yet another freopen(NULL) patch

[Jeff Johnston]

Patch checked in.

-- Jeff J.

Eric Blake wrote:
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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