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Commit 8350d237 authored by James Bottomley's avatar James Bottomley
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scsi_mid_low_api.txt update 

From: 	Douglas Gilbert <dougg@torque.net>
Signed-off-by: default avatarJames Bottomley <James.Bottomley@SteelEye.com>
parent 4e665bdd
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Documentation/scsi/scsi_mid_low_api.txt
View file @ 8350d237
......@@ -35,7 +35,7 @@ ISA or MCA adapters).]
The SCSI mid level isolates an LLD from other layers such as the SCSI
upper layer drivers and the block layer.
This version of the document roughly matches linux kernel version 2.6.0-test4.
This version of the document roughly matches linux kernel version 2.6.8 .
Documentation
=============
......@@ -323,6 +323,16 @@ struct Scsi_Host:
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.
......@@ -416,7 +426,7 @@ struct scsi_device * scsi_add_device(struct Scsi_Host *shost,
/**
* scsi_add_host - perform sysfs registration and SCSI bus scan.
* @shost: pointer to scsi host instance
* @dev: pointer to struct device host instance
* @dev: pointer to struct device of type scsi class
*
* Returns 0 on success, negative errno of failure (e.g. -ENOMEM)
*
......@@ -453,7 +463,7 @@ void scsi_add_timer(struct scsi_cmnd *scmd, int timeout,
/**
* scsi_adjust_queue_depth - change the queue depth on a SCSI device
* @SDpnt: pointer to SCSI device to change queue depth on
* @sdev: pointer to SCSI device to change queue depth on
* @tagged: 0 - no tagged queuing
* MSG_SIMPLE_TAG - simple (unordered) tagged queuing
* MSG_ORDERED_TAG - ordered tagged queuing
......@@ -474,8 +484,8 @@ void scsi_add_timer(struct scsi_cmnd *scmd, int timeout,
* Defined in: drivers/scsi/scsi.c [see source code for more notes]
*
**/
void scsi_adjust_queue_depth(struct scsi_device * SDpnt, int tagged,
int num_tags)
void scsi_adjust_queue_depth(struct scsi_device * sdev, int tagged,
int tags)
/**
......@@ -510,7 +520,7 @@ unsigned char *scsi_bios_ptable(struct block_device *dev)
/**
* scsi_block_requests - prevent further commands being queued to given host
*
* @SHpnt: pointer to host to block commands on
* @shost: pointer to host to block commands on
*
* Returns nothing
*
......@@ -521,7 +531,7 @@ unsigned char *scsi_bios_ptable(struct block_device *dev)
*
* Defined in: drivers/scsi/scsi_lib.c
**/
void scsi_block_requests(struct Scsi_Host * SHpnt)
void scsi_block_requests(struct Scsi_Host * shost)
/**
......@@ -543,9 +553,10 @@ int scsi_delete_timer(struct scsi_cmnd *scmd)
/**
* scsi_host_alloc - create and register a scsi host adapter instance.
* @shost_tp: pointer to scsi host template
* @xtr_bytes: extra bytes to allocate in hostdata array (which is the
* 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
......@@ -555,12 +566,15 @@ int scsi_delete_timer(struct scsi_cmnd *scmd)
* 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.
* 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.
*
* Defined in: drivers/scsi/hosts.c .
**/
struct Scsi_Host * scsi_host_alloc(struct scsi_host_template *, int xtr_bytes)
struct Scsi_Host * scsi_host_alloc(struct scsi_host_template * sht,
int privsize)
/**
......@@ -619,8 +633,8 @@ int scsi_partsize(unsigned char *buf, unsigned long capacity,
/**
* scsi_register - create and register a scsi host adapter instance.
* @shost_tp: pointer to scsi host template
* @xtr_bytes: extra bytes to allocate in hostdata array (which is the
* @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
......@@ -634,7 +648,8 @@ int scsi_partsize(unsigned char *buf, unsigned long capacity,
*
* Defined in: drivers/scsi/hosts.c .
**/
struct Scsi_Host * scsi_register(struct scsi_host_template *, int xtr_bytes)
struct Scsi_Host * scsi_register(struct scsi_host_template * sht,
int privsize)
/**
......@@ -711,15 +726,17 @@ void scsi_set_device(struct Scsi_Host * shost, struct device * dev)
* scsi_to_pci_dma_dir - convert SCSI subsystem direction flag to PCI
* @scsi_data_direction: SCSI subsystem direction flag
*
* Returns PCI_DMA_TODEVICE given SCSI_DATA_WRITE,
* PCI_DMA_FROMDEVICE given SCSI_DATA_READ
* PCI_DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
* else returns PCI_DMA_NONE
* Returns DMA_TO_DEVICE given SCSI_DATA_WRITE,
* DMA_FROM_DEVICE given SCSI_DATA_READ
* DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
* else returns DMA_NONE
*
* Might block: no
*
* Notes: The SCSI subsystem now uses the same values for these
* constants as the PCI subsystem so this function is a nop.
* The recommendation is not to use this conversion function anymore
* (in the 2.6 kernel series) as it is not needed.
*
* Defined in: drivers/scsi/scsi.h .
**/
......@@ -730,13 +747,15 @@ int scsi_to_pci_dma_dir(unsigned char scsi_data_direction)
* scsi_to_sbus_dma_dir - convert SCSI subsystem direction flag to SBUS
* @scsi_data_direction: SCSI subsystem direction flag
*
* Returns SBUS_DMA_TODEVICE given SCSI_DATA_WRITE,
* SBUS_DMA_FROMDEVICE given SCSI_DATA_READ
* SBUS_DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
* else returns SBUS_DMA_NONE
* Returns DMA_TO_DEVICE given SCSI_DATA_WRITE,
* FROM_DEVICE given SCSI_DATA_READ
* DMA_BIDIRECTIONAL given SCSI_DATA_UNKNOWN
* else returns DMA_NONE
*
* Notes: The SCSI subsystem now uses the same values for these
* constants as the SBUS subsystem so this function is a nop.
* The recommendation is not to use this conversion function anymore
* (in the 2.6 kernel series) as it is not needed.
*
* Might block: no
*
......@@ -749,7 +768,7 @@ int scsi_to_sbus_dma_dir(unsigned char scsi_data_direction)
* 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.
* @SDptr: pointer to SCSI device instance
* @sdev: pointer to SCSI device instance
* @depth: Current number of outstanding SCSI commands on this device,
* not counting the one returned as QUEUE_FULL.
*
......@@ -765,13 +784,13 @@ int scsi_to_sbus_dma_dir(unsigned char scsi_data_direction)
*
* Defined in: drivers/scsi/scsi.c .
**/
int scsi_track_queue_full(Scsi_Device *SDptr, int depth)
int scsi_track_queue_full(Scsi_Device *sdev, int depth)
/**
* scsi_unblock_requests - allow further commands to be queued to given host
*
* @SHpnt: pointer to host to unblock commands on
* @shost: pointer to host to unblock commands on
*
* Returns nothing
*
......@@ -779,7 +798,7 @@ int scsi_track_queue_full(Scsi_Device *SDptr, int depth)
*
* Defined in: drivers/scsi/scsi_lib.c .
**/
void scsi_unblock_requests(struct Scsi_Host * SHpnt)
void scsi_unblock_requests(struct Scsi_Host * shost)
/**
......@@ -901,20 +920,20 @@ Details:
*
* 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
* 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.
* 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
**/
......@@ -1110,7 +1129,7 @@ Details:
* Optionally defined in: LLD
**/
int proc_info(char * buffer, char ** start, off_t offset,
int length, int hostno, int writeto1_read0)
int length, int host_no, int writeto1_read0)
/**
......@@ -1120,42 +1139,42 @@ Details:
*
* Returns 0 on success.
*
* If there's a failure, return either:
* 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
* 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
* 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_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).
* - 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.
* 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 '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.
* 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.
*
* 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.
* 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.
......@@ -1317,7 +1336,12 @@ of interest:
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. 0 implies no maximum.
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_adjust_queue_depth().
......@@ -1328,6 +1352,9 @@ of interest:
0=>disallow SCSI command merging
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
......@@ -1335,7 +1362,8 @@ 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().
The structure is defined in include/scsi/scsi_host.h
The scsi_host structure is defined in include/scsi/scsi_host.h
struct scsi_device
------------------
......@@ -1347,11 +1375,66 @@ 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_adjust_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.
The structure is defined in include/scsi/scsi_cmnd.h
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_adjust_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/asm/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 device (i.e. 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'.
The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h
Locks
......@@ -1420,15 +1503,16 @@ to support it.
Credits
=======
The following people have contributed to this document:
Mike Anderson <andmike@us.ibm.com>
James Bottomley <James.Bottomley@steeleye.com>
Patrick Mansfield <patmans@us.ibm.com>
Christoph Hellwig <hch@infradead.org>
Doug Ledford <dledford@redhat.com>
Andries Brouwer <Andries.Brouwer@cwi.nl>
Randy Dunlap <rddunlap@osdl.org>
Mike Anderson <andmike at us dot ibm dot com>
James Bottomley <James dot Bottomley at steeleye 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>
Alan Stern <stern at rowland dot harvard dot edu>
Douglas Gilbert
dgilbert@interlog.com
29th August 2003
dgilbert at interlog dot com
25th August 2004
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