scst/scst/ToDo

To be done
----------

 - Kernel build integration (patch).

 - Reimplement VDISK handler with usage of async. read/write operations
   (in order to avoid unnecessary context switches) and direct access to
   the page cache (in order to avoid data copy between it and internal
   buffers). Requires modifications of the kernel.

 - Fix in-kernel O_DIRECT mode.
 
 - Close integration with Linux initiator SCSI mil-level, including 
   queue types (simple, ordered, etc.) and local initiators (sd, st, sg,
   etc.) support. Requires modifications of the kernel.

 - Improve task management and Unit Attention conditions handling
   using ACA in order to make them always reliable. Honoring NACA, QErr,
   TST, UA_INTLCK_CTRL bits. Requires deep modifications of the kernel.

 - Better handle of devices DMA restrictions.
 
 - Move linear searches to hash-table based.
 
 - HIGHMEM cleanup. Looks like HIGHMEM usage doesn't worth the effort and 
   performance hit, at least until VDISK handler doesn't use the page
   cache directly, so disable it for now, although the code looks ready.
   To enable it, set SCST_HIGHMEM in 1 in scst_priv.h. HIGHMEM is not 
   supported on 2.4 and is not going to be.

 - Small ToDo's spread all over the code.

 - Investigate possible missed emulated UA cases.

 - More target drivers errors handling (timeouts for commands, sent
   to target drivers, e.g. via xmit_response(), etc.) with some kind
   of error recovery.

 - Additional ability for target drivers to ask for command's retry also
   after xmit_response() and rdy_to_xfer() returned (for example, if a
   command was successfully sent to the target card, but later it was
   returned by the card with BUSY completion status).
 
 - Asynchronous Event Notification support.
 
 - Support of SCSI 3 variable length CDBs, as well as OSD's extensions.
 
 - Advanced SCSI commands support: COPY, EXTENDED COPY, PERSISTENT
   RESERVE IN/OUT, third party RESERVE, etc.