TUHS

tuhs@tuhs.org

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6534 discussions

Re: [TUHS] why does tar have the tape device hard coded into it and why is it mt1 instead of mt0

by Doug McIlroy

> I have no memory of why Ken used mt1 not mt0. Doug may know. I don't know either. Come to think of it, I can't remember ever using tar without option -f. Direct machine-to-machine trasfer, e.g. by uucp, took a lot of business away from magtape soon after tar was introduced. Incidentally, I think tar was written by Chuck Haley or Greg Chesson, not Ken. Doug

9 years, 7 months

Re: [TUHS] TUHS] why does tar have the tape device hard coded into it and why is it mt1 instead of mt0

by Doug McIlroy

Forget that I said, "I think that tar was written by Chuck Haley or Greg Chesson". Ken confirms that he wrote it, for dectape. Doug

9 years, 7 months

Re: [TUHS] Pre-v6 images and 2.11BSD patches

by Johnny Billquist

On 2015-12-12 07:16, William Pechter<pechter(a)gmail.com> wrote: > > Warren Toomey wrote: >> >On Sat, Dec 12, 2015 at 03:54:16PM +1100, Peter Jeremy wrote: >>> >>Also, I've seen suggestions that there's a 2.11BSD patch later than >>> >>447 but I can't find anything "official" andwww.2bsd.com is either >>> >>down or inaccessible from all the systems I have access to. Does >>> >>anyone know if 448 or later were released? And given the issues with >>> >>www.2bsd.com would someone be willing to mirror it (assuming we can >>> >>got a copy of it)? >> >[ Back to a real keyboard ]. Yes I'd be very happy to mirror 2bsd.com. >> >Does anybody know what's happened to Steven Schultz? >> > >> >Cheers, Warren >> >_______________________________________________ >> >TUHS mailing list >> >TUHS(a)minnie.tuhs.org >> >http://minnie.tuhs.org/cgi-bin/mailman/listinfo/tuhs > Last patch is 447 from June 2012. Uh. No. 447 is from December 31, 2008. See /VERSION in the patch set, which holds the patch version and date for the patch. And I did an unofficial 448 in 2010, which I have tried to spread, and which I suspect is the patch referred to above... > I can get to the site just fine... pasted the patch below if it helps > anyone. > I haven't heard anything about him. Haven't worked at the same company > since the early 1990's... I used to talk with him a lot in the past, but have not been able to raise him, and haven't seen anything from him in over 5 years... No idea what he is up to nowadays... Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt(a)softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

9 years, 7 months

Re: [TUHS] why is sum reporting different checksum's between v6 and v7

by jnc＠mercury.lcs.mit.edu

> From: Random832 > Interestingly, the SysIII sum.c program, which I assume yields the same > result for this input, appears to go through the whole input > accumulating the sum of all the bytes into a long, then adds the two > halves of the long at the end rather than after every byte. That's the same hack a lot of TCP/IP checksums routines used on machines with longer words; add the words, then fold the result in the shorter length at the end. The one I wrote for the 68K back in '84 did that. > This suggests that the two programs would give different results for > very large files that overflow a 32-bit value. No, I don't think so, depending on the exact detals of the implementation. As long as when folding the two halves together, you add any carry into the sum, you get the same result as doing it into a 16-bit sum. (If my memory of how this all works is correct - the neurons aren't what they used to be, especially late in the day... :-) > Also, if this sign extends, then its behavior on "negative" (high bit > set) bytes is likely to be very different from the SysIII one, which > uses getc. I have this bit set that in C, 'char' is defined to be signed, and furthermore that when you assign a shorter int to a longer one, the sign is extended. So if one has a char holding '0200' octal (i.e. -128), assigning it to a 16-bit int should result in the latter holding '0177600' (i.e. still -128). So in fact I think they probably act the same. Noel

9 years, 7 months

Re: [TUHS] why is sum reporting different checksum's between v6 and v7

by jnc＠mercury.lcs.mit.edu

> From: Will Senn > I noticed that the sum utility from v6 reports a different checksum > than it does using the sum utility from v7 for the same file. > ... does anyone know what's going on here? > Why is sum reporting different checksum's between v6 and v7? The two use different algorithms to accumulate the sum (I have added comments to the relevant portion of the V6 assembler one, to help understand it): V6: mov $buf,r2 / Pointer to buffer in R2 2: movb (r2)+,r4 / Get new byte into R4 (sign extends!) add r4,r5 / Add to running sum adc r5 / If overflow, add carry into low end of sum sob r0,2b / If any bytes left, go around again Read the description of MOVB in the PDP-11 Processor manual. V7: while ((c = getc(f)) != EOF) { nbytes++; if (sum&01) sum = (sum>>1) + 0x8000; else sum >>= 1; sum += c; sum &= 0xFFFF; } I'm not clear on some of that, so I'll leave its exact workings as an exercise, but I'm pretty sure it's not a equivalent algorithm (as in, something that would produce the same results); it's certainly not identical. (The right shift is basically a rotate, so it's not a straight sum, it's more like the Fletcher checksum used by XNS, if anyone remembers that.) Among the parts I don't get, for instance, sum is declared as 'unsigned', presumably 16 bits, so the last line _should_ be a NOP!? Also, with 'c' being implicitly declared as an 'int', does the assignment sign extend? I have this vague memory that it does. And does the right shift if the low bit is one really do what the code seems to indicate it does? I have this bit that ASR on the PDP-11 copies the high bit, not shifts in a 0 (check the processor manual). That is, of course, assuming that the compiler implements the '>>' with an ASR, not a ROR followed by a clear of the high bit, or something. Noel

9 years, 7 months

where is the v6tar source?

by Mark Longridge

Ok, it definitely sounds like the v6tar source is around somewhere so if someone could point me in the right direction... I've only seen the binary, and I can't remember where I got it. Mark

9 years, 7 months

why is sum reporting different checksum's between v6 and v7

by Will Senn

All, While working on the latest episode of my saga about moving files between v6 and v7, I noticed that the sum utility from v6 reports a different checksum than it does using the sum utility from v7 for the same file. To confirm, I did the following on both systems: # echo "Hello, World" > hi.txt # cat hi.txt Hello, World Then on v6: # sum hi.txt 1106 1 But on v7: # sum hi.txt 37264 1 There is no man page for the utility on v6, and it's assembler. On v7, there's a manpage and it's C: man sum ... Sum calculates and prints a 16-bit checksum for the named file, and also prints the number of blocks in the file. ... A few questions: 1. I'll eventually be able to read assembly and learn what the v6 utility is doing the hard way, but does anyone know what's going on here? 2. Why is sum reporting different checksum's between v6 and v7? 3. Do you know of an alternative to check that the bytes were transferred exactly? I used od and then compared the text representation of the bytes on the host using diff (other than differences in output between v6 and v7 related to duplicate lines, it worked ok but is clunky). Thanks, Will

9 years, 7 months

why does tar have the tape device hard coded into it and why is it mt1 instead of mt0

by Will Senn

All, In my exploration of v6, I followed the advice in "Setting up Unix - Seventh Edition" and copied v6tar from v7 to v6. Life is good. However, tar is using mt1 and it is hard coded into the source, tar.c: char magtape[] = "/dev/mt1"; As the subject line suggested, I have two questions for those of you who might know: 1. Why is it hard coded? 2. Why is it the second device and not the first? Interestingly, it took me a little while to figure out it was doing this because I didn't actually move files between v6 and v7 until today. Before this my tests had been limited to separate tests on v6 and v7 along the lines of: cd /wherever tar c . followed by tar t list of files cd /elsewhere tar x files extracted and matching What it was doing was writing to the non-existant /dev/mt1, which it then created, tarring up stuff, and exiting. Then when I listed the contents of the tarfile, or extracted the contents, it was successful. But, when I went to move the tape between v6 and v7, the tape (mt0) was blank, of course. It was at this point that I followed Noel's advice and "Used the source", and figured out that it was hard-coded as you see above. Thanks, Will

9 years, 7 months

ld (was v6tar from v7 on v6, too large?)

by Doug McIlroy

That's exactly right. ld performs the same task as LOAD did on BESYS, except it builds the result in the file system rather than user space. Over time it became clear that "linker" would be a better term, but that didn't warrant canning the old name. Gresham's law then came into play and saddled us with the ponderous and misleading term, "link editor". Doug > My understanding, which predates my contact with Unix, is that the > original toochains for single-job machines consisted of the assembler > or compiler, the output of which was loaded directly into core with > the loader. As things became more complicated (and slow), it made > sense to store the memory image somewhere on drum, and then load that > image directly when you wanted to run it. And that in some systems > the name "loader" stuck, even though it no longer loaded. Something > like the modern ISP use of the term "modem" to mean "router". But I > don't have anything to back up this version; comments welcome.

9 years, 7 months

Re: [TUHS] v6tar from v7 on v6, too large?

by jnc＠mercury.lcs.mit.edu

> estabur (who thought these names up, I know 8 characters is limiting, > but c'mon) 'establish user mode registers' > the 411 header is read by a loader Actually, it's read by the exec() system call (in sys1.c). Noel

9 years, 7 months

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