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Re: VMIN/VTIME and read expectations
Hit 'send' too soon.
Of course if you're using the modem control lines (CLOCAL=0) then a loss-of-carrier will also result in read returning 0.
So I guess there is a ambiguity after all.
On Dec 17, 2009, at 2:30 PM, Eric Norum wrote:
> When you're using VMIN=0, VTIME=255 you have ICANON=0 so 'end-of-file' doesn't really exist.
> 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
>>
>>
>
> --
> Eric Norum
> eric@norum.ca
>
>
>
>
--
Eric Norum
eric@norum.ca