#include "stdio_impl.h"
+#include <fcntl.h>
/* The basic idea of this implementation is to open a new FILE,
* hack the necessary parts of the new FILE into the old one, then
* close the new FILE. */
-/* Locking is not necessary because, in the event of failure, the stream
- * passed to freopen is invalid as soon as freopen is called. */
+/* Locking IS necessary because another thread may provably hold the
+ * lock, via flockfile or otherwise, when freopen is called, and in that
+ * case, freopen cannot act until the lock is released. */
+
+int __dup3(int, int, int);
FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *restrict f)
{
- int fl;
+ int fl = __fmodeflags(mode);
FILE *f2;
+ FLOCK(f);
+
fflush(f);
if (!filename) {
- f2 = fopen("/dev/null", mode);
- if (!f2) goto fail;
- fl = __syscall(SYS_fcntl, f2->fd, F_GETFL, 0);
+ if (fl&O_CLOEXEC)
+ __syscall(SYS_fcntl, f->fd, F_SETFD, FD_CLOEXEC);
+ fl &= ~(O_CREAT|O_EXCL|O_CLOEXEC);
if (syscall(SYS_fcntl, f->fd, F_SETFL, fl) < 0)
- goto fail2;
+ goto fail;
} else {
f2 = fopen(filename, mode);
if (!f2) goto fail;
- if (syscall(SYS_dup2, f2->fd, f->fd) < 0)
- goto fail2;
- }
+ if (f2->fd == f->fd) f2->fd = -1; /* avoid closing in fclose */
+ else if (__dup3(f2->fd, f->fd, fl&O_CLOEXEC)<0) goto fail2;
- f->flags = (f->flags & F_PERM) | f2->flags;
- f->read = f2->read;
- f->write = f2->write;
- f->seek = f2->seek;
- f->close = f2->close;
+ f->flags = (f->flags & F_PERM) | f2->flags;
+ f->read = f2->read;
+ f->write = f2->write;
+ f->seek = f2->seek;
+ f->close = f2->close;
- fclose(f2);
+ fclose(f2);
+ }
+
+ FUNLOCK(f);
return f;
fail2: