sector cache api

/*
The cache needs to be able to provide the following operating modes:
- read sector(s) to an already allocated buffer
  NOTE: we can provide an hint to cache whether the sectors should be cached or not if it's not already in the cache
- write sectors(s) from an already filled buffer
  NOTE: same remark
- read a sector and lock a buffer to it
- write a locked sector
- unlock a sector
*/