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/*-------------------------------------------------------------------------
*
* pread.c
* Implementation of pread[v](2) for platforms that lack one.
*
* Portions Copyright (c) 1996-2021, 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(). Likewise for the
* iovec version.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#ifdef WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
#include "port/pg_iovec.h"
#ifndef HAVE_PREAD
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))
{
if (GetLastError() == ERROR_HANDLE_EOF)
return 0;
_dosmaperr(GetLastError());
return -1;
}
return result;
#else
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
return read(fd, buf, size);
#endif
}
#endif
#ifndef HAVE_PREADV
ssize_t
pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#ifdef HAVE_READV
if (iovcnt == 1)
return pg_pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
return readv(fd, iov, iovcnt);
#else
ssize_t sum = 0;
ssize_t part;
for (int i = 0; i < iovcnt; ++i)
{
part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
if (part < 0)
{
if (i == 0)
return -1;
else
return sum;
}
sum += part;
offset += part;
if (part < iov[i].iov_len)
return sum;
}
return sum;
#endif
}
#endif
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