src/port/win32pread.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * win32pread.c
   4  *        Implementation of pread(2) for Windows.
   5  *
   6  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
   7  *
   8  * IDENTIFICATION
   9  *        src/port/win32pread.c
  10  *
  11  *-------------------------------------------------------------------------
  12  */
  13
  14
  15 #include "c.h"
  16
  17 #include <windows.h>
  18
  19 ssize_t
  20 pg_pread(int fd, void *buf, size_t size, off_t offset)
  21 {
  22         OVERLAPPED      overlapped = {0};
  23         HANDLE          handle;
  24         DWORD           result;
  25
  26         handle = (HANDLE) _get_osfhandle(fd);
  27         if (handle == INVALID_HANDLE_VALUE)
  28         {
  29                 errno = EBADF;
  30                 return -1;
  31         }
  32
  33         /* Avoid overflowing DWORD. */
  34         size = Min(size, 1024 * 1024 * 1024);
  35
  36         /* Note that this changes the file position, despite not using it. */
  37         overlapped.Offset = offset;
  38         if (!ReadFile(handle, buf, size, &result, &overlapped))
  39         {
  40                 if (GetLastError() == ERROR_HANDLE_EOF)
  41                         return 0;
  42
  43                 _dosmaperr(GetLastError());
  44                 return -1;
  45         }
  46
  47         return result;
  48 }