Re: [PATCH] pipe: increase minimum default pipe size to 2 pages

On Wed, Aug 04, 2021 at 08:04:35PM -0400, Alex Xu (Hello71) wrote:

Before this patch, the following program prints 4096 and hangs.
Afterwards, it prints 8192 and exits successfully. Note that you may
need to increase your RLIMIT_NOFILE before running the program.

int main() {
    int pipefd[2];
    for (int i = 0; i < 1025; i++)
        if (pipe(pipefd) == -1)
            return 1;
    size_t bufsz = fcntl(pipefd[1], F_GETPIPE_SZ);
    printf("%zd\n", bufsz);
    char *buf = calloc(bufsz, 1);
    write(pipefd[1], buf, bufsz);
    read(pipefd[0], buf, bufsz-1);
    write(pipefd[1], buf, 1);
}

Signed-off-by: Alex Xu (Hello71) <redacted>
---

Is this due to the changes that happened in 5.5?  If so, a cc: stable
and a fixes tag would be nice to have :)

See discussion at https://lore.kernel.org/lkml/1628086770.5rn8p04n6j.none@localhost/ (local).

This can go up in the changelog text too.

thanks,

greg k-h