diff options
Diffstat (limited to 'Documentation/scsi/scsi_mid_low_api.txt')
| -rw-r--r-- | Documentation/scsi/scsi_mid_low_api.txt | 232 |
1 files changed, 95 insertions, 137 deletions
diff --git a/Documentation/scsi/scsi_mid_low_api.txt b/Documentation/scsi/scsi_mid_low_api.txt index 7536823c0cb..d6a9bdeee7f 100644 --- a/Documentation/scsi/scsi_mid_low_api.txt +++ b/Documentation/scsi/scsi_mid_low_api.txt @@ -30,7 +30,7 @@ the motherboard (or both). Some aic7xxx based HBAs are dual controllers and thus represent two hosts. Like most modern HBAs, each aic7xxx host has its own PCI device address. [The one-to-one correspondence between a SCSI host and a PCI device is common but not required (e.g. with -ISA or MCA adapters).] +ISA adapters).] The SCSI mid level isolates an LLD from other layers such as the SCSI upper layer drivers and the block layer. @@ -43,7 +43,7 @@ There is a SCSI documentation directory within the kernel source tree, typically Documentation/scsi . Most documents are in plain (i.e. ASCII) text. This file is named scsi_mid_low_api.txt and can be found in that directory. A more recent copy of this document may be found -at http://www.torque.net/scsi/scsi_mid_low_api.txt.gz . +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 @@ -55,11 +55,6 @@ or in the same directory as the C source code. For example to find a url about the USB mass storage driver see the /usr/src/linux/drivers/usb/storage directory. -The Linux kernel source Documentation/DocBook/scsidrivers.tmpl file -refers to this file. With the appropriate DocBook tool-set, this permits -users to generate html, ps and pdf renderings of information within this -file (e.g. the interface functions). - Driver structure ================ Traditionally an LLD for the SCSI subsystem has been at least two files in @@ -150,7 +145,8 @@ scsi devices of which only the first 2 respond: LLD mid level LLD ===-------------------=========--------------------===------ scsi_host_alloc() --> -scsi_add_host() --------+ +scsi_add_host() ----> +scsi_scan_host() -------+ | slave_alloc() slave_configure() --> scsi_adjust_queue_depth() @@ -196,7 +192,7 @@ 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_add_host() function causes a scan for SCSI devices +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: @@ -346,7 +342,7 @@ 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_host_template Scsi_Host_Template;" +"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 @@ -372,14 +368,11 @@ names all start with "scsi_". Summary: scsi_activate_tcq - turn on tag command queueing scsi_add_device - creates new scsi device (lu) instance - scsi_add_host - perform sysfs registration and SCSI bus scan. - scsi_add_timer - (re-)start timer on a SCSI command. + scsi_add_host - perform sysfs registration and set up transport class scsi_adjust_queue_depth - change the queue depth on a SCSI device - scsi_assign_lock - replace default host_lock with given lock scsi_bios_ptable - return copy of block device's partition table scsi_block_requests - prevent further commands being queued to given host scsi_deactivate_tcq - turn off tag command queueing - scsi_delete_timer - cancel timer on a SCSI command. 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) @@ -388,6 +381,7 @@ Summary: 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()] @@ -427,10 +421,10 @@ void scsi_activate_tcq(struct scsi_device *sdev, int depth) * Might block: yes * * Notes: This call is usually performed internally during a scsi - * bus scan when an HBA is added (i.e. scsi_add_host()). So it + * 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_add_host() has completed. If successful - * this call we lead to slave_alloc() and slave_configure() callbacks + * 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 @@ -441,7 +435,7 @@ struct scsi_device * scsi_add_device(struct Scsi_Host *shost, /** - * scsi_add_host - perform sysfs registration and SCSI bus scan. + * 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 * @@ -450,7 +444,11 @@ struct scsi_device * scsi_add_device(struct Scsi_Host *shost, * Might block: no * * Notes: Only required in "hotplug initialization model" after a - * successful call to scsi_host_alloc(). + * 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 **/ @@ -458,27 +456,6 @@ int scsi_add_host(struct Scsi_Host *shost, struct device * dev) /** - * scsi_add_timer - (re-)start timer on a SCSI command. - * @scmd: pointer to scsi command instance - * @timeout: duration of timeout in "jiffies" - * @complete: pointer to function to call if timeout expires - * - * Returns nothing - * - * Might block: no - * - * Notes: Each scsi command has its own timer, and as it is added - * to the queue, we set up the timer. When the command completes, - * we cancel the timer. An LLD can use this function to change - * the existing timeout value. - * - * Defined in: drivers/scsi/scsi_error.c - **/ -void scsi_add_timer(struct scsi_cmnd *scmd, int timeout, - void (*complete)(struct scsi_cmnd *)) - - -/** * scsi_adjust_queue_depth - allow LLD to change queue depth on a SCSI device * @sdev: pointer to SCSI device to change queue depth on * @tagged: 0 - no tagged queuing @@ -506,20 +483,6 @@ void scsi_adjust_queue_depth(struct scsi_device * sdev, int tagged, /** - * scsi_assign_lock - replace default host_lock with given lock - * @shost: a pointer to a scsi host instance - * @lock: pointer to lock to replace host_lock for this host - * - * Returns nothing - * - * Might block: no - * - * Defined in: include/scsi/scsi_host.h . - **/ -void scsi_assign_lock(struct Scsi_Host *shost, spinlock_t *lock) - - -/** * scsi_bios_ptable - return copy of block device's partition table * @dev: pointer to block device * @@ -566,24 +529,6 @@ void scsi_deactivate_tcq(struct scsi_device *sdev, int depth) /** - * scsi_delete_timer - cancel timer on a SCSI command. - * @scmd: pointer to scsi command instance - * - * Returns 1 if able to cancel timer else 0 (i.e. too late or already - * cancelled). - * - * Might block: no [may in the future if it invokes del_timer_sync()] - * - * Notes: All commands issued by upper levels already have a timeout - * associated with them. An LLD can use this function to cancel the - * timer. - * - * Defined in: drivers/scsi/scsi_error.c - **/ -int scsi_delete_timer(struct scsi_cmnd *scmd) - - -/** * scsi_host_alloc - create a scsi host adapter instance and perform basic * initialization. * @sht: pointer to scsi host template @@ -600,7 +545,7 @@ int scsi_delete_timer(struct scsi_cmnd *scmd) * 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() is called. + * scsi_add_host() and scsi_scan_host() are called. * * Defined in: drivers/scsi/hosts.c . **/ @@ -740,6 +685,19 @@ 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. @@ -759,7 +717,7 @@ void scsi_report_bus_reset(struct Scsi_Host * shost, int channel) * * Defined in: drivers/scsi/scsi.c . **/ -int scsi_track_queue_full(Scsi_Device *sdev, int depth) +int scsi_track_queue_full(struct scsi_device *sdev, int depth) /** @@ -826,7 +784,6 @@ Summary: 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) - eh_strategy_handler - driver supplied alternate to scsi_unjam_host() info - supply information about given host ioctl - driver can respond to ioctls proc_info - supports /proc/scsi/{driver_name}/{host_no} @@ -925,8 +882,11 @@ Details: * * Calling context: kernel thread * - * Notes: Invoked from scsi_eh thread. No other commands will be - * queued on current host during eh. + * 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 **/ @@ -992,24 +952,6 @@ Details: /** - * eh_strategy_handler - driver supplied alternate to scsi_unjam_host() - * @shp: host on which error has occurred - * - * Returns TRUE if host unjammed, else FALSE. - * - * Locks: none - * - * Calling context: kernel thread - * - * Notes: Invoked from scsi_eh thread. LLD supplied alternate to - * scsi_unjam_host() found in scsi_error.c - * - * Optionally defined in: LLD - **/ - int eh_strategy_handler(struct Scsi_Host * shp) - - -/** * info - supply information about given host: driver name plus data * to distinguish given host * @shp: host to supply information about @@ -1100,9 +1042,9 @@ Details: /** - * queuecommand - queue scsi command, invoke 'done' on completion + * queuecommand - queue scsi command, invoke scp->scsi_done on completion + * @shost: pointer to the scsi host object * @scp: pointer to scsi command object - * @done: function pointer to be invoked on completion * * Returns 0 on success. * @@ -1130,42 +1072,45 @@ Details: * * Other types of errors that are detected immediately may be * flagged by setting scp->result to an appropriate value, - * invoking the '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. + * 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 'done' - * callback is executed. Note: the driver may call done before - * returning zero, but after it has called 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 done - * callback at any time. - * - * Locks: struct Scsi_Host::host_lock held on entry (with "irqsave") - * and is expected to be held on return. + * 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 '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 'done' callback may be invoked before this function returns. - * If the '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 - * 'done' callback is invoked, then the LLD driver should - * perform autosense and fill in the struct scsi_cmnd::sense_buffer + * 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_cmnd * scp, - void (*done)(struct scsi_cmnd *)) + int queuecommand(struct Scsi_Host *shost, struct scsi_cmnd * scp) /** @@ -1315,6 +1260,8 @@ of interest: 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 @@ -1327,6 +1274,11 @@ of interest: 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 @@ -1391,7 +1343,7 @@ Members of interest: 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 device (i.e. READs) that underrun. + 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 @@ -1399,6 +1351,18 @@ Members of interest: 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 @@ -1407,17 +1371,11 @@ 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 with the scsi_assign_lock() function. -Thereafter lock and unlock operations performed by the mid level use the -struct Scsi_Host::host_lock pointer. - -LLDs can override the use of struct Scsi_Host::default_lock by -using scsi_assign_lock(). The earliest opportunity to do this would -be in the detect() function after it has invoked scsi_register(). It -could be replaced by a coarser grain lock (e.g. per driver) or a -lock of equal granularity (i.e. per host). Using finer grain locks -(e.g. per SCSI device) may be possible by juggling locks in -queuecommand(). +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 ========= @@ -1469,12 +1427,12 @@ Credits ======= The following people have contributed to this document: Mike Anderson <andmike at us dot ibm dot com> - James Bottomley <James dot Bottomley at steeleye 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 <rddunlap at osdl dot org> + Randy Dunlap <rdunlap at xenotime dot net> Alan Stern <stern at rowland dot harvard dot edu> |