The buffer pool is a group of buffers used by the device driver to receive data. The buffer pool consists of two different groups of buffers. A buffer pool is set up by each entity that is communicating with the FC driver. An entity can specify up to two different sizes of buffers that, when used in conjunction with the system mbufs, allow the entity three different buffer sizes to be used for receiving data.
The minimum size of the buffer is 256 bytes. FCS will increase the buffer size to 256 bytes if the user specifies that the buffer size is smaller than 256 bytes.
The system mbufs are used for receiving small data packets (less than 512 bytes). The two buffer sizes that are set up with the buffer pool can be configured by the entity to meet their application needs. For example, if an application normally sends 32KB packets and also sends some packets that are greater than 512 bytes but less than 4096 bytes, then set up the buffer pool with buffer sizes of 32KB and 4096. This enables the buffers to efficiently receive all of the packets expected.
There is a buffer pool associated with TCP/IP that is shared by all clients communicating over TCP/IP. The buffer pool information is configurable and can be accessed by modifying the network interface layer for Fibre Channel.
Each entity programmed to use raw sockets must set up a buffer pool by using the bind() system call.