Initial implementation of the C99 feature whereby calling freopen() with

a NULL filename argument allows a stream's mode to be changed. At the
moment it just recycles the old file descriptor instead of storing the
filename somewhere and using that to reopen the file, as the standard
seems to require. Strictly conforming C99 applications probably can't
tell the difference but POSIX ones can.

PR:		46791

2 files changed, 94 insertions, 2 deletions

diff --git a/lib/libc/stdio/fopen.3 b/lib/libc/stdio/fopen.3
index eb39376..1508e59 100644
--- a/lib/libc/stdio/fopen.3
+++ b/lib/libc/stdio/fopen.3
@@ -36,7 +36,7 @@
 .\"     @(#)fopen.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd June 4, 1993
+.Dd January 26, 2003
 .Dt FOPEN 3
 .Os
 .Sh NAME
@@ -158,6 +158,41 @@ The
 argument is used just as in the
 .Fn fopen
 function.
+.Pp
+If the
+.Fa path
+argument is
+.Dv NULL ,
+.Fn freopen
+attempts to re-open the file associated with
+.Fa stream
+with a new mode.
+The new mode must be compatible with the mode that the stream was originally
+opened with:
+.Bl -bullet -offset indent
+.It
+Streams originally opened with mode
+.Dq Li r
+can only be reopened with that same mode.
+.It
+Streams originally opened with mode
+.Dq Li a
+can be reopened with the same mode, or mode
+.Dq Li w .
+.It
+Streams originally opened with mode
+.Dq Li w
+can be reopened with the same mode, or mode
+.Dq Li a .
+.It
+Streams originally opened with mode
+.Dq Li r+ ,
+.Dq Li w+ ,
+or
+.Dq Li a+
+can be reopened with any mode.
+.El
+.Pp
 The primary use of the
 .Fn freopen
 function
diff --git a/lib/libc/stdio/freopen.c b/lib/libc/stdio/freopen.c
index a22dedd..66794dd 100644
--- a/lib/libc/stdio/freopen.c
+++ b/lib/libc/stdio/freopen.c
@@ -64,7 +64,7 @@ freopen(file, mode, fp)
 	FILE *fp;
 {
 	int f;
-	int flags, isopen, oflags, sverrno, wantfd;
+	int dflags, flags, isopen, oflags, sverrno, wantfd;
 
 	if ((flags = __sflags(mode, &oflags)) == 0) {
 		(void) fclose(fp);
@@ -77,6 +77,59 @@ freopen(file, mode, fp)
 		__sinit();
 
 	/*
+	 * If the filename is a NULL pointer, the caller is asking us to
+	 * re-open the same file with a different mode. We allow this only
+	 * if the modes are compatible.
+	 */
+	if (file == NULL) {
+		/* See comment below regarding freopen() of closed files. */
+		if (fp->_flags == 0) {
+			FUNLOCKFILE(fp);
+			errno = EINVAL;
+			return (NULL);
+		}
+		if ((dflags = _fcntl(fp->_file, F_GETFL)) < 0) {
+			sverrno = errno;
+			fclose(fp);
+			FUNLOCKFILE(fp);
+			errno = sverrno;
+			return (NULL);
+		}
+		if ((dflags & O_ACCMODE) != O_RDWR && (dflags & O_ACCMODE) !=
+		    (oflags & O_ACCMODE)) {
+			fclose(fp);
+			FUNLOCKFILE(fp);
+			errno = EINVAL;
+			return (NULL);
+		}
+		if ((oflags ^ dflags) & O_APPEND) {
+			dflags &= ~O_APPEND;
+			dflags |= oflags & O_APPEND;
+			if (_fcntl(fp->_file, F_SETFL, dflags) < 0) {
+				sverrno = errno;
+				fclose(fp);
+				FUNLOCKFILE(fp);
+				errno = sverrno;
+				return (NULL);
+			}
+		}
+		if (oflags & O_TRUNC)
+			ftruncate(fp->_file, 0);
+		if (_fseeko(fp, 0, oflags & O_APPEND ? SEEK_END : SEEK_SET,
+		    0) < 0 && errno != ESPIPE) {
+			sverrno = errno;
+			fclose(fp);
+			FUNLOCKFILE(fp);
+			errno = sverrno;
+			return (NULL);
+		}
+		f = fp->_file;
+		isopen = 0;
+		wantfd = -1;
+		goto finish;
+	}
+
+	/*
 	 * There are actually programs that depend on being able to "freopen"
 	 * descriptors that weren't originally open.  Keep this from breaking.
 	 * Remember whether the stream was open to begin with, and which file
@@ -112,6 +165,7 @@ freopen(file, mode, fp)
 	}
 	sverrno = errno;
 
+finish:
 	/*
 	 * Finish closing fp.  Even if the open succeeded above, we cannot
 	 * keep fp->_base: it may be the wrong size.  This loses the effect
@@ -134,6 +188,9 @@ freopen(file, mode, fp)
 		FREELB(fp);
 	fp->_lb._size = 0;
 	fp->_extra->orientation = 0;
+	memset(&fp->_extra->state, 0, sizeof(fp->_extra->state));
+	memset(&fp->_extra->cstate, 0, sizeof(fp->_extra->cstate));
+	fp->_extra->cstatepos = 0;
 
 	if (f < 0) {			/* did not get it after all */
 		fp->_flags = 0;		/* set it free */