scst: Add scst_local driver.

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@@ -0,0 +1,263 @@
+SCST Local ...
+Richard Sharpe, 30-Nov-2008
+
+This is the SCST Local driver. Its function is to allow you to access devices
+that are exported via SCST directly on the same Linux system that they are
+exported from.
+
+No assumptions are made in the code about the device types on the target, so
+any device handlers that you load in SCST should be visible, including tapes
+and so forth.
+
+You can freely use any sg, sd, st, etc. devices imported from target,
+except the following: you can't mount file systems or put swap on them.
+This is a limitation of Linux memory/cache manager. See SCST README file
+for details.
+
+To build, simply issue 'make' in the scst_local directory.
+
+Try 'modinfo scst_local' for a listing of module parameters so far.
+
+Here is how I have used it so far:
+
+1. Load up scst:
+
+  modprobe scst
+  modprobe scst_vdisk
+
+2. Create a virtual disk (or your own device handler):
+
+  dd if=/dev/zero of=/some/path/vdisk1.img bs=16384 count=1000000
+  echo "add_device vm_disk1 filename=/some/path/vdisk1.img" >/sys/kernel/scst_tgt/handlers/vdisk_fileio/mgmt
+
+3. Load the scst_local driver:
+
+  insmod scst_local
+  echo "add vm_disk1 0" >/sys/kernel/scst_tgt/targets/scst_local/scst_local_tgt/luns/mgmt
+
+4. Check what you have
+
+   cat /proc/scsi/scsi
+  Attached devices:
+  Host: scsi0 Channel: 00 Id: 00 Lun: 00
+    Vendor: ATA      Model: ST9320320AS      Rev: 0303
+    Type:   Direct-Access                    ANSI  SCSI revision: 05
+  Host: scsi4 Channel: 00 Id: 00 Lun: 00
+    Vendor: TSSTcorp Model: CD/DVDW TS-L632D Rev: TO04
+    Type:   CD-ROM                           ANSI  SCSI revision: 05
+  Host: scsi7 Channel: 00 Id: 00 Lun: 00
+    Vendor: SCST_FIO Model: vm_disk1         Rev:  200
+    Type:   Direct-Access                    ANSI  SCSI revision: 04
+
+Or instead of manually "add_device" in (2) and step (3) write a
+scstadmin config:
+
+HANDLER vdisk_fileio {
+        DEVICE vm_disk1 {
+        	filename /some/path/vdisk1.img
+        }
+}
+
+TARGET_DRIVER scst_local {
+	TARGET scst_local_tgt {
+		LUN 0 vm_disk1
+	}
+}
+
+then:
+
+  insmod scst_local
+  scstadmin -config conf_file.cfg
+
+More advanced examples:
+
+For (3) you can:
+
+  insmod scst_local add_default_tgt=0
+  echo "add_target scst_local_tgt session_name=scst_local_host" >/sys/kernel/scst_tgt/targets/scst_local//mgmt
+  echo "add vm_disk1 0" >/sys/kernel/scst_tgt/targets/scst_local/scst_local_tgt/luns/mgmt
+
+Scst_local module's parameter add_default_tgt disables creation of
+default target "scst_local_tgt" and session "scst_local_host", so you
+needed to create it manually.
+
+There can be any number of targets and sessions created. Each SCST
+session corresponds to SCSI host. You can change which LUNs assigned to
+each session by using SCST access control. This mode is intended for
+user space target drivers (see below).
+
+Alternatively, you can write an scstadmin's config file conf_file.cfg:
+
+HANDLER vdisk_fileio {
+        DEVICE vm_disk1 {
+        	filename /some/path/vdisk1.img
+        }
+}
+
+TARGET_DRIVER scst_local {
+	TARGET scst_local_tgt {
+		session_name scst_local_host
+
+		LUN 0 vm_disk1
+	}
+}
+
+then:
+
+  insmod scst_local add_default_tgt=0
+  scstadmin -config conf_file.cfg
+
+NOTE! Although scstadmin allows to create scst_local's sessions using
+"session_name" expression, it doesn't save existing sessions during
+writing config file by "write_config" command. If you need this
+functionality, feel free to send a request for it in SCST development
+mailing list.
+
+5. Have fun.
+
+Some of this was coded while in Santa Clara, some in Bangalore, and some in
+Hyderabad. Noe doubt some will be coded on the way back to Santa Clara.
+
+The code still has bugs, so if you encounter any, email me the fixes at:
+
+   [email protected]
+
+I am thinking of renaming this to something more interesting.
+
+
+Sysfs interface
+===============
+
+See SCST's README for a common SCST sysfs description.
+
+Root of this driver is /sys/kernel/scst_tgt/targets/scst_local. It has
+the following additional entry:
+
+ - stats - read-only attribute with some statistical information.
+
+Each target subdirectory contains the following additional entries:
+
+ - phys_transport_version - contains and allows to change physical
+   transport version descriptor. It determines by which phisical
+   interface this target will look like. See SPC for more details. By
+   default, it is not defined (0).
+
+ - scsi_transport_version - contains and allows to change SCSI
+   transport version descriptor. It determines by which SCSI
+   transport this target will look like. See SPC for more details. By
+   default, it is SAS.
+
+Each session subdirectory contains the following additional entries:
+
+ - transport_id - contains this host's TransportID. This TransportID
+   used to identify initiator in Persisten Reservation commands. If you
+   change scsi_transport_version for a target, make sure you set for all
+   its sessions correct TransportID. See SPC for more details.
+
+ - host - links to the corresponding SCSI host. Using it you can find
+   local sg/bsg/sd/etc. devices of this session. For instance, this
+   links points out to host12, so you can find your sg devices by:
+
+$ lsscsi -g|grep "\[12:"
+[12:0:0:0]   disk    SCST_FIO rd1               200  /dev/sdc  /dev/sg2
+[12:0:0:1]   disk    SCST_FIO nullio            200  /dev/sdd  /dev/sg3
+
+They are /dev/sg2 and /dev/sg3.
+
+The following management commands available via /sys/kernel/scst_tgt/targets/scst_local/mgmt:
+
+ - add_target target_name [session_name=sess_name; [session_name=sess_name1;] [...]] -
+   creates a target with optionally one or more sessions.
+
+ - del_target target_name - deletes a target.
+
+ - add_session target_name session_name - adds to target target_name
+   session (SCSI host) with name session_name.
+
+ - del_session target_name session_name - deletes session session_name
+    from target target_name.
+
+
+Note on performance
+===================
+
+Although this driver implemented in the most performance effective way,
+including zero-copy passing data between SCSI/block subsystems and SCST,
+in many cases it is NOT suited to measure performance as a NULL link.
+For example, it is not suited for max IOPS measurements. This is because
+for such cases not performance of the link between the target and
+initiator is the bottleneck, but CPU or memory speed on the target or
+initiator. For scst_local you have both initiator and target on the same
+system, which means each your initiator and target are much less
+CPU/memory powerful.
+
+
+User space target drivers
+=========================
+
+Scst_local can be used to write full featured SCST target drivers in
+user space:
+
+1. For each SCSI target a user space target driver should create an
+   scst_local's target using "add_target" command.
+
+2. Then the user space target driver should, if needed, set its SCSI and
+   physical transport version descriptors using attributes
+   scsi_transport_version and phys_transport_version correspondingly in
+   /sys/kernel/scst_tgt/targets/scst_local/target_name directory.
+
+3. For incoming session (I_T nexus) from an initiator the user space
+   target driver should create scst_local's session using "add_session"
+   command.
+
+4. Then, if needed, the user space target driver should set TransportID
+   for this session (I_T nexus) using attribute
+   /sys/kernel/scst_tgt/targets/scst_local/target_name/sessions/session_name/transport_id
+
+5. Then the user space target driver should find out sg/bsg devices for
+   the LUNs the created session has using link
+   /sys/kernel/scst_tgt/targets/scst_local/target_name/sessions/session_name/host
+   as described above.
+
+6. Then the user space target driver can start serving the initiator using
+   found sg/bsg devices.
+
+For other connected initiators steps 3-6 should be repeated.
+
+
+Change log
+==========
+
+V0.1 24-Sep-2008 (Hyderabad) Initial coding, pretty chatty and messy,
+                             but worked.
+
+V0.2 25-Sep-2008 (Hong Kong) Cleaned up the code a lot, reduced the log
+			     chatter, fixed a bug where multiple LUNs did not
+			     work. Also, added logging control. Tested with
+			     five virtual disks. They all came up as /dev/sdb
+			     through /dev/sdf and I could dd to them. Also
+			     fixed a bug preventing multiple adapters.
+
+V0.3 26-Sep-2008 (Santa Clara) Added back a copyright plus cleaned up some
+			       unused functions and structures.
+
+V0.4 5-Oct-2008 (Santa Clara) Changed name to scst_local as suggested, cleaned
+			      up some unused variables (made them used) and
+			      change allocation to a kmem_cache pool.
+
+V0.5 5-Oct-2008 (Santa Clara) Added mgmt commands to handle dev reset and
+			      aborts. Not sure if aborts works. Also corrected
+			      the version info and renamed readme to README.
+
+V0.6 7-Oct-2008 (Santa Clara) Removed some redundant code and made some
+			      changes suggested by Vladislav.
+
+V0.7 11-Oct-2008 (Santa Clara) Moved into the scst tree. Cleaned up some
+			       unused functions, used TRACE macros etc.
+
+V0.9 30-Nov-2008 (Mtn View) Cleaned up an additional problem with symbols not
+			    being defined in older version of the kernel. Also
+			    fixed some English and cleaned up this doc.
+
+V1.0 10-Sep-2010 (Moscow)   Sysfs management added. Reviewed and cleaned up.
+

index fd24ec3..0263931 100644
@@ -248,4 +248,6 @@ config SCST_MEASURE_LATENCY
 
 	  If unsure, say "N".
 
+source "drivers/scst/scst_local/Kconfig"
+
 endmenu

index 2ffddc8..ac87362 100644
@@ -8,4 +8,4 @@ scst-y        += scst_sysfs.o
 scst-y        += scst_mem.o
 scst-y        += scst_debug.o
 
-obj-$(CONFIG_SCST)   += scst.o dev_handlers/
+obj-$(CONFIG_SCST)   += scst.o dev_handlers/ scst_local/

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+config SCST_LOCAL
+	tristate "SCST Local driver"
+	depends on SCST && !HIGHMEM4G && !HIGHMEM64G
+	---help---
+	  This module provides a LLD SCSI driver that connects to
+	  the SCST target mode subsystem in a loop-back manner.
+	  It allows you to test target-mode device-handlers locally.
+	  You will need the SCST subsystem as well.
+
+	  If unsure whether you really want or need this, say N.
+
+config SCST_LOCAL_FORCE_DIRECT_PROCESSING
+	bool "Force local processing"
+	depends on SCST_LOCAL
+	help
+	  This experimental option forces scst_local to make SCST process
+	  SCSI commands in the same context, in which they was submitted.
+	  Otherwise, they will be processed in SCST threads. Setting this
+	  option to "Y" will give some performance increase, but might be
+	  unsafe.
+
+	  If unsure, say "N".

new file mode 100644
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+obj-$(CONFIG_SCST_LOCAL) += scst_local.o
+