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, 13 insertions, 2 deletions

diff --git a/src/unistd/dup3.c b/src/unistd/dup3.c
index 18f6fcce..1f7134b3 100644
--- a/src/unistd/dup3.c
+++ b/src/unistd/dup3.c
@@ -1,10 +1,21 @@
 #define _GNU_SOURCE
 #include <unistd.h>
 #include <errno.h>
+#include <fcntl.h>
 #include "syscall.h"
+#include "libc.h"
 
-int dup3(int old, int new, int flags) {
+int __dup3(int old, int new, int flags)
+{
 	int r;
-	while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
+	if (old==new) return __syscall_ret(-EINVAL);
+	if (flags & O_CLOEXEC) {
+		while ((r=__syscall(SYS_dup3, old, new, flags))==-EBUSY);
+		if (r!=-ENOSYS) return __syscall_ret(r);
+	}
+	while ((r=__syscall(SYS_dup2, old, new))==-EBUSY);
+	if (flags & O_CLOEXEC) __syscall(SYS_fcntl, new, F_SETFD, FD_CLOEXEC);
 	return __syscall_ret(r);
 }
+
+weak_alias(__dup3, dup3);