Atul Vidwansa wrote: > ZFS Experts, > > Is it possible to use DMU as general purpose transaction engine? More > specifically, in following order: > > 1. Create transaction: > tx = dmu_tx_create(os); > error = dmu_tx_assign(tx, TXG_WAIT) > > 2. Decide what to modify(say create new object): > dmu_tx_hold_bonus(tx, DMU_NEW_OBJECT); > dmu_tx_hold_bonus(tx, dzp->z_id); > dmu_tx_hold_zap(tx, dzp->z_id, TRUE, name); > | > | > > 3. Commit transaction: > dmu_tx_commit(tx); > > The reason I am asking for this particular order because I may not > know the intent of transaction till late in the process. > If it is not possible, can I at least declare that the transaction is > going to change N objects (without specification of each object) and > each change is M blocks at most (without specification of object and > offset). If yes, how?
You must specify what will be modified (by using dmu_tx_hold_*) before doing dmu_tx_assign(). dmu_tx_assign() needs to know what may be modified in order to determine if there is enough space available. You can try to solve this problem by doing dmu_tx_hold_*() on anything that *might* be modified. Hopefully you have enough information up front to determine that to some degree of accuracy. Otherwise, you must go far enough in your process to determine what will be modified before doing the dmu_tx_hold_*() and dmu_tx_assign(). --matt
