write() via Qnet

QNX Newsgroups (Archives) qdn.public.qnxrtp.devtools
1

I have 2 QNX 6 (Patch B) computers (large and small), connected via Qnet.

#uname -a
#QNX large 6.00 2001/02/22-08:59:07est x86pc x86

Network looks fine. I’m trying to write file to Qnet’ed machine named
“small”.
Command

#cat any_file > /net/small/home/rk/filename

works fine. OK. So, I used small example like one from “Getting Started with
QNX Neutrino 2” Mr’s. Rob Krten (p. 101):

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>

int main(void)
{
int fd;

int ret;

fd = open("/net/small/home/rk/filename",
// O_WRONLY
O_CREAT, S_IRUSR | S_IWUSR
);

perror(“after open”);

ret = write(fd, “This is message passing”, 24);

perror(“after write”);

close(fd);

return (EXIT_SUCCESS);
}

With O_WRONLY flag in open() call result is:

after open: No such file or directory

#after write: Bad file descriptor

With O_CREAT flag and S_IRUSR | S_IWUSR mode:

after open: No error

#after write: Bad file descriptor

file /home/rk/filename on machine small was created, but with zero length.

Any ideas ?

Nick

2

Previously, Nick wrote in qdn.public.qnxrtp.devtools:

I have 2 QNX 6 (Patch B) computers (large and small), connected via Qnet.

#uname -a
#QNX large 6.00 2001/02/22-08:59:07est x86pc x86

Network looks fine. I’m trying to write file to Qnet’ed machine named
“small”.
Command

#cat any_file > /net/small/home/rk/filename

works fine. OK. So, I used small example like one from “Getting Started with
QNX Neutrino 2” Mr’s. Rob Krten (p. 101):

#include <stdio.h
#include <fcntl.h
#include <unistd.h
#include <sys/types.h
#include <sys/stat.h
#include <stdlib.h

int main(void)
{
int fd;

int ret;

fd = open("/net/small/home/rk/filename",
// O_WRONLY
O_CREAT, S_IRUSR | S_IWUSR
);

perror(“after open”);

ret = write(fd, “This is message passing”, 24);

perror(“after write”);

close(fd);

return (EXIT_SUCCESS);
}

With O_WRONLY flag in open() call result is:

after open: No such file or directory

#after write: Bad file descriptor

With O_CREAT flag and S_IRUSR | S_IWUSR mode:

after open: No error

#after write: Bad file descriptor

file /home/rk/filename on machine small was created, but with zero length.

Any ideas ?

Nick

Try sending the open mode as:
O_RDWR | O_CREAT
or
O_WRONLY | O_CREAT

The open mode needs O_CREAT if the file does not exist, and one form
of write permission. Your problem is that you are giving one or the
other of O_CREAT and O_WRONLY. You need both.

Cheers,
Andrew

3

On Thu, 26 Apr 2001 10:32:08 +0000, Andrew Thomas <Andrew@cogent.ca>
wrote:

Previously, Nick wrote in qdn.public.qnxrtp.devtools:
I have 2 QNX 6 (Patch B) computers (large and small), connected via Qnet.

#uname -a
#QNX large 6.00 2001/02/22-08:59:07est x86pc x86

Network looks fine. I’m trying to write file to Qnet’ed machine named
“small”.
Command

#cat any_file > /net/small/home/rk/filename

works fine. OK. So, I used small example like one from “Getting Started with
QNX Neutrino 2” Mr’s. Rob Krten (p. 101):

#include <stdio.h
#include <fcntl.h
#include <unistd.h
#include <sys/types.h
#include <sys/stat.h
#include <stdlib.h

int main(void)
{
int fd;

int ret;

fd = open("/net/small/home/rk/filename",
// O_WRONLY
O_CREAT, S_IRUSR | S_IWUSR
);

perror(“after open”);

ret = write(fd, “This is message passing”, 24);

perror(“after write”);

Side note: beware that errno is set only if an error occured, hence
if the write or open succeed the output of perror can
be misleading as it would show error of a previous function that
failed. In theory you should check ret and if( ret == -1 ) then
use perror.

4

Thanks, Andrew, it’s working!

Nick

“Andrew Thomas” <Andrew@cogent.ca> wrote in message
news:Voyager.010426103208.569378A@andrewhome.cogent.ca…

Previously, Nick wrote in qdn.public.qnxrtp.devtools:
I have 2 QNX 6 (Patch B) computers (large and small), connected via
Qnet.

#uname -a
#QNX large 6.00 2001/02/22-08:59:07est x86pc x86

Network looks fine. I’m trying to write file to Qnet’ed machine named
“small”.
Command

#cat any_file > /net/small/home/rk/filename

works fine. OK. So, I used small example like one from “Getting Started
with
QNX Neutrino 2” Mr’s. Rob Krten (p. 101):

#include <stdio.h
#include <fcntl.h
#include <unistd.h
#include <sys/types.h
#include <sys/stat.h
#include <stdlib.h

int main(void)
{
int fd;

int ret;

fd = open("/net/small/home/rk/filename",
// O_WRONLY
O_CREAT, S_IRUSR | S_IWUSR
);

perror(“after open”);

ret = write(fd, “This is message passing”, 24);

perror(“after write”);

close(fd);

return (EXIT_SUCCESS);
}

With O_WRONLY flag in open() call result is:

after open: No such file or directory

#after write: Bad file descriptor

With O_CREAT flag and S_IRUSR | S_IWUSR mode:

after open: No error

#after write: Bad file descriptor

file /home/rk/filename on machine small was created, but with zero
length.

Any ideas ?

Nick

Try sending the open mode as:
O_RDWR | O_CREAT
or
O_WRONLY | O_CREAT

The open mode needs O_CREAT if the file does not exist, and one form
of write permission. Your problem is that you are giving one or the
other of O_CREAT and O_WRONLY. You need both.

Cheers,
Andrew