freopen.c raw

   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  	FUNLOCK(f);
  44  	return f;
  45  
  46  fail2:
  47  	fclose(f2);
  48  fail:
  49  	fclose(f);
  50  	return NULL;
  51  }
  52  
  53  weak_alias(freopen, freopen64);
  54