greenplumn pread 源码
greenplumn pread 代码
文件路径：/src/port/pread.c
/*-------------------------------------------------------------------------
*
* pread.c
* Implementation of pread(2) for platforms that lack one.
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/port/pread.c
*
* Note that this implementation changes the current file position, unlike
* the POSIX function, so we use the name pg_pread().
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#ifdef WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
ssize_t
pg_pread(int fd, void *buf, size_t size, off_t offset)
{
#ifdef WIN32
OVERLAPPED overlapped = {0};
HANDLE handle;
DWORD result;
handle = (HANDLE) _get_osfhandle(fd);
if (handle == INVALID_HANDLE_VALUE)
{
errno = EBADF;
return -1;
}
overlapped.Offset = offset;
if (!ReadFile(handle, buf, size, &result, &overlapped))
{
_dosmaperr(GetLastError());
return -1;
}
return result;
#else
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
return read(fd, buf, size);
#endif
}
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