File: mmap_file.c

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/*
**      PJL C++ Library
**      mmap_file.c
**
**      Copyright (C) 1998  Paul J. Lucas
**
**      This program is free software; you can redistribute it and/or modify
**      it under the terms of the GNU General Public License as published by
**      the Free Software Foundation; either version 2 of the License, or
**      (at your option) any later version.
**
**      This program is distributed in the hope that it will be useful,
**      but WITHOUT ANY WARRANTY; without even the implied warranty of
**      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
**      GNU General Public License for more details.
**
**      You should have received a copy of the GNU General Public License
**      along with this program; if not, write to the Free Software
**      Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

// standard
#include <cerrno>
#include <fcntl.h>                      /* for open(2), O_RDONLY, etc */
#include <time.h>                       /* needed by sys/resource.h */
#include <sys/time.h>                   /* needed by FreeBSD systems */
#include <sys/resource.h>               /* for get/setrlimit(2) */
#include <sys/stat.h>                   /* for stat(2) */
#include <unistd.h>                     /* for close(2) */
#if defined( MULTI_THREADED ) && defined( RLIMIT_VMEM )
#include <pthread.h>
#endif

// local
#include "mmap_file.h"
#include "platform.h"

using namespace PJL;
using namespace std;

#ifdef  RLIMIT_VMEM                     /* SVR4 */
//*****************************************************************************
//
// SYNOPSIS
//
        extern "C" void max_out_limits()
//
// DESCRIPTION
//
//      Max-out our memory-mapped address space since we can potentially
//      mmap(2) very large files.
//
// NOTE
//
//      This function is declared extern "C" since it is called via the C
//      library function pthread_once() (if MULTI_THREADED is defined) and,
//      because it's a C function, it expects C linkage.
//
//*****************************************************************************
{
    struct rlimit r;
    ::getrlimit( RLIMIT_VMEM, &r );
    r.rlim_cur = r.rlim_max;
    ::setrlimit( RLIMIT_VMEM, &r );
}
#endif  /* RLIMIT_VMEM */

//*****************************************************************************
//
// SYNOPSIS
//
        int mmap_file::behavior( behavior_type behavior ) const
//
// DESCRIPTION
//
//      Give memory-paging strategy advise.
//
// PARAMETERS
//
//      behavior    The behavior to use.
//
// RETURN VALUE
//
//      Returns 0 only if successful; otherwise return errno.
//
//*****************************************************************************
{
#ifndef __APPLE__
    //
    // As of Mac OS X 10.2.1 (Darwin 6.1), madvise(2) seems broken, so don't
    // bother.
    //
#ifndef PJL_NO_MADVISE
    if ( ::madvise( static_cast<caddr_t>( addr_ ), size_, behavior ) == -1 )
        return errno_ = errno;
#endif
#endif  /* __APPLE__ */
    return 0;
}

//*****************************************************************************
//
// SYNOPSIS
//
        void mmap_file::close()
//
// DESCRIPTION
//
//      Munmaps and closes a file previously opened and mmapped by
//      mmap_file::open().
//
// SEE ALSO
//
//      close(2), mmap_file::open(3), munmap(2)
//
//*****************************************************************************
{
    if ( addr_ )
        ::munmap( static_cast<char*>( addr_ ), size_ );
    if ( fd_ )
        ::close( fd_ );
    init();
}

//*****************************************************************************
//
// SYNOPSIS
//
        void mmap_file::init()
//
// DESCRIPTION
//
//      Initialize an instance of mmap_file.
//
//*****************************************************************************
{
#ifdef  RLIMIT_VMEM                     /* SVR4 */
    //
    // This OS defines a separate resource limit for memory-mapped address
    // space as opposed to data, stack, or heap space.  Anyway, we want to max
    // it out so we can mmap(2) very large files.
    //
#ifdef  MULTI_THREADED
    static pthread_once_t max_out = PTHREAD_ONCE_INIT;
    ::pthread_once( &max_out, max_out_limits );
#else
    static bool maxed_out;
    if ( !maxed_out ) {
        max_out_limits();
        maxed_out = true;
    }
#endif  /* MULTI_THREADED */
#endif  /* RLIMIT_VMEM */

    size_ = 0;
    fd_ = 0;
    addr_ = 0;
    errno_ = 0;
}

//*****************************************************************************
//
// SYNOPSIS
//
        bool mmap_file::open( char const *path, ios::openmode mode )
//
// DESCRIPTION
//
//      Open and mmap a file.
//
// RETURN VALUE
//
//      Returns true only if the file was mmapped successfully.
//
// SEE ALSO
//
//      mmap(2), open(2), stat(2)
//
//*****************************************************************************
{
    close();

    struct stat stat_buf;
    if ( ::stat( path, &stat_buf ) == -1 ) {
        errno_ = errno;
        return false;
    }

    int flags = 0;
    if ( mode & ios::in  )  flags |= O_RDONLY;
    if ( mode & ios::out )  flags |= O_WRONLY;

    if ( ( fd_ = ::open( path, flags ) ) == -1 ) {
        fd_ = 0;
        errno_ = errno;
        return false;
    }

    int prot = PROT_NONE;
    if ( mode & ios::in  )  prot |= PROT_READ;
    if ( mode & ios::out )  prot |= PROT_WRITE;

    if ( !( size_ = stat_buf.st_size ) ) {
#ifdef  ENODATA
        errno_ = ENODATA;
#else
        //
        // For BSD systems, we're forced to use something other than ENODATA
        // since it's not available.  Unfortunately, there isn't something good
        // to use: EINVAL is the least bad.
        //
        errno_ = EINVAL;
#endif  /* ENODATA */
        return false;
    }

    addr_ = ::mmap( 0, size_, prot, MAP_SHARED, fd_, 0 );
    if ( addr_ == MAP_FAILED ) {
        addr_ = 0;
        errno_ = errno;
        return false;
    }

    return behavior( bt_normal ) == 0;
}
/* vim:set et sw=4 ts=4: */