[$] Block layer introduction part 2: the request layer

The Linux block layer provides an upstream interface to filesystems andblock-special devices allowing them to access a multitude of storagebackends in a uniform manner. It also provides downstream interfaces to devicedrivers and driver-support frameworks that allow those drivers andframeworks to receive requests in a manner most suitable to each. Somedrivers do not benefit from preliminary handling and just use the thin "biolayer" that we met previously. Otherdrivers benefitfrom some preprocessing that might detect batches of consecutive requests,may reorder requests based on various criteria, and which presents therequests as one or more well-defined streams. To service these drivers,there exists a section of the block layer that I refer to as the requestlayer.

Subscribers can read on below for guest author Neil Brown's article thatwill appear in next week's edition.