SCSI(3)

NAME
scsireq_buff_decode, scsireq_build, scsireq_decode, scsireq_encode scsireq_enter scsireq_new, scsireq_reset, SCSIREQ_ERROR, scsi_open scsi_debug scsi_debug_output - SCSI User library

SYNOPSIS
#include <sys/types.h>
#include <sys/scsiio.h>
#include <libscsi.h>
int
scsireq_buff_decode(u_char *ptr, size_t len, char *fmt, ...);
struct scsireq *
scsireq_build(struct scsireq *s, u_long len, caddr_t buf, u_long flags, char *fmt, ...);
int
scsireq_decode(struct scsireq *, char *fmt, ...);
int
scsireq_encode(struct scsireq *, char *fmt, ...);
int
scsireq_enter(int fid, struct scsireq *s);
struct scsireq *
scsireq_new(void);
struct scsireq *
scsireq_reset(struct scsireq *);
int
SCSIREQ_ERROR(struct scsireq *);
int
scsi_open(const char *path, int flags);
void
scsi_debug(FILE *f, int ret, struct scsireq *s);
FILE *
scsi_debug_output(char *s);

DESCRIPTION
These functions use the SCIOCCOMMAND ioctl(2) of the FreeBSD SCSI subsystem to provide user level access to SCSI commands. The programmer must know the SCSI CDB (Command Descriptor Block) to perform the desired command. These functions assist in building up the CDB, submitting it to the SCSI subsystem, and decoding the result.

Look at the scsi(8) command before using the library directly - simple programs are best implemented as scripts using that facility.

To provide for security, not all devices accept the SCIOCCOMAND ioctl. It is accepted by the control device for tape drives, partition D for disk drives, partition C for CD ROM drives, and any "unknown" device. The "super scsi" ssc(4) device also accepts the ioctl.

Most of the SCSI library functions build up and manipulate the scsireq structure found in the include file <sys/scsiio.h>:

    #define	SENSEBUFLEN 48

    typedef struct	scsireq {
    	u_long	flags;		/* info about the request status and type */
    	u_long	timeout;
    	u_char	cmd[16];	/* 12 is actually the max */
    	u_char	cmdlen;
    	caddr_t	databuf;	/* address in user space of buffer */
    	u_long	datalen;	/* size of user buffer (request) */
    	u_long	datalen_used;	/* size of user buffer (used)*/
    	u_char	sense[SENSEBUFLEN]; /* returned sense will be in here */
    	u_char	senselen;	/* sensedata request size (MAX of SENSEBUFLEN)*/
    	u_char	senselen_used;	/* return value only */
    	u_char	status;		/* what the scsi status was from the adapter */
    	u_char	retsts;		/* the return status for the command */
    	int	error;		/* error bits */
    } scsireq_t;

scsireq_new() allocates a new scsireq structure and returns a pointer to it or NULL if it can't allocate memory.

scsireq_reset() resets the structure to reasonable values and returns the same pointer passed in to it. It gracefully handles the NULL pointer passed in to it so that you can unconditionally use scsireq_new.

scsireq_build() builds up a scsireq structure based on the information provided in the variable argument list. It gracefully handles a NULL pointer passed to it.

len is the length of the data phase; the data transfer direction is determined by the flags argument.

buf is the data buffer used during the SCSI data phase. If it is NULL it is allocated via malloc and scsireq->databuf is set to point to the newly allocated memory.

flags are the flags defined in <sys/scsiio.h>:

    /* bit definitions for flags */
    #define SCCMD_READ		0x00000001
    #define SCCMD_WRITE		0x00000002
    #define SCCMD_IOV		0x00000004
    #define SCCMD_ESCAPE		0x00000010
    #define SCCMD_TARGET		0x00000020

Only two of these flags are supported in this release of the software: SCCMD_READ indicates a data in phase (a transfer into the user buffer at scsireg->databuf ), and SCCMD_WRITE indicates a data out phase (a transfer out of the user buffer).

fmt is a CDB format specifier used to build up the SCSI CDB. This text string is made up of a list of field specifiers. Field specifiers specify the value for each CDB field (including indicating that the value be taken from the next argument in the variable argument list), the width of the field in bits or bytes, and an optional name. White space is ignored, and the pound sign ('#') introduces a comment that ends at the end of the current line.

The optional name is the first part of a field specifier and is in curly braces. The text in curly braces in this example are the names:

    {PS} v:b1 {Reserved} 0:b1 {Page Code} v:b6 # Mode select page

This field specifier has two one bit fields and one six bit field. The second one bit field is the constant value 0 and the first one bit field and the six bit field are taken from the variable argument list. Multi byte fields are swapped into the SCSI byte order in the CDB and white space is ignored.

When the field is a hex value or the letter v, (e.g., 1A or v) then a single byte value is copied to the next unused byte of the CDB. When the letter v is used the next integer argument is taken from the variable argument list and that value used.

A constant hex value followed by a field width specifier or the letter v followed by a field width specifier (e.g., 3:4, 3:b4, 3:i3, specifies a field of a given bit or byte width. Either the constant value or (for the V specifier) the next integer value from the variable argument list is copied to the next unused bits or bytes of the CDB.

A decimal number or the letter b followed by a decimal number field width indicates a bit field of that width. The bit fields are packed as tightly as possible beginning with the high bit (so that it reads the same as the SCSI spec), and a new byte of the CDB is started whenever a byte fills completely or when an i field is encountered.

A field width specifier consisting of the letter i followed by either 1, 2, 3 or 4 indicates a 1, 2, 3 or 4 byte integral value that must be swapped into SCSI byte order (MSB first).

For the v field specifier the next integer argument is taken from the variable argument list and that value is used swapped into SCSI byte order.

scsireq_decode() is used to decode information from the data in phase of the SCSI transfer.

The decoding is similar to the command specifier processing of scsireq_build() except that the data is extracted from the data pointed to by scsireq->databuf. The stdarg list should be pointers to integers instead of integer values. A seek field type and a suppression modifier are added. The * suppression modifier (e.g., *i3 or *b4) suppresses assignment from the field and can be used to skip over bytes or bits in the data, without having to copy them to a dummy variable in the arg list.

The seek field type s permits you to skip over data. This seeks to an absolute position ( s3) or a relative position ( s+3) in the data, based on whether or not the presence of the '+' sign. The seek value can be specified as v and the next integer value from the argument list will be used as the seek value.

scsireq_buff_decode() decodes an arbitrary data buffer using the method described above in scsireq_decode().

scsireq_encode() encodes the data phase section of the structure. The encoding is handled identically as the encoding of the CDB structure by scsireq_build()

scsireq_enter() submits the built up structure for processing using the SCIOCCOMMAND ioctl.

SCSIREQ_ERROR() is a macro that determines if the result of the SCIOCCOMMAND ioctl may have been in error by examining the host adapter return code, whether sense was sent or not, and so on.

scsi_open() checks environment variables and initializes the library for consistent library use and then calls the regular open system call.

scsi_debug() prints the results of a scsireq_enter function to the specified stdio stream.

scsi_debug_output() requests that the results of all transactions be debugged to the supplied file using scsi_debug().

RETURN VALUES
The function scsireq_new() returns a pointer to storage allocated from malloc, and therefore potentially a NULL.

The functions scsireq_build() and scsireq_reset() return the same pointer as the one passed in.

The functions scsireq_buff_decode(and) scsireq_decode() return the number of assignments performed.

scsireq_encode() returns the number of fields processed.

The function scsireq_enter() returns the result of the ioctl call.

SEE ALSO
scsi(8), scsi(4)

BUGS
This only works completely for the 1542C. The host adapter code that sets up the residual amount of data transfer has to be added to each individual adapter. This library is usable on the other host adapters, however, the SCSI driver pretends that the proper amount of data is always transferred. If you have an Adaptec 174x and can hack contact dufault@hda.com and you can have the code to calculate residual data for the 174x series to integrate and test.

HISTORY
Many systems have comparable interfaces to permit a user to construct a SCSI command in user space.

The data structure is almost identical to the SGI /dev/scsi data structure. If anyone knows the name of the authors it should go here; Peter Dufault first read about it in a 1989 Sun Expert magazine.

Peter Dufault implemented a clone of SGI's interface in 386bsd that led to this library and the related kernel ioctl. If anyone needs that for compatibility contact dufault@hda.com.