libc-top-half/musl/src/stdio/freopen.c

   1 #ifdef __wasilibc_unmodified_upstream // WASI has no syscall, dup
   2 #include "stdio_impl.h"
   3 #else
   4 #include <wasi/libc.h>
   5 #endif
   6 #include <fcntl.h>
   7 #include <unistd.h>
   8 #ifdef __wasilibc_unmodified_upstream // WASI has no syscall, dup
   9 #else
  10 // Move this below fcntl.h and unistd.h so that the __syscall macro doesn't
  11 // cause trouble.
  12 #include "stdio_impl.h"
  13 #endif
  14
  15 /* The basic idea of this implementation is to open a new FILE,
  16  * hack the necessary parts of the new FILE into the old one, then
  17  * close the new FILE. */
  18
  19 /* Locking IS necessary because another thread may provably hold the
  20  * lock, via flockfile or otherwise, when freopen is called, and in that
  21  * case, freopen cannot act until the lock is released. */
  22
  23 FILE *freopen(const char *restrict filename, const char *restrict mode, FILE *restrict f)
  24 {
  25         int fl = __fmodeflags(mode);
  26         FILE *f2;
  27
  28         FLOCK(f);
  29
  30         fflush(f);
  31
  32         if (!filename) {
  33                 if (fl&O_CLOEXEC)
  34 #ifdef __wasilibc_unmodified_upstream // WASI has no syscall
  35                         __syscall(SYS_fcntl, f->fd, F_SETFD, FD_CLOEXEC);
  36 #else
  37                         fcntl(f->fd, F_SETFD, FD_CLOEXEC);
  38 #endif
  39                 fl &= ~(O_CREAT|O_EXCL|O_CLOEXEC);
  40 #ifdef __wasilibc_unmodified_upstream // WASI has no syscall
  41                 if (syscall(SYS_fcntl, f->fd, F_SETFL, fl) < 0)
  42 #else
  43                 if (fcntl(f->fd, F_SETFL, fl) < 0)
  44 #endif
  45                         goto fail;
  46         } else {
  47                 f2 = fopen(filename, mode);
  48                 if (!f2) goto fail;
  49                 if (f2->fd == f->fd) f2->fd = -1; /* avoid closing in fclose */
  50 #ifdef __wasilibc_unmodified_upstream // WASI has no dup
  51                 else if (__dup3(f2->fd, f->fd, fl&O_CLOEXEC)<0) goto fail2;
  52 #else
  53                 // WASI doesn't have dup3, but does have a way to renumber
  54                 // an existing file descriptor.
  55                 else {
  56                         if (__wasilibc_fd_renumber(f2->fd, f->fd)<0) goto fail2;
  57                         f2->fd = -1; /* avoid closing in fclose */
  58                 }
  59 #endif
  60
  61                 f->flags = (f->flags & F_PERM) | f2->flags;
  62                 f->read = f2->read;
  63                 f->write = f2->write;
  64                 f->seek = f2->seek;
  65                 f->close = f2->close;
  66
  67                 fclose(f2);
  68         }
  69
  70         FUNLOCK(f);
  71         return f;
  72
  73 fail2:
  74         fclose(f2);
  75 fail:
  76         fclose(f);
  77         return NULL;
  78 }
  79
  80 weak_alias(freopen, freopen64);