11 ms·

A Repository with 44 Years of Unix Evolution

189 points by LaSombra 11y ago

waynecochran 11y ago
The most infamous comment in the history of source code from Unix V6. Now I can search an see at what stage this was committed. 2230 /* 2231 * If the new process paused because it was 2232 * swapped out, set the stack level to the last call 3333 * to savu(u_ssav). This means that the return 2235 * actually returns from the last routine which did 2236 * the savu. 2237 * 2238 * You are not expected to understand this. 2239 */ 2240 if(rp->p_flag&SSWAP) { 2241 rp->p_flag =& ~SSWAP; 2242 aretu(u.u_ssav); 2243 }
- kps 11y ago
  I think that precedes any Unix revision control finer than ‘Sixth Edition’. (PWB, which included the SCCS port, was built on V6.)
- barrkel 11y ago
  I think this is only hard to understand if you are used to thinking at the level of the language rather than the CPU. I've done more evil things implementing language features in a compiler.
  - userbinator 11y ago
    From a brief glance at the surrounding code, this is part of the context switcher, which has to do stack switching. Also interesting to note that the whole function, swtch(), is only 71 lines. The entire kernel is less than 10kLOC. I agree that understanding this type of code would be very difficult if you're used to the HLL notion of nesting function calls, because these don't work like regular functions; a call actually "returns" into a different one. You can't easily understand coroutines, threads, processes, and context switching without seeing that functions are really a structuring that HLLs impose, not the CPU itself.
  - riffraff 11y ago
    well, it's "not expected to" (we won't ask you about at the exam) rather than "expected not to" (this is too difficult for you feeble minds) :)
barkingcat 11y ago
there are some textual errors and artifacts in the story "Calling ghostscript to convert provenance.pdf to provenance.png" for example.
- DSpinellis 11y ago
  Thank you for bringing this to my attention. I fixed it.
duiker101 11y ago
The first commit sits at page 11070, https://github.com/dspinellis/unix-history-repo/tree/7317268623b44e8f3a51c34e3ca717316f613958 https://github.com/dspinellis/unix-history-repo/tree/7317268...
- brento 11y ago
  Hehe. I looked for the first commit page as well. I wish GH had a first commit button in their pagination.
fit2rule 11y ago
As a 45 year old with 30 years of experience in the computer industry, such titles interest me, immensely. I grew up with Unix. I remember the days when Unix was a seriously advanced topic, available only to the elite privileged (adults) who were granted access to it as a technological resource only through machinations that were out of my scope of influence, as a 13 year old learning computing in 1983. It was a vast mystery. It was only with great effort on my part that access was eventually granted in the form of a login over a slow modem. That was enough for me to move to the next phase. Then, it was a mystery in terms of taxology. I had a near-infinite, seemingly overwhelming number of things to learn - more than what was in my high school curriculum, more than my little home 8-bit computer could teach me, more .. it seemed at the time .. than all the books on my shelf. Well, it was only a few years - actually probably less than 10 months - until I was able to grasp at least a little bit of the subject, and do something with it. That was enough to propel me into the professional sphere - where I was able to move from a clueless teenager into the clued-up programmer zone. And then (late 80's) it became a game of "which Unix do you want to know?", and that game was as thorny as any other. I chose Risc/OS (from MIPS, pre-SGI) and it worked out: I gained my own machine (physical hardware) as a result of commercial delivery of products - a few files of .c/.h - which I'd managed to build as a result of eager learning applied to real application. And then: Linux. This changed the world completely, at least for me at the time. When I first saw Linus' post on the minix-list, announcing his sharing of work I thought completely inapproachable and beyond the horizon, I immediately applied myself to catching up. And then, through the 90's, the commercial applications of these skills gave me an even deeper understanding of the subject - and Unix became less of a mystery and more of a resource for living. And so it was: for a decade I built Unix software, like no other, which resulted in many great things for many great people. Then, we flipped the century bit, and Unix - in spite of all the predictions from industry experts - was still with us. It didn't just go away because of pop-culture desires and mores, it was seriously entrenched. That 80's decision seemed all the more wise in 2001, when it became clear to me that Unix was not going away. So I kept at it. I coded all I could. I got a tiBook - astounded, but content nevertheless, that Apple (of all companies) was producing a portable Unix workstation - something that I'd dreamed of for over a decade. And there it was, the tiBook. So I've upgraded my way from there, to my current extremely satisfying device (MBP Retina) .. and beyond that, even beyond my wildest teenage dreams: here we are today - I carry around a Unix workstation in my pocket. Its my primary means of communication, just like I always knew it would be. It does all the things that I used to do with the Risc/OS pizza box. It does it in a way that makes total sense - a simple interface, like the embodiment of the holy pipe, but at my fingertips. It has been a challenge, a fantasy, and a real desire to see Unix become what it is today - but its also been a privilege. I think that all of my fellow hackers who professed faith in the technology, must feel the same - at least those who have watched it happen over decades. Truly, a unique human experience. And therefore I'm really glad to see this article. It has been very enlightening - and as well, personally satisfying - to see that others recognize the power of this technology, which took decades to become the force of power that it is today.
bodyfour 11y ago
> Tooling [...] compiling the 4.3 BSD compress program, which is no longer part of modern Unix systems, in order to decompress the 386BSD distributions. I don't think this was needed -- gunzip can actually read that format.
- DSpinellis 11y ago
  You're right; I had forgotten that. I simplified the corresponding process.
mp3geek 11y ago
I didn't relise FreeBSD used git, when did this happen?
- emaste 11y ago
  FreeBSD has supported a git mirror for years, although the primary VCS (the "source of truth") is still Subversion. A number of downstream consumers of FreeBSD use the git mirror though, and we have brought in patches from submitted pull requests.
  - riffraff 11y ago
    wasn't freebsd using perforce at some point?
    - DSpinellis 11y ago
      Internally.
    - feld 11y ago
      some developers still do
mp3geek 11y ago
I didn't relise FreeBSD used git, when did this happen?
cnst 11y ago
Isn't this a copyright violation?!?! Did the author obtain the permission from IEEE to publish this work on a publicly facing internet server?!
- Sanddancer 11y ago
  The Author's allowed to do this. While the copyright assignment requires any commercial use to be licensed through the IEEE, any personal use, including putting it on a web page, is allowed.
- atmosx 11y ago
  Well he is really close to IEEE[1], so I think if there was any legalize involved, he must covered it. I follow professor Spinellis since 2008 and he seems to be a really nice guy who pays exceptional attention to details. UPDATE: Apparently DSpinellis is the new editor in chief of IEEE software magazine[1]. [1] http://www.computer.org/web/computingnow/tools-of-the-trade http://www.computer.org/web/computingnow/tools-of-the-trade [2] http://www.computer.org/web/computingnow/software/edboard http://www.computer.org/web/computingnow/software/edboard
- jkldotio 11y ago
  Better call Darl McBride to make sure..
ackalker 11y ago
Joy! After the speedy download from Github (which weighs in at more than 40 times the capacity of the hard drive which held my first *nix system), I was able to locate a patch I submitted to FreeBSD in less than 12 seconds from running gitk on the file in question, thanks to the wonderful world of Git. I shudder at the thought of having to manage all of this using CVS, pulling changes using CVSup or whatnot. Thanks for sharing! :-)
- cnst 11y ago
  It has the sensors framework from 2007, too. :-)
cubitesystems 11y ago
What a delightful data set! I was very surprised to see the ocurence of goto lines in the Unix source code. Not to mention an increasing amount of them in the later years! I've heard [0] that Goto's are considered harmful. [0] http://www.u.arizona.edu/~rubinson/copyright_violations/Go_To_Considered_Harmful.html http://www.u.arizona.edu/~rubinson/copyright_violations/Go_T...
- weland 11y ago
  The original context in which Dijkstra wrote that was very different; he was primarily referring to old versions of Fortran and BASIC, where gotos where more or less the only (or the predominant) form of branching. In other words, something like if (foo() || bar()) xyzzy(); else idkfa(); would have often been written something like 100 F = FOO() 200 B = BAR() 300 IF F OR B 400 GOTO 4840 500 ELSE 600 GOTO 8000 700 .... and whatever was happening at 4840 would GOTO back to 700 (with predictable catastrophic results if anything before 700 changed) and so on. Local use of goto in the context of e.g. bailing out of an ini function if something failed early in the initialization sequence is useful and not frowned upon by people whose daily work consists of something other than writing coding standards. There are a few (well-meant!) exceptions that have to do with e.g. static analysis, but those tend not be so important outside the field of high-reliability systems.

189 points by LaSombra 11y ago

The most infamous comment in the history of source code from Unix V6. Now I can search an see at what stage this was committed. 2230 /* 2231 * If the new process paused because it was 2232 * swapped out, set the stack level to the last call 3333 * to savu(u_ssav). This means that the return 2235 * actually returns from the last routine which did 2236 * the savu. 2237 * 2238 * You are not expected to understand this. 2239 */ 2240 if(rp->p_flag&SSWAP) { 2241 rp->p_flag =& ~SSWAP; 2242 aretu(u.u_ssav); 2243 }

kps 11y ago
I think that precedes any Unix revision control finer than ‘Sixth Edition’. (PWB, which included the SCCS port, was built on V6.)
barrkel 11y ago
I think this is only hard to understand if you are used to thinking at the level of the language rather than the CPU. I've done more evil things implementing language features in a compiler.
- userbinator 11y ago
  From a brief glance at the surrounding code, this is part of the context switcher, which has to do stack switching. Also interesting to note that the whole function, swtch(), is only 71 lines. The entire kernel is less than 10kLOC. I agree that understanding this type of code would be very difficult if you're used to the HLL notion of nesting function calls, because these don't work like regular functions; a call actually "returns" into a different one. You can't easily understand coroutines, threads, processes, and context switching without seeing that functions are really a structuring that HLLs impose, not the CPU itself.
- riffraff 11y ago
  well, it's "not expected to" (we won't ask you about at the exam) rather than "expected not to" (this is too difficult for you feeble minds) :)

barkingcat 11y ago

there are some textual errors and artifacts in the story "Calling ghostscript to convert provenance.pdf to provenance.png" for example.

DSpinellis 11y ago
Thank you for bringing this to my attention. I fixed it.

duiker101 11y ago

The first commit sits at page 11070, https://github.com/dspinellis/unix-history-repo/tree/7317268623b44e8f3a51c34e3ca717316f613958 https://github.com/dspinellis/unix-history-repo/tree/7317268...

brento 11y ago
Hehe. I looked for the first commit page as well. I wish GH had a first commit button in their pagination.

fit2rule 11y ago

As a 45 year old with 30 years of experience in the computer industry, such titles interest me, immensely. I grew up with Unix. I remember the days when Unix was a seriously advanced topic, available only to the elite privileged (adults) who were granted access to it as a technological resource only through machinations that were out of my scope of influence, as a 13 year old learning computing in 1983. It was a vast mystery. It was only with great effort on my part that access was eventually granted in the form of a login over a slow modem. That was enough for me to move to the next phase. Then, it was a mystery in terms of taxology. I had a near-infinite, seemingly overwhelming number of things to learn - more than what was in my high school curriculum, more than my little home 8-bit computer could teach me, more .. it seemed at the time .. than all the books on my shelf. Well, it was only a few years - actually probably less than 10 months - until I was able to grasp at least a little bit of the subject, and do something with it. That was enough to propel me into the professional sphere - where I was able to move from a clueless teenager into the clued-up programmer zone. And then (late 80's) it became a game of "which Unix do you want to know?", and that game was as thorny as any other. I chose Risc/OS (from MIPS, pre-SGI) and it worked out: I gained my own machine (physical hardware) as a result of commercial delivery of products - a few files of .c/.h - which I'd managed to build as a result of eager learning applied to real application. And then: Linux. This changed the world completely, at least for me at the time. When I first saw Linus' post on the minix-list, announcing his sharing of work I thought completely inapproachable and beyond the horizon, I immediately applied myself to catching up. And then, through the 90's, the commercial applications of these skills gave me an even deeper understanding of the subject - and Unix became less of a mystery and more of a resource for living. And so it was: for a decade I built Unix software, like no other, which resulted in many great things for many great people. Then, we flipped the century bit, and Unix - in spite of all the predictions from industry experts - was still with us. It didn't just go away because of pop-culture desires and mores, it was seriously entrenched. That 80's decision seemed all the more wise in 2001, when it became clear to me that Unix was not going away. So I kept at it. I coded all I could. I got a tiBook - astounded, but content nevertheless, that Apple (of all companies) was producing a portable Unix workstation - something that I'd dreamed of for over a decade. And there it was, the tiBook. So I've upgraded my way from there, to my current extremely satisfying device (MBP Retina) .. and beyond that, even beyond my wildest teenage dreams: here we are today - I carry around a Unix workstation in my pocket. Its my primary means of communication, just like I always knew it would be. It does all the things that I used to do with the Risc/OS pizza box. It does it in a way that makes total sense - a simple interface, like the embodiment of the holy pipe, but at my fingertips. It has been a challenge, a fantasy, and a real desire to see Unix become what it is today - but its also been a privilege. I think that all of my fellow hackers who professed faith in the technology, must feel the same - at least those who have watched it happen over decades. Truly, a unique human experience. And therefore I'm really glad to see this article. It has been very enlightening - and as well, personally satisfying - to see that others recognize the power of this technology, which took decades to become the force of power that it is today.

bodyfour 11y ago

> Tooling [...] compiling the 4.3 BSD compress program, which is no longer part of modern Unix systems, in order to decompress the 386BSD distributions. I don't think this was needed -- gunzip can actually read that format.

DSpinellis 11y ago
You're right; I had forgotten that. I simplified the corresponding process.

mp3geek 11y ago

I didn't relise FreeBSD used git, when did this happen?

emaste 11y ago
FreeBSD has supported a git mirror for years, although the primary VCS (the "source of truth") is still Subversion. A number of downstream consumers of FreeBSD use the git mirror though, and we have brought in patches from submitted pull requests.
- riffraff 11y ago
  wasn't freebsd using perforce at some point?
  - DSpinellis 11y ago
    Internally.
  - feld 11y ago
    some developers still do

mp3geek 11y ago

I didn't relise FreeBSD used git, when did this happen?

cnst 11y ago

Isn't this a copyright violation?!?! Did the author obtain the permission from IEEE to publish this work on a publicly facing internet server?!

Sanddancer 11y ago
The Author's allowed to do this. While the copyright assignment requires any commercial use to be licensed through the IEEE, any personal use, including putting it on a web page, is allowed.
atmosx 11y ago
Well he is really close to IEEE[1], so I think if there was any legalize involved, he must covered it. I follow professor Spinellis since 2008 and he seems to be a really nice guy who pays exceptional attention to details. UPDATE: Apparently DSpinellis is the new editor in chief of IEEE software magazine[1]. [1] http://www.computer.org/web/computingnow/tools-of-the-trade http://www.computer.org/web/computingnow/tools-of-the-trade [2] http://www.computer.org/web/computingnow/software/edboard http://www.computer.org/web/computingnow/software/edboard
jkldotio 11y ago
Better call Darl McBride to make sure..

ackalker 11y ago

Joy! After the speedy download from Github (which weighs in at more than 40 times the capacity of the hard drive which held my first *nix system), I was able to locate a patch I submitted to FreeBSD in less than 12 seconds from running gitk on the file in question, thanks to the wonderful world of Git. I shudder at the thought of having to manage all of this using CVS, pulling changes using CVSup or whatnot. Thanks for sharing! :-)

cnst 11y ago
It has the sensors framework from 2007, too. :-)

cubitesystems 11y ago

What a delightful data set! I was very surprised to see the ocurence of goto lines in the Unix source code. Not to mention an increasing amount of them in the later years! I've heard [0] that Goto's are considered harmful. [0] http://www.u.arizona.edu/~rubinson/copyright_violations/Go_To_Considered_Harmful.html http://www.u.arizona.edu/~rubinson/copyright_violations/Go_T...

weland 11y ago
The original context in which Dijkstra wrote that was very different; he was primarily referring to old versions of Fortran and BASIC, where gotos where more or less the only (or the predominant) form of branching. In other words, something like if (foo() || bar()) xyzzy(); else idkfa(); would have often been written something like 100 F = FOO() 200 B = BAR() 300 IF F OR B 400 GOTO 4840 500 ELSE 600 GOTO 8000 700 .... and whatever was happening at 4840 would GOTO back to 700 (with predictable catastrophic results if anything before 700 changed) and so on. Local use of goto in the context of e.g. bailing out of an ini function if something failed early in the initialization sequence is useful and not frowned upon by people whose daily work consists of something other than writing coding standards. There are a few (well-meant!) exceptions that have to do with e.g. static analysis, but those tend not be so important outside the field of high-reliability systems.