win32pread.c

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/*-------------------------------------------------------------------------
 *
 * win32pread.c
 *    Implementation of pread(2) for Windows.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/win32pread.c
 *
 *-------------------------------------------------------------------------
 */
 
 
#include "c.h"
 
#include <windows.h>
 
ssize_t
pg_pread(int fd, void *buf, size_t size, off_t offset)
{
    OVERLAPPED  overlapped = {0};
    HANDLE      handle;
    DWORD       result;
 
    handle = (HANDLE) _get_osfhandle(fd);
    if (handle == INVALID_HANDLE_VALUE)
    {
        errno = EBADF;
        return -1;
    }
 
    /* Avoid overflowing DWORD. */
    size = Min(size, 1024 * 1024 * 1024);
 
    /* Note that this changes the file position, despite not using it. */
    overlapped.Offset = offset;
    if (!ReadFile(handle, buf, size, &result, &overlapped))
    {
        if (GetLastError() == ERROR_HANDLE_EOF)
            return 0;
 
        _dosmaperr(GetLastError());
        return -1;
    }
 
    return result;
}