diff options
Diffstat (limited to 'Documentation/scsi/scsi_mid_low_api.txt')
| -rw-r--r-- | Documentation/scsi/scsi_mid_low_api.txt | 96 |
1 files changed, 58 insertions, 38 deletions
diff --git a/Documentation/scsi/scsi_mid_low_api.txt b/Documentation/scsi/scsi_mid_low_api.txt index a6d5354639b..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 @@ -887,8 +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 **/ @@ -1044,9 +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. * @@ -1074,42 +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) /** @@ -1259,6 +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 @@ -1271,6 +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 @@ -1335,7 +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 @@ -1343,6 +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 |