The invention provides a system and method for dynamically unloading file
system filters in a stacked-call-back model where filters are stacked one
on top of the other to form a filter stack. A filter manager keeps track
of the progress of each I/O operation and calls each filter in turn with
the filter returning after it has completed processing the given
operation. The filter manager dynamically unloads a filter (or an
instance of a filter) that is positioned at any position in the filter
stack in a reasonable amount of time while I/O operations are actively
being processed. The filter/filter instance can be unloaded with
outstanding I/O operations on the filter either hosted by the filter or
pended by other filters. I/O operations are canceled, completed or
drained in order to unload the filter or filter instance. A filter may
veto the unloading of the filter.
