TUHS

tuhs@tuhs.org

6515 discussions

by Warren Toomey

I was just reading this book review: http://www.pathsensitive.com/2018/10/book-review-philosophy-of-software.html and came across these paragraphs: <book quote> The mechanism for file IO provided by the Unix operating system and its descendants, such as Linux, is a beautiful example of a deep interface. There are only five basic system calls for I/O, with simple signatures: int open(const char* path, int flags, mode_t permissions); ssize_t read(int fd, void* buffer, size_t count); ssize_t write(int fd, const void* buffer, size_t count); off_t lseek(int fd, off_t offset, int referencePosition); int close(int fd); </book quote> The POSIX file API is a great example, but not of a deep interface. Rather, it’s a great example of how code with a very complicated interface may look deceptively simple when reduced to C-style function signatures. It’s a stateful API with interesting orderings and interactions between calls. The flags and permissions parameters of open hide an enormous amount of complexity, with hidden requirements like “exactly one of these five bits should be specified.” open may return 20 different error codes, each with their own meaning, and many with references to specific implementations. The authors of SibylIFS tried to write down an exact description of the open interface. Their annotated version[1] of the POSIX standard is over 3000 words. Not counting basic machinery, it took them over 200 lines[2] to write down the properties of open in higher-order logic, and another 70 to give the interactions between open and close. [1]: https://github.com/sibylfs/sibylfs_src/blob/8a7f53ba58654249b0ec0725ce38878… [2]: https://github.com/sibylfs/sibylfs_src/blob/8a7f53ba58654249b0ec0725ce38878… I just thought it was a thought-provoking comment on the apparent elegance of the Unix file API that actually has some subtle complexity. Cheers, Warren

6 years, 6 months

Re: [TUHS] PDP-11/VAX Unix Chaosnet

by jnc＠mercury.lcs.mit.edu

> From: Lars Brinkhoff > Let's hope it's OK! Indeed! It will be fun to see that code. > I suppose I'll have to add a simulation of the Unibus CH11 Chaosnet > interface to SIMH. Why? Once 10M Ethernet hardware was available, people switched pretty rapidly to using that, instead of the CHAOS hardware. (It was available off the shelf, and the analog hardware was better designed.) That's part of the reason ARP is multi-protocol. Some hard-to-run cables (e.g. under the street from Tech Sq to main campus) stayed CHAOS hardware because it was easier to just keep using what was there, but most new machines got Ethernet cards. Noel

6 years, 6 months

PDP-11/VAX Unix Chaosnet

by Lars Brinkhoff

Hello, According to this: https://lm-3.github.io/amber.html#The-Unix-Implementation there were Chaosnet for PDP-11 Unix V7, and VAX Berkeley Unix. Does anyone have a copy of this? Thes repository: https://github.com/LM-3/chaos may or may not have something of that left, but has been hacked for Linux.

6 years, 6 months

Re: [TUHS] Unix APIs: elegant or not?

by jnc＠mercury.lcs.mit.edu

> From: Chris Hanson > you should virtually never use read(2), only ever something like this: > ... > And do this for every classic system call, since virtually no client > code should ever have to care about EINTR. "Virtually". Maybe there are places that want to know if their read call was interrupted; if you don't make this version available to them, how can they tell? Leaving the user as much choice as possible is the only way to go, IMO; why force them to do it the way _you_ think is best? And it makes the OS simpler; any time you can move functionality out of the OS, to the user, that's a Good Thing, IMO. There's nothing stopping people from using the EINTR-hiding wrapper. (Does the Standard I/O library do this, does anyone know?) Noel PS: Only system calls that can block can return EINTR; there are quite a few that don't, not sure what the counts are in modern Unix.

6 years, 6 months

Re: [TUHS] Unix APIs: elegant or not?

by Theodore Y. Ts'o

On Sun, 4 Nov 2018, Chris Hanson wrote: > Every piece of code that wants to call, say, read(2) needs to handle > not only real errors but also needs to special-case EINTR and retry > the read. Thus you should virtually never use read(2), only ever > something like this: > ... > And do this for every classic system call, since virtually no client > code should ever have to care about EINTR. It was early an > implementation expediency that became API and that everyone now has > to just deal with because you can’t expect the system call interface > you use to do this for you. > >This is the sort of wart that should’ve been fixed by System V and/or BSD 4 at latest. But it *was* fixed in BSD, and it's in POSIX as the SA_RESTART flag to sigaction (which gives you BSD signal semantics). POSIX supports both the original V7 and BSD signal semantics, because by then there were programs which expected system calls to be interrupted by signals (and to be fair, there are times when that's the more convenient way of handling an interrupt, as opposed to using setjump/longjump to break out of a restartable system call). - Ted P.S. The original implementation of ERESTARTSYS / ERESTARTNOHAND / ERESTARTNOINTR errno handling in Linux's system call return path was my fault. :-)

6 years, 7 months

Archaic yacc C grammar

by Lars Brinkhoff

Hello, This is Alan Snyder's C grammar. It's supposedly for yacc, but it's probably using some really ancient version. Maybe from when Alan did a stint at Bell labs and converted yacc from B to C. Does anyone recognize this type of yacc input? I don't have the corresponding yacc version, and the one in V6 isn't happy about this file. What would it take to update the grammar for V6 yacc? Add in some %term, replace \\ with %%? # C GRAMMAR # # 28 May 1978 # # Alan Snyder # # 26 acceptable conflicts: 2 S/R conflicts for (parsing) ambiguity between declarators and function_declarators 1 S/R conflict for the C ELSE ambiguity 4 R/R conflicts for the (parsing) problem with regard to integer constants as initial_values 12 R/R conflicts for the (parsing) problem with regard to identifiers in function calls 1 R/R conflict for the (parsing) problem with regard to identifiers in goto statements 4 R/R conflicts and 1 S/R conflict for TYPEDEFs 1 S/R conflict for ambiguous cast types (int ()) = (int x()) not (int (x)) Approximate description: 18 S/R ( shift 37 reduce 141 50 S/R ( shift 37 reduce 71 81 S/R ( shift 37 reduce 71 113 R/R ( reduce 141 reduce 140 113 R/R ( reduce 159 reduce 140 113 R/R * reduce 159 reduce 141 113 S/R : shift 199 reduce 141 183 R/R , reduce 203 reduce 24 183 R/R } reduce 203 reduce 24 204 R/R ( reduce 159 reduce 140 206 R/R ( reduce 148 reduce 139 207 R/R ( reduce 147 reduce 139 208 R/R ( reduce 145 reduce 139 209 R/R ( reduce 144 reduce 139 210 R/R ( reduce 146 reduce 139 211 R/R ( reduce 149 reduce 139 212 R/R ( reduce 150 reduce 139 215 R/R ( reduce 159 reduce 140 215 R/R ; reduce 159 reduce 138 225 R/R ( reduce 151 reduce 139 228 R/R ( reduce 159 reduce 140 284 R/R , reduce 203 reduce 25 284 R/R } reduce 203 reduce 25 291 S/R ) shift 339 reduce 165 343 R/R ( reduce 153 reduce 139 360 S/R ELSE shift 369 reduce 94 # # terminal symbols # ';' '}' '{' ']' '[' ')' '(' ':' ',' '.' '?' '~' '!' '&' '|' '^' '%' '/' '*' '-' '+' '=' '<' '>' '++' '--' '==' '!=' '<=' '>=' '<<' '>>' '->' '=op' '&&' '||' 'c' INT CHAR FLOAT DOUBLE STRUCT AUTO STATIC EXTERN RETURN GOTO IF ELSE SWITCH BREAK CONTINUE WHILE DO FOR DEFAULT CASE ENTRY REGISTER SIZEOF LONG SHORT UNSIGNED TYPEDEF 'l' 'm' 'n' 'o' 'p' 'q' 'r' 's' identifier integer floatcon string # precedence information # \< ',' \> '=' '=op' \> '?' ':' \< '||' \< '&&' \< '|' \< '^' \< '&' \< '==' '!=' \< '<' '>' '<=' '>=' \< '<<' '>>' \< '+' '-' \< '*' '/' '%' \> '!' '~' \> '++' '--' SIZEOF \< '[' '(' '.' '->' \\ # external definitions # program: program external_definition | external_definition: declaration | function_definition function_definition: function_specification function_body {afdef(#1,#2);} function_specification: decl_specifiers function_declarator {val=afdcl(1);} | function_declarator {val=afdcl(0);} function_body: formal_declarations compound_statement {val=#2;} formal_declarations: formal_decl_list {afpdcl();} | {afpdcl();} compound_statement: begin declaration_list statement_list end {val=#3;} | begin statement_list end {val=#2;} init_declarator_list: init_declarator | init_declarator_list ',' init_declarator init_declarator: $declarator initializer {aidecl();} | declarator {aidecl();} | function_declarator {adeclr(maktyp());} initializer: initial_value | '{' initial_value_expression_list '}' | '{' initial_value_expression_list ',' '}' initial_value_expression_list: initial_value_expression | initial_value_expression_list ',' initial_value_expression initial_value: integer {inz(i_int,#1);} | '-' integer {inz(i_int,-#2);} | floatcon {inz(i_float,#1);} | '-' floatcon {inz(i_negfloat,#2);} | identifier {inz(i_idn,#1);} | '&' identifier {inz(i_idn,#2);} | string {inz(i_string,#1);} initial_value_expression: constant {inz(i_int,#1);} | initial_value # declarations # declaration_list: declaration | declaration_list declaration declaration: decl_specifiers init_declarator_list ';' | literal_type_specifier ';' decl_specifiers: type_specifier {attrib(-1,#1);} | sc_specifier type_specifier {attrib(#1,#2);} | type_specifier sc_specifier {attrib(#2,#1);} type_specifier: type_identifier | literal_type_specifier literal_type_specifier: INT {val=TINT;} | CHAR {val=TCHAR;} | FLOAT {val=TFLOAT;} | DOUBLE {val=TDOUBLE;} | LONG {val=TINT;} | LONG INT {val=TINT;} | SHORT {val=TINT;} | SHORT INT {val=TINT;} | LONG FLOAT {val=TDOUBLE;} | UNSIGNED {val=TINT;} | UNSIGNED INT {val=TINT;} | struct '{' type_decl_list '}' {val=astruct(NULL,#3);} | struct $identifier '{' type_decl_list '}' {val=astruct(#2,#4);} | struct identifier {val=aostruct(#2);} sc_specifier: AUTO {val=c_auto;} | STATIC {val=c_static;} | EXTERN {val=c_extern;} | REGISTER {val=c_auto;} | TYPEDEF {val=c_typedef;} declarator_list: declarator | declarator_list ',' declarator declarator: dclr {val=adeclr(maktyp());} | identifier ':' constant {val=adeclr(afield(#1,#3));} | ':' constant {val=adeclr(afield(-1,#2));} $declarator: dclr {aiinz(adeclr(maktyp()));} dclr: '*' dclr {val=adclr(#2,MPTR);} | dclr '(' ')' {val=adclr(#1,MFUNC);} | dclr '[' ']' {val=adclr(#1,MARRAY,1);} | dclr '[' constant ']' {val=adclr(#1,MARRAY,#3);} | identifier {val=adclr(0,0);} | '(' dclr ')' {val=#2;} function_declarator: '*' function_declarator {val=adclr(#2,MPTR);} | function_declarator '(' ')' {val=adclr(#1,MFUNC);} | function_declarator '[' ']' {val=adclr(#1,MARRAY,1);} | function_declarator '[' constant ']' {val=adclr(#1,MARRAY,#3);} | identifier '(' ')' {val=adclr(adclr(0,0),MFUNC); parml=0;} | identifier '(' parameter_list ')' {val=adclr(adclr(0,0),MFUNC); parml=#3;} | '(' function_declarator ')' {val=#2;} parameter_list: identifier {val=push(#1);} | parameter_list ',' identifier {push(#3);} formal_decl_list: formal_declaration | formal_decl_list formal_declaration formal_declaration: type_declaration | REGISTER type_declaration type_decl_list: type_declaration | type_decl_list type_declaration type_declaration: $type_specifier declarator_list ';' {in_type_def=0; val=#2;} $type_specifier: type_specifier {in_type_def=1; attrib(-1,#1);} # statements # statement_list: statement | statement_list statement {val=astmtl(#1,#2);} statement: expression ';' {val=aexprstmt(#1);} | compound_statement | IF '(' expression ')' statement {val=aif(#3,#5,0);} | IF '(' expression ')' statement ELSE statement {val=aif(#3,#5,#7);} | while '(' expression ')' statement {val=awhile(#3,#5);} | for '(' .expression ';' .expression ';' .expression ')' statement {val=afor(#3,#5,#7,#9);} | do statement WHILE '(' expression ')' ';' {val=ado(#2,#5);} | switch '(' expression ')' statement {val=aswitch(#3,#5);} | CASE constant ':' statement {val=acase(#2,#4);} | DEFAULT ':' statement {val=adefault(#3);} | BREAK ';' {val=abreak();} | CONTINUE ';' {val=acontinue();} | RETURN ';' {val=areturn(0);} | RETURN expression ';' {val=areturn(#2);} | GOTO lexpression ';' {val=agoto(#2);} | identifier ':' statement {val=alabel(#1,#3);} | ENTRY identifier ':' statement {val=aentry(#2,#4);} | ';' {val=anull();} # expressions # .expression: expression | {val=0;} expression_list: expression \= '=' | expression_list ',' expression {val=aelist(#1,#3);} expression: expression '*' expression {val=node(n_times,#1,#3);} | expression '/' expression {val=node(n_div,#1,#3);} | expression '%' expression {val=node(n_mod,#1,#3);} | expression '+' expression {val=node(n_plus,#1,#3);} | expression '-' expression {val=node(n_minus,#1,#3);} | expression '<<' expression {val=node(n_ls,#1,#3);} | expression '>>' expression {val=node(n_rs,#1,#3);} | expression '<' expression {val=node(n_lt,#1,#3);} | expression '>' expression {val=node(n_gt,#1,#3);} | expression '<=' expression {val=node(n_le,#1,#3);} | expression '>=' expression {val=node(n_ge,#1,#3);} | expression '==' expression {val=node(n_eq,#1,#3);} | expression '!=' expression {val=node(n_ne,#1,#3);} | expression '&' expression {val=node(n_band,#1,#3);} | expression '^' expression {val=node(n_bxor,#1,#3);} | expression '|' expression {val=node(n_bior,#1,#3);} | expression '&&' expression {val=node(n_tv_and,#1,#3);} | expression '||' expression {val=node(n_tv_or,#1,#3);} | expression '?' expression ':' expression {val=node(n_qmark,#1,node(n_colon,#3,#5));} | expression '=' expression {val=node(n_assign,#1,#3);} | expression '=op' expression {val=node(n_ars+#2,#1,#3);} | expression ',' expression {val=node(n_comma,#1,#3);} | term # the following productions are ordered very carefully so that the desired thing is done in the case of a R/R conflict # lexpression: expression | identifier {val=aidn(alidn(#1));} fterm: term | identifier {val=aidn(afidn(#1));} type_identifier: identifier {val=atidn(#1);} term: term '++' {val=node(n_inca,#1);} | term '--' {val=node(n_deca,#1);} | '*' term {val=node(n_star,#2);} | '&' term {val=node(n_addr,#2);} | '-' term {val=node(n_uminus,#2);} | '!' term {val=node(n_tvnot,#2);} | '~' term {val=node(n_bnot,#2);} | '++' term {val=node(n_incb,#2);} | '--' term {val=node(n_decb,#2);} | SIZEOF term {val=node(n_sizeof,#2);} | SIZEOF '(' cast_type ')' \= SIZEOF {val=node(n_int,1);} # hack # | '(' cast_type ')' term \= '++' {val=#4;} # hack # | term '[' expression ']' {val=asubscript(#1,#3);} | fterm '(' expression_list ')' {val=acall(#1,#3);} | fterm '(' ')' {val=acall(#1,0);} | term '.' identifier {val=adot(#1,#3);} | term '->' identifier {val=aptr(#1,#3);} | identifier {val=aidn(aeidn(#1));} | integer {val=node(n_int,#1);} | floatcon {val=node(n_float,#1);} | string {val=node(n_string,#1);} | '(' expression ')' {val=#2;} cast_type: literal_type_specifier null_decl null_decl: # empty # | '(' ')' | '(' null_decl ')' '(' ')' | '*' null_decl | null_decl '[' ']' | null_decl '[' constant ']' | '(' null_decl ')' while: WHILE {apshw();} do: DO {apshd();} for: FOR {apshf();} switch: SWITCH {apshs();} struct: STRUCT {strlev++;} $identifier: identifier {val=astridn(#1);} begin: '{' {abegin();} end: '}' {aend();} constant: constant '*' constant {val=#1*#3;} | constant '/' constant {val=#1/#3;} | constant '%' constant {val=#1%#3;} | constant '+' constant {val=#1+#3;} | constant '-' constant {val=#1-#3;} | constant '<<' constant {val=#1<<#3;} | constant '>>' constant {val=#1>>#3;} | constant '<' constant {val=#1<#3;} | constant '>' constant {val=#1>#3;} | constant '<=' constant {val=#1<=#3;} | constant '>=' constant {val=#1>=#3;} | constant '==' constant {val=#1==#3;} | constant '!=' constant {val=#1!=#3;} | constant '&' constant {val=#1} | constant '^' constant {val=#1^#3;} | constant '|' constant {val=#1|#3;} | constant '&&' constant {val=#1&} | constant '||' constant {val=#1||#3;} | constant '?' constant ':' constant {val=(#1?#3:#5);} | c_term c_term: '-' c_term {val= -#2;} | '!' c_term {val= !#2;} | '~' c_term {val= ~#2;} | integer | '(' constant ')' {val=#2;}

6 years, 7 months

Reconstructed and newly set UNIX Manual

by Angelo Papenhoff

The last couple of days I worked on re-setting the V3-V6 manuals. I reconstructed V5 from the scan as best I could, unfortunately some pages were missing. You can find everything I used to do this here, please read the BUGS section: https://github.com/aap/unixman The results can be found here, as HTML and PDF: http://squoze.net/UNIX/v3man/ http://squoze.net/UNIX/v4man/ http://squoze.net/UNIX/v5man/ http://squoze.net/UNIX/v6man/ Reconstructing V1 and V2 n?roff source and converting the tty 37 output to ps is something I want to do too, but for now this was exhausting enough. Now for the questions that I arose while I was doing this: Are there scans of the V4 and V6 manual to check my pdfs against? Where does the V5 manual come from? As explained in the README, some pages are missing and some pages seem to be earlier than V4. Is there another V5 manual that one could check against? Why is lc (the LIL compiler) not in the TOC but has a page? And most importantly: is the old troff really lost? I would love to set the manual on the original systems at some point (and write a CAT -> ps converter, which should be fun). Doing all this work made me wish we still had earlier versions of UNIX and its tools around. Have fun with this! aap

6 years, 7 months

Re: [TUHS] Unix APIs: elegant or not?

by jnc＠mercury.lcs.mit.edu

> From: Clem Cole > (probably because Larry Allen implemented both UNIX Chaos and Aegis IIRC). Maybe there are two Larry Allen's - the one who did networking stuff at MIT-LCS was Larry W. Allen, and I'm pretty sure he didn't do Unix CHAOS code (he was part of our group at LCS, and we only did TCP/IP stuff; someone over in EE had a Unix with CHAOS code at the time, so it pre-dated his time with us). Noel

6 years, 7 months

Revisions of "C Reference Manual"

by Lars Brinkhoff

Hello, Which revisions of the "C Reference Manuals" are known to be out there? I found this: https://www.bell-labs.com/usr/dmr/www/cman.pdf Which seems to match the one from V6: https://github.com/dspinellis/unix-history-repo/tree/Research-V6-Snapshot-D… "C is also available on the HIS 6070 computer at Murray Hill and and on the IBM System/370 at Holmdel [3]." But then there's this: https://www.princeton.edu/ssp/joseph-henry-project/unix-and-c/bell_labs_136… "C is also available on the HIS 6070 computer ar Hurray Hill, using a compiler written bu A. Snyder and currently maintained by S. C. Johnson. A compiler for the IBM System/360/370 series is under construction." Due to the description of the IBM compiler, it seems to predate the V6 revision. Both above revisions use the =+ etc operators. Finally, this version edited by Snyder: https://github.com/PDP-10/its/blob/master/doc/c/c.refman "In addition to the UNIX C compiler, there exist C compilers for the HIS 6000 and the IBM System/370 [2]." This version documents both += and =+ operators.

6 years, 7 months

First ARPAnet transmission

by Dave Horsfall

Of interest to the old farts here... At 22:30 (but which timezone?) on this day in 1969 the first packet got as far as "lo" (for "login") then crashed on the "g". More details over on http://en.wikipedia.org/wiki/Leonard_Kleinrock#ARPANET (with thanks to Bill Cheswick for the link). -- Dave

6 years, 7 months

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TUHS