Review Request 129984: Prevent misdetection of EOF on Linux

[Kurt Hindenburg]

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Since this changes kpty, it needs to get reviewed on https://phabricator.kde.org/ - can you please open a request there?

- Kurt Hindenburg


On March 4, 2017, 10:56 p.m., Peter Wu wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/129984/
> -----------------------------------------------------------
> 
> (Updated March 4, 2017, 10:56 p.m.)
> 
> 
> Review request for Konsole and Kurt Hindenburg.
> 
> 
> Bugs: 372991
>     https://bugs.kde.org/show_bug.cgi?id=372991
> 
> 
> Repository: kpty
> 
> 
> Description
> -------
> 
> On Linux, even if slave activity is detected on a master fd, FIONREAD
> can still return zero available bytes in the buffer. Previously this
> would prevent further signals from being emitted even if new IO arrived
> (since the readNotifier is disabled) which in its turn prevented the
> Konsole output from being updated.
> 
> A race condition in the kernel is suspected, the first known broken
> kernel is v4.1.10-89-g5eb491ba5d06.
> 
> BUG: 372991
> 
> 
> Diffs
> -----
> 
>   src/kptydevice.cpp 22233a505d32d988795839cb592098c38f7fab33 
> 
> Diff: https://git.reviewboard.kde.org/r/129984/diff/
> 
> 
> Testing
> -------
> 
> Tested in conjunction with konsole v16.12.1-60-g151215a9 with this debug patch applied:
> ```
> diff --git a/src/kptydevice.cpp b/src/kptydevice.cpp
> index 92b443b..4dfcd02 100644
> --- a/src/kptydevice.cpp
> +++ b/src/kptydevice.cpp
> @@ -273,6 +273,7 @@ struct KPtyDevicePrivate : public KPtyPrivate {
>      KRingBuffer writeBuffer;
>  };
>  
> +#include <cstdio>
>  bool KPtyDevicePrivate::_k_canRead()
>  {
>      Q_Q(KPtyDevice);
> @@ -310,6 +311,9 @@ bool KPtyDevicePrivate::_k_canRead()
>          // select() will trigger again anyway if an EOF condition was found, and
>          // only then we will accept it.
>          if (!available && !maybeEof) {
> +            FILE *fp = fopen("/tmp/EOF", "a");
> +            fprintf(fp, "Maybe EOF!?\n");
> +            fclose(fp);
>              maybeEof = true;
>              return true;
>          } else if (available) {
> 
> ```
> 
> Indeed, the /tmp/EOF file is being written and the Konsole output no longer "hangs".
> 
> Closing a tab (via EOF in bash or closing the tab) somehow does not trigger this debug print, perhaps the watcher is disabled elsewhere. (This is an observation and not a problem.)
> 
> 
> Thanks,
> 
> Peter Wu
> 
>

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