1402 lines
58 KiB
Plaintext
1402 lines
58 KiB
Plaintext
Linux Kernel 2.6 series
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SCSI mid_level - lower_level driver interface
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=============================================
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Introduction
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============
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This document outlines the interface between the Linux SCSI mid level and
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SCSI lower level drivers. Lower level drivers (LLDs) are variously called
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host bus adapter (HBA) drivers and host drivers (HD). A "host" in this
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context is a bridge between a computer IO bus (e.g. PCI or ISA) and a
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single SCSI initiator port on a SCSI transport. An "initiator" port
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(SCSI terminology, see SAM-3 at http://www.t10.org) sends SCSI commands
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to "target" SCSI ports (e.g. disks). There can be many LLDs in a running
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system, but only one per hardware type. Most LLDs can control one or more
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SCSI HBAs. Some HBAs contain multiple hosts.
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In some cases the SCSI transport is an external bus that already has
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its own subsystem in Linux (e.g. USB and ieee1394). In such cases the
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SCSI subsystem LLD is a software bridge to the other driver subsystem.
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Examples are the usb-storage driver (found in the drivers/usb/storage
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directory) and the ieee1394/sbp2 driver (found in the drivers/ieee1394
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directory).
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For example, the aic7xxx LLD controls Adaptec SCSI parallel interface
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(SPI) controllers based on that company's 7xxx chip series. The aic7xxx
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LLD can be built into the kernel or loaded as a module. There can only be
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one aic7xxx LLD running in a Linux system but it may be controlling many
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HBAs. These HBAs might be either on PCI daughter-boards or built into
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the motherboard (or both). Some aic7xxx based HBAs are dual controllers
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and thus represent two hosts. Like most modern HBAs, each aic7xxx host
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has its own PCI device address. [The one-to-one correspondence between
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a SCSI host and a PCI device is common but not required (e.g. with
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ISA adapters).]
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The SCSI mid level isolates an LLD from other layers such as the SCSI
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upper layer drivers and the block layer.
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This version of the document roughly matches linux kernel version 2.6.8 .
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Documentation
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=============
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There is a SCSI documentation directory within the kernel source tree,
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typically Documentation/scsi . Most documents are in plain
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(i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be
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found in that directory. A more recent copy of this document may be found
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at http://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/.
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Many LLDs are documented there (e.g. aic7xxx.txt). The SCSI mid-level is
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briefly described in scsi.txt which contains a url to a document
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describing the SCSI subsystem in the lk 2.4 series. Two upper level
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drivers have documents in that directory: st.txt (SCSI tape driver) and
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scsi-generic.txt (for the sg driver).
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Some documentation (or urls) for LLDs may be found in the C source code
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or in the same directory as the C source code. For example to find a url
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about the USB mass storage driver see the
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/usr/src/linux/drivers/usb/storage directory.
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Driver structure
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================
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Traditionally an LLD for the SCSI subsystem has been at least two files in
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the drivers/scsi directory. For example, a driver called "xyz" has a header
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file "xyz.h" and a source file "xyz.c". [Actually there is no good reason
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why this couldn't all be in one file; the header file is superfluous.] Some
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drivers that have been ported to several operating systems have more than
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two files. For example the aic7xxx driver has separate files for generic
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and OS-specific code (e.g. FreeBSD and Linux). Such drivers tend to have
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their own directory under the drivers/scsi directory.
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When a new LLD is being added to Linux, the following files (found in the
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drivers/scsi directory) will need some attention: Makefile and Kconfig .
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It is probably best to study how existing LLDs are organized.
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As the 2.5 series development kernels evolve into the 2.6 series
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production series, changes are being introduced into this interface. An
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example of this is driver initialization code where there are now 2 models
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available. The older one, similar to what was found in the lk 2.4 series,
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is based on hosts that are detected at HBA driver load time. This will be
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referred to the "passive" initialization model. The newer model allows HBAs
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to be hot plugged (and unplugged) during the lifetime of the LLD and will
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be referred to as the "hotplug" initialization model. The newer model is
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preferred as it can handle both traditional SCSI equipment that is
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permanently connected as well as modern "SCSI" devices (e.g. USB or
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IEEE 1394 connected digital cameras) that are hotplugged. Both
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initialization models are discussed in the following sections.
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An LLD interfaces to the SCSI subsystem several ways:
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a) directly invoking functions supplied by the mid level
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b) passing a set of function pointers to a registration function
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supplied by the mid level. The mid level will then invoke these
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functions at some point in the future. The LLD will supply
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implementations of these functions.
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c) direct access to instances of well known data structures maintained
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by the mid level
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Those functions in group a) are listed in a section entitled "Mid level
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supplied functions" below.
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Those functions in group b) are listed in a section entitled "Interface
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functions" below. Their function pointers are placed in the members of
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"struct scsi_host_template", an instance of which is passed to
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scsi_host_alloc() ** . Those interface functions that the LLD does not
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wish to supply should have NULL placed in the corresponding member of
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struct scsi_host_template. Defining an instance of struct
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scsi_host_template at file scope will cause NULL to be placed in function
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pointer members not explicitly initialized.
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Those usages in group c) should be handled with care, especially in a
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"hotplug" environment. LLDs should be aware of the lifetime of instances
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that are shared with the mid level and other layers.
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All functions defined within an LLD and all data defined at file scope
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should be static. For example the slave_alloc() function in an LLD
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called "xxx" could be defined as
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"static int xxx_slave_alloc(struct scsi_device * sdev) { /* code */ }"
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** the scsi_host_alloc() function is a replacement for the rather vaguely
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named scsi_register() function in most situations. The scsi_register()
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and scsi_unregister() functions remain to support legacy LLDs that use
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the passive initialization model.
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Hotplug initialization model
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============================
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In this model an LLD controls when SCSI hosts are introduced and removed
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from the SCSI subsystem. Hosts can be introduced as early as driver
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initialization and removed as late as driver shutdown. Typically a driver
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will respond to a sysfs probe() callback that indicates an HBA has been
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detected. After confirming that the new device is one that the LLD wants
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to control, the LLD will initialize the HBA and then register a new host
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with the SCSI mid level.
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During LLD initialization the driver should register itself with the
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appropriate IO bus on which it expects to find HBA(s) (e.g. the PCI bus).
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This can probably be done via sysfs. Any driver parameters (especially
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those that are writable after the driver is loaded) could also be
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registered with sysfs at this point. The SCSI mid level first becomes
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aware of an LLD when that LLD registers its first HBA.
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At some later time, the LLD becomes aware of an HBA and what follows
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is a typical sequence of calls between the LLD and the mid level.
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This example shows the mid level scanning the newly introduced HBA for 3
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scsi devices of which only the first 2 respond:
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HBA PROBE: assume 2 SCSI devices found in scan
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LLD mid level LLD
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===-------------------=========--------------------===------
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scsi_host_alloc() -->
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scsi_add_host() ---->
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scsi_scan_host() -------+
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slave_alloc()
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slave_configure() --> scsi_change_queue_depth()
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slave_alloc()
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slave_configure()
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slave_alloc() ***
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slave_destroy() ***
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------------------------------------------------------------
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If the LLD wants to adjust the default queue settings, it can invoke
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scsi_change_queue_depth() in its slave_configure() routine.
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*** For scsi devices that the mid level tries to scan but do not
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respond, a slave_alloc(), slave_destroy() pair is called.
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When an HBA is being removed it could be as part of an orderly shutdown
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associated with the LLD module being unloaded (e.g. with the "rmmod"
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command) or in response to a "hot unplug" indicated by sysfs()'s
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remove() callback being invoked. In either case, the sequence is the
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same:
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HBA REMOVE: assume 2 SCSI devices attached
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LLD mid level LLD
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===----------------------=========-----------------===------
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scsi_remove_host() ---------+
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slave_destroy()
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slave_destroy()
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scsi_host_put()
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------------------------------------------------------------
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It may be useful for a LLD to keep track of struct Scsi_Host instances
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(a pointer is returned by scsi_host_alloc()). Such instances are "owned"
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by the mid-level. struct Scsi_Host instances are freed from
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scsi_host_put() when the reference count hits zero.
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Hot unplugging an HBA that controls a disk which is processing SCSI
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commands on a mounted file system is an interesting situation. Reference
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counting logic is being introduced into the mid level to cope with many
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of the issues involved. See the section on reference counting below.
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The hotplug concept may be extended to SCSI devices. Currently, when an
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HBA is added, the scsi_scan_host() function causes a scan for SCSI devices
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attached to the HBA's SCSI transport. On newer SCSI transports the HBA
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may become aware of a new SCSI device _after_ the scan has completed.
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An LLD can use this sequence to make the mid level aware of a SCSI device:
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SCSI DEVICE hotplug
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LLD mid level LLD
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===-------------------=========--------------------===------
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scsi_add_device() ------+
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slave_alloc()
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slave_configure() [--> scsi_change_queue_depth()]
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------------------------------------------------------------
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In a similar fashion, an LLD may become aware that a SCSI device has been
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removed (unplugged) or the connection to it has been interrupted. Some
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existing SCSI transports (e.g. SPI) may not become aware that a SCSI
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device has been removed until a subsequent SCSI command fails which will
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probably cause that device to be set offline by the mid level. An LLD that
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detects the removal of a SCSI device can instigate its removal from
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upper layers with this sequence:
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SCSI DEVICE hot unplug
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LLD mid level LLD
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===----------------------=========-----------------===------
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scsi_remove_device() -------+
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slave_destroy()
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------------------------------------------------------------
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It may be useful for an LLD to keep track of struct scsi_device instances
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(a pointer is passed as the parameter to slave_alloc() and
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slave_configure() callbacks). Such instances are "owned" by the mid-level.
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struct scsi_device instances are freed after slave_destroy().
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Passive initialization model
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============================
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These older LLDs include a file called "scsi_module.c" [yes the ".c" is a
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little surprising] in their source code. For that file to work an
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instance of struct scsi_host_template with the name "driver_template"
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needs to be defined. Here is a typical code sequence used in this model:
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static struct scsi_host_template driver_template = {
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...
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};
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#include "scsi_module.c"
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The scsi_module.c file contains two functions:
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- init_this_scsi_driver() which is executed when the LLD is
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initialized (i.e. boot time or module load time)
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- exit_this_scsi_driver() which is executed when the LLD is shut
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down (i.e. module unload time)
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Note: since these functions are tagged with __init and __exit qualifiers
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an LLD should not call them explicitly (since the kernel does that).
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Here is an example of an initialization sequence when two hosts are
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detected (so detect() returns 2) and the SCSI bus scan on each host
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finds 1 SCSI device (and a second device does not respond).
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LLD mid level LLD
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===----------------------=========-----------------===------
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init_this_scsi_driver() ----+
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detect() -----------------+
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| scsi_register()
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| scsi_register()
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slave_alloc()
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slave_configure() --> scsi_change_queue_depth()
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slave_alloc() ***
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slave_destroy() ***
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slave_alloc()
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slave_configure()
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slave_alloc() ***
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slave_destroy() ***
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------------------------------------------------------------
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The mid level invokes scsi_change_queue_depth() with "cmd_per_lun" for that
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host as the queue length. These settings can be overridden by a
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slave_configure() supplied by the LLD.
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*** For scsi devices that the mid level tries to scan but do not
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respond, a slave_alloc(), slave_destroy() pair is called.
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Here is an LLD shutdown sequence:
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LLD mid level LLD
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===----------------------=========-----------------===------
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exit_this_scsi_driver() ----+
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slave_destroy()
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release() --> scsi_unregister()
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slave_destroy()
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release() --> scsi_unregister()
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------------------------------------------------------------
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An LLD need not define slave_destroy() (i.e. it is optional).
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The shortcoming of the "passive initialization model" is that host
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registration and de-registration are (typically) tied to LLD initialization
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and shutdown. Once the LLD is initialized then a new host that appears
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(e.g. via hotplugging) cannot easily be added without a redundant
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driver shutdown and re-initialization. It may be possible to write an LLD
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that uses both initialization models.
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Reference Counting
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==================
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The Scsi_Host structure has had reference counting infrastructure added.
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This effectively spreads the ownership of struct Scsi_Host instances
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across the various SCSI layers which use them. Previously such instances
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were exclusively owned by the mid level. LLDs would not usually need to
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directly manipulate these reference counts but there may be some cases
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where they do.
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There are 3 reference counting functions of interest associated with
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struct Scsi_Host:
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- scsi_host_alloc(): returns a pointer to new instance of struct
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Scsi_Host which has its reference count ^^ set to 1
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- scsi_host_get(): adds 1 to the reference count of the given instance
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- scsi_host_put(): decrements 1 from the reference count of the given
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instance. If the reference count reaches 0 then the given instance
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is freed
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The Scsi_device structure has had reference counting infrastructure added.
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This effectively spreads the ownership of struct Scsi_device instances
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across the various SCSI layers which use them. Previously such instances
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were exclusively owned by the mid level. See the access functions declared
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towards the end of include/scsi/scsi_device.h . If an LLD wants to keep
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a copy of a pointer to a Scsi_device instance it should use scsi_device_get()
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to bump its reference count. When it is finished with the pointer it can
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use scsi_device_put() to decrement its reference count (and potentially
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delete it).
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^^ struct Scsi_Host actually has 2 reference counts which are manipulated
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in parallel by these functions.
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Conventions
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===========
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First, Linus Torvalds's thoughts on C coding style can be found in the
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Documentation/CodingStyle file.
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Next, there is a movement to "outlaw" typedefs introducing synonyms for
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struct tags. Both can be still found in the SCSI subsystem, but
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the typedefs have been moved to a single file, scsi_typedefs.h to
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make their future removal easier, for example:
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"typedef struct scsi_cmnd Scsi_Cmnd;"
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Also, most C99 enhancements are encouraged to the extent they are supported
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by the relevant gcc compilers. So C99 style structure and array
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initializers are encouraged where appropriate. Don't go too far,
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VLAs are not properly supported yet. An exception to this is the use of
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"//" style comments; /*...*/ comments are still preferred in Linux.
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Well written, tested and documented code, need not be re-formatted to
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comply with the above conventions. For example, the aic7xxx driver
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comes to Linux from FreeBSD and Adaptec's own labs. No doubt FreeBSD
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and Adaptec have their own coding conventions.
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Mid level supplied functions
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============================
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These functions are supplied by the SCSI mid level for use by LLDs.
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The names (i.e. entry points) of these functions are exported
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so an LLD that is a module can access them. The kernel will
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arrange for the SCSI mid level to be loaded and initialized before any LLD
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is initialized. The functions below are listed alphabetically and their
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names all start with "scsi_".
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Summary:
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scsi_add_device - creates new scsi device (lu) instance
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scsi_add_host - perform sysfs registration and set up transport class
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scsi_change_queue_depth - change the queue depth on a SCSI device
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scsi_bios_ptable - return copy of block device's partition table
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scsi_block_requests - prevent further commands being queued to given host
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scsi_host_alloc - return a new scsi_host instance whose refcount==1
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scsi_host_get - increments Scsi_Host instance's refcount
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scsi_host_put - decrements Scsi_Host instance's refcount (free if 0)
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scsi_partsize - parse partition table into cylinders, heads + sectors
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scsi_register - create and register a scsi host adapter instance.
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scsi_remove_device - detach and remove a SCSI device
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scsi_remove_host - detach and remove all SCSI devices owned by host
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scsi_report_bus_reset - report scsi _bus_ reset observed
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scsi_scan_host - scan SCSI bus
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scsi_track_queue_full - track successive QUEUE_FULL events
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scsi_unblock_requests - allow further commands to be queued to given host
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scsi_unregister - [calls scsi_host_put()]
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Details:
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/**
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* scsi_add_device - creates new scsi device (lu) instance
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* @shost: pointer to scsi host instance
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* @channel: channel number (rarely other than 0)
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* @id: target id number
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* @lun: logical unit number
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*
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* Returns pointer to new struct scsi_device instance or
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* ERR_PTR(-ENODEV) (or some other bent pointer) if something is
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* wrong (e.g. no lu responds at given address)
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*
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* Might block: yes
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*
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* Notes: This call is usually performed internally during a scsi
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* bus scan when an HBA is added (i.e. scsi_scan_host()). So it
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* should only be called if the HBA becomes aware of a new scsi
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* device (lu) after scsi_scan_host() has completed. If successful
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* this call can lead to slave_alloc() and slave_configure() callbacks
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* into the LLD.
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*
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* Defined in: drivers/scsi/scsi_scan.c
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**/
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struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
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unsigned int channel,
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unsigned int id, unsigned int lun)
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/**
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* scsi_add_host - perform sysfs registration and set up transport class
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* @shost: pointer to scsi host instance
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* @dev: pointer to struct device of type scsi class
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*
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* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
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*
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* Might block: no
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*
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* Notes: Only required in "hotplug initialization model" after a
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* successful call to scsi_host_alloc(). This function does not
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* scan the bus; this can be done by calling scsi_scan_host() or
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* in some other transport-specific way. The LLD must set up
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* the transport template before calling this function and may only
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* access the transport class data after this function has been called.
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*
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* Defined in: drivers/scsi/hosts.c
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**/
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int scsi_add_host(struct Scsi_Host *shost, struct device * dev)
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/**
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* scsi_change_queue_depth - allow LLD to change queue depth on a SCSI device
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* @sdev: pointer to SCSI device to change queue depth on
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* @tags Number of tags allowed if tagged queuing enabled,
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* or number of commands the LLD can queue up
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* in non-tagged mode (as per cmd_per_lun).
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*
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* Returns nothing
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*
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* Might block: no
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*
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* Notes: Can be invoked any time on a SCSI device controlled by this
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* LLD. [Specifically during and after slave_configure() and prior to
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* slave_destroy().] Can safely be invoked from interrupt code.
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*
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* Defined in: drivers/scsi/scsi.c [see source code for more notes]
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*
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**/
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int scsi_change_queue_depth(struct scsi_device *sdev, int tags)
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|
|
|
|
|
/**
|
|
* 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_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: If 'no_async_abort' is defined this callback
|
|
* will be invoked from scsi_eh thread. No other commands
|
|
* will then be queued on current host during eh.
|
|
* Otherwise it will be called whenever scsi_times_out()
|
|
* is called due to a command timeout.
|
|
*
|
|
* 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
|
|
*
|
|
* Calling context: kernel thread
|
|
*
|
|
* Notes: Invoked from scsi_eh thread. No other commands will be
|
|
* queued on current host during eh.
|
|
* With the default eh_strategy in place, if none of the _abort_,
|
|
* _device_reset_, _bus_reset_ or this eh handler function are
|
|
* defined (or they all return FAILED) then the device in question
|
|
* will be set offline whenever eh is invoked.
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
int eh_host_reset_handler(struct scsi_cmnd * scp)
|
|
|
|
|
|
/**
|
|
* info - supply information about given host: driver name plus data
|
|
* to distinguish given host
|
|
* @shp: host to supply information about
|
|
*
|
|
* Return ASCII null terminated string. [This driver is assumed to
|
|
* manage the memory pointed to and maintain it, typically for the
|
|
* lifetime of this host.]
|
|
*
|
|
* Locks: none
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: Often supplies PCI or ISA information such as IO addresses
|
|
* and interrupt numbers. If not supplied struct Scsi_Host::name used
|
|
* instead. It is assumed the returned information fits on one line
|
|
* (i.e. does not included embedded newlines).
|
|
* The SCSI_IOCTL_PROBE_HOST ioctl yields the string returned by this
|
|
* function (or struct Scsi_Host::name if this function is not
|
|
* available).
|
|
* In a similar manner, init_this_scsi_driver() outputs to the console
|
|
* each host's "info" (or name) for the driver it is registering.
|
|
* Also if proc_info() is not supplied, the output of this function
|
|
* is used instead.
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
const char * info(struct Scsi_Host * shp)
|
|
|
|
|
|
/**
|
|
* ioctl - driver can respond to ioctls
|
|
* @sdp: device that ioctl was issued for
|
|
* @cmd: ioctl number
|
|
* @arg: pointer to read or write data from. Since it points to
|
|
* user space, should use appropriate kernel functions
|
|
* (e.g. copy_from_user() ). In the Unix style this argument
|
|
* can also be viewed as an unsigned long.
|
|
*
|
|
* Returns negative "errno" value when there is a problem. 0 or a
|
|
* positive value indicates success and is returned to the user space.
|
|
*
|
|
* Locks: none
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: The SCSI subsystem uses a "trickle down" ioctl model.
|
|
* The user issues an ioctl() against an upper level driver
|
|
* (e.g. /dev/sdc) and if the upper level driver doesn't recognize
|
|
* the 'cmd' then it is passed to the SCSI mid level. If the SCSI
|
|
* mid level does not recognize it, then the LLD that controls
|
|
* the device receives the ioctl. According to recent Unix standards
|
|
* unsupported ioctl() 'cmd' numbers should return -ENOTTY.
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
int ioctl(struct scsi_device *sdp, int cmd, void *arg)
|
|
|
|
|
|
/**
|
|
* proc_info - supports /proc/scsi/{driver_name}/{host_no}
|
|
* @buffer: anchor point to output to (0==writeto1_read0) or fetch from
|
|
* (1==writeto1_read0).
|
|
* @start: where "interesting" data is written to. Ignored when
|
|
* 1==writeto1_read0.
|
|
* @offset: offset within buffer 0==writeto1_read0 is actually
|
|
* interested in. Ignored when 1==writeto1_read0 .
|
|
* @length: maximum (or actual) extent of buffer
|
|
* @host_no: host number of interest (struct Scsi_Host::host_no)
|
|
* @writeto1_read0: 1 -> data coming from user space towards driver
|
|
* (e.g. "echo some_string > /proc/scsi/xyz/2")
|
|
* 0 -> user what data from this driver
|
|
* (e.g. "cat /proc/scsi/xyz/2")
|
|
*
|
|
* Returns length when 1==writeto1_read0. Otherwise number of chars
|
|
* output to buffer past offset.
|
|
*
|
|
* Locks: none held
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: Driven from scsi_proc.c which interfaces to proc_fs. proc_fs
|
|
* support can now be configured out of the scsi subsystem.
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
int proc_info(char * buffer, char ** start, off_t offset,
|
|
int length, int host_no, int writeto1_read0)
|
|
|
|
|
|
/**
|
|
* queuecommand - queue scsi command, invoke scp->scsi_done on completion
|
|
* @shost: pointer to the scsi host object
|
|
* @scp: pointer to scsi command object
|
|
*
|
|
* Returns 0 on success.
|
|
*
|
|
* If there's a failure, return either:
|
|
*
|
|
* SCSI_MLQUEUE_DEVICE_BUSY if the device queue is full, or
|
|
* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
|
|
*
|
|
* On both of these returns, the mid-layer will requeue the I/O
|
|
*
|
|
* - if the return is SCSI_MLQUEUE_DEVICE_BUSY, only that particular
|
|
* device will be paused, and it will be unpaused when a command to
|
|
* the device returns (or after a brief delay if there are no more
|
|
* outstanding commands to it). Commands to other devices continue
|
|
* to be processed normally.
|
|
*
|
|
* - if the return is SCSI_MLQUEUE_HOST_BUSY, all I/O to the host
|
|
* is paused and will be unpaused when any command returns from
|
|
* the host (or after a brief delay if there are no outstanding
|
|
* commands to the host).
|
|
*
|
|
* For compatibility with earlier versions of queuecommand, any
|
|
* other return value is treated the same as
|
|
* SCSI_MLQUEUE_HOST_BUSY.
|
|
*
|
|
* Other types of errors that are detected immediately may be
|
|
* flagged by setting scp->result to an appropriate value,
|
|
* invoking the scp->scsi_done callback, and then returning 0
|
|
* from this function. If the command is not performed
|
|
* immediately (and the LLD is starting (or will start) the given
|
|
* command) then this function should place 0 in scp->result and
|
|
* return 0.
|
|
*
|
|
* Command ownership. If the driver returns zero, it owns the
|
|
* command and must take responsibility for ensuring the
|
|
* scp->scsi_done callback is executed. Note: the driver may
|
|
* call scp->scsi_done before returning zero, but after it has
|
|
* called scp->scsi_done, it may not return any value other than
|
|
* zero. If the driver makes a non-zero return, it must not
|
|
* execute the command's scsi_done callback at any time.
|
|
*
|
|
* Locks: up to and including 2.6.36, struct Scsi_Host::host_lock
|
|
* held on entry (with "irqsave") and is expected to be
|
|
* held on return. From 2.6.37 onwards, queuecommand is
|
|
* called without any locks held.
|
|
*
|
|
* Calling context: in interrupt (soft irq) or process context
|
|
*
|
|
* Notes: This function should be relatively fast. Normally it
|
|
* will not wait for IO to complete. Hence the scp->scsi_done
|
|
* callback is invoked (often directly from an interrupt service
|
|
* routine) some time after this function has returned. In some
|
|
* cases (e.g. pseudo adapter drivers that manufacture the
|
|
* response to a SCSI INQUIRY) the scp->scsi_done callback may be
|
|
* invoked before this function returns. If the scp->scsi_done
|
|
* callback is not invoked within a certain period the SCSI mid
|
|
* level will commence error processing. If a status of CHECK
|
|
* CONDITION is placed in "result" when the scp->scsi_done
|
|
* callback is invoked, then the LLD driver should perform
|
|
* autosense and fill in the struct scsi_cmnd::sense_buffer
|
|
* array. The scsi_cmnd::sense_buffer array is zeroed prior to
|
|
* the mid level queuing a command to an LLD.
|
|
*
|
|
* Defined in: LLD
|
|
**/
|
|
int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp)
|
|
|
|
|
|
/**
|
|
* release - release all resources associated with given host
|
|
* @shp: host to be released.
|
|
*
|
|
* Return value ignored (could soon be a function returning void).
|
|
*
|
|
* Locks: none held
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: Invoked from scsi_module.c's exit_this_scsi_driver().
|
|
* LLD's implementation of this function should call
|
|
* scsi_unregister(shp) prior to returning.
|
|
* Only needed for old-style host templates.
|
|
*
|
|
* Defined in: LLD (required in "passive initialization model",
|
|
* should not be defined in hotplug model)
|
|
**/
|
|
int release(struct Scsi_Host * shp)
|
|
|
|
|
|
/**
|
|
* slave_alloc - prior to any commands being sent to a new device
|
|
* (i.e. just prior to scan) this call is made
|
|
* @sdp: pointer to new device (about to be scanned)
|
|
*
|
|
* Returns 0 if ok. Any other return is assumed to be an error and
|
|
* the device is ignored.
|
|
*
|
|
* Locks: none
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: Allows the driver to allocate any resources for a device
|
|
* prior to its initial scan. The corresponding scsi device may not
|
|
* exist but the mid level is just about to scan for it (i.e. send
|
|
* and INQUIRY command plus ...). If a device is found then
|
|
* slave_configure() will be called while if a device is not found
|
|
* slave_destroy() is called.
|
|
* For more details see the include/scsi/scsi_host.h file.
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
int slave_alloc(struct scsi_device *sdp)
|
|
|
|
|
|
/**
|
|
* slave_configure - driver fine tuning for given device just after it
|
|
* has been first scanned (i.e. it responded to an
|
|
* INQUIRY)
|
|
* @sdp: device that has just been attached
|
|
*
|
|
* Returns 0 if ok. Any other return is assumed to be an error and
|
|
* the device is taken offline. [offline devices will _not_ have
|
|
* slave_destroy() called on them so clean up resources.]
|
|
*
|
|
* Locks: none
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: Allows the driver to inspect the response to the initial
|
|
* INQUIRY done by the scanning code and take appropriate action.
|
|
* For more details see the include/scsi/scsi_host.h file.
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
int slave_configure(struct scsi_device *sdp)
|
|
|
|
|
|
/**
|
|
* slave_destroy - given device is about to be shut down. All
|
|
* activity has ceased on this device.
|
|
* @sdp: device that is about to be shut down
|
|
*
|
|
* Returns nothing
|
|
*
|
|
* Locks: none
|
|
*
|
|
* Calling context: process
|
|
*
|
|
* Notes: Mid level structures for given device are still in place
|
|
* but are about to be torn down. Any per device resources allocated
|
|
* by this driver for given device should be freed now. No further
|
|
* commands will be sent for this sdp instance. [However the device
|
|
* could be re-attached in the future in which case a new instance
|
|
* of struct scsi_device would be supplied by future slave_alloc()
|
|
* and slave_configure() calls.]
|
|
*
|
|
* Optionally defined in: LLD
|
|
**/
|
|
void slave_destroy(struct scsi_device *sdp)
|
|
|
|
|
|
|
|
Data Structures
|
|
===============
|
|
struct scsi_host_template
|
|
-------------------------
|
|
There is one "struct scsi_host_template" instance per LLD ***. It is
|
|
typically initialized as a file scope static in a driver's header file. That
|
|
way members that are not explicitly initialized will be set to 0 or NULL.
|
|
Member of interest:
|
|
name - name of driver (may contain spaces, please limit to
|
|
less than 80 characters)
|
|
proc_name - name used in "/proc/scsi/<proc_name>/<host_no>" and
|
|
by sysfs in one of its "drivers" directories. Hence
|
|
"proc_name" should only contain characters acceptable
|
|
to a Unix file name.
|
|
(*queuecommand)() - primary callback that the mid level uses to inject
|
|
SCSI commands into an LLD.
|
|
The structure is defined and commented in include/scsi/scsi_host.h
|
|
|
|
*** In extreme situations a single driver may have several instances
|
|
if it controls several different classes of hardware (e.g. an LLD
|
|
that handles both ISA and PCI cards and has a separate instance of
|
|
struct scsi_host_template for each class).
|
|
|
|
struct Scsi_Host
|
|
----------------
|
|
There is one struct Scsi_Host instance per host (HBA) that an LLD
|
|
controls. The struct Scsi_Host structure has many members in common
|
|
with "struct scsi_host_template". When a new struct Scsi_Host instance
|
|
is created (in scsi_host_alloc() in hosts.c) those common members are
|
|
initialized from the driver's struct scsi_host_template instance. Members
|
|
of interest:
|
|
host_no - system wide unique number that is used for identifying
|
|
this host. Issued in ascending order from 0.
|
|
can_queue - must be greater than 0; do not send more than can_queue
|
|
commands to the adapter.
|
|
this_id - scsi id of host (scsi initiator) or -1 if not known
|
|
sg_tablesize - maximum scatter gather elements allowed by host.
|
|
0 implies scatter gather not supported by host
|
|
max_sectors - maximum number of sectors (usually 512 bytes) allowed
|
|
in a single SCSI command. The default value of 0 leads
|
|
to a setting of SCSI_DEFAULT_MAX_SECTORS (defined in
|
|
scsi_host.h) which is currently set to 1024. So for a
|
|
disk the maximum transfer size is 512 KB when max_sectors
|
|
is not defined. Note that this size may not be sufficient
|
|
for disk firmware uploads.
|
|
cmd_per_lun - maximum number of commands that can be queued on devices
|
|
controlled by the host. Overridden by LLD calls to
|
|
scsi_change_queue_depth().
|
|
unchecked_isa_dma - 1=>only use bottom 16 MB of ram (ISA DMA addressing
|
|
restriction), 0=>can use full 32 bit (or better) DMA
|
|
address space
|
|
use_clustering - 1=>SCSI commands in mid level's queue can be merged,
|
|
0=>disallow SCSI command merging
|
|
no_async_abort - 1=>Asynchronous aborts are not supported
|
|
0=>Timed-out commands will be aborted asynchronously
|
|
hostt - pointer to driver's struct scsi_host_template from which
|
|
this struct Scsi_Host instance was spawned
|
|
hostt->proc_name - name of LLD. This is the driver name that sysfs uses
|
|
transportt - pointer to driver's struct scsi_transport_template instance
|
|
(if any). FC and SPI transports currently supported.
|
|
sh_list - a double linked list of pointers to all struct Scsi_Host
|
|
instances (currently ordered by ascending host_no)
|
|
my_devices - a double linked list of pointers to struct scsi_device
|
|
instances that belong to this host.
|
|
hostdata[0] - area reserved for LLD at end of struct Scsi_Host. Size
|
|
is set by the second argument (named 'xtr_bytes') to
|
|
scsi_host_alloc() or scsi_register().
|
|
vendor_id - a unique value that identifies the vendor supplying
|
|
the LLD for the Scsi_Host. Used most often in validating
|
|
vendor-specific message requests. Value consists of an
|
|
identifier type and a vendor-specific value.
|
|
See scsi_netlink.h for a description of valid formats.
|
|
|
|
The scsi_host structure is defined in include/scsi/scsi_host.h
|
|
|
|
struct scsi_device
|
|
------------------
|
|
Generally, there is one instance of this structure for each SCSI logical unit
|
|
on a host. Scsi devices connected to a host are uniquely identified by a
|
|
channel number, target id and logical unit number (lun).
|
|
The structure is defined in include/scsi/scsi_device.h
|
|
|
|
struct scsi_cmnd
|
|
----------------
|
|
Instances of this structure convey SCSI commands to the LLD and responses
|
|
back to the mid level. The SCSI mid level will ensure that no more SCSI
|
|
commands become queued against the LLD than are indicated by
|
|
scsi_change_queue_depth() (or struct Scsi_Host::cmd_per_lun). There will
|
|
be at least one instance of struct scsi_cmnd available for each SCSI device.
|
|
Members of interest:
|
|
cmnd - array containing SCSI command
|
|
cmnd_len - length (in bytes) of SCSI command
|
|
sc_data_direction - direction of data transfer in data phase. See
|
|
"enum dma_data_direction" in include/linux/dma-mapping.h
|
|
request_bufflen - number of data bytes to transfer (0 if no data phase)
|
|
use_sg - ==0 -> no scatter gather list, hence transfer data
|
|
to/from request_buffer
|
|
- >0 -> scatter gather list (actually an array) in
|
|
request_buffer with use_sg elements
|
|
request_buffer - either contains data buffer or scatter gather list
|
|
depending on the setting of use_sg. Scatter gather
|
|
elements are defined by 'struct scatterlist' found
|
|
in include/linux/scatterlist.h .
|
|
done - function pointer that should be invoked by LLD when the
|
|
SCSI command is completed (successfully or otherwise).
|
|
Should only be called by an LLD if the LLD has accepted
|
|
the command (i.e. queuecommand() returned or will return
|
|
0). The LLD may invoke 'done' prior to queuecommand()
|
|
finishing.
|
|
result - should be set by LLD prior to calling 'done'. A value
|
|
of 0 implies a successfully completed command (and all
|
|
data (if any) has been transferred to or from the SCSI
|
|
target device). 'result' is a 32 bit unsigned integer that
|
|
can be viewed as 4 related bytes. The SCSI status value is
|
|
in the LSB. See include/scsi/scsi.h status_byte(),
|
|
msg_byte(), host_byte() and driver_byte() macros and
|
|
related constants.
|
|
sense_buffer - an array (maximum size: SCSI_SENSE_BUFFERSIZE bytes) that
|
|
should be written when the SCSI status (LSB of 'result')
|
|
is set to CHECK_CONDITION (2). When CHECK_CONDITION is
|
|
set, if the top nibble of sense_buffer[0] has the value 7
|
|
then the mid level will assume the sense_buffer array
|
|
contains a valid SCSI sense buffer; otherwise the mid
|
|
level will issue a REQUEST_SENSE SCSI command to
|
|
retrieve the sense buffer. The latter strategy is error
|
|
prone in the presence of command queuing so the LLD should
|
|
always "auto-sense".
|
|
device - pointer to scsi_device object that this command is
|
|
associated with.
|
|
resid - an LLD should set this signed integer to the requested
|
|
transfer length (i.e. 'request_bufflen') less the number
|
|
of bytes that are actually transferred. 'resid' is
|
|
preset to 0 so an LLD can ignore it if it cannot detect
|
|
underruns (overruns should be rare). If possible an LLD
|
|
should set 'resid' prior to invoking 'done'. The most
|
|
interesting case is data transfers from a SCSI target
|
|
device (e.g. READs) that underrun.
|
|
underflow - LLD should place (DID_ERROR << 16) in 'result' if
|
|
actual number of bytes transferred is less than this
|
|
figure. Not many LLDs implement this check and some that
|
|
do just output an error message to the log rather than
|
|
report a DID_ERROR. Better for an LLD to implement
|
|
'resid'.
|
|
|
|
It is recommended that a LLD set 'resid' on data transfers from a SCSI
|
|
target device (e.g. READs). It is especially important that 'resid' is set
|
|
when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR
|
|
(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much
|
|
data has been received then the safest approach is to indicate no bytes have
|
|
been received. For example: to indicate that no valid data has been received
|
|
a LLD might use these helpers:
|
|
scsi_set_resid(SCpnt, scsi_bufflen(SCpnt));
|
|
where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512
|
|
bytes blocks has been received 'resid' could be set like this:
|
|
scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512));
|
|
|
|
The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
|
|
|
|
|
|
Locks
|
|
=====
|
|
Each struct Scsi_Host instance has a spin_lock called struct
|
|
Scsi_Host::default_lock which is initialized in scsi_host_alloc() [found in
|
|
hosts.c]. Within the same function the struct Scsi_Host::host_lock pointer
|
|
is initialized to point at default_lock. Thereafter lock and unlock
|
|
operations performed by the mid level use the struct Scsi_Host::host_lock
|
|
pointer. Previously drivers could override the host_lock pointer but
|
|
this is not allowed anymore.
|
|
|
|
|
|
Autosense
|
|
=========
|
|
Autosense (or auto-sense) is defined in the SAM-2 document as "the
|
|
automatic return of sense data to the application client coincident
|
|
with the completion of a SCSI command" when a status of CHECK CONDITION
|
|
occurs. LLDs should perform autosense. This should be done when the LLD
|
|
detects a CHECK CONDITION status by either:
|
|
a) instructing the SCSI protocol (e.g. SCSI Parallel Interface (SPI))
|
|
to perform an extra data in phase on such responses
|
|
b) or, the LLD issuing a REQUEST SENSE command itself
|
|
|
|
Either way, when a status of CHECK CONDITION is detected, the mid level
|
|
decides whether the LLD has performed autosense by checking struct
|
|
scsi_cmnd::sense_buffer[0] . If this byte has an upper nibble of 7 (or 0xf)
|
|
then autosense is assumed to have taken place. If it has another value (and
|
|
this byte is initialized to 0 before each command) then the mid level will
|
|
issue a REQUEST SENSE command.
|
|
|
|
In the presence of queued commands the "nexus" that maintains sense
|
|
buffer data from the command that failed until a following REQUEST SENSE
|
|
may get out of synchronization. This is why it is best for the LLD
|
|
to perform autosense.
|
|
|
|
|
|
Changes since lk 2.4 series
|
|
===========================
|
|
io_request_lock has been replaced by several finer grained locks. The lock
|
|
relevant to LLDs is struct Scsi_Host::host_lock and there is
|
|
one per SCSI host.
|
|
|
|
The older error handling mechanism has been removed. This means the
|
|
LLD interface functions abort() and reset() have been removed.
|
|
The struct scsi_host_template::use_new_eh_code flag has been removed.
|
|
|
|
In the 2.4 series the SCSI subsystem configuration descriptions were
|
|
aggregated with the configuration descriptions from all other Linux
|
|
subsystems in the Documentation/Configure.help file. In the 2.6 series,
|
|
the SCSI subsystem now has its own (much smaller) drivers/scsi/Kconfig
|
|
file that contains both configuration and help information.
|
|
|
|
struct SHT has been renamed to struct scsi_host_template.
|
|
|
|
Addition of the "hotplug initialization model" and many extra functions
|
|
to support it.
|
|
|
|
|
|
Credits
|
|
=======
|
|
The following people have contributed to this document:
|
|
Mike Anderson <andmike at us dot ibm dot com>
|
|
James Bottomley <James dot Bottomley at hansenpartnership dot com>
|
|
Patrick Mansfield <patmans at us dot ibm dot com>
|
|
Christoph Hellwig <hch at infradead dot org>
|
|
Doug Ledford <dledford at redhat dot com>
|
|
Andries Brouwer <Andries dot Brouwer at cwi dot nl>
|
|
Randy Dunlap <rdunlap at xenotime dot net>
|
|
Alan Stern <stern at rowland dot harvard dot edu>
|
|
|
|
|
|
Douglas Gilbert
|
|
dgilbert at interlog dot com
|
|
21st September 2004
|