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55 lines
2.5 KiB
55 lines
2.5 KiB
4 months ago
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1. Overview
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A buffer pool enables processes to transfer buffers asynchronously.
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Without a buffer pool, a process calls a synchronous method of the other
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process and waits until the call finishes transferring a buffer. This adds
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unwanted latency due to context switching. With help from a buffer pool, a
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process can pass buffers asynchronously and reduce context switching latency.
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Passing an interface and a handle adds extra latency also. To mitigate the
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latency, passing IDs with local cache is used. For security concerns about
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rogue clients, FMQ is used to communicate between a buffer pool and a client
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process. FMQ is used to send buffer ownership change status from a client
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process to a buffer pool. Except FMQ, a buffer pool does not use any shared
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memory.
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2. FMQ
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FMQ is used to send buffer ownership status changes to a buffer pool from a
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buffer pool client. A buffer pool synchronizes FMQ messages when there is a
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hidl request from the clients. Every client has its own connection and FMQ
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to communicate with the buffer pool. So sending an FMQ message on behalf of
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other clients is not possible.
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FMQ messages are sent when a buffer is acquired or released. Also, FMQ messages
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are sent when a buffer is transferred from a client to another client. FMQ has
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its own ID from a buffer pool. A client is specified with the ID.
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To transfer a buffer, a sender must send an FMQ message. The message must
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include a receiver's ID and a transaction ID. A receiver must send the
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transaction ID to fetch a buffer from a buffer pool. Since the sender already
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registered the receiver via an FMQ message, The buffer pool must verify the
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receiver with the transaction ID. In order to prevent faking a receiver, a
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connection to a buffer pool from client is made and kept privately. Also part of
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transaction ID is a sender ID in order to prevent fake transactions from other
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clients. This must be verified with an FMQ message from a buffer pool.
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FMQ messages are defined in BufferStatus and BufferStatusMessage of 'types.hal'.
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3. Interfaces
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IConnection
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A connection to a buffer pool from a buffer pool client. The connection
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provides the functionalities to share buffers between buffer pool clients.
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The connection must be unique for each client.
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IAccessor
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An accessor to a buffer pool which makes a connection to the buffer pool.
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IAccesssor#connect creates an IConnection.
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IClientManager
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A manager of buffer pool clients and clients' connections to buffer pools. It
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sets up a process to be a receiver of buffers from a buffer pool. The manager
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is unique in a process.
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