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#include <linux/compiler.h>
Started: Aug 9 by Lawrence Foard (, to allow user
process control of SCSI devices.
Development Sponsored by Killy Corp. NY NY
Original driver (sg.h):
* Copyright (C) 1992 Lawrence Foard
Version 2 and 3 extensions to driver:
* Copyright (C) 1998 - 2003 Douglas Gilbert
Version: 3.5.29 (20030529)
This version is for 2.5 series kernels.
Changes since 3.5.28 (20030308)
- fix bug introduced in version 3.1.24 (last segment of sgat list)
Changes since 3.5.27 (20020812)
- remove procfs entries: hosts, host_hdr + host_strs (now in sysfs)
- add sysfs sg driver params: def_reserved_size, allow_dio, version
- new boot option: "sg_allow_dio" and module parameter: "allow_dio"
- multiple internal changes due to scsi subsystem rework
Changes since 3.5.26 (20020708)
- re-add direct IO using Kai Makisara's work
- re-tab to 8, start using C99-isms
- simplify memory management
Changes since 3.5.25 (20020504)
- driverfs additions
- copy_to/from_user() fixes [William Stinson]
- disable kiobufs support
For a full changelog see
Map of SG verions to the Linux kernels in which they appear:
---------- ----------------------------------
original all kernels < 2.2.6
2.1.40 2.2.20
3.0.x optional version 3 sg driver for 2.2 series
3.1.17++ 2.4.0++
3.5.23++ 2.5.0++
Major new features in SG 3.x driver (cf SG 2.x drivers)
- SG_IO ioctl() combines function if write() and read()
- new interface (sg_io_hdr_t) but still supports old interface
- scatter/gather in user space, direct IO, and mmap supported
The normal action of this driver is to use the adapter (HBA) driver to DMA
data into kernel buffers and then use the CPU to copy the data into the
user space (vice versa for writes). That is called "indirect" IO due to
the double handling of data. There are two methods offered to remove the
redundant copy: 1) direct IO which uses the kernel kiobuf mechanism and
2) using the mmap() system call to map the reserve buffer (this driver has
one reserve buffer per fd) into the user space. Both have their advantages.
In terms of absolute speed mmap() is faster. If speed is not a concern,
indirect IO should be fine. Read the documentation for more information.
** N.B. To use direct IO 'echo 1 > /proc/scsi/sg/allow_dio' may be
needed. That pseudo file's content is defaulted to 0. **
Historical note: this SCSI pass-through driver has been known as "sg" for
a decade. In broader kernel discussions "sg" is used to refer to scatter
gather techniques. The context should clarify which "sg" is referred to.
A web site for the SG device driver can be found at: [alternatively check the MAINTAINERS file]
The documentation for the sg version 3 driver can be found at:
This is a rendering from DocBook source [change the extension to "sgml"
or "xml"]. There are renderings in "ps", "pdf", "rtf" and "txt" (soon).
The older, version 2 documents discuss the original sg interface in detail:
A version of this document (potentially out of date) may also be found in
the kernel source tree, probably at:
Documentation/scsi/scsi-generic.txt .
Utility and test programs are available at the sg web site. They are
bundled as sg_utils (for the lk 2.2 series) and sg3_utils (for the
lk 2.4 series).
There is a HOWTO on the Linux SCSI subsystem in the lk 2.4 series at:
/* New interface introduced in the 3.x SG drivers follows */
typedef struct sg_iovec /* same structure as used by readv() Linux system */
{ /* call. It defines one scatter-gather element. */
void __user *iov_base; /* Starting address */
size_t iov_len; /* Length in bytes */
} sg_iovec_t;
typedef struct sg_io_hdr
int interface_id; /* [i] 'S' for SCSI generic (required) */
int dxfer_direction; /* [i] data transfer direction */
unsigned char cmd_len; /* [i] SCSI command length ( <= 16 bytes) */
unsigned char mx_sb_len; /* [i] max length to write to sbp */
unsigned short iovec_count; /* [i] 0 implies no scatter gather */
unsigned int dxfer_len; /* [i] byte count of data transfer */
void __user *dxferp; /* [i], [*io] points to data transfer memory
or scatter gather list */
unsigned char __user *cmdp; /* [i], [*i] points to command to perform */
void __user *sbp; /* [i], [*o] points to sense_buffer memory */
unsigned int timeout; /* [i] MAX_UINT->no timeout (unit: millisec) */
unsigned int flags; /* [i] 0 -> default, see SG_FLAG... */
int pack_id; /* [i->o] unused internally (normally) */
void __user * usr_ptr; /* [i->o] unused internally */
unsigned char status; /* [o] scsi status */
unsigned char masked_status;/* [o] shifted, masked scsi status */
unsigned char msg_status; /* [o] messaging level data (optional) */
unsigned char sb_len_wr; /* [o] byte count actually written to sbp */
unsigned short host_status; /* [o] errors from host adapter */
unsigned short driver_status;/* [o] errors from software driver */
int resid; /* [o] dxfer_len - actual_transferred */
unsigned int duration; /* [o] time taken by cmd (unit: millisec) */
unsigned int info; /* [o] auxiliary information */
} sg_io_hdr_t; /* 64 bytes long (on i386) */
/* Use negative values to flag difference from original sg_header structure */
#define SG_DXFER_NONE (-1) /* e.g. a SCSI Test Unit Ready command */
#define SG_DXFER_TO_DEV (-2) /* e.g. a SCSI WRITE command */
#define SG_DXFER_FROM_DEV (-3) /* e.g. a SCSI READ command */
#define SG_DXFER_TO_FROM_DEV (-4) /* treated like SG_DXFER_FROM_DEV with the
additional property than during indirect
IO the user buffer is copied into the
kernel buffers before the transfer */
#define SG_DXFER_UNKNOWN (-5) /* Unknown data direction */
/* following flag values can be "or"-ed together */
#define SG_FLAG_DIRECT_IO 1 /* default is indirect IO */
#define SG_FLAG_UNUSED_LUN_INHIBIT 2 /* default is overwrite lun in SCSI */
/* command block (when <= SCSI_2) */
#define SG_FLAG_MMAP_IO 4 /* request memory mapped IO */
#define SG_FLAG_NO_DXFER 0x10000 /* no transfer of kernel buffers to/from */
/* user space (debug indirect IO) */
/* following 'info' values are "or"-ed together */
#define SG_INFO_OK_MASK 0x1
#define SG_INFO_OK 0x0 /* no sense, host nor driver "noise" */
#define SG_INFO_CHECK 0x1 /* something abnormal happened */
#define SG_INFO_INDIRECT_IO 0x0 /* data xfer via kernel buffers (or no xfer) */
#define SG_INFO_DIRECT_IO 0x2 /* direct IO requested and performed */
#define SG_INFO_MIXED_IO 0x4 /* part direct, part indirect IO */
typedef struct sg_scsi_id { /* used by SG_GET_SCSI_ID ioctl() */
int host_no; /* as in "scsi<n>" where 'n' is one of 0, 1, 2 etc */
int channel;
int scsi_id; /* scsi id of target device */
int lun;
int scsi_type; /* TYPE_... defined in scsi/scsi.h */
short h_cmd_per_lun;/* host (adapter) maximum commands per lun */
short d_queue_depth;/* device (or adapter) maximum queue length */
int unused[2]; /* probably find a good use, set 0 for now */
} sg_scsi_id_t; /* 32 bytes long on i386 */
typedef struct sg_req_info { /* used by SG_GET_REQUEST_TABLE ioctl() */
char req_state; /* 0 -> not used, 1 -> written, 2 -> ready to read */
char orphan; /* 0 -> normal request, 1 -> from interruped SG_IO */
char sg_io_owned; /* 0 -> complete with read(), 1 -> owned by SG_IO */
char problem; /* 0 -> no problem detected, 1 -> error to report */
int pack_id; /* pack_id associated with request */
void __user *usr_ptr; /* user provided pointer (in new interface) */
unsigned int duration; /* millisecs elapsed since written (req_state==1)
or request duration (req_state==2) */
int unused;
} sg_req_info_t; /* 20 bytes long on i386 */
/* IOCTLs: Those ioctls that are relevant to the SG 3.x drivers follow.
[Those that only apply to the SG 2.x drivers are at the end of the file.]
(_GET_s yield result via 'int *' 3rd argument unless otherwise indicated) */
#define SG_EMULATED_HOST 0x2203 /* true for emulated host adapter (ATAPI) */
/* Used to configure SCSI command transformation layer for ATAPI devices */
/* Only supported by the ide-scsi driver */
#define SG_SET_TRANSFORM 0x2204 /* N.B. 3rd arg is not pointer but value: */
/* 3rd arg = 0 to disable transform, 1 to enable it */
#define SG_GET_TRANSFORM 0x2205
#define SG_SET_RESERVED_SIZE 0x2275 /* request a new reserved buffer size */
#define SG_GET_RESERVED_SIZE 0x2272 /* actual size of reserved buffer */
/* The following ioctl has a 'sg_scsi_id_t *' object as its 3rd argument. */
#define SG_GET_SCSI_ID 0x2276 /* Yields fd's bus, chan, dev, lun + type */
/* SCSI id information can also be obtained from SCSI_IOCTL_GET_IDLUN */
/* Override host setting and always DMA using low memory ( <16MB on i386) */
#define SG_SET_FORCE_LOW_DMA 0x2279 /* 0-> use adapter setting, 1-> force */
#define SG_GET_LOW_DMA 0x227a /* 0-> use all ram for dma; 1-> low dma ram */
/* When SG_SET_FORCE_PACK_ID set to 1, pack_id is input to read() which
tries to fetch a packet with a matching pack_id, waits, or returns EAGAIN.
If pack_id is -1 then read oldest waiting. When ...FORCE_PACK_ID set to 0
then pack_id ignored by read() and oldest readable fetched. */
#define SG_SET_FORCE_PACK_ID 0x227b
#define SG_GET_PACK_ID 0x227c /* Yields oldest readable pack_id (or -1) */
#define SG_GET_NUM_WAITING 0x227d /* Number of commands awaiting read() */
/* Yields max scatter gather tablesize allowed by current host adapter */
#define SG_GET_SG_TABLESIZE 0x227F /* 0 implies can't do scatter gather */
#define SG_GET_VERSION_NUM 0x2282 /* Example: version 2.1.34 yields 20134 */
/* Returns -EBUSY if occupied. 3rd argument pointer to int (see next) */
#define SG_SCSI_RESET 0x2284
/* Associated values that can be given to SG_SCSI_RESET follow */
/* synchronous SCSI command ioctl, (only in version 3 interface) */
#define SG_IO 0x2285 /* similar effect as write() followed by read() */
#define SG_GET_REQUEST_TABLE 0x2286 /* yields table of active requests */
/* How to treat EINTR during SG_IO ioctl(), only in SG 3.x series */
#define SG_SET_KEEP_ORPHAN 0x2287 /* 1 -> hold for read(), 0 -> drop (def) */
#define SG_GET_KEEP_ORPHAN 0x2288
/* yields scsi midlevel's access_count for this SCSI device */
#define SG_GET_ACCESS_COUNT 0x2289
#define SG_SCATTER_SZ (8 * 4096) /* PAGE_SIZE not available to user */
/* Largest size (in bytes) a single scatter-gather list element can have.
The value must be a power of 2 and <= (PAGE_SIZE * 32) [131072 bytes on
i386]. The minimum value is PAGE_SIZE. If scatter-gather not supported
by adapter then this value is the largest data block that can be
read/written by a single scsi command. The user can find the value of
PAGE_SIZE by calling getpagesize() defined in unistd.h . */
/* Defaults, commented if they differ from original sg driver */
#define SG_DEF_FORCE_LOW_DMA 0 /* was 1 -> memory below 16MB on i386 */
#define SG_DEF_RESERVED_SIZE SG_SCATTER_SZ /* load time option */
/* maximum outstanding requests, write() yields EDOM if exceeded */
#define SG_MAX_QUEUE 16
#define SG_BIG_BUFF SG_DEF_RESERVED_SIZE /* for backward compatibility */
/* Alternate style type names, "..._t" variants preferred */
typedef struct sg_io_hdr Sg_io_hdr;
typedef struct sg_io_vec Sg_io_vec;
typedef struct sg_scsi_id Sg_scsi_id;
typedef struct sg_req_info Sg_req_info;
/* vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv */
/* The older SG interface based on the 'sg_header' structure follows. */
/* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ */
#define SG_MAX_SENSE 16 /* this only applies to the sg_header interface */
struct sg_header
int pack_len; /* [o] reply_len (ie useless), ignored as input */
int reply_len; /* [i] max length of expected reply (inc. sg_header) */
int pack_id; /* [io] id number of packet (use ints >= 0) */
int result; /* [o] 0==ok, else (+ve) Unix errno (best ignored) */
unsigned int twelve_byte:1;
/* [i] Force 12 byte command length for group 6 & 7 commands */
unsigned int target_status:5; /* [o] scsi status from target */
unsigned int host_status:8; /* [o] host status (see "DID" codes) */
unsigned int driver_status:8; /* [o] driver status+suggestion */
unsigned int other_flags:10; /* unused */
unsigned char sense_buffer[SG_MAX_SENSE]; /* [o] Output in 3 cases:
when target_status is CHECK_CONDITION or
when target_status is COMMAND_TERMINATED or
when (driver_status & DRIVER_SENSE) is true. */
}; /* This structure is 36 bytes long on i386 */
/* IOCTLs: The following are not required (or ignored) when the sg_io_hdr_t
interface is used. They are kept for backward compatibility with
the original and version 2 drivers. */
#define SG_SET_TIMEOUT 0x2201 /* unit: jiffies (10ms on i386) */
#define SG_GET_TIMEOUT 0x2202 /* yield timeout as _return_ value */
/* Get/set command queuing state per fd (default is SG_DEF_COMMAND_Q.
Each time a sg_io_hdr_t object is seen on this file descriptor, this
command queuing flag is set on (overriding the previous setting). */
#define SG_GET_COMMAND_Q 0x2270 /* Yields 0 (queuing off) or 1 (on) */
#define SG_SET_COMMAND_Q 0x2271 /* Change queuing state with 0 or 1 */
/* Turn on/off error sense trace (1 and 0 respectively, default is off).
Try using: "# cat /proc/scsi/sg/debug" instead in the v3 driver */
#define SG_SET_DEBUG 0x227e /* 0 -> turn off debug */
#define SG_NEXT_CMD_LEN 0x2283 /* override SCSI command length with given
number on the next write() on this file descriptor */
/* Defaults, commented if they differ from original sg driver */
#ifdef __KERNEL__
#define SG_DEFAULT_TIMEOUT_USER (60*USER_HZ) /* HZ == 'jiffies in 1 second' */
#define SG_DEFAULT_TIMEOUT (60*HZ) /* HZ == 'jiffies in 1 second' */
#define SG_DEF_COMMAND_Q 0 /* command queuing is always on when
the new interface is used */