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Kernel: Implement peek() function for DoubleBuffer

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This allows us to "peek" into a DoubleBuffer without incrementing
the m_read_buffer_index, which is needed to implement MSG_PEEK.
This commit is contained in:
Justin 2021-04-28 23:22:21 +02:00 committed by Andreas Kling
parent 9bcdbe205b
commit 2d098c88dc
Notes: sideshowbarker 2024-07-18 18:57:17 +09:00 
Author: https://github.com/sw1tchbl4d3r 🔰
Commit: https://github.com/SerenityOS/serenity/commit/2d098c88dc6
Pull-request: https://github.com/SerenityOS/serenity/pull/6715
Reviewed-by: https://github.com/IdanHo
Reviewed-by: https://github.com/sin-ack
2 changed files with 25 additions and 2 deletions
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21
Kernel/DoubleBuffer.cpp
View File

@ -44,7 +44,6 @@ ssize_t DoubleBuffer::write(const UserOrKernelBuffer& data, size_t size)
{
if (!size || m_storage.is_null())
return 0;
VERIFY(size > 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;
@ -61,7 +60,6 @@ ssize_t DoubleBuffer::read(UserOrKernelBuffer& data, size_t size)
{
if (!size || m_storage.is_null())
return 0;
VERIFY(size > 0);
Locker locker(m_lock);
if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0)
flip();
@ -77,4 +75,23 @@ ssize_t DoubleBuffer::read(UserOrKernelBuffer& data, size_t size)
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;
}
}

6
Kernel/DoubleBuffer.h
View File

@ -29,6 +29,12 @@ public:
auto buffer = UserOrKernelBuffer::for_kernel_buffer(data);
return read(buffer, size);
}
[[nodiscard]] ssize_t peek(UserOrKernelBuffer&, size_t);
[[nodiscard]] ssize_t peek(u8* data, size_t size)
{
auto buffer = UserOrKernelBuffer::for_kernel_buffer(data);
return peek(buffer, size);
}
bool is_empty() const { return m_empty; }