in reply to Re: named pipe and "Text file busy"
in thread named pipe and "Text file busy"

yes, you're right with your example: in my case instead of cat file.fifo >/dev/null i use my Perl script to read the FIFO.
Your example works fine for me as well, so i believe there's smth wrong with my Perl script.
I've checked there are no processes left after Ctrl-C the script. Here's the sequence of steps i perform:
1. Start the script that opens file.fifo and wait for data to arrive
2. in the shell: echo "test" > file.fifo. This works fine, the script reads "test" with no problems
3. Ctrl-C my Perl script
4. do echo "test" > file.fifo again. Result - "Text file busy"

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Re^3: named pipe and "Text file busy"
by tuxz0r (Pilgrim) on Nov 25, 2007 at 17:41 UTC
    From your steps, it looks like you start the reader (the perl script), then write something to the file, then kill the reader, then try to write to the file again. I think this is expected behavior (unless the FIFO is opened in non-blocking mode) because an open for reading or writing will block unless another open for the opposite is done (both ends need to be opened, reading and writing). When you kill the reader end of the named pipe your writer blocks because there is no one on the other end to read from it.

    I can't get my examples to recreate the ETXTBSY error, but I suspect that is what this is referring too. If you tail the FIFO in another terminal window and then do that last echo you should work w/o the error.

    ---
    echo S 1 [ Y V U | perl -ane 'print reverse map { $_ = chr(ord($_)-1) } @F;'
    Warning: Any code posted by tuxz0r is untested, unless otherwise stated, and is used at your own risk.

[reply]
      The expected behavior will be for the writer to block (unless open in non-blocking mode) - not to exit with an error. You can test this in the shell with "echo" and "cat". "text file busy" results after the writer tries to open the FIFO - it does not even get to the writing stage. I can confirm that with the C program i wrote that tries to open the FIFO with "open" system call and then returns errno 26 - "text file busy".
[reply]
        I must be missing something here. Can you post some code? I tried tail -fon the FIFO in one terminal, and then wrote a C program which opens the FIFO in "w" write mode. If the open fails, I use strerror(errno) to show the message and I don't get "Text file busy".

        Here's the small C program to write to the FIFO I used: 

        #include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>

int main(void)
{
        char buf[100];
        int fd = open("file.fifo", O_NONBLOCK|O_WRONLY);
        if (fd < 0) {
                fprintf(stderr, "error (%d): %s\n", errno, strerror(er
+rno));
                return 1;
        }

        sprintf(buf, "%s\n", "a new line");
        int bytes = write(fd, buf, strlen(buf) + 1);

        printf("wrote %d bytes", bytes);

        close(fd);
        return 0;
}

        [download]
        Is this how you are opening the file? When I run this program without the tail -f in the other window, I get ERRNO 6, "Device not configured", not "Text file busy". If I use open without the O_NONBLOCK the program hangs in the open as we both expect.

        ---
        echo S 1 [ Y V U | perl -ane 'print reverse map { $_ = chr(ord($_)-1) } @F;'
        Warning: Any code posted by tuxz0r is untested, unless otherwise stated, and is used at your own risk.

[reply]
[d/l]

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