ideas, and other reasons, his ability to directly change the FreeBSD code was eventually revoked. Despite this, the DragonFly BSD and FreeBSD projects still work together contributing bug fixes, driver updates and other system improvements to each other.
Intended to be the logical continuation of the FreeBSD 4.x series, DragonFly's development has diverged significantly from FreeBSD's, including a new Light Weight Kernel Threads
Light Weight Kernel Threads
Light Weight Kernel Threads or LWKT is a term from computer science in general and in DragonFlyBSD in particular. LWKTs differ from normal kernel threads in that they can preempt normal kernel threads. According to Matt Dillon, DragonFlyBSD creator:...
implementation (LWKT) and a light weight ports/messaging system. Many concepts planned for DragonFly were inspired by AmigaOS
AmigaOS
AmigaOS is the default native operating system of the Amiga personal computer. It was developed first by Commodore International, and initially introduced in 1985 with the Amiga 1000...
.
Kernel
Like most modern kernels, DragonFly is a hybridHybrid kernel
A hybrid kernel is a kernel architecture based on combining aspects of microkernel and monolithic kernel architectures used in computer operating systems. The category is controversial due to the similarity to monolithic kernel; the term has been dismissed by Linus Torvalds as simple marketing...
, containing features of both monolithic and microkernels, such as the message passing capability of microkernels enabling larger portions of the OS to benefit from protected memory, as well as retaining the speed of monolithic kernels for certain critical tasks. The messaging subsystem being developed is similar to those found in microkernels such as Mach, though it is less complex by design. DragonFly's messaging subsystem has the ability to act in either a synchronous or asynchronous fashion, and attempts to use this capability to achieve the best performance possible in any given situation.
There is progress being made to provide both device input/output
Input/output
In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
(I/O) and virtual file system
Virtual file system
A virtual file system or virtual filesystem switch is an abstraction layer on top of a more concrete file system. The purpose of a VFS is to allow client applications to access different types of concrete file systems in a uniform way...
(VFS) messaging capabilities that will allow the remainder of the project goals to be met. The new infrastructure will allow many parts of the kernel to be migrated out into userland, whereby they will be more easily debugged as they will be smaller, isolated programs, instead of being small parts entwined in a larger chunk of code. The migration of select kernel code into userspace has the additional benefit of making the system more robust; if a userspace driver crashes, it will not crash the kernel.
System call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
s are being split into userland and kernel versions, as well as being encapsulated into messages. This will help reduce the size and complexity of the kernel by moving variants of standard system calls into a userland compatibility layer
Compatibility layer
A compatibility layer is a term that refers to components that allow for non-native support of components.In software engineering, a compatibility layer allows binaries for a legacy or foreign system to run on a host system. This translates system calls for the foreign system into native system...
, as well as help maintain forwards and backwards compatibility between DragonFly versions. Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
and other Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
OS compatibility code is being migrated out similarly. Multiple instances of the native userland compatibility layer created in jails
FreeBSD Jail
The FreeBSD jail mechanism is an implementation of operating system-level virtualization that allows administrators to partition a FreeBSD-based computer system into several independent mini-systems called jails....
could give DragonFly functionality similar to that found in UML
User-mode Linux
User-mode Linux enables multiple virtual Linux systems to run as an application within a normal Linux system...
. Unlike UML (which is essentially a port of Linux to itself as if the host kernel was a different hardware platform), DragonFly's virtualization doesn't require special drivers to communicate with the real hardware on the computer.
CPU localization
In DragonFly, threads are locked to CPUsCentral processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
by design, and each processor has its own LWKT scheduler. Threads are never preemptively switched from one processor to another; they are only migrated by the passing of an IPI
Inter-Processor Interrupt
An inter-processor interrupt is a special type of interrupt by which one processor may interrupt another processor in a multiprocessor system. IPIs are typically used to implement a cache coherency synchronization point.- Windows :...
message between the CPUs involved. Inter-processor thread scheduling is also accomplished by sending asynchronous IPI messages. One advantage to this clean compartmentalization of the threading subsystem is that the processors' on-board caches
CPU cache
A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations...
in SMP systems do not contain duplicated data, allowing for higher performance by giving each processor in the system the ability to use its own cache to store different things to work on.
The LWKT subsystem is being employed to partition work among multiple kernel threads (for example in the networking code; one thread per protocol per processor), reducing contention by removing the need to share certain resources among various kernel tasks. This thread partitioning implementation of CPU localization algorithms is arguably the key differentiating feature of DragonFly's design.
Protecting shared resources
In order to run safely on multiprocessor machines, access to shared resources (files, data structures etc.) must be serializedSerialization
In computer science, in the context of data storage and transmission, serialization is the process of converting a data structure or object state into a format that can be stored and "resurrected" later in the same or another computer environment...
so that threads or processes do not attempt to modify the same resource at the same time. In order to prevent multiple threads from accessing or modifying a shared resource simultaneously, DragonFly employs critical sections, and serializing tokens to prevent concurrent access. Whereas both Linux and FreeBSD 5 employ fine-grained mutex models to achieve higher performance on multiprocessor
Multiprocessor
Computer system having two or more processing units each sharing main memory and peripherals, in order to simultaneously process programs.Sometimes the term Multiprocessor is confused with the term Multiprocessing....
systems, DragonFly does not. Until recently, DragonFly also employed SPLs, but these were replaced with critical sections.
Much of the system's core, including the LWKT subsystem, the IPI messaging subsystem and the new kernel memory allocator, are lockless, meaning that they work without using mutexes, and operate on a per-CPU basis. Critical sections are used to protect against local interrupts and operate on a per-CPU basis, guaranteeing that a thread currently being executed will not be preempted.
Serializing tokens
Serializing tokens
In computer science, serializing tokens are a concept in concurrency control arising from the ongoing development of DragonFly BSD. According to Matthew Dillon, they are most akin to SPLs, except a token works across multiple CPUs while SPLs only work within a single CPU's domain.Serializing...
are used to prevent concurrent accesses from other CPUs and may be held simultaneously by multiple threads, ensuring that only one of those threads is running at any given time. Blocked or sleeping threads therefore do not prevent other threads from accessing the shared resource unlike a thread that is holding a mutex. Among other things, the use of serializing tokens prevents many of the situations that could result in deadlock
Deadlock
A deadlock is a situation where in two or more competing actions are each waiting for the other to finish, and thus neither ever does. It is often seen in a paradox like the "chicken or the egg"...
s and priority inversion
Priority inversion
In computer science, priority inversion is a problematic scenario in scheduling when a higher priority task is indirectly preempted by a lower priority task effectively "inverting" the relative priorities of the two tasks....
s when using mutexes, as well as greatly simplifying the design and implementation of a many-step procedure that would require a resource to be shared among multiple threads. The serializing token code is evolving into something quite similar to the "Read-copy-update
Read-copy-update
In computer operating systems, read-copy-update is a synchronization mechanism implementing a kind of mutual exclusionPlease note that RCU does not implement mutual exclusion in the conventional sense: RCU readers can and do run concurrently with RCU updates...
" feature now available in Linux. Unlike Linux's current RCU implementation, DragonFly's is being implemented such that only processors competing for the same token are affected rather than all processors in the computer.
Threading
As support for multiple processor architectures complicates SMPSymmetric multiprocessing
In computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
support, DragonFly BSD limits its supported platforms to x86 and x86-64
X86-64
x86-64 is an extension of the x86 instruction set. It supports vastly larger virtual and physical address spaces than are possible on x86, thereby allowing programmers to conveniently work with much larger data sets. x86-64 also provides 64-bit general purpose registers and numerous other...
, with both single processor and SMP
Symmetric multiprocessing
In computing, symmetric multiprocessing involves a multiprocessor computer hardware architecture where two or more identical processors are connected to a single shared main memory and are controlled by a single OS instance. Most common multiprocessor systems today use an SMP architecture...
models. Since version 1.10, DragonFly supports 1:1 userland threading (one kernel thread for every userland thread), which is seen as a relatively simple and easy to maintain solution. Inherited from FreeBSD, DragonFly also supports SMP multi-threading imported.
Virtual kernel
Since release 1.8 DragonFly has a new virtualization mechanism similar to UML, allowing to run another kernel in the userland. The virtual kernel is run in completely isolated environment with emulated network and storage interfaces, thus simplifying testing the drivers, kernel subsystems and clustering features.Memory management
Early on in its development, DragonFly acquired a slab allocator, which replaced the aging FreeBSD 4 kernel memory allocator. The new slab allocator requires neither mutexes nor blocking operations for memory assignment tasks and, unlike the code it replaced, is multiprocessor safe. It was eventually ported to be utilized outside the kernel in a replacement to the old userland malloc implementation.DragonFly uses SFBUFs (Super-Fast BUFfers) and MSFBUFs (Multi-SFBUFs). A SFBUF is used to manage ephemeral single-page mappings and cache them when appropriate. They are used for retrieving a reference to data that is held by a single VM page. This simple, yet powerful, abstraction gives a broad number of abilities, such as zero-copy
Zero-copy
"Zero-copy" describes computer operations in which the CPU does not perform the task of copying data from one memory area to another. This is most often used to save on processing power and memory use when sending files over a network.- Principle :...
achieved in the sendfile(2) system call.
SFBUFs are used in numerous parts of the kernel, such as the Vnode Object Pager and the PIPE
Pipeline (Unix)
In Unix-like computer operating systems , a pipeline is the original software pipeline: a set of processes chained by their standard streams, so that the output of each process feeds directly as input to the next one. Each connection is implemented by an anonymous pipe...
subsystems (indirectly via XIOs) for supporting high-bandwidth transfers. An SFBUF can only be used for a single VM page; MSFBUFs are used for managing ephemeral mappings of multiple-pages.
The SFBUF concept was devised by David Greenman of the FreeBSD Project when he wrote the sendfile(2) system call; it was later revised by Dr. Alan L. Cox and Matthew Dillon. MSFBUFs were designed by Hiten Pandya and Matthew Dillon.
Package management
DragonFly previously used FreeBSD's PortsFreeBSD Ports
The FreeBSD Ports collection is a package management system for the FreeBSD operating system, providing an easy and consistent way of installing software packages. As of October 2011, there are over 22,700 ports available in the collection...
system for third party software, but since the 1.4 release, NetBSD's pkgsrc
Pkgsrc
pkgsrc is a package management system for Unix-like operating systems. It was forked from the FreeBSD ports collection in 1997 as the primary package management system for NetBSD. Since then it has evolved independently: in 1999, support for Solaris was added, later followed by support for other...
is the official package management system
Package management system
In software, a package management system, also called package manager, is a collection of software tools to automate the process of installing, upgrading, configuring, and removing software packages for a computer's operating system in a consistent manner...
. With
pkgsrc, the DragonFly developers are largely freed of having to maintain a large number of third party programs while still having access to up to date applications. The pkgsrc developers also benefit from this arrangement as it helps to ensure the portability of the code.Still
pkgsrc is seen as a temporary solution. One of the project stated goals is an advanced VFSVirtual file system
A virtual file system or virtual filesystem switch is an abstraction layer on top of a more concrete file system. The purpose of a VFS is to allow client applications to access different types of concrete file systems in a uniform way...
-based package management system capable of dealing with multiple packages versions.
CARP support
The initial implementation of Common Address Redundancy ProtocolCommon Address Redundancy Protocol
The Common Address Redundancy Protocol or CARP is a protocol which allows multiple hosts on the same local network to share a set of IP addresses. Its primary purpose is to provide failover redundancy, especially when used with firewalls and routers. In some configurations CARP can also provide...
(commonly referred as CARP) to was finished in March 2007. As of 2011, CARP support is integrated into DragonFly BSD.
HAMMER file system
Alongside with Unix File SystemUnix File System
The Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
, which is typically the default file system
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
on BSDs, DragonFly BSD supports HAMMER file system. It was developed specifically for DragonFly BSD to provide a feature-rich yet better designed analogue of then increasingly popular ZFS
ZFS
In computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
.
HAMMER supports configurable file system history, snapshot
Snapshot (computer storage)
In computer systems, a snapshot is the state of a system at a particular point in time. The term was coined as an analogy to that in photography. It can refer to an actual copy of the state of a system or to a capability provided by certain systems....
s, checksum
Checksum
A checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...
ming, data deduplication
Data deduplication
In computing, data deduplication is a specialized data compression technique for eliminating coarse-grained redundant data. The technique is used to improve storage utilization and can also be applied to network data transfers to reduce the number of bytes that must be sent across a link...
and other features typical for file systems of its kind. Though its performance is currently beyond the similar file systems like ZFS or btrfs
Btrfs
Btrfs is a GPL-licensed copy-on-write file system for Linux.Development began at Oracle Corporation in 2007....
, it is recognised as an interesting and perspective option.
devfs
In 2007 DragonFly BSD received a new device file systemDevice file system
In Unix-like operating systems, a device file or special file is an interface for a device driver that appears in a file system as if it were an ordinary file. There are also special device files in MS-DOS and Microsoft Windows...
, which dynamically adds and removed device nodes, allows accessing devices by connection paths, recognises drives by serial number
Serial number
A serial number is a unique number assigned for identification which varies from its successor or predecessor by a fixed discrete integer value...
s and removes the need for pre-populated
/dev file system hierarchy. It was implemented as a Google Summer of CodeGoogle Summer of Code
The Google Summer of Code is an annual program, first held from May to August 2005, in which Google awards stipends to hundreds of students who successfully complete a requested free or open-source software coding project during the summer...
'2009 project.
Application snapshots
DragonFly BSD supports AmigaAmiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...
-style resident applications feature: it takes a snapshot of a large, dynamically linked program's virtual memory space after loading, allowing future instances of the program to start much more quickly than it otherwise would have. This replaces the prelinking capability that was being worked on earlier in the project's history, as the resident support is much more efficient. Large programs like those found in KDE
KDE
KDE is an international free software community producing an integrated set of cross-platform applications designed to run on Linux, FreeBSD, Microsoft Windows, Solaris and Mac OS X systems...
with many shared libraries
Library (computer science)
In computer science, a library is a collection of resources used to develop software. These may include pre-written code and subroutines, classes, values or type specifications....
will benefit the most from this support.
Development and distribution
DragonFly forked from FreeBSD 4.8 and imports features and bug fixes from FreeBSD 4 and 5 where appropriate, such as ACPIAdvanced Configuration and Power Interface
In computing, the Advanced Configuration and Power Interface specification provides an open standard for device configuration and power management by the operating system....
and a new ATA driver framework from FreeBSD 4. As the number of DragonFly developers is currently small, with most of them focused on implementing basic functionality, device driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s are being kept mostly in sync with FreeBSD 5.x, the branch of FreeBSD where all new drivers are being written. The DragonFly developers are slowly moving toward using the "busdma
Busdma
In computing, busdma is a set of application programming interfaces designed to help make device drivers less dependent on platform-specific code, thereby allowing the host operating system to be more easily ported to new computer hardware....
" APIs, which will help to make the system easier to port to new architectures, but it is not a major focus at this time.
As with FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
and OpenBSD
OpenBSD
OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
, the developers of DragonFly BSD are slowly replacing K&R style C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
code with more modern, ANSI
ANSI C
ANSI C refers to the family of successive standards published by the American National Standards Institute for the C programming language. Software developers writing in C are encouraged to conform to the standards, as doing so aids portability between compilers.-History and outlook:The first...
equivalents. Similar to other operating systems, DragonFly's version of the GNU Compiler Collection
GNU Compiler Collection
The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain...
has an enhancement called the Stack-Smashing Protector (ProPolice) enabled by default, providing some additional protection against buffer overflow
Buffer overflow
In computer security and programming, a buffer overflow, or buffer overrun, is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory. This is a special case of violation of memory safety....
based attacks. It should be noted that , the kernel is no longer built with this protection by default.
Being a derivative of FreeBSD, DragonFly has inherited an easy-to-use integrated build system that can rebuild the entire base system from source with only a few commands. The DragonFly developers use the Git
Git (software)
Git is a distributed revision control system with an emphasis on speed. Git was initially designed and developed by Linus Torvalds for Linux kernel development. Every Git working directory is a full-fledged repository with complete history and full revision tracking capabilities, not dependent on...
version control system to manage changes to the DragonFly source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
. Unlike its parent FreeBSD, DragonFly has both stable and unstable releases in a single source tree, due to a smaller developer base.
Like the other BSD kernels (and those of most modern operating systems), DragonFly employs a built-in kernel debugger
Kernel debugger
A kernel debugger is a debugger present in some kernels to ease debugging and kernel development by the kernel developers. A kernel debugger might be a stub implementing low-level operations, with a full-blown debugger such as gdb, running on another machine, sending commands to the stub over a...
to help the developers find kernel bugs. Furthermore, , a debug kernel, which makes bug reports more useful for tracking down kernel-related problems, is installed by default, at the expense of a relatively small quantity of disk space. When a new kernel is installed, the backup copy of the previous kernel and its modules are stripped of their debugging symbols to further minimize disk space usage.
Distribution media
The operating system is distributed as a Live CDLive CD
A live CD, live DVD, or live disc is a CD or DVD containing a bootable computer operating system. Live CDs are unique in that they have the ability to run a complete, modern operating system on a computer lacking mutable secondary storage, such as a hard disk drive...
and Live USB
Live USB
A live USB is a USB flash drive or a USB external hard disk drive containing a full operating system that can be booted. Live USBs are closely related to live CDs, but sometimes have the ability to persistently save settings and permanently install software packages back onto the USB device...
(full X11
X Window System
The X window system is a computer software system and network protocol that provides a basis for graphical user interfaces and rich input device capability for networked computers...
flavour available) that boots into a complete DragonFly system. It includes the base system and a complete set of manual pages, and may include source code and useful packages in future versions. The advantage of this is that with a single CD you can install the software onto a computer, use a full set of tools to repair a damaged installation, or demonstrate the capabilities of the system without installing it. Daily snapshots for both i386 and x86-64 architectures are available from the master site for those who want to install the most recent versions of DragonFly without building from source.
Like the other free open source BSDs, DragonFly is distributed under the terms of the modern version of the BSD license.
Release history
| Version | Date | Changes |
|---|---|---|
| 2.10 |
|
|
| 2.8 |
FreeBSD FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant... Logical volume management In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes... Dm-crypt dm-crypt is a transparent disk encryption subsystem in Linux kernel versions 2.6 and later and in DragonFly BSD. It is part of the device mapper infrastructure, and uses cryptographic routines from the kernel's Crypto API... Giant lock In operating systems, a giant lock, also known as a big-lock or kernel-lock, is a lock which may be used in the kernel to provide the concurrency control required by symmetric multiprocessing systems.... usage |
|
| 2.6 |
TMPFS tmpfs is a common name for a temporary file storage facility on many Unix-like operating systems. It is intended to appear as a mounted file system, but stored in volatile memory instead of a persistent storage device... ported from NetBSD |
|
| 2.4 |
|
|
| 2.2 |
Live USB A live USB is a USB flash drive or a USB external hard disk drive containing a full operating system that can be booted. Live USBs are closely related to live CDs, but sometimes have the ability to persistently save settings and permanently install software packages back onto the USB device... |
|
| 2.0 |
|
|
| 1.12 |
Bluetooth Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security... stack Intel 80386 The Intel 80386, also known as the i386, or just 386, was a 32-bit microprocessor introduced by Intel in 1985. The first versions had 275,000 transistors and were used as the central processing unit of many workstations and high-end personal computers of the time... CPU dropped X86-64 x86-64 is an extension of the x86 instruction set. It supports vastly larger virtual and physical address spaces than are possible on x86, thereby allowing programmers to conveniently work with much larger data sets. x86-64 also provides 64-bit general purpose registers and numerous other... support (not functional) |
|
| 1.10 |
Advanced Host Controller Interface The Advanced Host Controller Interface is a technical standard defined by Intel that specifies the operation of Serial ATA host bus adapters in a non-implementation-specific manner.... support GUID Partition Table In computer hardware, GUID Partition Table is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface standard , it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict... support |
|
| 1.8 |
User-mode Linux User-mode Linux enables multiple virtual Linux systems to run as an application within a normal Linux system... or KVM KVM KVM can mean:* K. V. Mahadevan, South Indian music composer* Kalamazoo Valley Museum, a museum in Kalamazoo, Michigan* Kheti Virasat Mission, a farmers' movement in Punjab* KV Mechelen, a Belgian football club... ) |
|
| 1.6 |
IEEE 802.11 IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent... framework refactored |
|
| 1.4 |
GNU Compiler Collection The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain... 3.4 pkgsrc used by defaultCitrus Project The CITRUS project aims to implement a complete multilingual programming environment for BSD-based operating systems... imported from the NetBSD |
|
| 1.2 |
ALTQ ALTQ is an ALTernate Queueing framework for BSD. ALTQ provides queueing disciplines and other QoS related components required to realize resource-sharing and Quality of Service. It is most commonly implemented on BSD-based routers... and PF PF - Computer science :* Page fault, a type of exception in computer programming* Page file, a file used as an extension for computer memory* PF , OpenBSD's stateful packet filter* PF keys, a type of function keys on old keyboards... Thread-local storage Thread-local storage is a computer programming method that uses static or global memory local to a thread.This is sometimes needed because normally all threads in a process share the same address space, which is sometimes undesirable... X Window System The X window system is a computer software system and network protocol that provides a basis for graphical user interfaces and rich input device capability for networked computers... support pkgsrc support |
|
| 1.0 |
Application checkpointing Checkpointing is a technique for inserting fault tolerance into computing systems. It basically consists of storing a snapshot of the current application state, and later on, use it for restarting the execution in case of failure.- Technique properties :... support. |
Userland VFS with journaling
Userland VFS - the ability to migrate filesystem drivers into userspace, will take a lot of work to accomplish. Some of this work is already complete, though there is still much to do. The namecache code has been extracted from and made independent of the VFS code, and converting the VFS code to DragonFly's threaded messaging interface is Matt's next major focus. This will be more difficult than converting the device I/O and system calls was, due to the fact that the VFS system inherited from FreeBSD uses a massively reentrant model.The userland VFS system is a prerequisite of a number of desired features to be incorporated into DragonFly. Dillon envisions a new package management system based at least in part, on VFS environments which give the packages the environment they expect to be in, independent of the larger filesystem environment and its quirks. In addition to system call message filtering, VFS environments are also to play a role in future security mechanisms, by restricting users or processes to their own isolated environments.
A new journaling layer is being developed for DragonFly for the purpose of transparently backing up entire filesystems in real-time, securely over a network. What remains to be done is the ability to restore a filesystem to a previous state, as well as general stability enhancements. This differs from traditional meta-data journaling filesystems in two ways: (1) it will work with all supported filesystems, as it is implemented in the VFS layer instead of in the individual filesystem drivers, and (2) it will back up all of the data contained on a disk or partition, instead of just meta-data, allowing for the recovery of even the most damaged of installations.
While working on the journaling code, Dillon realized that the userland VFS he envisioned may be closer than he initially thought, though it is still some ways off.
SSI clustering
Ultimately, Dillon wants DragonFly to natively enable secure anonymous system clustering over the InternetInternet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
, and the light weight ports/messaging system will help to provide this capability. Security settings aside, there is technically no difference between messages created locally or on another computer over a network. Achieving this single-system image
Single-system image
In distributed computing, a single system image cluster is a cluster of machines that appears to be one single system. The concept is often considered synonymous with that of a distributed operating system, but a single image may be presented for more limited purposes, just job scheduling for...
capability transparently will be a big job, and will take quite some time to properly implement, even with the new foundation fully in place. While some of the short term goals of the project will be completed in months, other features may take years to complete. SSI clustering will have applications in scientific computing.