fread and fwrite demystified: stdio on UNIX V7

(This is a guest post by xorhash.)

1. Introduction

Did I say I’m done with UNIX Seventh Edition (V7)? How silly of me; of course I’m not. V7 is easy to study, after all.

Something that’s always bothered me about the stdio.h primitives fread() and fwrite() are their weak guarantees about what they actually do. Is a short read or write “normal” in the sense that I should normally expect it? While this makes no answer about modern-day operating systems, a look at V7 may enlighten me about what the historical precedent is.

As an aside: It’s worth noting that the stdio.h functions are some of the few that require a header. It was common historical practice not to declare functions in headers, just see crypt(3) as an example.

I will first display the man page, then ask the questions I want to answer, then look at the implementation and finally use that gained knowledge to answer the questions.

2. Into the Man Page

The man page for fread() and fwrite() is rather terse. Modern-day man pages for those functions are equally terse, though, so this is not exactly a novelty of age. Here’s what it reads:

NAME

fread, fwrite – buffered binary input/output

SYNOPSIS

#include <stdio.h>

fread(ptr, sizeof(*ptr), nitems, stream)
FILE
*stream;

fwrite(ptr, sizeof(*ptr), nitems, stream)
FILE
*stream;

DESCRIPTION

Fread reads, into a block beginning at ptr, nitems of data of the type of *ptr from the named input stream. It returns the number of items actually read.

Fwrite appends at most nitems of data of the type of *ptr beginning at ptr to the named output stream. It returns the number of items actually written.

SEE ALSO

read(2), write(2), fopen(3), getc(3), putc(3), gets(3), puts(3), printf(3), scanf(3)

DIAGNOSTICS

Fread and fwrite return 0 upon end of file or error.

So there are the following edge cases that are interesting:

  • In fread(): If sizeof(*ptr) is greater than the entire file, what happens?
  • If sizeof(*ptr) * nitems overflows, what happens?
  • Is the “number of items actually read/written” guaranteed to be the number of items that can be read/written (until either EOF or I/O error)?
  • Is the “number of items actually written” guaranteed to have written every item in its entirety?
  • What qualifies as error?

3. A Look at fread()

Note: All file paths for source code are relative to /usr/src/libc/stdio/ unless noted otherwise. You can read along at the TUHS website.

rdwr.c implements fread(). fread() is simple enough; it’s just a nested loop. The outer loop runs nitems times. The outer loop sets the number of bytes to read (sizeof(*ptr)) and runs the inner loop. The inner loop calls getc() on the input FILE *stream and writes each byte to *ptr until either getc() returns a value less < 0 or all bytes have been read.

/usr/include/stdio.h implements getc(FILE *p) as a C preprocessor macro. If there is still data in the buffer, it returns the next character and advances the buffer by one. Interestingly, *(p)-&gt;_ptr++&amp;0377 is used to return the character, despite _ptr being a char *. I’m not sure why that &amp;0377 (&amp;0xFF is there. If there is no data in the buffer, it instead returns _filbuf(p).

filbuf.c implements _filbuf(). This function is a lot more complex than the other ones until now. It begins with a check for the _IORW flag and, if set, sets the _IOREAD flag as well. It then checks if _IOREAD is not set or if _IOSTRG is set and returns EOF (defined as -1 in stdio.h) if so. These all seem rather inconsequential to me. I can’t make heads or tails of _IOSTRG, however, but it seems irrelevant; _IOSTRG is only ever set internally in sprintf and sscanf for temporary internal FILE objects. After those two flag checks, _filbuf() allocates a buffer into iop-&lt;_base, which seems to be the base pointer of the buffer. If flag _IONBF is set, which happens when setbuf() is used to switch to unbuffered I/O, a temporary, static buffer is used instead. Then read() is called, requesting either 1 bytes if unbuffered I/O is requested or BUFSIZ bytes. If read() returned 0, the FILE is flagged as end-of-file and EOF is returned by _filbuf(). If read() returned <0, the FILE is flagged as error and EOF is returned by _filbuf(). Otherwise, the first character that has been read is returned by _filbuf() and the buffer pointer incremented by one.

According to its man page, read() only returns 0 on end-of-file. It can also return -1 on “many conditions”, namely “physical I/O errors, bad buffer address, preposterous nbytes, file descriptor not that of an input file”

As an aside, BUFSIZ still exists today. ISO C11 § 7.21.2 no. 9 dictates that BUFSIZ must be at least 256. V7 defines it as 512 in stdio.h. One is inclined to note that on V7, a filesystem block was understood 512 bytes length, so this was presumably chosen for efficient I/O buffering.

4. A Look at fwrite()

rdwr.c also implements fwrite(). fwrite() is effectively the same as fread(), except the inner loop uses putc(). After every inner loop, a call to ferror() is made. If there was indeed an error, the outer loop is stopped.

/usr/include/stdio.h implements putc(int x, FILE *p) as a C preprocessor macro. If there is still room in the buffer, the write happens into the buffer. Otherwise, _flsbuf() is called.

flsbuf.c implements _flsbuf(int c, FILE *iop). This function, too, is more complex than the ones until now, but becomes more obvious after reading _filbuf(). It starts with a check if _IORW is set and if so, it’ll set _IOWRT and clear the EOF flag. Then it branches into two major branches: the _IONBF branch without buffering, which is a straight call to write(), and the other branch, which allocates a buffer if none exists already or otherwise calls write() if the buffer is full. If write() returned less than expected, the error flag is set and EOF returned. Otherwise, it returns the character that was written.

According to its man page, write() returns the number of characters (bytes) actually written; a non-zero value “should be regarded as an error”. With only a cursory glance over the code, this appears to happen for similar reasons as read(), which is either physical I/O error or bad parameters.

5. Conclusions

In fread(): If sizeof(*ptr) is greater than the entire file, what happens?
On this under-read, fread() will end up reading the entire file into the memory at ptr and still return 0. The I/O happens byte-wise via getc(), filling up the buffer until getc() returns EOF. However, it will not return EOF until a read() returns 0 on EOF or -1 on error. This result may be meaningful to the caller.

If sizeof(*ptr) * nitems overflows, what happens?
No overflow can happen because there is no multiplication. Instead, two loops are used, which avoids the overflow issue entirely. (If there are strict filesystem constraints, however, it may be de-facto impossible to read enough bytes that sizeof(*ptr) * nitems overflows. And of course, there’s no way you could have enough RAM on a PDP-11 for the result to actually fit into memory.)

Is the “number of items actually read/written” guaranteed to be the number of items that can be read/written (until either EOF or I/O error)?
Partially: Both fread() and fwrite() short-circuit on error. This causes the number of items that have actually been read or written successfully to be returned. The only relevant error condition is filesystem I/O error. Due to the byte-wise I/O, it’s possible that there was a partial read or write for the last element, however. Therefore, it would be more accurate to say that the “number of items actually read/written” is guaranteed to be the number of non-partial items that can be read/written. A short read or short write is an abnormal condition.

Is the “number of items actually written” guaranteed to have written every item in its entirety?
No, it isn’t. A partial write is possible. If a series of structs is written and then to be read out again, however, this is not a problem: fread() and fwrite() only return the count of full items read or written. Therefore, the partial write will not cause a partial read issue. If a set of bytes is written, this is an issue: There will be incomplete data – possibly to be parsed by the program. It is therefore to preferable to write (and especially read) arrays of structs than to write and read arrays of bytes. (From a modern-day perspective, this is horrendous design because this means data files are not portable across platforms.)

What qualifies as error?
Effectively, only a physical I/O error or a kernel bug. Short fread() or fwrite() return values are abnormal conditions. I’m not sure if there is the possibility that the process got a signal and the current read() or write() ends up writing nothing before the EINTR; this seems to be more of a modern-day problem than something V7 concerned itself.

Teaching an Almost 40-year Old UNIX about Backspace

(This is a guest post by xorhash.)

Introduction

I have been messing with the UNIX®† operating system, Seventh Edition (commonly known as UNIX V7 or just V7) for a while now. V7 dates from 1979, so it’s about 40 years old at this point. The last post was on V7/x86, but since I’ve run into various issues with it, I moved on to a proper installation of V7 on SIMH. The Internet has some really good resources on installing V7 in SIMH. Thus, I set out on my own journey on installing and using V7 a while ago, but that was remarkably uneventful.

One convenience that I have been dearly missing since the switch from V7/x86 is a functioning backspace key. There seem to be multiple different definitions of backspace:

  1. BS, as in ASCII character 8 (010, 0x08, also represented as ^H), and
  2. DEL, as in ASCII character 127 (0177, 0x7F, also represented as ^?).

V7 does not accept either for input by default. Instead, # is used as the erase character and @ is used as the kill character. These defaults have been there since UNIX V1. In fact, they have been “there” since Multics, where they got chosen seemingly arbitrarily. The erase character erases the character before it. The kill character kills (deletes) the whole line. For example, “ba##gooo#d” would be interpreted as “good” and “bad line@good line” would be interpreted as “good line”.

There is some debate on whether BS or DEL is the correct character for terminals to send when the user presses the backspace key. However, most programs have settled on DEL today. tmux forces DEL, even if the terminal emulator sends BS, so simply changing my terminal to send BS was not an option. The change from the defaults outlined here to today’s modern-day defaults occurred between 4.1BSD and 4.2BSD. enf on Hacker News has written a nice overview of the various conventions.

Changing the Defaults

These defaults can be overridden, however. Any character can be set as erase or kill character using stty(1). It accepts the caret notation, so that ^U stands for ctrl-u. Today’s defaults (and my goal) are:

Function Character
erase DEL (^?)
kill ^U

I wanted to change the defaults. Fortunately, stty(1) allows changing them. The caret notation represents ctrl as ^. The effect of holding ctrl and typing a character is bitwise-ANDing it with 037 (0x1F) as implemented in /usr/src/cmd/stty.c and mentioned in the stty(1) man page, so the notation as understood by stty(1) for ^? is broken for DEL: ASCII ? bitwise-AND 037 is US (unit separator), so ^? requires special handling. stty(1) in V7 does not know about this special case. Because of this, a separate program – or a change to stty(1) – is required to call stty(2) and change the erase character to DEL. Changing the kill character was easy enough, however:
$ stty kill '^U'

So I wrote that program and found out that DEL still didn’t work as expected, though ^U did. # stopped working as erase character, so something certainly did change. This is because in V7, DEL is the interrupt character. Today, the interrupt character is ^C.

Clearly, I needed to change the interrupt character. But how? Given that stty(1) nor the underlying syscall stty(2) seemed to let me change it, I looked at the code for tty(4) in /usr/sys/dev/tty.c and /usr/sys/h/tty.h. And in the header file, lo and behold:

#define  CERASE  '#'    /* default special characters */
#define CEOT 004
#define CKILL '@'
#define CQUIT 034 /* FS, cntl shift L */
#define CINTR 0177 /* DEL */
#define CSTOP 023 /* Stop output: ctl-s */
#define CSTART 021 /* Start output: ctl-q */
#define CBRK 0377

I assumed just changing these defaults would fix the defaults system-wide, which I found preferable to a solution in .profile anyway. Changed the header, one cycle of make all, make unix, cp unix /unix and a reboot later, the system exhibited the same behavior. No change to the default erase, kill or interrupt characters. I double-checked /usr/sys/dev/tty.c, and it indeed copied the characters from the header. Something, somewhere must be overwriting my new defaults.

Studying the man pages in vol. 1 of the manual, I found that on multi-user boot init calls /etc/rc, then calls getty(8), which then calls login(1), which ultimately spawns the shell. /etc/rc didn’t do anything interesting related to the console or ttys, so the culprit must be either getty(8) or login(1). As it turns out, both of them are the culprits!

getty(8) changes the erase character to #, the kill character to @ and the struct tchars to { '\177', '\034', '\021', '\023', '\004', '\377' }. At this point, I realized that:

  1. there’s a struct tchars,
  2. it can be changed from userland.

The first member of struct tchars is char t_intrc, the interrupt character. So I could’ve had a much easier solution by writing some code to change the struct tchars, if only I’d actually read the manual. I’m too far in to just settle with a .profile solution and a custom executable, though. Besides, I still couldn’t actually fix my typos at the login prompt unless I make a broader change. I’d have noticed the first point if only I’d actually read the man page for tty(4). Oops.

login(1) changes the erase character to # and the kill character to @. At least the shell leaves them alone. Seriously, three places to set these defaults is crazy.

Fixing the Characters

The plan was simple, namely, perform the following substitution:

Function Old Character Old Character
ASCII (Octal)
New Character New Character
ASCII (Octal)
erase # 043 DEL 0177
kill @ 0100 ^U 025
interrupt DEL 0177 ^C 003

So I changed the characters in tty(4), getty(8) and login(1). It worked! Almost. Now DEL did indeed erase. However, there was no feedback for it. When I typed DEL, the cursor would stay where it is.

Pondering the code for tty(4) again, I found that there is a variable called partab, which determines delays and what kind of special handling to apply if any. In particular, BS has an entry whose handler looks like this:

  /* backspace */
case 2:
if (*colp)
(*colp)--;
break;

Naïve as I was, I just changed the entry for DEL from “non-printing” to “backspace”, hoping that would help. Another recompilation cycle and reboot later, nothing changed. DEL still only silently erased. So I changed the handler for another character, recompiled, rebooted. Nothing changed. Again. At that point, I noticed something else must have been up.

I found out that the tty is in so-called echo mode. That means that all characters typed get echoed back to the tty. It just so happens that the representation of DEL is actually none at all. Thus it only looked like nothing changed, while the character was actually properly echoed back. However, when temporarily changing the erase character to BS (^H) and typing ^H manually, I would get the erase effect and the cursor moved back by one character on screen. When changing the erase character to something else like # and typing ^H manually, I would get no erasure, but the cursor moved back by one character on screen anyway. I now properly got the separation of character effect and representation on screen. Because of this unprintable-ness of DEL, I needed to add a special case for it in ttyoutput():

  if (c==0177) {
ttyoutput(010, tp);
ttyoutput(' ', tp);
ttyoutput(010, tp);
return;
}

What this does is first send a BS to move the cursor back by one, then send a space to rub out the previous character on screen and then send another BS to get to the previous cursor position. Fortunately, my terminal lives in a world where doing this is instantaneous.

Getting the Diff

For future generations as well as myself when I inevitably majorly break this installation of V7, I wanted to make a diff. However, my V7 is installed in SIMH. I am not a very intelligent man, I didn’t keep backup copies of the files I’d changed. Getting data out of this emulated machine is an exercise in frustration.

Transmission over ethernet is out by virtue of there being no ethernet in V7. I could simulate a tape drive and write a tar file to it, but neither did I find any tools to convert from simulated tape drive to raw data, nor did I feel like writing my own. I could simulate a line printer, but neither did V7 ship with the LP11 driver (apparently by mistake), nor did I feel like copy/pasting a long lpr program in – a simple cat(1) to /dev/lp would just generate fairly garbled output. I could simulate another hard drive, but even if I format it, nothing could read the ancient file system anyway, except maybe mount_v7fs(8) on NetBSD. Though setting up NetBSD for the sole purpose of mounting another virtual machine’s hard drive sounds silly enough that I might do it in the future.

While V7 does ship with uucp(1), it requires a device to communicate through. It seems that communication over a tty is possible V7-side, but in my case, quite difficult. I use the version of SIMH as packaged on Debian because I’m a lazy person. For some reason, the DZ11 terminal emulator was removed from that package. The DUP11 bit synchronous interface, which I hope is the same as the DU-11 mentioned /usr/sys/du.c, was not part of SIMH at the time of packaging. V7 only speaks the g protocol (see Ptbl in /usr/src/cmd/uucp/cntrl.c), which requires the connection to be 8-bit clean. Even if the simulator for a DZ11 were packaged, it would most likely be unsuitable because telnet isn’t 8-bit clean by default and I’m not sure if the DZ11 driver can negotiate 8-bit clean Telnet. That aside, I’m not sure if Taylor UUCP for Linux would be able to handle “impure” TCP communications over the simulated interface, rather than a direct connection to another instance of Taylor UUCP. Then there is the issue of general compatibility between the two systems. As reader DOS pointed out, there seem to be quite some difficulties. Those difficulties were experienced on V7/x86, however. I’m not ruling out that the issues encountered are specific to V7/x86. In any case, UUCP is an adventure for another time. I expect it’ll be such a mess that it’ll deserve its own post.

In the end, I printed everything on screen using cat(1) and copied that out. Then I performed a manual diff against the original source code tree because tabs got converted to spaces in the process. Then I applied the changes to clean copies that did have the tabs. And finally, I actually invoked diff(1).

Closing Thoughts

Figuring all this out took me a few days. Penetrating how the system is put together was surprisingly fairly hard at first, but then the difficulty curve eased up. It was an interesting exercise in some kind of “reverse engineering” and I definitely learned something about tty handling. I was, however, not pleased with using ed(1), even if I do know the basics. vi(1) is a blessing that I did not appreciate enough until recently. Had I also been unable to access recursive grep(1) on my host and scroll through the code, I would’ve probably given up. Writing UNIX under those kinds of editing conditions is an amazing feat. I have nothing but the greatest respect for software developers of those days.

Here’s the diff, but V7 predates patch(1), so you’ll be stuck manually applying it: backspace.diff

† UNIX is a trademark of The Open Group.

 

Life in UNIX® V7: an attempt at a simple task

(This is a guest post by xorhash.)

1. Introduction

ChuckMcM on Hacker News (https://news.ycombinator.com/item?id=15990351) reacted to my previous entry here about trying to typeset old troff sources with groff. It was said that ‘‘you really can’t appreciate troff (and runoff and scribe) unless you do all of your document preparation on a fixed width font 24 line by 80 column terminal’’.

‘‘Challenge accepted’’ I said to myself. However, it would be quite boring to just do my document preparation in this kind of situation. Thus, I raised the ante: I will do my document preparation on a fixed width font 24 line by 80 column terminal on an ancient UNIX . That document is the one you are reading here.

2. Getting an old version of UNIX

While it would have been interesting to run my experiment on SIMH with a genuine UNIX , I was feeling far too lazy for that. Another constraint I made for myself is that I wanted to use the Internet as little as possible. Past the installation phase, only resources that are on the filesystem or part of the Seventh Edition Manual should be consulted. However, if I have to work with SIMH, chances are I’d be possibly fighting the emulator and the old emulated hardware much more than the software.

2.1. FreeBSD 1.0

My first thought was that I could just go for FreeBSD 1.0 or something. FreeBSD 1.0 dates from around 1993. That was surprisingly recent, but I needed a way to get the data off this thing again, so I did want networking. As luck would have it, FreeBSD 1.0 refused to install, giving me a hard read error when trying to read the floppy. FreeBSD 2.0 was from 1995 and already had colorful menus to install itself (!). That’s no use for an exercise in masochism.

2.2. V7/x86

I turned to browsing http://gunkies.org/wiki/Main_Page for a bit, hoping to find something to work with. Lo and behold, it pointed me to http://www.nordier.com/v7x86/! V7/x86 is a port of UNIX version 7 to the x86. It made some changes to V7, among those are:

1.

including the more pager,

2.

including the vi editor,

3.

providing a console for the screen, rather than expecting a teletype, and

4.

including an installation script.

The version of vi that ships with it is surprisingly usable, even by today’s standards. I believe I would’ve gone mad if I’d had to use ed to write this text with.

3. Installing V7/x86

The V7/x86 installer requires that a partition exists with the correct partition type. It ships with a tool called ptdisk to do that, but because /boot/mbr does not exist on the installation environment, it cannot initialize a disk that does not already have a partition table (http://www.nordier.com/v7x86/files/ISSUES). Thus I used a (recent) release of FreeBSD to create it. At first, FreeBSD couldn’t find its own CD-ROM, which left me quite confused. As it turns out, it being unable to find the CD-ROM was a side effect of assigning only 64 megabytes of RAM to the virtual machine. Once I’d bumped the RAM to 1GB, the FreeBSD booting procedure worked and I could create the partition for V7/x86. V7/x86 itself comes packaged on a standard ISO file and with a simple installation script. It seems it requires an IDE drive, but I did not investigate support for other types of hard drives, in particular SATA drives, much further. There seem to be no USB drivers, so USB keyboards may not work, either.

During the installation, my hard drive started making a lot of scary noises for a few minutes, so I aborted the installation procedure. After moving the disk image to a RAM disk (thank you, Linux, for giving me the power of tmpfs), I restarted the installation and it went in a flash. The scary noises were probably related to copying data with a block size of 20, which I assume was 20 bytes per block: The virtual hard disk was opened with O_DIRECT, i.e., all writes got flushed to it immediately. Rewriting the hard drive sector 20 bytes at a time must’ve been rather stressful for the drive.

4. Using V7/x86

I thought I knew my UNIX , but the 70s apparently had a few things to teach me. Fortunately, getting the system into a usable state was fairly simple because http://www.nordier.com/v7x86/doc/v7x86intro.pdf got me started. The most important notes are:

1.

V7 boots in single-user mode by default. Only when you exit single-user mode, /etc/rc is actually run and the system comes up in multi-user mode.

2.

Using su is recommended because root has an insane environment by default. To erase, # is used, rather than backspace (^H). The TERM variable is not set, breaking vi. /usr/ucb is not on the path, making more unavailable.

3.

The character to interrupt a running command is DEL, not ^C. It does not seem possible to remap this.

more is a necessity on a console. I do not have a teletype, meaning I cannot just ‘‘scroll’’ by reading the text on the sheet so far. Therefore, man is fairly useless without also piping its output to more.

Creating a user account was simple enough, though: Edit /etc/passwd, run passwd for the new user, make the home directory, done. However, my first attempt failed hard because I was not aware of the stty erase situation. I now have a directory in /usr that reads ‘‘xorhash’’, but is definitely not the ASCII string ‘‘xorhash’’. It’s ‘‘o^Hxorhash’’. The same problem applies to hitting the arrow keys out of habit to access the command history, only to butcher the partial command you were writing that way.

Another mild inconvenience is the lack of alternative keyboard layouts. There is only the standard US English keyboard layout. I’m not used to it and it took me a while to figure out where some relevant keys ($, ^, &, / and – in particular) are. Though I suppose if I really wanted to, I could mess around with the kernel and the console driver, which is probably the intended way to change the keyboard layout in the first place.

5. Writing a document

Equipped with a new user, I turned to writing this text down before my memory fails me on the installation details.

5.1. The vi Editor

I am infinitely thankful for having vi in the V7/x86 distribution. Truly, I cannot express enough gratitude after just seeing a glimpse of ed in the V7/x86 introduction document. It has some quirks compared to my daily vim setup, though. Backspacing across lines is not possible. c only shows you until where you’re deleting by marking the end with $. You only get one undo, and undoing the undo is its own undo entry. And of course, there’s no syntax highlighting in that day and age.

5.2. troff/nroff

And now for the guests of this show for which the whole exercise was undertaken. The information in volume 2A of the 7th Edition manuals was surprisingly useful to get me started with the ms macros. I didn’t bother reading the troff/nroff User’s Manual as I only wanted to use the program, not write a macro package myself. The ms macro set seemed to be the way to go for that. In this case, nroff did much more heavy lifting than troff. After all, troff is designed the Graphic Systems C/A/T phototypesetter. I don’t have one of those. M. E. Lesk’s Typing Documents on the UNIX System: Using the −ms Macros with Troff and Nroff and Brian W. Kernighan’s A TROFF Tutorial proved invaluable trying to get this text formatted in nroff.

The ‘‘testing’’ cycle is fairly painful, too. When reading the nroff output, some formatting information (italics, bold) is lost. more can only advance pagewise, which makes it difficult to observe paragraphs in their entirety. It also cannot jump or scroll very fast so that finding issues in the later pages becomes infuriating, which I solved by splitting the file up into multiple files, one for each section heading.

5.3. The refer program and V7/x86

Since I was writing this in roff anyway, I figured I might as well take advantage of its capabilities – I wanted to use refer. It is meant to keep a list of references (think BibTeX). Trying to run it, I got this:

$ /bin/refer
/bin/refer: syntax error at line 1: ‘)’
unexpected

The system was trying to run the file as shell script. This also happens for tbl. It was actually an executable for which support got removed during the port (see https://pastebin.com/cxRhR7u9). I contacted Robert Nordier about this; he suggested I remove the -i and -n flags and recompile refer. Now it runs, exhibiting strange behavior instead: https://pastebin.com/0dQtnxSV For all intents and purposes, refer is quite unusable like this. Fixing this is beyond my capacity, unfortunately, and (understandably) Robert Nordier does not feel up to diving into it, either. Thus, we’ll have to live without the luxury of a list of references.

6. Getting the Data off the Disk

I’m writing this text on V7/x86 in a virtual machine. There are multiple ways I could try to get it off the disk image, such as via a floppy image or something. However, that sounds like effort. I’ll try to search for it in the raw disk image instead and just copy it out from there. Update: I’ve had to go through the shared floppy route. The data in this file is split up on the underlying file system. Fortunately, /dev/ entries are just really fancy files. Therefore, I could just write with tar to the floppy directly without having to first create an actual file system. The host could then use that “floppy” as a tar file directly.

Even when I have these roff sources, I still need to get them in a readable format. I’ll have to cheat and use groff -Thtml to generate an HTML version to put on the blog. However, to preserve some semblance of authenticity, I’ll also put the raw roff source up, along with the result of running nroff over it on the version running on V7/x86. That version of nroff attributes the trademark to Bell Laboratories. This is wrong. UNIX is a registered trademark of The Open Group.

7. Impressions

ChuckMcM was right. When you’re grateful for vi, staring at a blob of text with no syntax highlighting and with limited space, you start appreciating troff/nroff much more. In particular, LaTeX tends to have fairly verbose commands. Scanning through those without syntax highlighting becomes more difficult. However, ‘‘parsing’’ troff/nroff syntax is much easier on one’s mind. Additionally, the terse commands help because

\section{Impressions}

stands out much less than

.NH
Impressions
.PP

That can be helped by adding whitespace, but then you remove some precious context on your tiny 80×24 screen. troff/nroff are very much children of their time, but they’re not as bad as I may have made them look last time. Having said that, there’s no way you’ll ever convince me to actually touch troff/nroff macros.

As for the system as a whole, I was positively surprised how usable it was by today’s standards. The biggest challenge is getting the system up and shutting it down again, as well as moving data to and from it. I did miss having a search function whenever I was looking for information on roff in volume 2A of the manual.

I have the greatest of respect for the V7/x86 project. Porting an ancient operating system that hardcoded various aspects of the PDP-11 in scattered places must have been extremely frustrating. The drivers were written in the ancient version of C that is used on V7 (see /usr/sys/dev).

 

Unix v7 for the x86!

Ok so this isn’t exactly emulation, since you can already run Unix v7 via simh’s PDP11 emulator, however you cannot overlook the coolness factor of this. They have ported v7 to the i486 cpu.

http://www.nordier.com/v7x86/index.html

In other news I’ve done a very preliminary port of the SLiRP stack from Qemu to SIMH. What is cool about this, is that it allows user mode networking so that you do not have to configure any drivers on the host. Currently I have 4.3BSD-Reno running under the MicroVAX II simulator. I’m going to add some extra utilities (gzip/gcc/gnumake/ircii-4/lynx?/wget?/apache?), convert the SMM into PDF’s, and make it into an install package, much like the 4.2BSD on sourceforge.

If anyone want’s to alpha test it, let me know, otherwise the next post will most likely be the release of 4.3BSD-RENO with NAT!

Happy Thanksgiving!