On Linux, ioctl(2) returns several different errors[1]:
EBADF d is not a valid descriptor.
EFAULT argp references an inaccessible memory area.
EINVAL Request or argp is not valid.
ENOTTY d is not associated with a character special device.
ENOTTY The specified request does not apply to the kind of object that
the descriptor d references.
In the case of FIONREAD, Cygwin doesn't seem to distinguish between
EINVAL and ENOTTY, and this causes at least one major bug:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35536
I have patched GCJ and GNU classpath to work around it, but this really
needs to be fixed in Cygwin itself.
Yaakov
[1] http://www.kernel.org/doc/man-pages/online/pages/man2/ioctl.2.html
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