TUHS May 2017

tuhs@tuhs.org

58 participants
45 discussions

Re: [TUHS] The evolution of Unix facilities and architecture

by Doug McIlroy

> We all took the code back and promised to get patches out ASAP and not tell any one about it. Fascinating. Chnages were installed frequently in the Unix lab, mostly at night without fanfare. But an actual zero-day should have been big enough news for me to have heard about. I'm pretty sure I didn't; Dennis evidently kept his counsel. Doug

6 years, 11 months

Re: [TUHS] The evolution of Unix facilities and architecture

by jnc＠mercury.lcs.mit.edu

> From: "Ron Natalie" > Ordered writes go back to the original BSD fast file system, no? I seem > to recall that when we switched from our V6/V7 disks, the filesystem got > a lot more stable in crashes. I had a vague memory of reading about that, so I looked in the canonical FFS paper (McKusick et al, "A Fast File System for UNIX" [1984)]) but found no mention of it. I did find a paper about 'fsck' (McKusick, Kowalski, "Fsck: The UNIX File System Check Program") which talks (in Section 2.5. "Updates to the file system") about how "problem[s] with asynchronous inode updates can be avoided by doing all inode deallocations synchronously", but it's not clear if they're talking about something that was actually done, or just saying (hypothetically) that that's how one would fix it. Is is possible that the changes to the file system (e.g. the way free blocks were kept) made it more crash-proof? Noel

6 years, 11 months

Re: [TUHS] C declarations.

by Richard Tobin

> The problem with that is that * doesn't really bind to the type name. > It binds to the variable. > > char* cp1, cp2; // cp1 is pointer to char, cp2 is just a char. > > I always found it confusing that the * is used to indicate an pointer > here, where as when you want to change an lvalue to a pointer, you use > &. The way to read it is that you are declaring *cp1 as a char. -- Richard -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.

6 years, 11 months

Re: [TUHS] The evolution of Unix facilities and architecture

by jnc＠mercury.lcs.mit.edu

> From: Warner Losh > There's a dcheck.c in the TUHS v7 sources. How's that related? That was one of the earlier tools - not sure how far back it goes, but it's in V6, but not V5. It consistency checks the directory tree. Another tool, 'icheck', consistency checks file blocks and the free list. Noel

6 years, 11 months

The evolution of Unix facilities and architecture

by Diomidis Spinellis

I've made available on GitHub a series of tables showing the evolution of Unix facilities (as documented in the man pages) over the system's lifetime [1] and two diagrams where I attempted to draw the corresponding architecture [2]. I've also documented the process in a short blog post [3]. I'd welcome any suggestions for corrections and improvements you may have, particularly for the architecture diagrams. [1] https://dspinellis.github.io/unix-history-man/ [2] https://dspinellis.github.io/unix-architecture/ [3] https://www.spinellis.gr/blog/20170510/ Cheers, Diomidis

6 years, 11 months

Re: [TUHS] Discuss of style and design of computer programs from a

by Nemo

On 6 May 2017 at 11:23, ron minnich <rminnich(a)gmail.com> wrote (in part): [...] > Lest you think things are better now, Linux uses self modifying code to > optimize certain critical operations, and at one talk I heard the speaker > say that he'd like to put more self modifying code into Linux, "because it's > fun". Oh boy. Fun, indeed! Even self-modifying chips are being touted -- Yikes! N.

6 years, 11 months

Re: [TUHS] Discuss of style and design of computer programs from a user standpoint

by Doug McIlroy

> tr -cs A-Za-z '\n' | > tr A-Z a-z | > sort | > uniq -c | > sort -rn | > sed ${1}q > > This is real genius. Not genius. Experience. In the Bentley/Knuth/McIlroy paper I said, "[Old] Unix hands know instinctively how to solve this one in a jiffy." While that is certainly true, the script was informed by my having written "spell", which itself was an elaboration of a model pioneered by Steve Johnson. By 1986, when BKM was published, the lore was baked in: word-processing scripts in a similar vein were stock in trade. A very early exercise of this sort was Dennis Ritchie's enumeration of anagrams in the unabridged Merriam-Webster. Since the word list barely fit on the tiny disk of the time, the job entailed unimaginable marshalling of resources. I was mightily impressed then, and still am. Doug

6 years, 11 months

Re: [TUHS] Discuss of style and design of computer programs from a user stand point [was dmr note on BSD's sins]

by Clem Cole

On Thu, May 4, 2017 at 7:14 PM, Larry McVoy <lm(a)mcvoy.com> wrote: > some of those Berkeley flags (not specifically for cat, but almost > certainly including those for cat) were really quite useful. Amen!!! I think that this is key point. What is in good taste or good style? Doug's distain for the results of: less --help | wc is found in bad design, a poor user interface, little fore thought, *etc.* Most of what is there has been added over Eric Scheinbrood's original more(1) I do not believe are used that often, but some of them are of course, and you can not tell who uses what!! So how do you decide what get rid of? How do you learn what people really need -- IMO: much of that is * experience *and this thing we call 'good taste.' As opposed to what I think happened with less(1) and many others similar programs (programmers peeing on the code because they code and the source was available -- I can add this feature to it and I think it is cool. As opposed to asking, what do really get and not having a 'master builder' arbitrating or vetting things). The problem we have is that we don't yet have a way of defining good taste. One might suggest that it takes years of civilization and also that tastes do change over time. Pike's minimalistic view (which I think is taken to the extreme in the joke about automobile dashboard on Brian Kernighan's car) sets the bar to one end and probably one of the reason why UNIX had a bad reputation, certainly by non-computer scientists, when it first appeared as being difficult. Another extreme is systems that put in you a box and never let you do anything but what we told you do; which I find just as frighten and frustration builds there when I use them. Clearly systems that are so noisy that can not find what really want, or need is another dimension of the same bad design. So what to do? [more in a minute...] Larry is right. Many of the 'features' added to UNIX (and Linux) over time have been and *are useful*. Small and simple as it was (and I really admire Ken, Dennis and the Team for its creation), but in 2017 I really don't want to run the Sixth Edition for my day to day work anymore - which I happily did in 1977. But the problem is, as we got 'unlimited address space' of 32 and 64 bits, and more room for more 'useful' things, we also got a great deal of rubbish and waste. I am interpreting Doug's point about less --help | wc is that is that are so many thorns and weeds, it hard to see to see the flowers in the garden. I'd like to observe that is that most college courses in CS I have seen talk about how to construct a programs, algorithms, structures - i.e. the mechanics of some operation. But this discussion is about the human element. What we feel is good or bad and how it related to how to use the program. I think about my friends that have degrees in literature, art and architecture. In all cases, they spend a lot of time examining past examples, of good and bad - and thinking and discussing what makes them so. I'm actually happy to see it was Professor McIlroy that is one of the folks taking a stand on current craziness. I think this is only going to get better if a new crop of students that have been trained in 'good taste.' So, I wonder do any of the schools like Darthmouth and the like teach courses that study 'style' and taste in CS. Yes, it is a young field but we have been around long enough that we do a body of work good and bad to consider. I think there is a book or two and a few lectures in there somewhere. Thoughts? Clem

6 years, 11 months

Re: [TUHS] Discuss of style and design of computer programs from a user stand point

by David

> From: Michael Kjörling <michael(a)kjorling.se> > To: tuhs(a)minnie.tuhs.org > Subject: Re: [TUHS] Discuss of style and design of computer programs > from a user stand point > Message-ID: <20170506091857.GE12539(a)yeono.kjorling.se> > Content-Type: text/plain; charset=utf-8 > > I would actually take that one step further: When you are writing > code, you are _first and foremost_ communicating with whatever human > will need to read or modify the code later. That human might be you, a > colleague, or the violent psychopath who knows both where you live and > where your little kids go to school (might as well be you). You should > strive to write the code accordingly, _even if_ the odds of the threat > ever materializing are slim at most. Style matters a lot, there. > Interesting, I was going to say about the same thing about the violent psychopath who has to maintain your code after you leave. When I lectured at UCSD or was giving talks on style for ViaSat I always said the same thing: Whatever you write, the fellow who is going to wind up maintaining it is a known axe killer, now released from prison, completely reformed. He learned computer programming on MS/DOS 3.1 and a slightly broken version of Pascal. He will be given your home phone number and address so if he has any questions about the code you wrote he can get in contact with you. This always got a few chuckles. I then pointed out that whenever anyone gets code that someone else wrote, the recipient always thinks that they can ‘clean up’ what is there because the original author clearly doesn’t understand what proper code looks like. Over time, I’ve learned that everyone has a style when writing code, just like handwriting and given enough time, I can spot who the author of a block of code is just from the indenting, placement of ( and ) around a statement and other small traits. What makes good code is the ability to convey the meaning of the algorithm from the original author to all those who come after. Sometimes even the most unusual code can be quite clear, while the most cleanly formatted and commented code can be opaque to all. David

6 years, 11 months

Re: [TUHS] Discuss of style and design of computer programs from a user stand point [was dmr note on BSD's sins]

by Doug McIlroy

6 years, 11 months

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TUHS May 2017