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* DevNotes: Add entry cgf-000002.

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* fhandler_tty.cc (bytes_available): Revert to previous Oct-2011 behavior where
a dummy buffer is used to determine how many bytes will be read.
(fhandler_pty_master::ioctl): Correct coercion in assignment.
This commit is contained in:
Christopher Faylor
2012-05-04 03:00:43 +00:00
parent 1c46670094
commit fb9d631817
3 changed files with 53 additions and 2 deletions
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winsup/cygwin/DevNotes
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@ -1,3 +1,42 @@
2012-05-03 cgf-000002
<1.7.15>
Fix problem where too much input was attempted to be read from a
pty slave. Fixes: http://cygwin.com/ml/cygwin/2012-05/msg00049.html
</1.7.15>
My change on 2012/04/05 reintroduced the problem first described by:
http://cygwin.com/ml/cygwin/2011-10/threads.html#00445
The problem then was, IIRC, due to the fact that bytes sent to the pty
pipe were not written as records. Changing pipe to PIPE_TYPE_MESSAGE in
pipe.cc fixed the problem since writing lines to one side of the pipe
caused exactly that the number of characters to be read on the other
even if there were more characters in the pipe.
To debug this, I first replaced fhandler_tty.cc with the 1.258,
2012/04/05 version. The test case started working when I did that.
So, then, I replaced individual functions, one at a time, in
fhandler_tty.cc with their previous versions. I'd expected this to be a
problem with fhandler_pty_master::process_slave_output since that had
seen the most changes but was surprised to see that the culprit was
fhandler_pty_slave::read().
The reason was that I really needed the bytes_available() function to
return the number of bytes which would be read in the next operation
rather than the number of bytes available in the pipe. That's because
there may be a number of lines available to be read but the number of
bytes which will be read by ReadFile should reflect the mode of the pty
and, if there is a line to read, only the number of bytes in the line
should be seen as available for the next read.
Having bytes_available() return the number of bytes which would be read
seemed to fix the problem but it could subtly change the behavior of
other callers of this function. However, I actually think this is
probably a good thing since they probably should have been seeing the
line behavior.
2012-05-02 cgf-000001
<1.7.15>