This may sound noobish, especially as I'm ( as you may have guessed ) trying to write an Operating System. At the moment I'm stuck on trying to make a file system.
What I want is a similar file system as Linux Ubuntu which is EXT4 ( at least mine is ). I want to try and also either write it in C.
Any idea's on how I can go about this? And/or any tutorials that you might have found that may help me ( I have tried searching with no luck ) :L
Thanks in advance!
Jamie.
Really smart and experienced people who have studied this problem extensively have made bugs that ate users' data. The difference between a bug in the computation layer (e.g. a kernel crash) and a bug in the storage layer is that silently eating users' data is very bad - much worse than giving wrong answers in spreadsheets (excel is buggy yet popular) or intermittently sigfaulting while preserving data on disk (this is easily mitigated by frequent autosave).
Start by studying simpler designs, like the minix filesystems from the old operating systems book [1] (the same one Linus Torvalds started with, twenty years ago).
Like others said, ext2 without journaling, extents or ACLs is a better starting point than ext4. The source code for it is in the Linux kernel and in the e2fsprogs userspace tools package[2]. The format is well documented.
As for tutorials, consider who makes them and why they spend effort on this task. Tutorials are generally made by stakeholders in platforms to bring in new people to develop using that platform, to use the network effect to grow the platform and profit from being already-established actors in a larger ecosystem.
Do you see a business model in growing the number of people who implement their own incompatible buggy[3] file systems? Only if you sell software engineering degrees. So Microsoft only writes tutorials on how to use NTFS, not on how to implement it. Same for Sun and ZFS, Red Hat and Google with EXT2/3/4, SGI with XFS, IBM with JFS, Oracle with BTRFS, etc.
If you want education instead of training, you need to read books and study smart peoples' code they use in production, not look for tutorials.
http://en.wikipedia.org/wiki/Operating_Systems:_Design_and_Implementation
http://e2fsprogs.sourceforge.net/
How much use, in how many different use pattern with it see? Consider bugs discovered in production FSs after years of use on millions of computers. It is unlikely your code will be less buggy, even if you're as smart as Matthew Dillon.
Try looking at an existing implementation, like the one in Linux.
Related
I have been taking online courses on Operating systems, and I heard them say, that XV6 operating system can be used learn implementation of operating systems, thats all.But after I searched on the internet there aren't enough resources, which would get me started with it.
My question is, why should I use it,and how will it help me in understanding operating system.
(Please be gentle with information you throw at me, I am a newbie :( )
Any effort is appreciated
There are only 2 possibilities:
too complex to be useful for teaching
too simple to be useful for teaching
Things like fancy features/enhanced functionality, mitigating security issues, dealing with hardware bugs/errata, performance, scalability and supporting a very wide range of different hardware all increase the complexity of the code; and if you look at a real commercial OS (e.g. Linux maybe) that has to care about all of these things it's hard to learn about one thing (e.g. memory management) without all the complexity getting in the way and making it significantly harder to learn.
If you have a simple OS that does none of those things (no fancy features, no mitigation of security issues, ...) then it's much much easier to learn basic principles from it; but it also becomes impossible to use it to learn about fancy features, mitigating security issues, dealing with hardware bugs/errata, ...
The solution is to start with a simple OS (e.g. XV6) to learn the basics, then switch to a real OS later to learn everything else.
However; most OS courses at Universities are not intended to teach you about writing an OS. Instead they're intended to give you basic information about operating systems so that you can use that knowledge when writing application programs for existing operating systems. For that reason (and because there's time constraints) they only do the first part (with a simple OS like XV6) and then the course finishes.
1.XV6 is used for teaching in many universities.
2.It's also a tool OS for many program
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Does anyone know where I might find sample solutions written in C for low level / systems level applications? A really good website or book recommendation would be cool too.
I've learned some of the basics, but would like to see some code within the context of a real solution written in C, and specifically for a lower-level problem. Id' be interested in how C is used within the context of OS programming, for example. What are some areas where C is used for lower-level programming?
Thanks.
I would suggest you to study MINIX3 from Tanenbaum: http://www.minix3.org/
Its a microkernel architecture, and with his book ( http://vig.prenhall.com/catalog/academic/product/0,1144,0131429388,00.html ) it is really enlightning.
As of my opinion, studying the linux kernel is a bit hardcore for a start ;), and out of a academical point of view the microkernel architecture is superior to the monolithic kernel.
Furthermore, with only a few thousands lines of code, unlike the Linux Kernel, its consumable in a realistic timetable.
And its a real serious project, the European Union sponsored some Millions towards it as far as i am aware of. I think i remind him saying that in one of his talks.
And you have a X-Server running there, a gcc-toolchain etcpp.
Have fun :)
EDIT: As i read the comments, someone mentions the Ruby interpreter. Its written in a mixture of C and Ruby, and as far as it was mentioned in one episode of se-radio.net, it is really nice sourcecode. Though i have to admit, i havent looked into it myself. Might be worth the dig into it if you have some interest in Ruby too.
I'd suggest looking at some (for you) interesting open source projects written in C. For example, there's busybox, a piece of software that runs on embedded devices and has lots of smaller programs to study. You could, for example, take the source for the telnet client on one side and the corresponding RFC on the other. Or, for a steeper learning curve, you could also try studying the open source OSes, like the Linux kernel (here's the tree for browsing) or the BSDs. It's a lot more involved than busybox, but you can still find some parts that are fairly easy to understand if you're familiar with the context.
Studying the Linux kernel, maybe in conjunction with one of the several books on the kernel or device drivers would provide a wealth of material. Much of this is available free.
any or all of the books by W. Richard Stevens that walk though the implementation (TCP/IP Illustrated) or use (UNIX Network Programming) of the networking stack or his Advanced Programming in the UNIX Environment book.
If you have a leaning toward Windows there are several good books, even if they're quite old, including:
Programming Server-Side Applications for Microsoft Windows 2000 by Richter and Clark
Programming Applications for Microsoft Windows by Richter
I would suggest the following sources might be interesting r.e. Operating Systems from a learning perspective. Be aware there have been many advancements actually present in modern kernels:
The original linux code.
xv6. This is a simple unix OS that goes along with MIT's excellent OpenCourseWare course on Operating Systems.
Other ideas:
The current grub stage 1 bootloader isn't that complicated - it's pretty hard to be complicated with 512 bytes to play with.
The Linux kernel module guide gives you an introduction to building kernel modules. You could experiment with building custom, yet pointless, drivers that add say character devices to /dev/ or proc devices to /proc and work towards implementing something interesting. People have implemented web servers in kernel space...
If you want to experiment with Windows kernels, have a go with Native NT applications. I'd start with printing a pointless boot message, then move up to drivers.
Beyond that, it's hard to suggest where you might want to go. Systems level is a wide space.
In the context of low level programming, C and C++ are portable assembler. In many of the above spaces the standard library is either partially or totally missing and extra functionality may be implemented by existing parts of the system-level code you're modifying, so you have to be aware of the API functions available to you in any given space and what you need to implement yourself, as well as what your memory and processing requirements must be. For example, a bootloader written to the MBR has to use bios interrupts and starts in real (16-bit) mode. Those are the constraints of the hardware design. Likewise, functions like fopen() aren't available in kernel space since they wrap system calls - you'd need to use kernel specific constructs to achieve this if it really made sense to write a file from kernel space.
Both has bindings for C, both can play various formats.
Which one is more superior? in terms of simplicity, performance, overhead and memory footprint.
Also which one is better at handling multiple streams?
I have not programmed with either of those, but I believe that OpenAL has been designed to render and output multiple-channel audio for games, with real-time performance as a requirement.
libSoX is more for input and output from audio files, as well as for format conversions. There are lots of plugins but AFAIK it has not been designed for real-time audio output. It seems significantly simpler to use, though.
You might also want to have a look at libsndfile.
What exactly is it that you want to do?
While I have never used OpenAL, I've heard a lot of bad things about it that make it sound unprofessional and basically a dead end. From Wikipedia:
OpenAL was originally developed by Loki Software in order to help them in their business of porting Windows games to Linux. After the demise of Loki, the project was maintained for a time by the free software/open source community, and implemented on NVIDIA nForce sound cards and motherboards. It is now hosted (and largely developed) by Creative Technology with on-going support from Apple, Blue Ripple Sound, and free software/open source enthusiasts.
While the OpenAL charter says that there will be an "Architecture Review Board" (ARB) modeled on the OpenGL ARB, no such organization has ever been formed and the OpenAL specification is generally handled and discussed via email on its public mailing list.
Since 1.1, the implementation by Creative has turned proprietary, with the last releases in free licenses still accessible through the project's subversion. However, OpenAL Soft is a widespread Open Source alternative.
There was also an issue with it messing up the state of the calling application; I believe just linking it caused some global constructors to run before the invocation of main in a way that altered the program's initial environment, and broke some programs (MPlayer perhaps?). It's unclear to me whether this issue was ever fixed, but it screams bad library and I would be skeptical of ever trusting a library historically contained such abuses.
Once upon a time, a team of guys sat down and wrote an application in C, running on VMS on a VAX. It was a rather important undertaking and runs a reasonably important back-end operation at LargeCo. This whole shebang works so well that twenty-five years later it's still chugging along and doing it's thing.
Time passes and people retire and it so happens that the Last Man Standing has turned over the keys to a new generation who - we might imagine - are less than thrilled to find themselves caretakers of a system old enough to be their younger brother. Yet, as underwhelmed as they are by the idea of dealing with Ultra Legacy Systems, they can't justify the cost of replacing the venerable application.
LMS discovered that I habla unix and put this question to me. And since I habla unix but don't speak the C I shall summarize and put it to you. Long Story Short:
LMS wants to port LegacyApp, written in C. from VMS to unix. Resources? Any books he can read? People he can talk to?
The first question I'd need to ask is why, and I'd be leading the conversation in the direction of "Do you really need to port it off of VMS". There are a number of things worth mentioning about VMS:
-> VMS is still actively developed and maintained by HP. They just release V8.4 for Field Test last week (see http://h71000.www7.hp.com/openvmsft/).
-> VMS is available on new hardware; specifically HP's Integrity servers based on the Itanium processor.
-> VMS is also available on virtual platforms via the Charon Emulation products.
-> Popular estimates are that there are about 300,000 VMS systems still in active use today. LMS may be the last man at LargeCo, but he's far from the last man standing worldwide.
-> Lots of information out there, see openvms.org for example, to see lots of current information on VMS, all from current users.
OK - you still want to port off of VMS. How do you do it? Well, it depends on lots of stuff.
-> As others have said, how standard is the code? Chances are, not very. The more VMS-isms, the more difficult the job. 'nuff said.
-> What is the database? If it's Oracle, probably not too tough to move to Oracle on some other platform. If it's some sort of custom DB based on RMS index files, then you've got more work to do, you'll need to re-create that pseudo DB, or, understand it enough to replace it with some relational DB.
-> Besides C, what else is used to create the application? What's on the front end? DECforms? FMS? Is there a transaction engine, e.g. ACMS? RTR? These things will have a huge impact on the feasibility and effort required to port to UNIX.
-> What other products are involved? Are there any 3rd party libraries being used? Are there 3rd party products in use that are critical to the application or functionality?
-> Is this system clustered? If so why? You'll need to meet those same goals with the UNIX box.
-> There are companies out there that will help you do it, and claim to have tools to make it easier, but my experience is that these companies tend to be selling you more services than products (i.e. you need to hire them to use the tools. It'll be expensive).
The book UNIX for OpenVMS Users will give the VMS novice some help in understanding VMS, but, as the title says, the book is really intended for the opposite purpose.
Everything written on VMS uses lots of VMS specific stuff it was just so convenient.
There are a few companies that sell compatibility libs to make the port easier - they wont be cheap though, VMS tended to be used where reliability mattered more than cost.
The other option is to run openVMS on some modern hardware, possibly in a VM.
I am sure Brian has made his decision by now, but for my sins of working for many years in DEC OpenVMS language support (yes, some people had this dubious honour) the real question I would have asked a customer such as Brian is: is it a real-time application or not? If it is the former, then it would be heavily dependent on many VMS system services which would rule out a 'port' and indicate a re-write. If it were the latter then the frequency of VMS system services should (possibly) be limited and make a port viable.
The acid test for me, would be to SEARCH *.c "SYS$", "LIB$" i.e. to search all of the C source files for "SYS$" and "LIB$" tags which prefix VMS system services. If the count for these are in the 10s then a port is probably likely, between 10 and 100 makes it possibly likely, but over a 100 makes a successful port highly unlikely.
Hope this helps
You have several choices.
Get the OpenVMS source, and continue to maintain Open VMS as if it were a Linux distribution. Some folks don't mind keeping up with Linux distributions and OpenVMS distributions. It can be done.
Try to recompile the VMS C into Linux. This can be trivial if the C used only standard libraries. This can be very, very difficult if the C used a lot of VMS libraries.
Once you have facts at your fingertips, you can reevaluate this course of action. Since you didn't list a bunch of VMS library methods this program uses, it's impossible to tell how entangled it is with the OS.
This may be trivial or impossible. It's difficult to tell without analysis of the source.
Write bridge libraries from VMS to Linux. If your program only does a few VMS things, this isn't very difficult. If your program does extensive VMS things, this is craziness.
The bridge -- in the long run -- is a terrible idea. Managers love it, however.
An alternative is to replace the VMS library calls with proper, portable Linux calls rather than write bridges. This is better in the long run, because it excises the non-portable features of the program.
Rewrite it from scratch in Python. That is usually simpler than trying to port the C code. It will be shorter, cleaner, simpler, and portable.
If you're willing to keep running VMS in a VM, you can look into CHARON-VAX ( http://www.charon-vax.com/ ). As previously mentioned, the ease of porting really depends a lot on how much of the VMS extensions were used; searching the source code for $ characters embedded in strings (usually with a 3-character leading substring, such as lib$gettime or dsc$descriptor or sys$foobar etc) will give you at least a basic idea of what VMS system functions are called and how likely they are to be portable, if the name is reasonably obvious.
If it ain't broke, don't fix it! Why port it or migrate the app if you don't have to? Why not run it on a current install of OpenVMS running on an HP Itanium server; that is assuming you wish to upgrade the hardware, which may not even be necessary if your VAX hardware is still running strong.
To learn C, you might as well drag it from the horse's mouth: "The C Programming Language" by its inventors, Kernighan and Ritchie.
I can recommend "The UNIX programming environment" by (again) Brian Kernighan; a more authoritative source you'll hardly find, and it teaches you both Unix/C idioms and a bit of C programming at the same time.
For more depth and detail on C, I heartily enjoyed a book by Peter van der Linden: "Expert C Programming - Deep C Secrets".
You'll also want to wrestle LMS for a library documentation of VMS-specific C functions with (of course) special emphasis on those actually used in the app. That's where your porting effort will be.
The job could be easy or difficult, depending on how much machine-specific cleverness and bit-twiddling is done, and how many VMS-specific system calls are used. It would be very good if word size was equal (in other words, if your VMS box has a word size of 32 bits, don't run the code on a 64 bit version of Unix!)
Brian, I'm not sure if LMS specified/cared to port C-code or the WHOLE process. As too often people think of languages out of scope of systems.
If there're was a process built on VMS, most likely it used at least scheduling/batch facilities, which are often scripted in DCL (rather simple and clear language, unlike shell or perl scripting).
So the cost of porting the whole process may be higher than originally perceived by your LMS. Add here the reliability aspect, given your crunches with C, which is nothing impossible, of course, with enthusiasm and determination.
If you want simply give the C-code a try, as previously posted, search it for the "$" hits. Or just cc it with all headers present, the basics of compile-link command should be enough.
Alternatively, this looks like a consultant's call, as indeed such jobs were abundant at the "exodus" time. All said VMS remains quite a robust platform (24x7 is a norm!), unless the harware dies, then there're still tons of "exodus" spares. GOOD LUCK!
About a year and a half later, maybe you've already figured out what to do. My organization has recently decided to stick with OpenVMS instead of switching to Linux even though the old guard recently left. We just couldn't argue with what we felt was a very stable and reliable system. We are currently switching from Alpha servers to Integrity servers for end of life reasons. HP has been very helpful with our transition.
For that matter, there may be Linux vendors out there who can help with the transition. Ask your new hardware vendor if they have any recommendations.
Depending on what languages you already know, C is not that hard to learn. I taught myself C in the course of learning C++ after finally prying myself loose from Pascal.
(VAX Pascal, plus Rdb/VMS, plus DCL formed a combination that was hard to beat.)
If the software is typical C, you'll spend more time learning the library functions than learning the language.
It's pretty lightweight stuff, but I went through the online tutorials for C++ that Microsoft makes available in conjunction with the express edition of Visual Studio for C++.
Here's the beginner's tutorial:
http://msdn.microsoft.com/en-us/beginner/cc305129.aspx
It's probably worth making the effort to ask why LMS wants to port the application to Unix. The answer may seem obvious, but properly exploring the reasons has its benefits. I would assume:
OpenVMS is an "ultra legacy platform", and for that reason alone is something that is not worth running an application on anymore;
It's tough to find anyone who is willing to maintain an application that runs on OpenVMS these days;
The hardware on-which OpenVMS runs is threatening to become moribund.
We have a similar challenge, but in our case the application in question not only runs on OpenVMS but is also written in COBOL. I would have to say that your situation is rosy in comparison given that your application is written in a cross-platform language.
In any case, I think if you're about to make a big decision like moving from OpenVMS to Unix it would be prudent to do a little due diligence. In your case, try to assess just how portable the code is--only then will you know what the scale of the effort is (worst case could quite easily be a multiple of best case). In C, code portability is mostly a function of the dependencies--are they "standard" or are they VMS-specific?
Our enquiries revealed that HP would be supporting OpenVMS on Itanium until at least 2022. There isn't necessarily a need to rush to another platform--perhaps you could keep things on OpenVMS whilst embarking on an effort to prepare the application for porting (make it less dependent on OpenVMS specifics).
VMS has a surprisingly healthy community and if it's the lack of Unix that's the issue, then maybe GNV could help bridge the gap?
Well u have a few options. if this code needs to be ported rather quickly, i would write a bridge library to emulate the vms libs. whener you get it back up and running on a *nix, then go through replacing the vms library calls with native/portable calls for *nix.
Also if there is a lot of optimizations in the code ie inline assembly and bit twiddling. then you will have to rewrite thi code, which will take an understanding of the VAX arch. also. be sure to check word size differences and endian differences
I am working on an embedded application that uses NAND flash for storage.
As it looks now, we won't use Linux or any other RTOS. The application must handle unexpected power downs.
We have been looking on different file system solutions, including YAFFS2, JFFS2, FAT+FTL as well as solutions from HCC Embedded.
I have heard FAT+FTL is a normal choice, but I am worried about data loss in case of unexpected power downs as well as performance. Would be grateful if anyone could share insights and experience about this
FAT-FTL is a "normal choice", but not necessarily a good choice.
YAFFS2 is newer than JFFS2 and seems to be faster and more scalable for large NANDs. This presentation of the "Embedded Linux Conference Europe" compares these two and other flash file systems.
Another solution is LogFS (note: log stands here for logorithmic, not for log-structured). It should also be more scalable, but I have no idea how muture it is.
There's UBIFS. The only implementation I know of is in the Linux kernel, and it depends on the Linux kernel's UBI interface. However, the fundamental algorithms should be implementable without too much trouble in whatever environment you are using. As for production-readiness, Nokia uses UBIFS in their N900 smartphone, and plug computers based on the SheevaPlug have support for it, too. I have found the Linux implementation to be reliable, even on flaky hardware that likes to reset itself at random. Unlike JFFS2, UBIFS does not need to read the entire filesystem at startup.
You may want to reconsider your "no Linux" decision, since using Linux would make it a lot easier to use UBIFS.
There is a commercial vendor called DataLight which offers a robust flash file system, but of course it's not free.
They have an interesting white paper (PDF) (take with a grain of salt) on performances.