Programming example

The Linux SCSI Generic (sg) HOWTO
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# Appendix C. Programming example

This appendix contains an example program. It is an abridged version of sg_simple2.c found in the sg3_utils package. It send a SCSI INQUIRY command to the nominated sg device and prints out some of the response or outputs error information. Hopefully showing the error processing does not cloud what is being illustrated.

    #include <unistd.h>
    #include <fcntl.h>
    #include <stdio.h>
    #include <string.h>
    #include <errno.h>
    #include <sys/ioctl.h>
    #include <scsi/sg.h> /* take care: fetches glibc's /usr/include/scsi/sg.h */

    /* This is a simple program executing a SCSI INQUIRY command using the
       sg_io_hdr interface of the SCSI generic (sg) driver.

    *  Copyright (C) 2001 D. Gilbert
    *  This program is free software.   Version 1.01 (20020226)
    */

    #define INQ_REPLY_LEN 96
    #define INQ_CMD_CODE 0x12
    #define INQ_CMD_LEN 6

    int main(int argc, char * argv[])
    {
        int sg_fd, k;
        unsigned char inqCmdBlk[INQ_CMD_LEN] =
                        {INQ_CMD_CODE, 0, 0, 0, INQ_REPLY_LEN, 0};
    /* This is a "standard" SCSI INQUIRY command. It is standard because the
     * CMDDT and EVPD bits (in the second byte) are zero. All SCSI targets
     * should respond promptly to a standard INQUIRY */
        unsigned char inqBuff[INQ_REPLY_LEN];
        unsigned char sense_buffer[32];
        sg_io_hdr_t io_hdr;

        if (2 != argc) {
            printf("Usage: 'sg_simple0 <sg_device>'\n");
            return 1;
        }
        if ((sg_fd = open(argv[1], O_RDONLY)) < 0) {
        	/* Note that most SCSI commands require the O_RDWR flag to be set */
            perror("error opening given file name");
            return 1;
        }
        /* It is prudent to check we have a sg device by trying an ioctl */
        if ((ioctl(sg_fd, SG_GET_VERSION_NUM, &k) < 0) || (k < 30000)) {
            printf("%s is not an sg device, or old sg driver\n", argv[1]);
            return 1;
        }
        /* Prepare INQUIRY command */
        memset(&io_hdr, 0, sizeof(sg_io_hdr_t));
        io_hdr.interface_id = 'S';
        io_hdr.cmd_len = sizeof(inqCmdBlk);
        /* io_hdr.iovec_count = 0; */  /* memset takes care of this */
        io_hdr.mx_sb_len = sizeof(sense_buffer);
        io_hdr.dxfer_direction = SG_DXFER_FROM_DEV;
        io_hdr.dxfer_len = INQ_REPLY_LEN;
        io_hdr.dxferp = inqBuff;
        io_hdr.cmdp = inqCmdBlk;
        io_hdr.sbp = sense_buffer;
        io_hdr.timeout = 20000;     /* 20000 millisecs == 20 seconds */
        /* io_hdr.flags = 0; */     /* take defaults: indirect IO, etc */
        /* io_hdr.pack_id = 0; */
        /* io_hdr.usr_ptr = NULL; */

        if (ioctl(sg_fd, SG_IO, &io_hdr) < 0) {
            perror("sg_simple0: Inquiry SG_IO ioctl error");
            return 1;
        }

        /* now for the error processing */
        if ((io_hdr.info & SG_INFO_OK_MASK) != SG_INFO_OK) {
            if (io_hdr.sb_len_wr > 0) {
                printf("INQUIRY sense data: ");
                for (k = 0; k < io_hdr.sb_len_wr; ++k) {
                    if ((k > 0) && (0 == (k % 10)))
                        printf("\n  ");
                    printf("0x%02x ", sense_buffer[k]);
                }
                printf("\n");
            }
            if (io_hdr.masked_status)
                printf("INQUIRY SCSI status=0x%x\n", io_hdr.status);
            if (io_hdr.host_status)
                printf("INQUIRY host_status=0x%x\n", io_hdr.host_status);
            if (io_hdr.driver_status)
                printf("INQUIRY driver_status=0x%x\n", io_hdr.driver_status);
        }
        else {  /* assume INQUIRY response is present */
            char * p = (char *)inqBuff;
            printf("Some of the INQUIRY command's response:\n");
            printf("    %.8s  %.16s  %.4s\n", p + 8, p + 16, p + 32);
            printf("INQUIRY duration=%u millisecs, resid=%d\n",
                   io_hdr.duration, io_hdr.resid);
        }
        close(sg_fd);
        return 0;
    }

The sg_simple4.c program is an example of using mmap-ed IO in the sg3_utils package. An example of using direct IO can be found in sg_rbuf.c in the same package.

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