greatly improve freopen behavior

1. don't open /dev/null just as a basis to copy flags; use shared
__fmodeflags function to get the right file flags for the mode.

2. handle the case (probably invalid, but whatever) case where the
original stream's file descriptor was closed; previously, the logic
re-closed it.

3. accept the "e" mode flag for close-on-exec; update dup3 to fallback
to using dup2 so we can simply call __dup3 instead of putting fallback
logic in freopen itself.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/stdio/__fmodeflags.c b/src/stdio/__fmodeflags.c
new file mode 100644
index 00000000..da9f23b6
--- /dev/null
+++ b/src/stdio/__fmodeflags.c
@@ -0,0 +1,16 @@
+#include <fcntl.h>
+#include <string.h>
+
+int __fmodeflags(const char *mode)
+{
+	int flags;
+	if (strchr(mode, '+')) flags = O_RDWR;
+	else if (*mode == 'r') flags = O_RDONLY;
+	else flags = O_WRONLY;
+	if (strchr(mode, 'x')) flags |= O_EXCL;
+	if (strchr(mode, 'e')) flags |= O_CLOEXEC;
+	if (*mode != 'r') flags |= O_CREAT;
+	if (*mode == 'w') flags |= O_TRUNC;
+	if (*mode == 'a') flags |= O_APPEND;
+	return flags;
+}