/****************************************************************************** * * creates a DAG to perform a large-write operation: * * / Rod \ / Wnd \ * H -- block- Rod - Xor - Cmt - Wnd --- T * \ Rod / \ Wnp / * \[Wnq]/ * * The XOR node also does the Q calculation in the P+Q architecture. * All nodes are before the commit node (Cmt) are assumed to be atomic and * undoable - or - they make no changes to permanent state. * * Rod = read old data * Cmt = commit node * Wnp = write new parity * Wnd = write new data * Wnq = write new "q" * [] denotes optional segments in the graph * * Parameters: raidPtr - description of the physical array * asmap - logical & physical addresses for this access * bp - buffer ptr (holds write data) * flags - general flags (e.g. disk locking) * allocList - list of memory allocated in DAG creation * nfaults - number of faults array can tolerate * (equal to # redundancy units in stripe) * redfuncs - list of redundancy generating functions * *****************************************************************************/