kernel/comm.c - page fault in thread
Cihan Altinay
cihan at uq.edu.au
Wed Nov 9 20:06:23 CST 2005
Uwe Bonnes wrote:
>>>>>>"Cihan" == Cihan Altinay <cihan at uq.edu.au> writes:
>
>
> Cihan> Uwe Bonnes wrote:
> >>>>>>> "Cihan" == Cihan ALTINAY <cihan at uq.edu.au> writes:
> >>
> Cihan> Hi again, Sorry for the double post and the stupid default
> Cihan> From-Header (not my machine). I replaced my modified comm.c with
> Cihan> the latest CVS, made the changes as described below and still got
> Cihan> communication errors (the device replies that commands are
> Cihan> malformed). So I attempted to apply the changes I made one-by-one
> Cihan> to see when the errors disappear. And the first (and easiest)
> Cihan> change helped: When replacing both tcflush(fd,TCOFLUSH) by
> Cihan> tcdrain(fd) in the PurgeComm function all errors disappear and
> Cihan> the program works as expected. Now, I know that the two
> Cihan> functions do different things and according to the API
> Cihan> specification of PurgeComm tcflush seems more appropriate. So I
> Cihan> wonder if this is not really a fix but only a workaround for a
> Cihan> different problem (maybe a race condition as mentioned earlier?).
> >>
> Cihan> I know that G-Ware does some funny (stupid?) things and there are
> Cihan> always at least 2 threads running that poll for input/output. One
> Cihan> effect is that it still opens ~200 file handles to the port but,
> Cihan> more importantly, maybe they interact in a way it shouldn't
> Cihan> happen?
> >> Obvious my WaitCommEvent implementation is not right for G-Ware
> >> (b.t.w.: any pointers to a dwonloadable version?). Can you write test
> >> case for to show where the current implementation is at fault? Maybe
> >> the server needs to be involved...
>
> Cihan> You can find G-Ware 5.0.6 here as posted in the first message:
> Cihan> http://www.clearone.com/docs/downloads/G-Ware5.0.6.zip [20MB]
>
> Cihan> However, without a suitable echo canceller device there is
> Cihan> probably not much you can see. If you like I can send a short log
> Cihan> of the input/output behaviour under windows and under wine to
> Cihan> show the difference (basically the input seems to accumulate more
> Cihan> under wine and it happens more often that we read >200 bytes at
> Cihan> once whereas this doesn't happen under windows). I would like to
> Cihan> write a test case but we don't have 'real' Windows [here at
> Cihan> university]. Instead, we were using VMWare up till now just to
> Cihan> get this program running (that's why it's so important for us to
> Cihan> be able to use wine).
>
> If tests show a difference in behaviour betweem Wine and VMWare, I guess
> wine will be wrong. I can than test with my XP machine, if you send me the
> test.
I studied the test cases in tests/comm.c but I am not sure how to
implement a test that requires input from the serial port. I saw the
loopback possibility but I cannot test it.
Do I need to write a test case for the first issue as well (where
*commio->buffer is written to after it is already freed)? It seems
quite obvious that the thread may still be running after the client
frees its buffers.
> Cihan> In regards to this I found out something else today while
> Cihan> testing: When I run the program under wine with the changes
> Cihan> applied I mentioned before, then everything works fine. Starting
> Cihan> vmware with a serial port enabled and closing it down again and
> Cihan> trying to run G-Ware under wine again breaks things: I get
> Cihan> 'Timeout' errors and the like. It took me a while to see the
> Cihan> reason: Under wine I get extra bytes inserted in the data and a
> Cihan> check of the serial parameters shows why - vmware enables the
> Cihan> INPCK flag of the serial port when exiting (who knows why) and
> Cihan> wine doesn't reset the the flags but only OR's and AND's it with
> Cihan> flags needed. I would say vmware is not behaving correctly but
> Cihan> on the other hand we never set the input flags to a fixed state
> Cihan> which makes things unpredictable. Any comments?
>
> Here the test would be: Open the port, set the INPCK flag. Then close it and
> then try to provoke the error you observe.
>
> I guess wine should reset the parity check flag...
Sorry I just found out that the extra bytes are actually caused by the
PARMRK input flag. Interestingly vmware leaves this (and the INPCK) flag
on while G-Ware is running and it still works so it seems vmware is
handling the mark character without passing it on.
I wrote a little test program to confirm that this time. All it does is:
- Get current tty settings via ioctl
- toggle the PARMRK flag
- Write back settings
(1) Run vmware->Run wine->fail (getting bogus 0xff in data stream)
(2) toggle flag->run wine->success
(3) toggle flag->run wine->fail
etc.
I found in the documentation that the PARMRK flag duplicates 0xff in
the stream to avoid confusion with the actual error character. I
verified that by inspecting the stream with/without flag set.
Can we simply clear the PARMRK flag in wine or is there something
similar under windows?
Cheers,
Cihan
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