Subject: Re: Setting termios VMIN > 0 and VTIME > 0 on non blocking file
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Message-ID: <ac1d31f7-a945-5a0f-2fa0-1e9646b14bcc@gmail.com>
Date: Tue, 17 Mar 2020 16:54:35 +0100
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On 2020-03-17 13:16, Corinna Vinschen wrote:
> Hi Åke,
>
> On Mar 16 10:35, Corinna Vinschen wrote:
>> On Mar 14 11:36, Åke Rehnman via Cygwin wrote:
>>> On 2020-03-14 11:23, Åke Rehnman wrote:
>>>>>> BTW there is a gremlin in the "else if (ev)" line....
>>>>> A gremlin?  Would you mind to explain?  Btw., if you find a bug
>>>>> in the code, we do take patches :) https://cygwin.com/contrib.html
>>>> If we have an error event in ev it will make a blocking read even if
>>>> VTIME==0.
>> Ah, yeah, I was aware of that, I just ignored it for now since I'm not
>> sure what the best way to handle that is.
>>
>> Two options come to mind, either ignoring these errors entirely, or
>> returning -1 with errno set to EIO, along the lines of the Linux test
>> for tty_io_error() at the start of tty_read.
>>
>> However, I have a sinking feeling that the function needs a rewrite
>> anyway.
>>
>> For instance, consider reading in blocking mode, which may result in
>> running the for loop more than once.  If the first loop successfully
>> read 4 bytes, and the second loop runs into an error from
>> ClearCommError, the function will return -1 with errno set, completely
>> ignoring the fact that 4 bytes have been read already.
>>
>> It should return 4 in this case, and only the next run of
>> fhandler_serial::raw_read *might* return -1.
>>
>> This code really shows its age...
> I have revamped the fhandler_serial::raw_read function, but I need
> somebody for testing.  Any chance you volunteer for that job?
> We may need a couple of days to iron out all problems, but I think
> the code is more sound now than the original function.  I even
> added a couple of comments to the code (*gasp*) so there's stuff
> to discuss and to see why I did it that way.
>
> For a quicker turn around we can also use Freenode IRC, see
> https://cygwin.com/irc.html
>
> Interested?

Sure, bring it on!

/Ake


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