RGBCube/serenity
1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-07-25 15:27:35 +00:00
Code Issues Activity Actions

Kernel: Implement peek() function for DoubleBuffer

Browse source 
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
2 changed files with 25 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

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()) if (!size || m_storage.is_null())
return 0; return 0;
VERIFY(size > 0);
Locker locker(m_lock); Locker locker(m_lock);
size_t bytes_to_write = min(size, m_space_for_writing); size_t bytes_to_write = min(size, m_space_for_writing);
u8* write_ptr = m_write_buffer->data + m_write_buffer->size; 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()) if (!size || m_storage.is_null())
return 0; return 0;
VERIFY(size > 0);
Locker locker(m_lock); Locker locker(m_lock);
if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0) if (m_read_buffer_index >= m_read_buffer->size && m_write_buffer->size != 0)
flip(); flip();
@ -77,4 +75,23 @@ ssize_t DoubleBuffer::read(UserOrKernelBuffer& data, size_t size)
return (ssize_t)nread; 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); auto buffer = UserOrKernelBuffer::for_kernel_buffer(data);
return read(buffer, size); 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; } bool is_empty() const { return m_empty; }