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SubjectRe: [PATCH] n_tty: wake up poll(POLLRDNORM) on receiving data
On Mon, Jan 24, 2022 at 08:17:22AM +0000, TATSUKAWA KOSUKE(立川 江介) wrote:
> Event POLLRDNORM should be equivalent to POLLIN when used as event in
> poll().

Where is that documented?

> However, in n_tty driver, POLLRDNORM does not return until
> timeout even if there is terminal input, whereas POLLIN returns.
>
> The following test program works until kernel-3.17, but the test stops
> in poll() after commit 57087d515441 ("tty: Fix spurious poll() wakeups").
>
> [Steps to run test program]
> $ cc -o test-pollrdnorm test-pollrdnorm.c
> $ ./test-pollrdnorm
> foo <-- Type in something from the terminal followed by [RET].
> The string should be echoed back.
>
> ------------------------< test-pollrdnorm.c >------------------------
> #include <stdio.h>
> #include <errno.h>
> #include <poll.h>
> #include <unistd.h>
>
> void main(void)
> {
> int n;
> unsigned char buf[8];
> struct pollfd fds[1] = {{ 0, POLLRDNORM, 0 }};
>
> n = poll(fds, 1, -1);
> if (n < 0)
> perror("poll");
> n = read(0, buf, 8);
> if (n < 0)
> perror("read");
> if (n > 0)
> write(1, buf, n);
> }
> ------------------------------------------------------------------------
>
> The attached patch fixes this problem.
>
> Signed-off-by: Kosuke Tatsukawa <tatsu-ab1@nec.com>
> Fixes: commit 57087d515441 ("tty: Fix spurious poll() wakeups")

No need for "commit" here, please remove as the documentation asks you
to.

Can you resend this with this fixed up, and a pointer to where the
documentation is for this functionality.

thanks,

greg k-h

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