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 
freopen(const char * restrict filename,const char * restrict mode,FILE * restrict f)13 FILE* 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 
48 fail2:
49     fclose(f2);
50 fail:
51     fclose(f);
52     return NULL;
53 }
54