SharedBuffer.cpp

Go to the documentation of this file.

/*******************************************************************************
  Copyright(c) 2022 Ludovic Pollet. All rights reserved.
 
 This library is free software; you can redistribute it and/or
 modify it under the terms of the GNU Library General Public
 License version 2 as published by the Free Software Foundation.
 
 This library 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
 Library General Public License for more details.
 
 You should have received a copy of the GNU Library General Public License
 along with this library; see the file COPYING.LIB.  If not, write to
 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 Boston, MA 02110-1301, USA.
*******************************************************************************/
 
extern "C" {
    // Load shm_open_anon but force it to have static symbol only
    static int shm_open_anon(void);
    #include "../libs/indicore/shm_open_anon.c"
}
 
#include <system_error>
 
#include "SharedBuffer.h"
 
 
#ifdef __linux__
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <linux/unistd.h>
#endif
 
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
 
#include <string.h>
 
#include <sys/mman.h>
 
 
SharedBuffer::SharedBuffer()
{
    fd = -1;
    size = 0;
}
 
SharedBuffer::~SharedBuffer()
{
    release();
}
 
void SharedBuffer::attach(int fd)
{
    release();
    this->fd = fd;
    if (fd == -1)
    {
        size = 0;
        return;
    }
 
    struct stat sb;
 
    if (fstat(fd, &sb) == -1)
    {
        int e = errno;
        throw std::system_error(e, std::generic_category(), "Unable to stat buffer");
    }
 
    size = sb.st_size;
}
 
void SharedBuffer::release()
{
    if (fd != -1)
    {
        close(fd);
        fd = -1;
    }
    size = 0;
}
 
int SharedBuffer::getFd() const
{
    if (fd == -1)
    {
        throw std::runtime_error("SharedBuffer is not allocated");
    }
    return fd;
}
 
 
void SharedBuffer::write(const void * data, ssize_t offset, ssize_t writeSize)
{
    if (writeSize == 0)
    {
        return;
    }
 
    if (size < offset + writeSize)
    {
        throw std::runtime_error("Attempt to write beyond past");
    }
 
    void * mmapped = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (mmapped == MAP_FAILED)
    {
        perror("mmap");
        throw std::runtime_error("Mmap failed");
    }
 
    memcpy((void*)((char*)mmapped + offset), data, writeSize);
 
    if (munmap(mmapped, size) == -1)
    {
        perror("munmap");
        throw std::runtime_error("Munmap failed");
    }
 
}
 
void SharedBuffer::allocate(ssize_t nsize)
{
    release();
    fd = shm_open_anon();
    if (fd == -1)
    {
        throw std::system_error(errno, std::generic_category(), "memfd_create");
    }
 
    int ret = ftruncate(fd, nsize);
    if (ret == -1)
    {
        throw std::system_error(errno, std::generic_category(), "memfd_create");
    }
 
    size = nsize;
}