1#include "stdio_impl.h"
2#include <fcntl.h>
3#include <unistd.h>
4
5/* The basic idea of this implementation is to open a new FILE,
6 * hack the necessary parts of the new FILE into the old one, then
7 * close the new FILE. */
8
9/* Locking IS necessary because another thread may provably hold the
10 * lock, via flockfile or otherwise, when freopen is called, and in that
11 * case, freopen cannot act until the lock is released. */
12
13FILE* freopen(const char* restrict filename, const char* restrict mode, FILE* restrict f) {
14    int fl = __fmodeflags(mode);
15    FILE* f2;
16
17    FLOCK(f);
18
19    fflush(f);
20
21    if (!filename) {
22        if (fl & O_CLOEXEC)
23            fcntl(f->fd, F_SETFD, FD_CLOEXEC);
24        fl &= ~(O_CREAT | O_EXCL | O_CLOEXEC);
25        if (fcntl(f->fd, F_SETFL, fl) < 0)
26            goto fail;
27    } else {
28        f2 = fopen(filename, mode);
29        if (!f2)
30            goto fail;
31        if (f2->fd == f->fd)
32            f2->fd = -1; /* avoid closing in fclose */
33        else if (dup3(f2->fd, f->fd, fl & O_CLOEXEC) < 0)
34            goto fail2;
35
36        f->flags = (f->flags & F_PERM) | f2->flags;
37        f->read = f2->read;
38        f->write = f2->write;
39        f->seek = f2->seek;
40        f->close = f2->close;
41
42        fclose(f2);
43    }
44
45    FUNLOCK(f);
46    return f;
47
48fail2:
49    fclose(f2);
50fail:
51    fclose(f);
52    return NULL;
53}
54