src/stdio/freopen.c

   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
  13 FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *restrict f)
  14 {
  15         int fl = __fmodeflags(mode);
  16         FILE *f2;
  17
  18         FLOCK(f);
  19
  20         fflush(f);
  21
  22         if (!filename) {
  23                 if (fl&O_CLOEXEC)
  24                         __syscall(SYS_fcntl, f->fd, F_SETFD, FD_CLOEXEC);
  25                 fl &= ~(O_CREAT|O_EXCL|O_CLOEXEC);
  26                 if (syscall(SYS_fcntl, f->fd, F_SETFL, fl) < 0)
  27                         goto fail;
  28         } else {
  29                 f2 = fopen(filename, mode);
  30                 if (!f2) goto fail;
  31                 if (f2->fd == f->fd) f2->fd = -1; /* avoid closing in fclose */
  32                 else if (__dup3(f2->fd, f->fd, fl&O_CLOEXEC)<0) goto fail2;
  33
  34                 f->flags = (f->flags & F_PERM) | f2->flags;
  35                 f->read = f2->read;
  36                 f->write = f2->write;
  37                 f->seek = f2->seek;
  38                 f->close = f2->close;
  39
  40                 fclose(f2);
  41         }
  42
  43         f->mode = 0;
  44         f->locale = 0;
  45         FUNLOCK(f);
  46         return f;
  47
  48 fail2:
  49         fclose(f2);
  50 fail:
  51         fclose(f);
  52         return NULL;
  53 }