Re: [9fans] pipefile

[Steve Harris <scharris@worldnet.att.net>]

On Sun, 30 Jul 2000 14:54:30 rob pike wrote:

> The command is called pipefile; it interposes a command
> between you and the named file.  ...

I'm trying to understand this, but I can't figure out how the original 
file is actually read/written by this code.  

I think I'm misunderstanding, but it looks to me like the code produces 
a 
"closed loop" of two pipes with the filter command in between, with one 
side 
"data" bound over and replacing the original file (I'm with it so far I 
think).
But I don't see how the other side of the pipe, "data1", is connected at 
all 
with the contents of the original file ( before it had the 
 	bind(TEMP "/data", file, MREPL) 
done over it ). In fact I don't see how you can access the original file 

contents at all after the bind() call above has been done in the 
namespace.

Or do we not care about the original file at all?  Does rio make 
keyboard
input available for reading through /dev/cons even if we've bound 
something 
over the original file with MREPL?


What am I missing?

Here's the section I don't understand:

> 	file = argv[0];
> 	if(bind("#|", TEMP, MREPL) < 0)
> 		sysfatal("bind pipe %s: %r", TEMP);
> 	if(bind(TEMP "/data", file, MREPL) < 0)
> 		sysfatal("bind %s %s: %r", TEMP "/data", file);
> 
> 	if(bcmd != nil){
> 		fd0 = open(TEMP "/data1", ORDWR);
> 		if(fd0 < 0)
> 			sysfatal("open %s: %r", TEMP "/data1");
> 		connect(bcmd, fd0, fd0);
> 		close(fd0);
> 	}else{
> 		fd0 = open(TEMP "/data1", OREAD);
> 		if(fd0 < 0)
> 			sysfatal("open %s: %r", TEMP "/data1");
> 		connect(wcmd, fd0, 1);
> 		fd1 = open(TEMP "/data1", OWRITE);
> 		if(fd1 < 0)
> 			sysfatal("open %s: %r", TEMP "/data1");
> 		connect(rcmd, 0, fd1);
> 		close(fd0);
> 		close(fd1);
> 	}
> 	unmount(nil, TEMP);
> 	exits(nil);
> }
>