I have encountered a strange problem dealing with pipes
and forking. The program basicaly does this:
cat file | tbl | eqn | groff
Now, I have a parent process that forks children
that that exec the stuff that they should. The pipes defined
in the parent are the ones used.
The chain goes like this
Parent creates N pipes (R/W pairs)
for i=N; i>0;i--
{
Parent forks child and gives it the read part of pipe i and
the write part of pipe i-1 (relative parent)
Child sets its stdin to pipe i and stdout to pipe i-1
Child execs program
}
Parent reads from the last pipe and writes to file.
Pipe: 0 1 2 3 4 5 6 7 8 9
parent: |R|W|R|W|R|W|R|W|R|W|
child: <-| | | \(going backwards\)
(I hope I formulated it right here, it's a bit messy)
Now the program works for small files, but for larger ones it truncates the file size to a multiple of the pipe buffer size k * (4096 bytes). I have no clue why this is, since the read() function waits for an EOF. The read function should also remove the things that it reads, so the pipe buffer should be continuously emptied.
I have asked several persons that know IPC far better then I do and they all agree that the code should work. But it doesnt.
Any ideas would be very welcome since I've been pulling my hair over this the last few days, without coming any closer to any explanation.
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#include <stdio.h>
#include <string.h>
#include <errno.h>
#define NOLL NULL
#define TROFF "/usr/bin/groff"
#define TBL "/usr/bin/tbl"
#define EQN "/usr/bin/eqn"
#define VIEWER "/mpkg/gv/3.5.8/bin/gv"
#define PRINTER "/usr/bin/lpr"
#define KATT "/bin/cat"
/to handle variables in a bunldle/
typedef struct
{
char** files;
char* toGroff;
int doPrint;
int doView;
int numFiles;
}param;
void doParse(param* pars, int argc, char argv);
void handleFile(param pars, int file);
void processChild(char prg, char** arg, int* inout, int pass);
/*
Pipe: 0 1 2 3 4 5 6 7 8 9
parent: |R|W|R|W|R|W|R|W|R|W|
child: <-| | | (inverted and going backwards)
*/
void processChild(char* prg, char** arg, int* inout, int pass)
{
int eRet; //error
int cPid; //pod
int* status; //status
char buff[10000]; //out buffer
cPid = 0;
switch (cPid = fork()) //new clone
{
case 0:
dup2\(inout[0], 1\); // invert the pipe so that parent stdout is child stdin
dup2\(inout[1], 0\);
for\(eRet = 3; eRet < 3\+10; close\(eRet\+\+\)\); //close all the
unused pipes except stdin, stdout and stderr
if (!pass)
{
eRet = execv(prg, arg); //exec with args
printf("return %d, %s\n",eRet, strerror(errno)); //should not happen
}
else
{
eRet = read(0, buff, 10000);
write(1, buff, eRet);
eRet = 0;
}
exit(0);
case -1:
printf("unhable to fork! error processing %s\t%s\n",prg,
arg[0]);
exit(6);
\}
}
void handleFile(param* pars, int file)
{
FILE* dafile;
int i;
int afpid;
int pipor[10]; //pipes
int inout[2]; //current pipe
int* inoutinout; //pointer to current pipe
char* tmpFile;
char* buff[500000]; //final output buffer
int rch;
//naturally organized optional parameters
char* noop[] = {"cat", pars->files[file], NOLL, NOLL}; //parameters
to program
for(i = 0; i<50000;buff[i\+\+]=NOLL);
for(i = 0; i<10;i++) //go througbht the pipes
{
if(pipe(inout) == -1)
{
printf("Error processing %s, unable to open pipe\n",
pars->files[file]);
exit(9);
}
pipor[i\+\+] = inout[0]; //stdin
pipor [i]= inout[1]; //std out
}
close\(pipor[9]\); //cat doesnt need stdin
inoutinout = pipor+7; //move pointer five steps (going backwards)
processChild(KATT, noop, inoutinout, 0); //process the cat
//close pipes
close(pipor[8]);
close(pipor[7]);
//parameters to tbl
noop[1] = NOLL;
noop[0] = "tbl";
inoutinout = pipor+5; //move pointer three steps
processChild(TBL, noop, inoutinout, 0);
close(pipor[6]);
close(pipor[5]);
//parameters to eqn - we have a problem
noop[1] = NOLL;
noop[0] = "eqn";
inoutinout = pipor+3; // three steps
processChild(EQN, noop, inoutinout, 0);
close(pipor[4]);
close(pipor[3]);
noop[1] = pars->toGroff;
noop[0] = "groff";
inoutinout = pipor+1; //one step
processChild(TROFF, noop, inoutinout, 0);
close(pipor[2]);
close(pipor[1]);
tmpFile = tmpnam(NOLL);
dafile = fopen(tmpFile,"a");
rch = read(pipor[0], buff, sizeof(buff));
printf("Size:%d\n",fputs(buff,dafile));
fclose(dafile);
printf("%s\n", tmpFile);
/// <SNIP> some irreleavant code
}
/// <SNIP> some irreleavant code