Re: VMIN/VTIME and read expectations

[Eric Norum <eric at norum dot ca>]

???
How did you make the TERMIOS stuff work on a socket?
I use SO_SNDTIMEOand SO_RCVTIMEO options for sockets on RTEMS.  This causes read to return -1 with errno=EWOULDBLOCK on timeout.  
We should probably take this correspondence off the newlib 

On Dec 17, 2009, at 3:27 PM, Joel Sherrill wrote:

> On 12/17/2009 04:30 PM, Eric Norum wrote:
>> When you're using VMIN=0, VTIME=255 you have ICANON=0 so 'end-of-file' doesn't really exist.
>>   
> 
> I was kind of guessing that.  Unfortunately  this is in the RTEMS login code.
> I can make it work OK for serial ports but when attached to a socket, I
> have no idea how to detect when the socket is dropped.
> 
> I switched to calling read() and as documented, it always returns 0
> when there is no data.  When the connection is dropped, it returns 0
> VERY quickly.  Do you think this part is a bug in the read on a socket?
> 
> If this turns into an RTEMS specific issue, we need to switch lists.
> But I would really like to know what is correct. :)
> 
> --joel
>> On Dec 17, 2009, at 2:16 PM, Joel Sherrill wrote:
>> 
>>   
>>> Hi,
>>> 
>>> I have been looking into a program on RTEMS that
>>> uses VMIN=0, VTIME=255. The program calls
>>> fgetc() which calls read().
>>> 
>>> fp->_flags == 0x2806 before the fgetc() call.
>>> read() times out and returns 0.
>>> fgetc() returns -1 and fp->_flags == 0x2826
>>> 
>>> 
>>> The 0x0020 being set is _SEOF.
>>> 
>>> My questions are:
>>> 
>>> + Is this correct behaviour?
>>> 
>>> + How does the application programmer distinguish
>>> between a real EOF and an unsatisfied read?  Even the
>>> Fedora read(2) man page says:
>>> 
>>>       On success, the number of bytes read is returned (zero indicates end of
>>>       file), and the file position is advanced by this number.
>>> 
>>> So even if I dropped down to read(2), I still don't know
>>> how to distinguish EOF from a read timeout.
>>> 
>>> Thanks.
>>> 
>>> -- 
>>> Joel Sherrill, Ph.D.             Director of Research&   Development
>>> joel.sherrill@OARcorp.com        On-Line Applications Research
>>> Ask me about RTEMS: a free RTOS  Huntsville AL 35805
>>>   Support Available             (256) 722-9985
>>> 
>>> 
>>>     
>>   
> 
> 
> -- 
> Joel Sherrill, Ph.D.             Director of Research&  Development
> joel.sherrill@OARcorp.com        On-Line Applications Research
> Ask me about RTEMS: a free RTOS  Huntsville AL 35805
>   Support Available             (256) 722-9985
> 
> 

-- 
Eric Norum
eric@norum.ca