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                          Linux Kernel 2.6 series

                 SCSI mid_level - lower_level driver interface

                 =============================================

Introduction

============

This document outlines the interface between the Linux SCSI mid level and

SCSI lower level drivers. Lower level drivers (LLDs) are variously called

host bus adapter (HBA) drivers and host drivers (HD). A "host" in this

context is a bridge between a computer IO bus (e.g. PCI or ISA) and a

single SCSI initiator port on a SCSI transport. An "initiator" port

(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands

to "target" SCSI ports (e.g. disks). There can be many LLDs in a running

system, but only one per hardware type. Most LLDs can control one or more

SCSI HBAs. Some HBAs contain multiple hosts.

In some cases the SCSI transport is an external bus that already has

its own subsystem in Linux (e.g. USB and ieee1394). In such cases the

SCSI subsystem LLD is a software bridge to the other driver subsystem.

Examples are the usb-storage driver (found in the drivers/usb/storage

directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394

directory).

For example, the aic7xxx LLD controls Adaptec SCSI parallel interface

(SPI) controllers based on that company's 7xxx chip series. The aic7xxx

LLD can be built into the kernel or loaded as a module. There can only be

one aic7xxx LLD running in a Linux system but it may be controlling many

HBAs. These HBAs might be either on PCI daughter-boards or built into

the motherboard (or both). Some aic7xxx based HBAs are dual controllers

and thus represent two hosts. Like most modern HBAs, each aic7xxx host

has its own PCI device address. [The one-to-one correspondence between

a SCSI host and a PCI device is common but not required (e.g. with

ISA or MCA adapters).]

The SCSI mid level isolates an LLD from other layers such as the SCSI

upper layer drivers and the block layer.

This version of the document roughly matches linux kernel version 2.6.8 .

Documentation

=============

There is a SCSI documentation directory within the kernel source tree,

typically Documentation/scsi . Most documents are in plain

(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be

found in that directory. A more recent copy of this document may be found

at http://www.torque.net/scsi/scsi_mid_low_api.txt.gz .

Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is

briefly described in scsi.txt which contains a url to a document

describing the SCSI subsystem in the lk 2.4 series. Two upper level

drivers have documents in that directory: st.txt (SCSI tape driver) and

scsi-generic.txt (for the sg driver).

Some documentation (or urls) for LLDs may be found in the C source code

or in the same directory as the C source code. For example to find a url

about the USB mass storage driver see the

/usr/src/linux/drivers/usb/storage directory.

The Linux kernel source Documentation/DocBook/scsidrivers.tmpl file

refers to this file. With the appropriate DocBook tool-set, this permits

users to generate html, ps and pdf renderings of information within this

file (e.g. the interface functions).

Driver structure

================

Traditionally an LLD for the SCSI subsystem has been at least two files in

the drivers/scsi directory. For example, a driver called "xyz" has a header

file "xyz.h" and a source file "xyz.c". [Actually there is no good reason

why this couldn't all be in one file; the header file is superfluous.] Some

drivers that have been ported to several operating systems have more than

two files. For example the aic7xxx driver has separate files for generic

and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have

their own directory under the drivers/scsi directory.

When a new LLD is being added to Linux, the following files (found in the

drivers/scsi directory) will need some attention: Makefile and Kconfig .

It is probably best to study how existing LLDs are organized.

As the 2.5 series development kernels evolve into the 2.6 series

production series, changes are being introduced into this interface. An

example of this is driver initialization code where there are now 2 models

available. The older one, similar to what was found in the lk 2.4 series,

is based on hosts that are detected at HBA driver load time. This will be

referred to the "passive" initialization model. The newer model allows HBAs

to be hot plugged (and unplugged) during the lifetime of the LLD and will

be referred to as the "hotplug" initialization model. The newer model is

preferred as it can handle both traditional SCSI equipment that is

permanently connected as well as modern "SCSI" devices (e.g. USB or

IEEE 1394 connected digital cameras) that are hotplugged. Both

initialization models are discussed in the following sections.

An LLD interfaces to the SCSI subsystem several ways:

  a) directly invoking functions supplied by the mid level

  b) passing a set of function pointers to a registration function

     supplied by the mid level. The mid level will then invoke these

     functions at some point in the future. The LLD will supply

     implementations of these functions.

  c) direct access to instances of well known data structures maintained

     by the mid level

Those functions in group a) are listed in a section entitled "Mid level

supplied functions" below.

Those functions in group b) are listed in a section entitled "Interface

functions" below. Their function pointers are placed in the members of

"struct scsi_host_template", an instance of which is passed to

scsi_host_alloc() ** .  Those interface functions that the LLD does not

wish to supply should have NULL placed in the corresponding member of

struct scsi_host_template.  Defining an instance of struct

scsi_host_template at file scope will cause NULL to be  placed in function

 pointer members not explicitly initialized.

Those usages in group c) should be handled with care, especially in a

"hotplug" environment. LLDs should be aware of the lifetime of instances

that are shared with the mid level and other layers.

All functions defined within an LLD and all data defined at file scope

should be static. For example the slave_alloc() function in an LLD

called "xxx" could be defined as

"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"

** the scsi_host_alloc() function is a replacement for the rather vaguely

named scsi_register() function in most situations. The scsi_register()

and scsi_unregister() functions remain to support legacy LLDs that use

the passive initialization model.

Hotplug initialization model

============================

In this model an LLD controls when SCSI hosts are introduced and removed

from the SCSI subsystem. Hosts can be introduced as early as driver

initialization and removed as late as driver shutdown. Typically a driver

will respond to a sysfs probe() callback that indicates an HBA has been

detected. After confirming that the new device is one that the LLD wants

to control, the LLD will initialize the HBA and then register a new host

with the SCSI mid level.

During LLD initialization the driver should register itself with the

appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).

This can probably be done via sysfs. Any driver parameters (especially

those that are writable after the driver is loaded) could also be

registered with sysfs at this point. The SCSI mid level first becomes

aware of an LLD when that LLD registers its first HBA.

At some later time, the LLD becomes aware of an HBA and what follows

is a typical sequence of calls between the LLD and the mid level.

This example shows the mid level scanning the newly introduced HBA for 3

scsi devices of which only the first 2 respond:

     HBA PROBE: assume 2 SCSI devices found in scan

LLD                   mid level                    LLD

===-------------------=========--------------------===------

scsi_host_alloc()  -->

scsi_add_host()  ---->

scsi_scan_host()  -------+

                         |

                    slave_alloc()

                    slave_configure() -->  scsi_adjust_queue_depth()

                         |

                    slave_alloc()

                    slave_configure()

                         |

                    slave_alloc()   ***

                    slave_destroy() ***

------------------------------------------------------------

If the LLD wants to adjust the default queue settings, it can invoke

scsi_adjust_queue_depth() in its slave_configure() routine.

*** For scsi devices that the mid level tries to scan but do not

    respond, a slave_alloc(), slave_destroy() pair is called.

When an HBA is being removed it could be as part of an orderly shutdown

associated with the LLD module being unloaded (e.g. with the "rmmod"

command) or in response to a "hot unplug" indicated by sysfs()'s

remove() callback being invoked. In either case, the sequence is the

same:

        HBA REMOVE: assume 2 SCSI devices attached

LLD                      mid level                 LLD

===----------------------=========-----------------===------

scsi_remove_host() ---------+

                            |

                     slave_destroy()

                     slave_destroy()

scsi_host_put()

------------------------------------------------------------

It may be useful for a LLD to keep track of struct Scsi_Host instances

(a pointer is returned by scsi_host_alloc()). Such instances are "owned"

by the mid-level.  struct Scsi_Host instances are freed from

scsi_host_put() when the reference count hits zero.

Hot unplugging an HBA that controls a disk which is processing SCSI

commands on a mounted file system is an interesting situation. Reference

counting logic is being introduced into the mid level to cope with many

of the issues involved. See the section on reference counting below.

The hotplug concept may be extended to SCSI devices. Currently, when an

HBA is added, the scsi_scan_host() function causes a scan for SCSI devices

attached to the HBA's SCSI transport. On newer SCSI transports the HBA

may become aware of a new SCSI device _after_ the scan has completed.

An LLD can use this sequence to make the mid level aware of a SCSI device:

                 SCSI DEVICE hotplug

LLD                   mid level                    LLD

===-------------------=========--------------------===------

scsi_add_device()  ------+

                         |

                    slave_alloc()

                    slave_configure()   [--> scsi_adjust_queue_depth()]

------------------------------------------------------------

In a similar fashion, an LLD may become aware that a SCSI device has been

removed (unplugged) or the connection to it has been interrupted. Some

existing SCSI transports (e.g. SPI) may not become aware that a SCSI

device has been removed until a subsequent SCSI command fails which will

probably cause that device to be set offline by the mid level. An LLD that

detects the removal of a SCSI device can instigate its removal from

upper layers with this sequence:

                  SCSI DEVICE hot unplug

LLD                      mid level                 LLD

===----------------------=========-----------------===------

scsi_remove_device() -------+

                            |

                     slave_destroy()

------------------------------------------------------------

It may be useful for an LLD to keep track of struct scsi_device instances

(a pointer is passed as the parameter to slave_alloc() and

slave_configure() callbacks). Such instances are "owned" by the mid-level.

struct scsi_device instances are freed after slave_destroy().

Passive initialization model

============================

These older LLDs include a file called "scsi_module.c" [yes the ".c" is a

little surprising] in their source code. For that file to work an

instance of struct scsi_host_template with the name "driver_template"

needs to be defined. Here is a typical code sequence used in this model:

    static struct scsi_host_template driver_template = {

        ...

    };

    #include "scsi_module.c"

The scsi_module.c file contains two functions:

  - init_this_scsi_driver() which is executed when the LLD is

    initialized (i.e. boot time or module load time)

  - exit_this_scsi_driver() which is executed when the LLD is shut

    down (i.e. module unload time)

Note: since these functions are tagged with __init and __exit qualifiers

an LLD should not call them explicitly (since the kernel does that).

Here is an example of an initialization sequence when two hosts are

detected (so detect() returns 2) and the SCSI bus scan on each host

finds 1 SCSI device (and a second device does not respond).

LLD                      mid level                 LLD

===----------------------=========-----------------===------

init_this_scsi_driver() ----+

                            |

                         detect()  -----------------+

                            |                       |

                            |                scsi_register()

                            |                scsi_register()

                            |

                      slave_alloc()

                      slave_configure()  -->  scsi_adjust_queue_depth()

                      slave_alloc()   ***

                      slave_destroy() ***

                            |

                      slave_alloc()

                      slave_configure()

                      slave_alloc()   ***

                      slave_destroy() ***

------------------------------------------------------------

The mid level invokes scsi_adjust_queue_depth() with tagged queuing off and

"cmd_per_lun" for that host as the queue length. These settings can be

overridden by a slave_configure() supplied by the LLD.

*** For scsi devices that the mid level tries to scan but do not

    respond, a slave_alloc(), slave_destroy() pair is called.

Here is an LLD shutdown sequence:

LLD                      mid level                 LLD

===----------------------=========-----------------===------

exit_this_scsi_driver() ----+

                            |

                     slave_destroy()

                        release()   -->   scsi_unregister()

                            |

                     slave_destroy()

                        release()   -->   scsi_unregister()

------------------------------------------------------------

An LLD need not define slave_destroy() (i.e. it is optional).

The shortcoming of the "passive initialization model" is that host

registration and de-registration are (typically) tied to LLD initialization

and shutdown. Once the LLD is initialized then a new host that appears

(e.g. via hotplugging) cannot easily be added without a redundant

driver shutdown and re-initialization. It may be possible to write an LLD

that uses both initialization models.

Reference Counting

==================

The Scsi_Host structure has had reference counting infrastructure added.

This effectively spreads the ownership of struct Scsi_Host instances

across the various SCSI layers which use them. Previously such instances

were exclusively owned by the mid level. LLDs would not usually need to

directly manipulate these reference counts but there may be some cases

where they do.

There are 3 reference counting functions of interest associated with

struct Scsi_Host:

  - scsi_host_alloc(): returns a pointer to new instance of struct

        Scsi_Host which has its reference count ^^ set to 1

  - scsi_host_get(): adds 1 to the reference count of the given instance

  - scsi_host_put(): decrements 1 from the reference count of the given

        instance. If the reference count reaches 0 then the given instance

        is freed

The Scsi_device structure has had reference counting infrastructure added.

This effectively spreads the ownership of struct Scsi_device instances

across the various SCSI layers which use them. Previously such instances

were exclusively owned by the mid level. See the access functions declared

towards the end of include/scsi/scsi_device.h . If an LLD wants to keep

a copy of a pointer to a Scsi_device instance it should use scsi_device_get()

to bump its reference count. When it is finished with the pointer it can

use scsi_device_put() to decrement its reference count (and potentially

delete it).

^^ struct Scsi_Host actually has 2 reference counts which are manipulated

in parallel by these functions.

Conventions

===========

First, Linus Torvalds's thoughts on C coding style can be found in the

Documentation/CodingStyle file.

Next, there is a movement to "outlaw" typedefs introducing synonyms for

struct tags. Both can be still found in the SCSI subsystem, but

the typedefs have been moved to a single file, scsi_typedefs.h to

make their future removal easier, for example:

"typedef struct scsi_cmnd Scsi_Cmnd;"

Also, most C99 enhancements are encouraged to the extent they are supported

by the relevant gcc compilers. So C99 style structure and array

initializers are encouraged where appropriate. Don't go too far,

VLAs are not properly supported yet.  An exception to this is the use of

"//" style comments; /*...*/ comments are still preferred in Linux.

Well written, tested and documented code, need not be re-formatted to

comply with the above conventions. For example, the aic7xxx driver

comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD

and Adaptec have their own coding conventions.

Mid level supplied functions

============================

These functions are supplied by the SCSI mid level for use by LLDs.

The names (i.e. entry points) of these functions are exported

so an LLD that is a module can access them. The kernel will

arrange for the SCSI mid level to be loaded and initialized before any LLD

is initialized. The functions below are listed alphabetically and their

names all start with "scsi_".

Summary:

   scsi_activate_tcq - turn on tag command queueing

   scsi_add_device - creates new scsi device (lu) instance

   scsi_add_host - perform sysfs registration and set up transport class

   scsi_adjust_queue_depth - change the queue depth on a SCSI device

   scsi_bios_ptable - return copy of block device's partition table

   scsi_block_requests - prevent further commands being queued to given host

   scsi_deactivate_tcq - turn off tag command queueing

   scsi_host_alloc - return a new scsi_host instance whose refcount==1

   scsi_host_get - increments Scsi_Host instance's refcount

   scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)

   scsi_partsize - parse partition table into cylinders, heads + sectors

   scsi_register - create and register a scsi host adapter instance.

   scsi_remove_device - detach and remove a SCSI device

   scsi_remove_host - detach and remove all SCSI devices owned by host

   scsi_report_bus_reset - report scsi _bus_ reset observed

   scsi_scan_host - scan SCSI bus

   scsi_track_queue_full - track successive QUEUE_FULL events

   scsi_unblock_requests - allow further commands to be queued to given host

   scsi_unregister - [calls scsi_host_put()]

Details:

/**

 * scsi_activate_tcq - turn on tag command queueing ("ordered" task attribute)

 * @sdev:       device to turn on TCQ for

 * @depth:      queue depth

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Notes: Eventually, it is hoped depth would be the maximum depth

 *      the device could cope with and the real queue depth

 *      would be adjustable from 0 to depth.

 *

 *      Defined (inline) in: include/scsi/scsi_tcq.h

 **/

void scsi_activate_tcq(struct scsi_device *sdev, int depth)

/**

 * scsi_add_device - creates new scsi device (lu) instance

 * @shost:   pointer to scsi host instance

 * @channel: channel number (rarely other than 0)

 * @id:      target id number

 * @lun:     logical unit number

 *

 *      Returns pointer to new struct scsi_device instance or

 *      ERR_PTR(-ENODEV) (or some other bent pointer) if something is

 *      wrong (e.g. no lu responds at given address)

 *

 *      Might block: yes

 *

 *      Notes: This call is usually performed internally during a scsi

 *      bus scan when an HBA is added (i.e. scsi_scan_host()). So it

 *      should only be called if the HBA becomes aware of a new scsi

 *      device (lu) after scsi_scan_host() has completed. If successful

 *      this call can lead to slave_alloc() and slave_configure() callbacks

 *      into the LLD.

 *

 *      Defined in: drivers/scsi/scsi_scan.c

 **/

struct scsi_device * scsi_add_device(struct Scsi_Host *shost,

                                     unsigned int channel,

                                     unsigned int id, unsigned int lun)

/**

 * scsi_add_host - perform sysfs registration and set up transport class

 * @shost:   pointer to scsi host instance

 * @dev:     pointer to struct device of type scsi class

 *

 *      Returns 0 on success, negative errno of failure (e.g. -ENOMEM)

 *

 *      Might block: no

 *

 *      Notes: Only required in "hotplug initialization model" after a

 *      successful call to scsi_host_alloc().  This function does not

 *      scan the bus; this can be done by calling scsi_scan_host() or

 *      in some other transport-specific way.  The LLD must set up

 *      the transport template before calling this function and may only

 *      access the transport class data after this function has been called.

 *

 *      Defined in: drivers/scsi/hosts.c

 **/

int scsi_add_host(struct Scsi_Host *shost, struct device * dev)

/**

 * scsi_adjust_queue_depth - allow LLD to change queue depth on a SCSI device

 * @sdev:       pointer to SCSI device to change queue depth on

 * @tagged:     0 - no tagged queuing

 *              MSG_SIMPLE_TAG - simple tagged queuing

 *              MSG_ORDERED_TAG - ordered tagged queuing

 * @tags        Number of tags allowed if tagged queuing enabled,

 *              or number of commands the LLD can queue up

 *              in non-tagged mode (as per cmd_per_lun).

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Notes: Can be invoked any time on a SCSI device controlled by this

 *      LLD. [Specifically during and after slave_configure() and prior to

 *      slave_destroy().] Can safely be invoked from interrupt code. Actual

 *      queue depth change may be delayed until the next command is being

 *      processed. See also scsi_activate_tcq() and scsi_deactivate_tcq().

 *

 *      Defined in: drivers/scsi/scsi.c [see source code for more notes]

 *

 **/

void scsi_adjust_queue_depth(struct scsi_device * sdev, int tagged,

                             int tags)

/**

 * scsi_bios_ptable - return copy of block device's partition table

 * @dev:        pointer to block device

 *

 *      Returns pointer to partition table, or NULL for failure

 *

 *      Might block: yes

 *

 *      Notes: Caller owns memory returned (free with kfree() )

 *

 *      Defined in: drivers/scsi/scsicam.c

 **/

unsigned char *scsi_bios_ptable(struct block_device *dev)

/**

 * scsi_block_requests - prevent further commands being queued to given host

 *

 * @shost: pointer to host to block commands on

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Notes: There is no timer nor any other means by which the requests

 *      get unblocked other than the LLD calling scsi_unblock_requests().

 *

 *      Defined in: drivers/scsi/scsi_lib.c

**/

void scsi_block_requests(struct Scsi_Host * shost)

/**

 * scsi_deactivate_tcq - turn off tag command queueing

 * @sdev:       device to turn off TCQ for

 * @depth:      queue depth (stored in sdev)

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Defined (inline) in: include/scsi/scsi_tcq.h

 **/

void scsi_deactivate_tcq(struct scsi_device *sdev, int depth)

/**

 * scsi_host_alloc - create a scsi host adapter instance and perform basic

 *                   initialization.

 * @sht:        pointer to scsi host template

 * @privsize:   extra bytes to allocate in hostdata array (which is the

 *              last member of the returned Scsi_Host instance)

 *

 *      Returns pointer to new Scsi_Host instance or NULL on failure

 *

 *      Might block: yes

 *

 *      Notes: When this call returns to the LLD, the SCSI bus scan on

 *      this host has _not_ yet been done.

 *      The hostdata array (by default zero length) is a per host scratch

 *      area for the LLD's exclusive use.

 *      Both associated refcounting objects have their refcount set to 1.

 *      Full registration (in sysfs) and a bus scan are performed later when

 *      scsi_add_host() and scsi_scan_host() are called.

 *

 *      Defined in: drivers/scsi/hosts.c .

 **/

struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,

                                   int privsize)

/**

 * scsi_host_get - increment Scsi_Host instance refcount

 * @shost:   pointer to struct Scsi_Host instance

 *

 *      Returns nothing

 *

 *      Might block: currently may block but may be changed to not block

 *

 *      Notes: Actually increments the counts in two sub-objects

 *

 *      Defined in: drivers/scsi/hosts.c

 **/

void scsi_host_get(struct Scsi_Host *shost)

/**

 * scsi_host_put - decrement Scsi_Host instance refcount, free if 0

 * @shost:   pointer to struct Scsi_Host instance

 *

 *      Returns nothing

 *

 *      Might block: currently may block but may be changed to not block

 *

 *      Notes: Actually decrements the counts in two sub-objects. If the

 *      latter refcount reaches 0, the Scsi_Host instance is freed.

 *      The LLD need not worry exactly when the Scsi_Host instance is

 *      freed, it just shouldn't access the instance after it has balanced

 *      out its refcount usage.

 *

 *      Defined in: drivers/scsi/hosts.c

 **/

void scsi_host_put(struct Scsi_Host *shost)

/**

 * scsi_partsize - parse partition table into cylinders, heads + sectors

 * @buf: pointer to partition table

 * @capacity: size of (total) disk in 512 byte sectors

 * @cyls: outputs number of cylinders calculated via this pointer

 * @hds: outputs number of heads calculated via this pointer

 * @secs: outputs number of sectors calculated via this pointer

 *

 *      Returns 0 on success, -1 on failure

 *

 *      Might block: no

 *

 *      Notes: Caller owns memory returned (free with kfree() )

 *

 *      Defined in: drivers/scsi/scsicam.c

 **/

int scsi_partsize(unsigned char *buf, unsigned long capacity,

                  unsigned int *cyls, unsigned int *hds, unsigned int *secs)

/**

 * scsi_register - create and register a scsi host adapter instance.

 * @sht:        pointer to scsi host template

 * @privsize:   extra bytes to allocate in hostdata array (which is the

 *              last member of the returned Scsi_Host instance)

 *

 *      Returns pointer to new Scsi_Host instance or NULL on failure

 *

 *      Might block: yes

 *

 *      Notes: When this call returns to the LLD, the SCSI bus scan on

 *      this host has _not_ yet been done.

 *      The hostdata array (by default zero length) is a per host scratch

 *      area for the LLD.

 *

 *      Defined in: drivers/scsi/hosts.c .

 **/

struct Scsi_Host * scsi_register(struct scsi_host_template * sht,

                                 int privsize)

/**

 * scsi_remove_device - detach and remove a SCSI device

 * @sdev:      a pointer to a scsi device instance

 *

 *      Returns value: 0 on success, -EINVAL if device not attached

 *

 *      Might block: yes

 *

 *      Notes: If an LLD becomes aware that a scsi device (lu) has

 *      been removed but its host is still present then it can request

 *      the removal of that scsi device. If successful this call will

 *      lead to the slave_destroy() callback being invoked. sdev is an

 *      invalid pointer after this call.

 *

 *      Defined in: drivers/scsi/scsi_sysfs.c .

 **/

int scsi_remove_device(struct scsi_device *sdev)

/**

 * scsi_remove_host - detach and remove all SCSI devices owned by host

 * @shost:      a pointer to a scsi host instance

 *

 *      Returns value: 0 on success, 1 on failure (e.g. LLD busy ??)

 *

 *      Might block: yes

 *

 *      Notes: Should only be invoked if the "hotplug initialization

 *      model" is being used. It should be called _prior_ to

 *      scsi_unregister().

 *

 *      Defined in: drivers/scsi/hosts.c .

 **/

int scsi_remove_host(struct Scsi_Host *shost)

/**

 * scsi_report_bus_reset - report scsi _bus_ reset observed

 * @shost: a pointer to a scsi host involved

 * @channel: channel (within) host on which scsi bus reset occurred

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Notes: This only needs to be called if the reset is one which

 *      originates from an unknown location.  Resets originated by the

 *      mid level itself don't need to call this, but there should be

 *      no harm.  The main purpose of this is to make sure that a

 *      CHECK_CONDITION is properly treated.

 *

 *      Defined in: drivers/scsi/scsi_error.c .

 **/

void scsi_report_bus_reset(struct Scsi_Host * shost, int channel)

/**

 * scsi_scan_host - scan SCSI bus

 * @shost: a pointer to a scsi host instance

 *

 *      Might block: yes

 *

 *      Notes: Should be called after scsi_add_host()

 *

 *      Defined in: drivers/scsi/scsi_scan.c

 **/

void scsi_scan_host(struct Scsi_Host *shost)

/**

 * scsi_track_queue_full - track successive QUEUE_FULL events on given

 *                      device to determine if and when there is a need

 *                      to adjust the queue depth on the device.

 * @sdev:  pointer to SCSI device instance

 * @depth: Current number of outstanding SCSI commands on this device,

 *         not counting the one returned as QUEUE_FULL.

 *

 *      Returns 0  - no change needed

 *              >0 - adjust queue depth to this new depth

 *              -1 - drop back to untagged operation using host->cmd_per_lun

 *                   as the untagged command depth

 *

 *      Might block: no

 *

 *      Notes: LLDs may call this at any time and we will do "The Right

 *              Thing"; interrupt context safe.

 *

 *      Defined in: drivers/scsi/scsi.c .

 **/

int scsi_track_queue_full(struct scsi_device *sdev, int depth)

/**

 * scsi_unblock_requests - allow further commands to be queued to given host

 *

 * @shost: pointer to host to unblock commands on

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Defined in: drivers/scsi/scsi_lib.c .

**/

void scsi_unblock_requests(struct Scsi_Host * shost)

/**

 * scsi_unregister - unregister and free memory used by host instance

 * @shp:        pointer to scsi host instance to unregister.

 *

 *      Returns nothing

 *

 *      Might block: no

 *

 *      Notes: Should not be invoked if the "hotplug initialization

 *      model" is being used. Called internally by exit_this_scsi_driver()

 *      in the "passive initialization model". Hence a LLD has no need to

 *      call this function directly.

 *

 *      Defined in: drivers/scsi/hosts.c .

 **/

void scsi_unregister(struct Scsi_Host * shp)

Interface Functions

===================

Interface functions are supplied (defined) by LLDs and their function

pointers are placed in an instance of struct scsi_host_template which

is passed to scsi_host_alloc() [or scsi_register() / init_this_scsi_driver()].

Some are mandatory. Interface functions should be declared static. The

accepted convention is that driver "xyz" will declare its slave_configure()

function as:

    static int xyz_slave_configure(struct scsi_device * sdev);

and so forth for all interface functions listed below.

A pointer to this function should be placed in the 'slave_configure' member

of a "struct scsi_host_template" instance. A pointer to such an instance

should be passed to the mid level's scsi_host_alloc() [or scsi_register() /

init_this_scsi_driver()].

The interface functions are also described in the include/scsi/scsi_host.h

file immediately above their definition point in "struct scsi_host_template".

In some cases more detail is given in scsi_host.h than below.

The interface functions are listed below in alphabetical order.

Summary:

   bios_param - fetch head, sector, cylinder info for a disk

   detect - detects HBAs this driver wants to control

   eh_timed_out - notify the host that a command timer expired

   eh_abort_handler - abort given command

   eh_bus_reset_handler - issue SCSI bus reset

   eh_device_reset_handler - issue SCSI device reset

   eh_host_reset_handler - reset host (host bus adapter)

   info - supply information about given host

   ioctl - driver can respond to ioctls

   proc_info - supports /proc/scsi/{driver_name}/{host_no}

   queuecommand - queue scsi command, invoke 'done' on completion

   release - release all resources associated with given host

   slave_alloc - prior to any commands being sent to a new device

   slave_configure - driver fine tuning for given device after attach

   slave_destroy - given device is about to be shut down

Details:

/**

 *      bios_param - fetch head, sector, cylinder info for a disk

 *      @sdev: pointer to scsi device context (defined in

 *             include/scsi/scsi_device.h)

 *      @bdev: pointer to block device context (defined in fs.h)

 *      @capacity:  device size (in 512 byte sectors)

 *      @params: three element array to place output:

 *              params[0] number of heads (max 255)

 *              params[1] number of sectors (max 63)

 *              params[2] number of cylinders

 *

 *      Return value is ignored

 *

 *      Locks: none

 *

 *      Calling context: process (sd)

 *

 *      Notes: an arbitrary geometry (based on READ CAPACITY) is used

 *      if this function is not provided. The params array is

 *      pre-initialized with made up values just in case this function

 *      doesn't output anything.

 *

 *      Optionally defined in: LLD

 **/

    int bios_param(struct scsi_device * sdev, struct block_device *bdev,

                   sector_t capacity, int params[3])

/**

 *      detect - detects HBAs this driver wants to control

 *      @shtp: host template for this driver.

 *

 *      Returns number of hosts this driver wants to control. 0 means no

 *      suitable hosts found.

 *

 *      Locks: none held

 *

 *      Calling context: process [invoked from init_this_scsi_driver()]

 *

 *      Notes: First function called from the SCSI mid level on this

 *      driver. Upper level drivers (e.g. sd) may not (yet) be present.

 *      For each host found, this method should call scsi_register()

 *      [see hosts.c].

 *

 *      Defined in: LLD (required if "passive initialization mode" is used,

 *                       not invoked in "hotplug initialization mode")

 **/

    int detect(struct scsi_host_template * shtp)

/**

 *      eh_timed_out - The timer for the command has just fired

 *      @scp: identifies command timing out

 *

 *      Returns:

 *

 *      EH_HANDLED:             I fixed the error, please complete the command

 *      EH_RESET_TIMER:         I need more time, reset the timer and

 *                              begin counting again

 *      EH_NOT_HANDLED          Begin normal error recovery

 *

 *

 *      Locks: None held

 *

 *      Calling context: interrupt

 *

 *      Notes: This is to give the LLD an opportunity to do local recovery.

 *      This recovery is limited to determining if the outstanding command

 *      will ever complete.  You may not abort and restart the command from

 *      this callback.

 *

 *      Optionally defined in: LLD

 **/

     int eh_timed_out(struct scsi_cmnd * scp)

/**

 *      eh_abort_handler - abort command associated with scp

 *      @scp: identifies command to be aborted

 *

 *      Returns SUCCESS if command aborted else FAILED

 *

 *      Locks: None held

 *

 *      Calling context: kernel thread

 *

 *      Notes: Invoked from scsi_eh thread. No other commands will be

 *      queued on current host during eh.

 *

 *      Optionally defined in: LLD

 **/

     int eh_abort_handler(struct scsi_cmnd * scp)

/**

 *      eh_bus_reset_handler - issue SCSI bus reset

 *      @scp: SCSI bus that contains this device should be reset

 *

 *      Returns SUCCESS if command aborted else FAILED

 *

 *      Locks: None held

 *

 *      Calling context: kernel thread

 *

 *      Notes: Invoked from scsi_eh thread. No other commands will be

 *      queued on current host during eh.

 *

 *      Optionally defined in: LLD

 **/

     int eh_bus_reset_handler(struct scsi_cmnd * scp)

/**

 *      eh_device_reset_handler - issue SCSI device reset

 *      @scp: identifies SCSI device to be reset

 *

 *      Returns SUCCESS if command aborted else FAILED

 *

 *      Locks: None held

 *

 *      Calling context: kernel thread

 *

 *      Notes: Invoked from scsi_eh thread. No other commands will be

 *      queued on current host during eh.

 *

 *      Optionally defined in: LLD

 **/

     int eh_device_reset_handler(struct scsi_cmnd * scp)

/**

 *      eh_host_reset_handler - reset host (host bus adapter)

 *      @scp: SCSI host that contains this device should be reset

 *

 *      Returns SUCCESS if command aborted else FAILED

 *

 *      Locks: None held