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diff --git a/Documentation/scsi/scsi_mid_low_api.txt b/Documentation/scsi/scsi_mid_low_api.txt deleted file mode 100644 index 537f04728487..000000000000 --- a/Documentation/scsi/scsi_mid_low_api.txt +++ /dev/null @@ -1,1259 +0,0 @@ - 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 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://web.archive.org/web/20070107183357rn_1/sg.torque.net/scsi/. -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. - -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. - - -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_change_queue_depth() - | - slave_alloc() - slave_configure() - | - slave_alloc() *** - slave_destroy() *** ------------------------------------------------------------- - -If the LLD wants to adjust the default queue settings, it can invoke -scsi_change_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_change_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(). - - -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/process/coding-style.rst 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_add_device - creates new scsi device (lu) instance - scsi_add_host - perform sysfs registration and set up transport class - scsi_change_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_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_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_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_change_queue_depth - allow LLD to change queue depth on a SCSI device - * @sdev: pointer to SCSI device to change queue depth on - * @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. - * - * Defined in: drivers/scsi/scsi.c [see source code for more notes] - * - **/ -int scsi_change_queue_depth(struct scsi_device *sdev, 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_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_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 - 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 - 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]) - - -/** - * 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) - - -/** - * 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. - Set this to SG_ALL or less to avoid chained SG lists. - Must be at least 1. - 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 - 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 |