rework langinfo code for ABI compat and for use by time code

[musl] / src / stdio / freopen.c

diff --git a/src/stdio/freopen.c b/src/stdio/freopen.c
index 8d3af9f..6c1b575 100644 (file)
--- a/src/stdio/freopen.c
+++ b/src/stdio/freopen.c
@@ -1,40 +1,47 @@
 #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. */
 
-FILE *freopen(const char *filename, const char *mode, FILE *f)
+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_fcntl(f2->fd, F_GETFL, 0);
-               if (fl < 0 || __syscall_fcntl(f->fd, F_SETFL, fl) < 0)
-                       goto fail2;
+               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 fail;
        } else {
                f2 = fopen(filename, mode);
                if (!f2) goto fail;
-               if (__syscall_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->flush = f2->flush;
+               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: