ioctl: FIONREAD and ENOTTY

Christopher Faylor cgf-use-the-mailinglist-please@cygwin.com
Thu Jul 21 19:58:00 GMT 2011


On Thu, Jul 21, 2011 at 07:47:17PM +0200, Corinna Vinschen wrote:
>On Jul 21 13:05, Christopher Faylor wrote:
>> On Thu, Jul 21, 2011 at 04:39:31PM +0200, Corinna Vinschen wrote:
>> >On Jul 20 17:37, Yaakov (Cygwin/X) wrote:
>> >> On Wed, 2011-07-20 at 17:46 +0200, Corinna Vinschen wrote:
>> >> > On Jul 20 03:11, Yaakov (Cygwin/X) wrote:
>> >> > > 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.
>> >> > 
>> >> > Would this patch be sufficient?
>> >> > 
>> >> > Index: fhandler.cc
>> >> > ===================================================================
>> >> > RCS file: /cvs/src/src/winsup/cygwin/fhandler.cc,v
>> >> > retrieving revision 1.397
>> >> > diff -u -p -r1.397 fhandler.cc
>> >> > --- fhandler.cc	5 Jul 2011 12:02:10 -0000	1.397
>> >> > +++ fhandler.cc	20 Jul 2011 15:46:40 -0000
>> >> > @@ -1151,6 +1151,10 @@ fhandler_base::ioctl (unsigned int cmd, 
>> >> >        set_nonblocking (*(int *) buf);
>> >> >        res = 0;
>> >> >        break;
>> >> > +    case FIONREAD:
>> >> > +      set_errno (ENOTTY);
>> >> > +      res = -1;
>> >> > +      break;
>> >> >      default:
>> >> >        set_errno (EINVAL);
>> >> >        res = -1;
>> >> 
>> >> Given my testcases, give me a few days to check this out.
>> >
>> >Ok, but the patch doesn't build as is.  You have to add
>> >
>> >  #include <asm/socket.h>
>> >
>> >to get the FIONREAD definition.  Sorry about that.
>> 
>> Btw, I don't think the above is sufficient.  I think you'll have to add a
>> similar test to other fhandlers (like fhandler_windows) which completely
>> implement ioctl without reverting to fhandler_base.
>
>Hmm, isn't that just a bug in these ioctl methods?  I think they
>all should fall through to fhandler_base::ioctl.

Yep.  I think you're right.  I'll handle that if you want.

cgf

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