Test get and set pipe/fifo buffer size.

Makefile

pipe-size: pipe-size.o
	$(CC) $< -o $@

pipe-size.c

#include <unistd.h>
#include <errno.h>
#include <stdio.h>
// Must use Linux specific fcntl header.
#include </usr/include/linux/fcntl.h>

int main(int argc, char *argv[]) {
    if (argc > 2) {
        printf("Usage: %s [fifo]\n\n"
                "Test get and set pipe buffer size\n",
                argv[0]);
        return 1;
    }

    int fd = 0; // Default to stdin, so we can test fcntl over pipe.

    if (argc == 2) {
        // The specified file should be a fifo.
        fd = open(argv[1], O_RDONLY);
        if (fd < 0) {
            perror("open failed");
            return 1;
        }
    }
    
    long pipe_size = (long)fcntl(fd, F_GETPIPE_SZ);
    if (pipe_size == -1) {
        perror("get pipe size failed.");
    }
    printf("default pipe size: %ld\n", pipe_size);

    int ret = fcntl(fd, F_SETPIPE_SZ, 1024 * 1024);
    if (ret < 0) {
        perror("set pipe size failed.");
    }

    pipe_size = (long)fcntl(fd, F_GETPIPE_SZ);
    if (pipe_size == -1) {
        perror("get pipe size 2 failed.");
    }
    printf("new pipe size: %ld\n", pipe_size);

    close(fd);
}

test.sh

#!/bin/bash

echo "Max pipe size for unprivileged user:"
cat /proc/sys/fs/pipe-max-size

echo

echo "Test with pipe"
echo "testdata" | ./pipe-size

echo

echo "Test with fifo"
mkfifo fifo
./pipe-size fifo &
echo "testdata" > fifo

rm fifo

Hi,

Thanks for posting this code! I'm running Debian Jessie on my Raspberry Pi and I'd like to set a higher buffer size for my FIFO pipes.

I've increased the max pipe buffer size:
sudo sysctl fs.pipe-max-size=4194304

Testing with a pipe works:

$ echo "testdata" | ./pipe-size
default pipe size: 65536
new pipe size: 1048576

Testing with a fifo produces no errors, but crashes my session:

echo "Test with fifo"
mkfifo fifo
./pipe-size fifo &
echo "testdata" > fifo
default pipe size: 65536
new pipe size: 1048576
Connection to raspberrypi.local closed.

Do you know why this would be?