[RFC PATCH 0/4] scsi: use xarray for devices and targets

[Hannes Reinecke <hare@suse.de>]

Hi all,

based on the ideas from Doug Gilbert here's now my take on using
xarrays for devices and targets.
It revolves around two ideas:
- 'channel' and 'id' are never ever used to the full 32 bit range;
  'channels' are well below 10, and no driver is using more than
  16 bits for the id. So we can reduce the type of 'channel' and
  'id' to 16 bits, and use the 32 bit value 'channel << 16 | id'
  as the index into the target xarray.
- Most SCSI LUNs are below 256 (to ensure compability with older
  systems). So there we can use the LUN number as the index into
  the xarray; for larger LUN numbers we'll allocate a separate
  index.

With these change we can implement an efficient lookup mechanism,
devolving into direct lookup for most cases.
And iteration should be as efficient as the current, list-based,
approach.

This is compile-tested only, to give you an impression of the
overall idea and to get the discussion rolling.

Hannes Reinecke (4):
  scsi: convert target lookup to xarray
  target_core_pscsi: use __scsi_device_lookup()
  scsi: move target device list to xarray
  scsi: remove direct device lookup per host

 drivers/scsi/hosts.c               |   3 +-
 drivers/scsi/scsi.c                | 129 ++++++++++++++++++++++++++++---------
 drivers/scsi/scsi_lib.c            |   8 +--
 drivers/scsi/scsi_scan.c           |  66 +++++++++----------
 drivers/scsi/scsi_sysfs.c          |  39 +++++++----
 drivers/target/target_core_pscsi.c |   8 +--
 include/scsi/scsi_device.h         |  21 +++---
 include/scsi/scsi_host.h           |   5 +-
 8 files changed, 175 insertions(+), 104 deletions(-)

-- 
2.16.4