yet another freopen(NULL) patch

[Eric Blake <ebb9 at byu dot net>]

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It turns out that on cygwin, when stdin is connected to a tty,
STDIN_FILENO is open O_RDWR even though stdin is read-only.  So, from the
point of view of freopen(NULL, "rb", stdin), a read-only FILE atop an
O_RDWR file descriptor is a better option than the current behavior of
failing and closing stdin altogether because the desired O_RDONLY was not
the same as the existing O_RDWR.

2006-03-06  Eric Blake  <ebb9@byu.net>

	* libc/stdio/freopen.c (_freopen_r) [HAVE_FCNTL]: For NULL
	filename, allow read-only or write-only FILE atop O_RDWR file
	descriptor.
	* libc/stdio64/freopen64.c (_freopen64_r) [HAVE_FCNTL]: Likewise.

- --
Life is short - so eat dessert first!

Eric Blake             ebb9@byu.net
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Index: newlib/libc/stdio/freopen.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio/freopen.c,v
retrieving revision 1.15
diff -u -r1.15 freopen.c
--- newlib/libc/stdio/freopen.c	10 Jan 2006 17:09:43 -0000	1.15
+++ newlib/libc/stdio/freopen.c	6 Mar 2006 05:01:42 -0000
@@ -56,10 +56,10 @@
 <[file]> and <[mode]> are used just as in <<fopen>>.
 
 If <[file]> is <<NULL>>, the underlying stream is modified rather than
-closed.  The file cannot change access mode (for example, if it was
-previously read-only, <[mode]> must be "r", "rb", or "rt"), but can
-change status such as append or binary mode.  If modification is not
-possible, failure occurs.
+closed.  The file cannot be given a more permissive access mode (for
+example, a <[mode]> of "w" will fail on a read-only file descriptor),
+but can change status such as append or binary mode.  If modification
+is not possible, failure occurs.
 
 RETURNS
 If successful, the result is the same as the argument <[fp]>.  If the
@@ -148,12 +148,14 @@
 #ifdef HAVE_FCNTL
       int oldflags;
       /*
-       * Reuse the file descriptor, but only if the access mode is
-       * unchanged.  F_SETFL correctly ignores creation flags.
+       * Reuse the file descriptor, but only if the new access mode is
+       * equal or less permissive than the old.  F_SETFL correctly
+       * ignores creation flags.
        */
       f = fp->_file;
       if ((oldflags = _fcntl_r (ptr, f, F_GETFL, 0)) == -1
-          || ((oldflags ^ oflags) & O_ACCMODE) != 0
+          || ! ((oldflags & O_ACCMODE) == O_RDWR
+                || ((oldflags ^ oflags) & O_ACCMODE) == 0)
           || _fcntl_r (ptr, f, F_SETFL, oflags) == -1)
         f = -1;
 #else
Index: newlib/libc/stdio64/freopen64.c
===================================================================
RCS file: /cvs/src/src/newlib/libc/stdio64/freopen64.c,v
retrieving revision 1.10
diff -u -r1.10 freopen64.c
--- newlib/libc/stdio64/freopen64.c	10 Jan 2006 17:09:43 -0000	1.10
+++ newlib/libc/stdio64/freopen64.c	6 Mar 2006 05:01:42 -0000
@@ -56,10 +56,10 @@
 <[file]> and <[mode]> are used just as in <<fopen>>.
 
 If <[file]> is <<NULL>>, the underlying stream is modified rather than
-closed.  The file cannot change access mode (for example, if it was
-previously read-only, <[mode]> must be "r", "rb", or "rt"), but can
-change status such as append or binary mode.  If modification is not
-possible, failure occurs.
+closed.  The file cannot be given a more permissive access mode (for
+example, a <[mode]> of "w" will fail on a read-only file descriptor),
+but can change status such as append or binary mode.  If modification
+is not possible, failure occurs.
 
 RETURNS
 If successful, the result is the same as the argument <[fp]>.  If the
@@ -148,12 +148,14 @@
 #ifdef HAVE_FCNTL
       int oldflags;
       /*
-       * Reuse the file descriptor, but only if the access mode is
-       * unchanged.  F_SETFL correctly ignores creation flags.
+       * Reuse the file descriptor, but only if the new access mode is
+       * equal or less permissive than the old.  F_SETFL correctly
+       * ignores creation flags.
        */
       f = fp->_file;
       if ((oldflags = _fcntl_r (ptr, f, F_GETFL, 0)) == -1
-          || ((oldflags ^ oflags) & O_ACCMODE) != 0
+          || ! ((oldflags & O_ACCMODE) == O_RDWR
+                || ((oldflags ^ oflags) & O_ACCMODE) == 0)
           || _fcntl_r (ptr, f, F_SETFL, oflags) == -1)
         f = -1;
 #else