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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/StringView.h>
#include <Kernel/DoubleBuffer.h>
namespace Kernel {
inline void DoubleBuffer::compute_lockfree_metadata()
{
InterruptDisabler disabler;
m_empty = m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size == 0;
m_space_for_writing = m_capacity - m_write_buffer->size;
}
DoubleBuffer::DoubleBuffer(size_t capacity)
: m_write_buffer(&m_buffer1)
, m_read_buffer(&m_buffer2)
, m_storage(KBuffer::create_with_size(capacity * 2, Region::Access::Read | Region::Access::Write, "DoubleBuffer"))
, m_capacity(capacity)
{
m_buffer1.data = m_storage.data();
m_buffer1.size = 0;
m_buffer2.data = m_storage.data() + capacity;
m_buffer2.size = 0;
m_space_for_writing = capacity;
}
void DoubleBuffer::flip()
{
if (m_storage.is_null())
return;
VERIFY(m_read_buffer_index == m_read_buffer->size);
swap(m_read_buffer, m_write_buffer);
m_write_buffer->size = 0;
m_read_buffer_index = 0;
compute_lockfree_metadata();
}
ssize_t DoubleBuffer::write(const UserOrKernelBuffer& data, size_t size)
{
if (!size || m_storage.is_null())
return 0;
Locker locker(m_lock);
size_t bytes_to_write = min(size, m_space_for_writing);
u8* write_ptr = m_write_buffer->data + m_write_buffer->size;
if (!data.read(write_ptr, bytes_to_write))
return -EFAULT;
m_write_buffer->size += bytes_to_write;
compute_lockfree_metadata();
if (m_unblock_callback && !m_empty)
m_unblock_callback();
return (ssize_t)bytes_to_write;
}
ssize_t DoubleBuffer::read(UserOrKernelBuffer& data, size_t size)
{
if (!size || m_storage.is_null())
return 0;
Locker locker(m_lock);
if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0)
flip();
if (m_read_buffer_index >= m_read_buffer->size)
return 0;
size_t nread = min(m_read_buffer->size - m_read_buffer_index, size);
if (!data.write(m_read_buffer->data + m_read_buffer_index, nread))
return -EFAULT;
m_read_buffer_index += nread;
compute_lockfree_metadata();
if (m_unblock_callback && m_space_for_writing > 0)
m_unblock_callback();
return (ssize_t)nread;
}
ssize_t DoubleBuffer::peek(UserOrKernelBuffer& data, size_t size)
{
if (!size || m_storage.is_null())
return 0;
Locker locker(m_lock);
if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0) {
flip();
}
if (m_read_buffer_index >= m_read_buffer->size)
return 0;
size_t nread = min(m_read_buffer->size - m_read_buffer_index, size);
if (!data.write(m_read_buffer->data + m_read_buffer_index, nread))
return -EFAULT;
compute_lockfree_metadata();
if (m_unblock_callback && m_space_for_writing > 0)
m_unblock_callback();
return (ssize_t)nread;
}
}
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