/* $Id: fileio-sg-at-posix.cpp 77635 2019-03-10 14:51:26Z vboxsync $ */
/** @file
 * IPRT - File I/O, RTFileSgReadAt & RTFileSgWriteAt, posixy.
 */

/*
 * Copyright (C) 2006-2019 Oracle Corporation
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 *
 * The contents of this file may alternatively be used under the terms
 * of the Common Development and Distribution License Version 1.0
 * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
 * VirtualBox OSE distribution, in which case the provisions of the
 * CDDL are applicable instead of those of the GPL.
 *
 * You may elect to license modified versions of this file under the
 * terms and conditions of either the GPL or the CDDL or both.
 */


/*********************************************************************************************************************************
*   Header Files                                                                                                                 *
*********************************************************************************************************************************/
/*
 * Determin whether we've got preadv and pwritev.
 */
#include <iprt/cdefs.h>
#ifdef RT_OS_LINUX
/* Linux has these since glibc 2.10 and Linux 2.6.30: */
# include <features.h>
# ifdef __GLIBC_PREREQ
#  if __GLIBC_PREREQ(2,10)
#   define HAVE_PREADV_AND_PWRITEV 1
#else
#  endif
# endif

#elif defined(RT_OS_FREEBSD)
/* FreeBSD has these since 6.0: */
# include <osreldate.h>
# ifdef __FreeBSD_version
#  if __FreeBSD_version >= 600000
#   define HAVE_PREADV_AND_PWRITEV 1
#  endif
# endif

#endif

#ifndef HAVE_PREADV_AND_PWRITEV

# include "../../generic/fileio-sg-at-generic.cpp"

#else /* HAVE_PREADV_AND_PWRITEV - rest of the file */

# include <errno.h>
# include <sys/types.h>
# include <sys/uio.h>
# include <unistd.h>
# include <limits.h>
# if defined(RT_OS_DARWIN) || defined(RT_OS_FREEBSD) || defined(RT_OS_NETBSD) || defined(RT_OS_OPENBSD)
#  include <sys/syslimits.h>
# endif

# include "internal/iprt.h"
# include <iprt/file.h>

# include <iprt/assert.h>
# include <iprt/err.h>
# include <iprt/log.h>

# ifndef UIO_MAXIOV
#  ifdef IOV_MAX
#   define UIO_MAXIOV IOV_MAX
#  else
#   error "UIO_MAXIOV and IOV_MAX are undefined"
#  endif
# endif


/* These assumptions simplifies things a lot here. */
AssertCompileMembersSameSizeAndOffset(struct iovec, iov_base, RTSGSEG, pvSeg);
AssertCompileMembersSameSizeAndOffset(struct iovec, iov_len,  RTSGSEG, cbSeg);


RTDECL(int)  RTFileSgReadAt(RTFILE hFile, RTFOFF off, PRTSGBUF pSgBuf, size_t cbToRead, size_t *pcbRead)
{
    /*
     * Make sure we set pcbRead.
     */
    if (pcbRead)
        *pcbRead = 0;

    /*
     * Special case: Zero read == seek.
     */
    if (cbToRead == 0)
        return RTFileSeek(hFile, off, RTFILE_SEEK_BEGIN, NULL);

    /*
     * We can use the segment array directly if we're at the start of the
     * current S/G segment and cbToRead matches the remainder exactly.
     */
    size_t cbTotalRead = 0;

    size_t const cbSgBufLeft = RTSgBufCalcLengthLeft(pSgBuf);
    AssertMsgReturn(cbSgBufLeft >= cbToRead, ("%#zx vs %#zx\n", cbSgBufLeft, cbToRead), VERR_INVALID_PARAMETER);

    if (cbToRead == cbSgBufLeft)
        while (RTSgBufIsAtStartOfSegment(pSgBuf))
        {
            size_t const cSegsLeft  = pSgBuf->cSegs - pSgBuf->idxSeg;
            ssize_t      cbThisRead = preadv(RTFileToNative(hFile), (const struct iovec *)&pSgBuf->paSegs[pSgBuf->idxSeg],
                                             RT_MIN(cSegsLeft, UIO_MAXIOV), off);
            if (cbThisRead >= 0)
            {
                AssertStmt((size_t)cbThisRead <= cbToRead, cbThisRead = cbToRead);

                RTSgBufAdvance(pSgBuf, cbThisRead);
                cbTotalRead += cbThisRead;
                cbToRead    -= cbThisRead;
                if (cbToRead == 0)
                {
                    if (pcbRead)
                        *pcbRead = cbTotalRead;
                    return VINF_SUCCESS;
                }

                if (   pcbRead
                    && (   cSegsLeft <= UIO_MAXIOV
                        || cbThisRead == 0 /* typically EOF */ ))
                {
                    *pcbRead = cbTotalRead;
                    return VINF_SUCCESS;
                }
                if (cbThisRead == 0)
                    return VERR_EOF;

                off += cbThisRead;
            }
            else if (cbTotalRead > 0 && pcbRead)
            {
                *pcbRead = cbTotalRead;
                return VINF_SUCCESS;
            }
            else
                return RTErrConvertFromErrno(errno);
        }

    /*
     * Unaligned start or not reading the whole buffer.  For reasons of
     * simplicity, we work the input segment by segment like the generic code.
     */
    int rc = VINF_SUCCESS;
    while (cbToRead > 0)
    {
        size_t cbSeg;
        void  *pvSeg = RTSgBufGetCurrentSegment(pSgBuf, cbToRead, &cbSeg);
        size_t cbThisRead = cbSeg;
        rc = RTFileReadAt(hFile, off, pvSeg, cbSeg, pcbRead ? &cbThisRead : NULL);
        if (RT_SUCCESS(rc))
        {
            RTSgBufAdvance(pSgBuf, cbThisRead);
            cbTotalRead += cbThisRead;
        }
        else
            break;
        if ((size_t)cbThisRead < cbSeg)
        {
            AssertStmt(pcbRead, rc = VERR_INTERNAL_ERROR_2);
            break;
        }

        Assert(cbSeg == cbThisRead);
        cbToRead -= cbSeg;
        off      += cbSeg;
    }
    if (pcbRead)
        *pcbRead = cbTotalRead;
    return rc;
}


RTDECL(int)  RTFileSgWriteAt(RTFILE hFile, RTFOFF off, PRTSGBUF pSgBuf, size_t cbToWrite, size_t *pcbWritten)
{
    /*
     * Make sure we set pcbWritten.
     */
    if (pcbWritten)
        *pcbWritten = 0;

    /*
     * Special case: Zero write == seek.
     */
    if (cbToWrite == 0)
        return RTFileSeek(hFile, off, RTFILE_SEEK_BEGIN, NULL);

    /*
     * We can use the segment array directly if we're at the start of the
     * current S/G segment and cbToWrite matches the remainder exactly.
     */
    size_t cbTotalWritten = 0;

    size_t const cbSgBufLeft = RTSgBufCalcLengthLeft(pSgBuf);
    AssertMsgReturn(cbSgBufLeft >= cbToWrite, ("%#zx vs %#zx\n", cbSgBufLeft, cbToWrite), VERR_INVALID_PARAMETER);

    if (cbToWrite == cbSgBufLeft)
        while (RTSgBufIsAtStartOfSegment(pSgBuf))
        {
            size_t const cSegsLeft     = pSgBuf->cSegs - pSgBuf->idxSeg;
            ssize_t      cbThisWritten = pwritev(RTFileToNative(hFile), (const struct iovec *)&pSgBuf->paSegs[pSgBuf->idxSeg],
                                                 RT_MIN(cSegsLeft, UIO_MAXIOV), off);
            if (cbThisWritten >= 0)
            {
                AssertStmt((size_t)cbThisWritten <= cbToWrite, cbThisWritten = cbToWrite);

                RTSgBufAdvance(pSgBuf, cbThisWritten);
                cbTotalWritten += cbThisWritten;
                cbToWrite      -= cbThisWritten;
                if (cbToWrite == 0)
                {
                    if (pcbWritten)
                        *pcbWritten = cbTotalWritten;
                    return VINF_SUCCESS;
                }

                if (   pcbWritten
                    && (   cSegsLeft <= UIO_MAXIOV
                        || cbThisWritten == 0 /* non-file, full buffer/whatever */ ))
                {
                    *pcbWritten = cbTotalWritten;
                    return VINF_SUCCESS;
                }
                if (cbThisWritten == 0)
                    return VERR_TRY_AGAIN;

                off += cbThisWritten;
            }
            else if (cbTotalWritten > 0 && pcbWritten)
            {
                *pcbWritten = cbTotalWritten;
                return VINF_SUCCESS;
            }
            else
                return RTErrConvertFromErrno(errno);
        }

    /*
     * Unaligned start or not writing the whole buffer.  For reasons of
     * simplicity, we work the input segment by segment like the generic code.
     */
    int rc = VINF_SUCCESS;
    while (cbToWrite > 0)
    {
        size_t cbSeg;
        void  *pvSeg = RTSgBufGetCurrentSegment(pSgBuf, cbToWrite, &cbSeg);
        size_t cbThisWritten = cbSeg;
        rc = RTFileWriteAt(hFile, off, pvSeg, cbSeg, pcbWritten ? &cbThisWritten : NULL);
        if (RT_SUCCESS(rc))
        {
            RTSgBufAdvance(pSgBuf, cbThisWritten);
            cbTotalWritten += cbThisWritten;
        }
        else
            break;
        if ((size_t)cbThisWritten < cbSeg)
        {
            AssertStmt(pcbWritten, rc = VERR_INTERNAL_ERROR_2);
            break;
        }

        Assert(cbSeg == cbThisWritten);
        cbToWrite -= cbSeg;
        off       += cbSeg;
    }
    if (pcbWritten)
        *pcbWritten = cbTotalWritten;
    return rc;
}

#endif /* HAVE_PREADV_AND_PWRITEV */