On Tue, Sep 11 2007, Hannes Reinecke wrote: > Hi all, > > this is a proposal for a different implementation of request callbacks. The > existing ->endio callback of a request is actually a destructor function, > to be called to terminate a request and free all structures. > > However, on certain occasions (like request-based multipathing) it is > desirable to have a callback function for a request which is called right > after the request is finished, ie in end_that_request_first() before any > bio->bi_endio callback is called. > > So a simple solution for this is to clone the request and add a new > 'marker' bio in front of the bio list of the request. This callback will be > attached a structure in bi_private which keeps a pointer to the cloned and > the original request, thus serving as a callback for the request itself. > > Proposed patch attached. As usual comments are welcome. Honestly, I think this approach is a much worse design than the NEC callback option. Exporting __make_request() (which is an INTERNAL function) aside, this looks like one big hack with pseudo bio attached to front of list, the enable/disable elevator stuff (does that even work on stacked devices?). -- Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
