Refragmentation<A NAME=1379> </A>

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Messages are generally built with fragment length equal to the MTU of the host's pvmd, allowing them to be forwarded without refragmentation. In some cases, the pvmd can receive a packet (from a task) too long to be sent to another pvmd. The pvmd refragments the packet by replicating its descriptor as many times as necessary. A single databuf is shared between the descriptors. The pk_dat and pk_len fields of the descriptors cover successive chunks of the original packet, each chunk small enough to send. The SOM and EOM flags are adjusted (if the original packet is the start or end of a message). At send time, netoutput() saves the data under where it writes the packet header, sends the packet, and then restores the data.