serenity/Kernel/Memory/RingBuffer.cpp

/*
 * Copyright (c) 2021, Sahan Fernando <sahan.h.fernando@gmail.com>.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <Kernel/Memory/MemoryManager.h>
#include <Kernel/Memory/RingBuffer.h>
#include <Kernel/UserOrKernelBuffer.h>

namespace Kernel::Memory {

ErrorOr<NonnullOwnPtr<RingBuffer>> RingBuffer::try_create(StringView region_name, size_t capacity)
{
    auto region_size = TRY(page_round_up(capacity));
    auto region = TRY(MM.allocate_contiguous_kernel_region(region_size, region_name, Region::Access::Read | Region::Access::Write));
    return adopt_nonnull_own_or_enomem(new (nothrow) RingBuffer(move(region), capacity));
}

RingBuffer::RingBuffer(NonnullOwnPtr<Memory::Region> region, size_t capacity)
    : m_region(move(region))
    , m_capacity_in_bytes(capacity)
{
}

bool RingBuffer::copy_data_in(UserOrKernelBuffer const& buffer, size_t offset, size_t length, PhysicalAddress& start_of_copied_data, size_t& bytes_copied)
{
    size_t start_of_free_area = (m_start_of_used + m_num_used_bytes) % m_capacity_in_bytes;
    bytes_copied = min(m_capacity_in_bytes - m_num_used_bytes, min(m_capacity_in_bytes - start_of_free_area, length));
    if (bytes_copied == 0)
        return false;
    if (auto result = buffer.read(m_region->vaddr().offset(start_of_free_area).as_ptr(), offset, bytes_copied); result.is_error())
        return false;
    m_num_used_bytes += bytes_copied;
    start_of_copied_data = m_region->physical_page(start_of_free_area / PAGE_SIZE)->paddr().offset(start_of_free_area % PAGE_SIZE);
    return true;
}

ErrorOr<size_t> RingBuffer::copy_data_out(size_t size, UserOrKernelBuffer& buffer) const
{
    auto start = m_start_of_used % m_capacity_in_bytes;
    auto num_bytes = min(min(m_num_used_bytes, size), m_capacity_in_bytes - start);
    TRY(buffer.write(m_region->vaddr().offset(start).as_ptr(), num_bytes));
    return num_bytes;
}

ErrorOr<PhysicalAddress> RingBuffer::reserve_space(size_t size)
{
    if (m_capacity_in_bytes < m_num_used_bytes + size)
        return ENOSPC;
    size_t start_of_free_area = (m_start_of_used + m_num_used_bytes) % m_capacity_in_bytes;
    m_num_used_bytes += size;
    PhysicalAddress start_of_reserved_space = m_region->physical_page(start_of_free_area / PAGE_SIZE)->paddr().offset(start_of_free_area % PAGE_SIZE);
    return start_of_reserved_space;
}

void RingBuffer::reclaim_space(PhysicalAddress chunk_start, size_t chunk_size)
{
    VERIFY(start_of_used() == chunk_start);
    VERIFY(m_num_used_bytes >= chunk_size);
    m_num_used_bytes -= chunk_size;
    m_start_of_used += chunk_size;
}

PhysicalAddress RingBuffer::start_of_used() const
{
    size_t start = m_start_of_used % m_capacity_in_bytes;
    return m_region->physical_page(start / PAGE_SIZE)->paddr().offset(start % PAGE_SIZE);
}

}