Hi all,
Im trying to do a simple program which ask the user for a unix command with the arguments. The program fork and the two process communicate with pipes. The child process call execvp with the command and the father process read the result of the execvp via the pipe.
This program works well with basic commands like ls or echo but when there's interaction between the user and the process for example tr a-z A-Z I think i get a broken pipe on the writing end of my pipe from the parent to the child.
In the parent process, I also have to poll between what the user type and what the child process send but I don't think this is the problem.
here's my code, the name variable and error messages are in french but you get the idea. thank u very much and sorry for bad english.
If you have any questions feel free to ask
Code:
void executerCommande( char *commande[], int descripteur, char* option )
{
int tubeEntree[2];
int tubeSortie[2];
int erreur;
erreur = pipe( tubeEntree );
if ( erreur == -1 )
{
printf( "Erreur lors de la création du tube %s\n", strerror( errno ) );
exit( 1 );
}
erreur = pipe( tubeSortie );
if ( erreur == -1 )
{
printf( "Erreur lors de la création du tube %s\n", strerror( errno ) );
exit( 1 );
}
pid_t pid = fork();
if ( pid == -1 ) // erreur
{
perror( "fork a échoué" );
exit( 1 );
}
else if ( pid == 0 ) // child
{
close( tubeEntree[1] ); // closing writing end of tube from parent to child
close( tubeSortie[0] ); // closing reading end of tube from child to parent
dup2( tubeSortie[1], STDOUT_FILENO ); // redirecting stdout to writing end of tube from child to parent
close( tubeSortie[1] ); // fermeture du doublon
dup2( tubeEntree[0], STDIN_FILENO ); // redirecting stdin to reading end of tube from parent to child
close( tubeEntree[0] ); // fermeture du doublon
execvp( commande[0], commande );
}
else // parent
{
int evenement;
int commandeTerminee = 0;
char tampon [256];
struct pollfd entrees[2];
entrees[0].fd = 0; // check stdin
entrees[0].events = POLLIN | POLLPRI; // surveiller pour des données normales ou prioritaires
entrees[0].revents = 0;
entrees[1].fd = tubeSortie[0]; // check reading end of tube from child to parent
entrees[1].events = POLLIN | POLLPRI; // surveiller pour des données normales ou prioritaires
entrees[1].revents = 0;
close( tubeEntree[0] ); // closing reading end of tube from parent to child
close( tubeSortie[1] ); // closing writing end of tube from child to parent
while ( commandeTerminee == 0 )
{
evenement = poll( entrees, 2, 0 );
if ( evenement == -1 )
{
printf( "Erreur lors du poll %s\n", strerror( errno ) );
exit( 1 );
}
if ( ( entrees[0].revents & POLLIN ) || ( entrees[0].revents & POLLPRI ) )
{
memset(tampon, '\0', 256);
read( entrees[0].fd, tampon, 256 );
if ( ( strcmp( option, "-i" ) == 0 ) || ( strcmp( option, "-io" ) == 0 ) )
{
erreur = write ( descripteur, tampon, strlen( tampon ) );
if ( erreur == -1 )
{
printf( "Erreur lors de l'écriture sur le fichier %s\n", strerror( errno ) );
exit( 1 );
}
}
erreur = write ( tubeEntree[1], tampon, strlen( tampon ) );
printf( "Ecriture enfant\n" );
if ( erreur == -1 )
{
printf( "Erreur lors de l'écriture dans le tube d'entrée %s\n", strerror( errno ) );
exit( 1 );
}
entrees[0].revents = 0;
}
if ( ( entrees[1].revents & POLLIN ) || ( entrees[1].revents & POLLPRI ) )
{
do {
memset(tampon, '\0', 256);
erreur = read( entrees[1].fd, tampon, 256 );
if ( erreur == -1 )
{
printf( "Erreur lors de la lecture du tube de sortie %s\n", strerror ( errno ) );
exit( 1 );
}
if ( ( strcmp( option, "-o" ) == 0 ) || ( strcmp( option, "-io" ) == 0 ) )
{
erreur = write( descripteur, tampon, strlen( tampon ) );
if ( erreur == -1 )
{
printf( "Erreur lors de l'écriture sur le fichier %s\n", strerror ( errno ) );
exit( 1 );
}
}
printf( "%s", tampon );
} while (erreur != 0);
entrees[1].revents = 0;
}
if ( entrees[1].revents & POLLHUP )
{
commandeTerminee = 1;
}
}
pid = wait( NULL );
}
}
---------- Post updated at 12:49 PM ---------- Previous update was at 11:26 AM ----------
I have force a read in the pipe connecting the child process ( the command ) to my parent process and there's nothing so my problem is either 1) the information coming from the user is not arriving at the child or the child is not writing properly in the exit pipe.
Any help would be appreciated... Its my first time with pipes
here's my code, the name variable and error messages are in french but you get the idea.
Not really, I don't. I have no idea what "descripteur" is and why you're writing to it, for example.
It would also help to know what you're trying to do with this command, and what it's actually doing. And maybe minor details like what your operating system is. Because if you're running linux, you could try strace -f ./command parameters to see a trace of system calls as it runs, which will tell you exactly who's waiting for what when.
---------- Post updated at 09:31 PM ---------- Previous update was at 09:03 PM ----------
descripteur is descriptor in french its because the parent process is suppose to collect the data from the child and write it in a file specified by descriptor.
I spent all day on this and decide to check the return value fo my dup2 and got an error when redirecting the output of my child process from stdout to the pipe tubeSortie[1].
I try replacing fileno(stdout) with 1 but i keep getting the same error:
Erreur lors du dup stdout Unknown error: 0
Im using mac os x with darwin
check this
Code:
void executerCommande( char *commande[], int descripteur, char* option )
{
int tubeEntree[2];
int tubeSortie[2];
int erreur;
erreur = pipe( tubeEntree );
if ( erreur == -1 )
{
printf( "Erreur lors de la création du tube %s\n", strerror( errno ) );
exit( 1 );
}
erreur = pipe( tubeSortie );
if ( erreur == -1 )
{
printf( "Erreur lors de la création du tube %s\n", strerror( errno ) );
exit( 1 );
}
pid_t pid = fork();
if ( pid == -1 ) // erreur
{
perror( "fork a échoué" );
exit( 1 );
}
else if ( pid == 0 ) // child
{
erreur = close( tubeEntree[1] ); // closing writing end of tube from parent to child
if ( erreur == -1 )
{
printf( "Erreur lors du close %s\n", strerror( errno ) );
exit( 1 );
}
erreur = close( tubeSortie[0] ); // closing reading end of tube from child to parent
if ( erreur == -1 )
{
printf( "Erreur lors du close %s\n", strerror( errno ) );
exit( 1 );
}
if ( dup2 ( tubeSortie[1], fileno(stdout) ) == -1 ); // redirecting stdout to writing end of tube from child to parent
{
printf( "Erreur lors du dup stdout %s\n", strerror( errno ) );
exit( 1 );
}
Once that's fixed: Your code does actually write to the pipe.
Code:
# the code does tr 'a-z' 'A-Z'
while true ; do echo -n a ; done | ./a.out
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA...
But the read end doesn't see data until the write end is full (or closes). That's probably at least 65536 bytes, if not much more, so you don't see enough by just typing. On EOF you should close the writing pipe and break the loop, which will cause the pipe to send everything it had.
---------- Post updated at 09:52 PM ---------- Previous update was at 09:40 PM ----------
Code:
fileno(stdout)
You don't need to do this. STDOUT_FILENO was right in the first place.
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