A read operation is an operation that reads data into a mutable buffer sequence argument of a type meeting MutableBufferSequence ([buffer.reqmts.mutablebuffersequence]) requirements. The mutable buffer sequence specifies memory where the data should be placed. A read operation shall always fill a buffer in the sequence completely before proceeding to the next.
A write operation is an operation that writes data from a constant buffer sequence argument of a type meeting ConstBufferSequence ([buffer.reqmts.constbuffersequence]) requirements. The constant buffer sequence specifies memory where the data to be written is located. A write operation shall always write a buffer in the sequence completely before proceeding to the next.
If a read or write operation is also an asynchronous operation ([async.reqmts.async]), the operation shall maintain one or more copies of the buffer sequence until such time as the operation no longer requires access to the memory specified by the buffers in the sequence. The program shall ensure the memory remains valid until:
the last copy of the buffer sequence is destroyed, or
the completion handler for the asynchronous operation is invoked,
whichever comes first.