serenity/Kernel/FileSystem/FIFO.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <AK/HashTable.h>
#include <AK/Singleton.h>
#include <AK/StdLibExtras.h>
#include <AK/StringView.h>
#include <Kernel/FileSystem/FIFO.h>
#include <Kernel/FileSystem/FileDescription.h>
#include <Kernel/Lock.h>
#include <Kernel/Process.h>
#include <Kernel/Thread.h>

//#define FIFO_DEBUG

namespace Kernel {

static AK::Singleton<Lockable<HashTable<FIFO*>>> s_table;

static Lockable<HashTable<FIFO*>>& all_fifos()
{
    return *s_table;
}

static int s_next_fifo_id = 1;

NonnullRefPtr<FIFO> FIFO::create(uid_t uid)
{
    return adopt(*new FIFO(uid));
}

NonnullRefPtr<FileDescription> FIFO::open_direction(FIFO::Direction direction)
{
    auto description = FileDescription::create(*this);
    attach(direction);
    description->set_fifo_direction({}, direction);
    return description;
}

NonnullRefPtr<FileDescription> FIFO::open_direction_blocking(FIFO::Direction direction)
{
    Locker locker(m_open_lock);

    auto description = open_direction(direction);

    if (direction == Direction::Reader) {
        m_read_open_queue.wake_all();

        if (m_writers == 0) {
            locker.unlock();
            m_write_open_queue.wait_on(nullptr, "FIFO");
            locker.lock();
        }
    }

    if (direction == Direction::Writer) {
        m_write_open_queue.wake_all();

        if (m_readers == 0) {
            locker.unlock();
            m_read_open_queue.wait_on(nullptr, "FIFO");
            locker.lock();
        }
    }

    return description;
}

FIFO::FIFO(uid_t uid)
    : m_uid(uid)
{
    LOCKER(all_fifos().lock());
    all_fifos().resource().set(this);
    m_fifo_id = ++s_next_fifo_id;

    // Use the same block condition for read and write
    m_buffer.set_unblock_callback([this]() {
        evaluate_block_conditions();
    });
}

FIFO::~FIFO()
{
    LOCKER(all_fifos().lock());
    all_fifos().resource().remove(this);
}

void FIFO::attach(Direction direction)
{
    if (direction == Direction::Reader) {
        ++m_readers;
#ifdef FIFO_DEBUG
        klog() << "open reader (" << m_readers << ")";
#endif
    } else if (direction == Direction::Writer) {
        ++m_writers;
#ifdef FIFO_DEBUG
        klog() << "open writer (" << m_writers << ")";
#endif
    }

    evaluate_block_conditions();
}

void FIFO::detach(Direction direction)
{
    if (direction == Direction::Reader) {
#ifdef FIFO_DEBUG
        klog() << "close reader (" << m_readers << " - 1)";
#endif
        ASSERT(m_readers);
        --m_readers;
    } else if (direction == Direction::Writer) {
#ifdef FIFO_DEBUG
        klog() << "close writer (" << m_writers << " - 1)";
#endif
        ASSERT(m_writers);
        --m_writers;
    }

    evaluate_block_conditions();
}

bool FIFO::can_read(const FileDescription&, size_t) const
{
    return !m_buffer.is_empty() || !m_writers;
}

bool FIFO::can_write(const FileDescription&, size_t) const
{
    return m_buffer.space_for_writing() || !m_readers;
}

KResultOr<size_t> FIFO::read(FileDescription&, size_t, UserOrKernelBuffer& buffer, size_t size)
{
    if (!m_writers && m_buffer.is_empty())
        return 0;
    return m_buffer.read(buffer, size);
}

KResultOr<size_t> FIFO::write(FileDescription&, size_t, const UserOrKernelBuffer& buffer, size_t size)
{
    if (!m_readers) {
        Thread::current()->send_signal(SIGPIPE, Process::current());
        return -EPIPE;
    }
    return m_buffer.write(buffer, size);
}

String FIFO::absolute_path(const FileDescription&) const
{
    return String::format("fifo:%u", m_fifo_id);
}

KResult FIFO::stat(::stat& st) const
{
    memset(&st, 0, sizeof(st));
    st.st_mode = S_IFIFO;
    return KSuccess;
}

}