Changes to Linux Kernel 2.2.5

Even if the device driver framework is desired to be followed strictly, there are some places in ll_rw_block () which need modification. Otherwise, deadlocks may occur and performance may be impacted.

• Deadlock may occur as for each request structure in pseudo device queue request_fn of pseudo device will create (one or more) request structures that will be queued to the underlying device queue. If all the request structures are used up for the pseudo device queue, none of them can be processed as processing them in the underlying device requires some request structures. ll_rw_block() code has been modified so that the pseudo device queue can occupy only half of the maximum slots in the request structures array.

• Performance will be affected because the kernel will use plug to gather requests for the pseudo device but this will add to the delay in processing the requests. For a pseudo device, clustering of requests is not required, so the ll_rw_block() code has been modified so that plugging is avoided for the pseudo device.