Messages in this thread | | | From | TATSUKAWA KOSUKE(立川 江介) <> | Subject | Re: [PATCH] n_tty: wake up poll(POLLRDNORM) on receiving data | Date | Wed, 26 Jan 2022 23:34:39 +0000 |
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Hi, thank you for the reply.
> 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?
It's in "man poll". Below is an excerpt from the man page. POLLRDNORM Equivalent to POLLIN.
I'll send a v2 patch in a separate message.
Many other calls to wake_up_interruptible_poll() in the kernel source code already specify "POLLIN | POLLRDNORM", but there are places under drivers/tty which only passes POLLIN (i.e. pty.c, tty_io.c, tty_ldisc.c). I haven't yet made test programs to hit the other locations and I wasn't sure if they should also be fixed just for consistency.
Best regards.
> > 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 --- Kosuke TATSUKAWA | 1st Platform Software Division | NEC Solution Innovators | tatsu-ab1@nec.com
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