/* A utility program for the Linux OS SCSI generic ("sg") device driver.
*  Copyright (C) 2001 - 2013 D. Gilbert
*  This program is free software; you can redistribute it and/or modify
*  it under the terms of the GNU General Public License as published by
*  the Free Software Foundation; either version 2, or (at your option)
*  any later version.

   This program reads data from the given SCSI device (typically a disk
   or cdrom) and discards that data. Its primary goal is to time
   multiple reads all starting from the same logical address. Its interface
   is a subset of another member of this package: sg_dd which is a
   "dd" variant. The input file can be a scsi generic device, a block device,
   a raw device or a seekable file. Streams such as stdin are not acceptable.
   The block size ('bs') is assumed to be 512 if not given.

   This version should compile with Linux sg drivers with version numbers
   >= 30000 . For mmap-ed IO the sg version number >= 30122 .

*/

#define _XOPEN_SOURCE 500
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <ctype.h>
#include <errno.h>
#define __STDC_FORMAT_MACROS 1
#include <inttypes.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <linux/major.h>

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "sg_lib.h"
#include "sg_io_linux.h"


static const char * version_str = "1.20 20131014";

#define DEF_BLOCK_SIZE 512
#define DEF_BLOCKS_PER_TRANSFER 128
#define DEF_SCSI_CDBSZ 10
#define MAX_SCSI_CDBSZ 16

#define ME "sg_read: "

#ifndef SG_FLAG_MMAP_IO
#define SG_FLAG_MMAP_IO 4
#endif

#define SENSE_BUFF_LEN 64       /* Arbitrary, could be larger */
#define DEF_TIMEOUT 40000       /* 40,000 millisecs == 40 seconds */

#ifndef RAW_MAJOR
#define RAW_MAJOR 255   /*unlikey value */
#endif

#define FT_OTHER 1              /* filetype other than sg or raw device */
#define FT_SG 2                 /* filetype is sg char device */
#define FT_RAW 4                /* filetype is raw char device */
#define FT_BLOCK 8              /* filetype is block device */
#define FT_ERROR 64             /* couldn't "stat" file */

#define MIN_RESERVED_SIZE 8192

static int sum_of_resids = 0;

static int64_t dd_count = -1;
static int64_t orig_count = 0;
static int64_t in_full = 0;
static int in_partial = 0;

static int pack_id_count = 0;
static int verbose = 0;

static const char * proc_allow_dio = "/proc/scsi/sg/allow_dio";

static void install_handler (int sig_num, void (*sig_handler) (int sig))
{
    struct sigaction sigact;

    sigaction (sig_num, NULL, &sigact);
    if (sigact.sa_handler != SIG_IGN) {
        sigact.sa_handler = sig_handler;
        sigemptyset (&sigact.sa_mask);
        sigact.sa_flags = 0;
        sigaction (sig_num, &sigact, NULL);
    }
}

static void print_stats(int iters, const char * str)
{
    if (orig_count > 0) {
        if (0 != dd_count)
            fprintf(stderr, "  remaining block count=%" PRId64 "\n",
                    dd_count);
        fprintf(stderr, "%" PRId64 "+%d records in", in_full - in_partial,
                in_partial);
        if (iters > 0)
            fprintf(stderr, ", %s commands issued: %d\n", (str ? str : ""),
                    iters);
        else
            fprintf(stderr, "\n");
    } else if (iters > 0)
        fprintf(stderr, "%s commands issued: %d\n", (str ? str : ""), iters);
}

static void interrupt_handler(int sig)
{
    struct sigaction sigact;

    sigact.sa_handler = SIG_DFL;
    sigemptyset (&sigact.sa_mask);
    sigact.sa_flags = 0;
    sigaction (sig, &sigact, NULL);
    fprintf(stderr, "Interrupted by signal,");
    print_stats(0, NULL);
    kill (getpid (), sig);
}

static void siginfo_handler(int sig)
{
    if (sig) { ; }      /* unused, dummy to suppress warning */
    fprintf(stderr, "Progress report, continuing ...\n");
    print_stats(0, NULL);
}

static int dd_filetype(const char * filename)
{
    struct stat st;

    if (stat(filename, &st) < 0)
        return FT_ERROR;
    if (S_ISCHR(st.st_mode)) {
        if (RAW_MAJOR == major(st.st_rdev))
            return FT_RAW;
        else if (SCSI_GENERIC_MAJOR == major(st.st_rdev))
            return FT_SG;
    } else if (S_ISBLK(st.st_mode))
        return FT_BLOCK;
    return FT_OTHER;
}

static void usage()
{
    fprintf(stderr, "Usage: "
           "sg_read  [blk_sgio=0|1] [bpt=BPT] [bs=BS] "
           "[cdbsz=6|10|12|16]\n"
           "                count=COUNT [dio=0|1] [dpo=0|1] [fua=0|1] "
           "if=IFILE\n"
           "                [mmap=0|1] [no_dfxer=0|1] [odir=0|1] "
           "[skip=SKIP]\n"
           "                [time=TI] [verbose=VERB] [--help] "
           "[--version]\n"
           "  where:\n"
           "    blk_sgio 0->normal IO for block devices, 1->SCSI commands "
           "via SG_IO\n"
           "    bpt      is blocks_per_transfer (default is 128, or 64 KiB "
           "for default BS)\n"
           "             setting 'bpt=0' will do COUNT zero block SCSI "
           "READs\n"
           "    bs       must match sector size if IFILE accessed via SCSI "
           "commands\n"
           "             (def=512)\n"
           "    cdbsz    size of SCSI READ command (default is 10)\n"
           "    count    total bytes read will be BS*COUNT (if no "
           "error)\n"
           "             (if negative, do |COUNT| zero block SCSI READs)\n"
           "    dio      1-> attempt direct IO on sg device, 0->indirect IO "
           "(def)\n");
    fprintf(stderr,
           "    dpo      1-> set disable page out (DPO) in SCSI READs\n"
           "    fua      1-> set force unit access (FUA) in SCSI READs\n"
           "    if       an sg, block or raw device, or a seekable file (not "
           "stdin)\n"
           "    mmap     1->perform mmaped IO on sg device, 0->indirect IO "
           "(def)\n"
           "    no_dxfer 1->DMA to kernel buffers only, not user space, "
           "0->normal(def)\n"
           "    odir     1->open block device O_DIRECT, 0->don't (def)\n"
           "    skip     each transfer starts at this logical address "
           "(def=0)\n"
           "    time     0->do nothing(def), 1->time from 1st cmd, 2->time "
           "from 2nd, ...\n"
           "    verbose  increase level of verbosity (def: 0)\n"
           "    --help   print this usage message then exit\n"
           "    --version  print version number then exit\n\n"
           "Issue SCSI READ commands, each starting from the same logical "
           "block address\n");
}

static int sg_build_scsi_cdb(unsigned char * cdbp, int cdb_sz,
                             unsigned int blocks, int64_t start_block,
                             int write_true, int fua, int dpo)
{
    int rd_opcode[] = {0x8, 0x28, 0xa8, 0x88};
    int wr_opcode[] = {0xa, 0x2a, 0xaa, 0x8a};
    int sz_ind;

    memset(cdbp, 0, cdb_sz);
    if (dpo)
        cdbp[1] |= 0x10;
    if (fua)
        cdbp[1] |= 0x8;
    switch (cdb_sz) {
    case 6:
        sz_ind = 0;
        cdbp[0] = (unsigned char)(write_true ? wr_opcode[sz_ind] :
                                               rd_opcode[sz_ind]);
        cdbp[1] = (unsigned char)((start_block >> 16) & 0x1f);
        cdbp[2] = (unsigned char)((start_block >> 8) & 0xff);
        cdbp[3] = (unsigned char)(start_block & 0xff);
        cdbp[4] = (256 == blocks) ? 0 : (unsigned char)blocks;
        if (blocks > 256) {
            fprintf(stderr, ME "for 6 byte commands, maximum number of "
                            "blocks is 256\n");
            return 1;
        }
        if ((start_block + blocks - 1) & (~0x1fffff)) {
            fprintf(stderr, ME "for 6 byte commands, can't address blocks"
                            " beyond %d\n", 0x1fffff);
            return 1;
        }
        if (dpo || fua) {
            fprintf(stderr, ME "for 6 byte commands, neither dpo nor fua"
                            " bits supported\n");
            return 1;
        }
        break;
    case 10:
        sz_ind = 1;
        cdbp[0] = (unsigned char)(write_true ? wr_opcode[sz_ind] :
                                               rd_opcode[sz_ind]);
        cdbp[2] = (unsigned char)((start_block >> 24) & 0xff);
        cdbp[3] = (unsigned char)((start_block >> 16) & 0xff);
        cdbp[4] = (unsigned char)((start_block >> 8) & 0xff);
        cdbp[5] = (unsigned char)(start_block & 0xff);
        cdbp[7] = (unsigned char)((blocks >> 8) & 0xff);
        cdbp[8] = (unsigned char)(blocks & 0xff);
        if (blocks & (~0xffff)) {
            fprintf(stderr, ME "for 10 byte commands, maximum number of "
                            "blocks is %d\n", 0xffff);
            return 1;
        }
        break;
    case 12:
        sz_ind = 2;
        cdbp[0] = (unsigned char)(write_true ? wr_opcode[sz_ind] :
                                               rd_opcode[sz_ind]);
        cdbp[2] = (unsigned char)((start_block >> 24) & 0xff);
        cdbp[3] = (unsigned char)((start_block >> 16) & 0xff);
        cdbp[4] = (unsigned char)((start_block >> 8) & 0xff);
        cdbp[5] = (unsigned char)(start_block & 0xff);
        cdbp[6] = (unsigned char)((blocks >> 24) & 0xff);
        cdbp[7] = (unsigned char)((blocks >> 16) & 0xff);
        cdbp[8] = (unsigned char)((blocks >> 8) & 0xff);
        cdbp[9] = (unsigned char)(blocks & 0xff);
        break;
    case 16:
        sz_ind = 3;
        cdbp[0] = (unsigned char)(write_true ? wr_opcode[sz_ind] :
                                               rd_opcode[sz_ind]);
        cdbp[2] = (unsigned char)((start_block >> 56) & 0xff);
        cdbp[3] = (unsigned char)((start_block >> 48) & 0xff);
        cdbp[4] = (unsigned char)((start_block >> 40) & 0xff);
        cdbp[5] = (unsigned char)((start_block >> 32) & 0xff);
        cdbp[6] = (unsigned char)((start_block >> 24) & 0xff);
        cdbp[7] = (unsigned char)((start_block >> 16) & 0xff);
        cdbp[8] = (unsigned char)((start_block >> 8) & 0xff);
        cdbp[9] = (unsigned char)(start_block & 0xff);
        cdbp[10] = (unsigned char)((blocks >> 24) & 0xff);
        cdbp[11] = (unsigned char)((blocks >> 16) & 0xff);
        cdbp[12] = (unsigned char)((blocks >> 8) & 0xff);
        cdbp[13] = (unsigned char)(blocks & 0xff);
        break;
    default:
        fprintf(stderr, ME "expected cdb size of 6, 10, 12, or 16 but got"
                        " %d\n", cdb_sz);
        return 1;
    }
    return 0;
}

/* -3 medium/hardware error, -2 -> not ready, 0 -> successful,
   1 -> recoverable (ENOMEM), 2 -> try again (e.g. unit attention),
   3 -> try again (e.g. aborted command), -1 -> other unrecoverable error */
static int sg_bread(int sg_fd, unsigned char * buff, int blocks,
                    int64_t from_block, int bs, int cdbsz,
                    int fua, int dpo, int * diop, int do_mmap,
                    int no_dxfer)
{
    int k;
    unsigned char rdCmd[MAX_SCSI_CDBSZ];
    unsigned char senseBuff[SENSE_BUFF_LEN];
    struct sg_io_hdr io_hdr;

    if (sg_build_scsi_cdb(rdCmd, cdbsz, blocks, from_block, 0, fua, dpo)) {
        fprintf(stderr, ME "bad cdb build, from_block=%" PRId64
                ", blocks=%d\n", from_block, blocks);
        return -1;
    }
    memset(&io_hdr, 0, sizeof(struct sg_io_hdr));
    io_hdr.interface_id = 'S';
    io_hdr.cmd_len = cdbsz;
    io_hdr.cmdp = rdCmd;
    if (blocks > 0) {
        io_hdr.dxfer_direction = SG_DXFER_FROM_DEV;
        io_hdr.dxfer_len = bs * blocks;
        /* next: shows dxferp unused during mmap-ed IO */
        if (! do_mmap)
            io_hdr.dxferp = buff;
        if (diop && *diop)
            io_hdr.flags |= SG_FLAG_DIRECT_IO;
        else if (do_mmap)
            io_hdr.flags |= SG_FLAG_MMAP_IO;
        else if (no_dxfer)
            io_hdr.flags |= SG_FLAG_NO_DXFER;
    } else
        io_hdr.dxfer_direction = SG_DXFER_NONE;
    io_hdr.mx_sb_len = SENSE_BUFF_LEN;
    io_hdr.sbp = senseBuff;
    io_hdr.timeout = DEF_TIMEOUT;
    io_hdr.pack_id = pack_id_count++;
    if (verbose > 1) {
        fprintf(stderr, "    read cdb: ");
        for (k = 0; k < cdbsz; ++k)
            fprintf(stderr, "%02x ", rdCmd[k]);
        fprintf(stderr, "\n");
    }

    if (ioctl(sg_fd, SG_IO, &io_hdr) < 0) {
        if (ENOMEM == errno)
            return 1;
        perror("reading (SG_IO) on sg device, error");
        return -1;
    }

    if (verbose > 2)
        fprintf(stderr, "      duration=%u ms\n", io_hdr.duration);
    switch (sg_err_category3(&io_hdr)) {
    case SG_LIB_CAT_RECOVERED:
        if (verbose > 1)
                sg_chk_n_print3("reading, continue", &io_hdr, 1);
        /* fall through */
    case SG_LIB_CAT_CLEAN:
        break;
    case SG_LIB_CAT_UNIT_ATTENTION:
        if (verbose)
            sg_chk_n_print3("reading", &io_hdr, verbose - 1);
        return 2;
    case SG_LIB_CAT_ABORTED_COMMAND:
        if (verbose)
            sg_chk_n_print3("reading", &io_hdr, verbose - 1);
        return 3;
    case SG_LIB_CAT_NOT_READY:
        if (verbose)
            sg_chk_n_print3("reading", &io_hdr, verbose - 1);
        return -2;
    case SG_LIB_CAT_MEDIUM_HARD:
        if (verbose)
            sg_chk_n_print3("reading", &io_hdr, verbose - 1);
        return -3;
    default:
        sg_chk_n_print3("reading", &io_hdr, verbose);
        return -1;
    }
    if (blocks > 0) {
        if (diop && *diop &&
            ((io_hdr.info & SG_INFO_DIRECT_IO_MASK) != SG_INFO_DIRECT_IO))
            *diop = 0;      /* flag that dio not done (completely) */
        sum_of_resids += io_hdr.resid;
    }
    return 0;
}

#define STR_SZ 1024
#define INF_SZ 512
#define EBUFF_SZ 512


int main(int argc, char * argv[])
{
    int64_t skip = 0;
    int bs = 0;
    int bpt = DEF_BLOCKS_PER_TRANSFER;
    char str[STR_SZ];
    char * key;
    char * buf;
    char inf[INF_SZ];
    char outf[INF_SZ];
    int in_type = FT_OTHER;
    int do_dio = 0;
    int do_odir = 0;
    int do_blk_sgio = 0;
    int do_mmap = 0;
    int no_dxfer = 0;
    int do_time = 0;
    int fua = 0;
    int dpo = 0;
    int scsi_cdbsz = DEF_SCSI_CDBSZ;
    int dio_incomplete = 0;
    int count_given = 0;
    int res, k, t, buf_sz, dio_tmp, iters;
    int infd, blocks, flags, blocks_per;
    unsigned char * wrkBuff = NULL;
    unsigned char * wrkPos = NULL;
    char ebuff[EBUFF_SZ];
    struct timeval start_tm, end_tm;
    const char * read_str;
    int ret = 0;
    size_t psz;

#if defined(HAVE_SYSCONF) && defined(_SC_PAGESIZE)
    psz = sysconf(_SC_PAGESIZE); /* POSIX.1 (was getpagesize()) */
#else
    psz = 4096;     /* give up, pick likely figure */
#endif
    inf[0] = '\0';

    for (k = 1; k < argc; k++) {
        if (argv[k]) {
            strncpy(str, argv[k], STR_SZ);
            str[STR_SZ - 1] = '\0';
        } else
            continue;
        for (key = str, buf = key; (*buf && (*buf != '=')); )
            buf++;
        if (*buf)
            *buf++ = '\0';
        if (0 == strcmp(key,"blk_sgio"))
            do_blk_sgio = sg_get_num(buf);
        else if (0 == strcmp(key,"bpt")) {
            bpt = sg_get_num(buf);
            if (-1 == bpt) {
                fprintf(stderr, ME "bad argument to 'bpt'\n");
                return SG_LIB_SYNTAX_ERROR;
            }
        } else if (0 == strcmp(key,"bs")) {
            bs = sg_get_num(buf);
            if (-1 == bs) {
                fprintf(stderr, ME "bad argument to 'bs'\n");
                return SG_LIB_SYNTAX_ERROR;
            }
        } else if (0 == strcmp(key,"cdbsz"))
            scsi_cdbsz = sg_get_num(buf);
        else if (0 == strcmp(key,"count")) {
            count_given = 1;
            if ('-' == *buf) {
                dd_count = sg_get_llnum(buf + 1);
                if (-1 == dd_count) {
                    fprintf(stderr, ME "bad argument to 'count'\n");
                    return SG_LIB_SYNTAX_ERROR;
                }
                dd_count = - dd_count;
            } else {
                dd_count = sg_get_llnum(buf);
                if (-1 == dd_count) {
                    fprintf(stderr, ME "bad argument to 'count'\n");
                    return SG_LIB_SYNTAX_ERROR;
                }
            }
        } else if (0 == strcmp(key,"dio"))
            do_dio = sg_get_num(buf);
        else if (0 == strcmp(key,"dpo"))
            dpo = sg_get_num(buf);
        else if (0 == strcmp(key,"fua"))
            fua = sg_get_num(buf);
        else if (strcmp(key,"if") == 0)
            strncpy(inf, buf, INF_SZ);
        else if (0 == strcmp(key,"mmap"))
            do_mmap = sg_get_num(buf);
        else if (0 == strcmp(key,"no_dxfer"))
            no_dxfer = sg_get_num(buf);
        else if (0 == strcmp(key,"odir"))
            do_odir = sg_get_num(buf);
        else if (strcmp(key,"of") == 0)
            strncpy(outf, buf, INF_SZ);
        else if (0 == strcmp(key,"skip")) {
            skip = sg_get_llnum(buf);
            if (-1 == skip) {
                fprintf(stderr, ME "bad argument to 'skip'\n");
                return SG_LIB_SYNTAX_ERROR;
            }
        } else if (0 == strcmp(key,"time"))
            do_time = sg_get_num(buf);
        else if (0 == strncmp(key, "verb", 4))
            verbose = sg_get_num(buf);
        else if (0 == strncmp(key, "--help", 6)) {
            usage();
            return 0;
        } else if (0 == strncmp(key, "--vers", 6)) {
            fprintf(stderr, ME ": %s\n", version_str);
            return 0;
        } else {
            fprintf(stderr, "Unrecognized argument '%s'\n", key);
            usage();
            return SG_LIB_SYNTAX_ERROR;
        }
    }
    if (bs <= 0) {
        bs = DEF_BLOCK_SIZE;
        if ((dd_count > 0) && (bpt > 0))
            fprintf(stderr, "Assume default 'bs' (block size) of %d bytes\n",
                    bs);
    }
    if (! count_given) {
        fprintf(stderr, "'count' must be given\n");
        usage();
        return SG_LIB_SYNTAX_ERROR;
    }
    if (skip < 0) {
        fprintf(stderr, "skip cannot be negative\n");
        return SG_LIB_SYNTAX_ERROR;
    }
    if (bpt < 1) {
        if (0 == bpt) {
            if (dd_count > 0)
                dd_count = - dd_count;
        } else {
            fprintf(stderr, "bpt must be greater than 0\n");
            return SG_LIB_SYNTAX_ERROR;
        }
    }
    if (do_dio && do_mmap) {
        fprintf(stderr, "cannot select both dio and mmap\n");
        return SG_LIB_SYNTAX_ERROR;
    }
    if (no_dxfer && (do_dio || do_mmap)) {
        fprintf(stderr, "cannot select no_dxfer with dio or mmap\n");
        return SG_LIB_SYNTAX_ERROR;
    }

    install_handler (SIGINT, interrupt_handler);
    install_handler (SIGQUIT, interrupt_handler);
    install_handler (SIGPIPE, interrupt_handler);
    install_handler (SIGUSR1, siginfo_handler);

    if (! inf[0]) {
        fprintf(stderr, "must provide 'if=<filename>'\n");
        usage();
        return SG_LIB_SYNTAX_ERROR;
    }
    if (0 == strcmp("-", inf)) {
        fprintf(stderr, "'-' (stdin) invalid as <filename>\n");
        usage();
        return SG_LIB_SYNTAX_ERROR;
    }
    in_type = dd_filetype(inf);
    if (FT_ERROR == in_type) {
        fprintf(stderr, "Unable to access: %s\n", inf);
        return SG_LIB_FILE_ERROR;
    } else if ((FT_BLOCK & in_type) && do_blk_sgio)
        in_type |= FT_SG;

    if (FT_SG & in_type) {
        if ((dd_count < 0) && (6 == scsi_cdbsz)) {
            fprintf(stderr, ME "SCSI READ (6) can't do zero block "
                    "reads\n");
            return SG_LIB_SYNTAX_ERROR;
        }
        flags = O_RDWR;
        if (do_odir)
            flags |= O_DIRECT;
        if ((infd = open(inf, flags)) < 0) {
            flags = O_RDONLY;
            if (do_odir)
                flags |= O_DIRECT;
            if ((infd = open(inf, flags)) < 0) {
                snprintf(ebuff, EBUFF_SZ,
                         ME "could not open %s for sg reading", inf);
                perror(ebuff);
                return SG_LIB_FILE_ERROR;
            }
        }
        if (verbose)
            fprintf(stderr, "Opened %s for SG_IO with flags=0x%x\n", inf,
                    flags);
        if ((dd_count > 0) && (! (FT_BLOCK & in_type))) {
            if (verbose > 2) {
                if (ioctl(infd, SG_GET_RESERVED_SIZE, &t) >= 0)
                    fprintf(stderr, "  SG_GET_RESERVED_SIZE yields: %d\n", t);
            }
            t = bs * bpt;
            if ((do_mmap) && (0 != (t % psz)))
                t = ((t / psz) + 1) * psz;    /* round up to next pagesize */
            res = ioctl(infd, SG_SET_RESERVED_SIZE, &t);
            if (res < 0)
                perror(ME "SG_SET_RESERVED_SIZE error");
            res = ioctl(infd, SG_GET_VERSION_NUM, &t);
            if ((res < 0) || (t < 30000)) {
                fprintf(stderr, ME "sg driver prior to 3.x.y\n");
                return SG_LIB_CAT_OTHER;
            }
            if (do_mmap && (t < 30122)) {
                fprintf(stderr, ME "mmap-ed IO needs a sg driver version "
                        ">= 3.1.22\n");
                return SG_LIB_CAT_OTHER;
            }
        }
    } else {
        if (do_mmap) {
            fprintf(stderr, ME "mmap-ed IO only support on sg "
                    "devices\n");
            return SG_LIB_CAT_OTHER;
        }
        if (dd_count < 0) {
            fprintf(stderr, ME "negative 'count' only supported with "
                    "SCSI READs\n");
            return SG_LIB_CAT_OTHER;
        }
        flags = O_RDONLY;
        if (do_odir)
            flags |= O_DIRECT;
        if ((infd = open(inf, flags)) < 0) {
            snprintf(ebuff,  EBUFF_SZ,
                     ME "could not open %s for reading", inf);
            perror(ebuff);
            return SG_LIB_FILE_ERROR;
        }
        if (verbose)
            fprintf(stderr, "Opened %s for Unix reads with flags=0x%x\n",
                    inf, flags);
        if (skip > 0) {
            off64_t offset = skip;

            offset *= bs;       /* could exceed 32 bits here! */
            if (lseek64(infd, offset, SEEK_SET) < 0) {
                snprintf(ebuff,  EBUFF_SZ,
                    ME "couldn't skip to required position on %s", inf);
                perror(ebuff);
                return SG_LIB_FILE_ERROR;
            }
        }
    }

    if (0 == dd_count)
        return 0;
    orig_count = dd_count;

    if (dd_count > 0) {
        if (do_dio || do_odir || (FT_RAW & in_type)) {
            wrkBuff = (unsigned char *)malloc(bs * bpt + psz);
            if (0 == wrkBuff) {
                fprintf(stderr, "Not enough user memory for aligned "
                        "storage\n");
                return SG_LIB_CAT_OTHER;
            }
            /* perhaps use posix_memalign() instead */
            wrkPos = (unsigned char *)(((unsigned long)wrkBuff + psz - 1) &
                                       (~(psz - 1)));
        } else if (do_mmap) {
            wrkPos = (unsigned char *)mmap(NULL, bs * bpt,
                        PROT_READ | PROT_WRITE, MAP_SHARED, infd, 0);
            if (MAP_FAILED == wrkPos) {
                perror(ME "error from mmap()");
                return SG_LIB_CAT_OTHER;
            }
        } else {
            wrkBuff = (unsigned char *)malloc(bs * bpt);
            if (0 == wrkBuff) {
                fprintf(stderr, "Not enough user memory\n");
                return SG_LIB_CAT_OTHER;
            }
            wrkPos = wrkBuff;
        }
    }

    blocks_per = bpt;
    start_tm.tv_sec = 0;   /* just in case start set condition not met */
    start_tm.tv_usec = 0;

    if (verbose && (dd_count < 0))
        fprintf(stderr, "About to issue %" PRId64 " zero block SCSI READs\n",
                0 - dd_count);

    /* main loop */
    for (iters = 0; dd_count != 0; ++iters) {
        if ((do_time > 0) && (iters == (do_time - 1)))
            gettimeofday(&start_tm, NULL);
        if (dd_count < 0)
            blocks = 0;
        else
            blocks = (dd_count > blocks_per) ? blocks_per : dd_count;
        if (FT_SG & in_type) {
            dio_tmp = do_dio;
            res = sg_bread(infd, wrkPos, blocks, skip, bs, scsi_cdbsz,
                           fua, dpo, &dio_tmp, do_mmap, no_dxfer);
            if (1 == res) {     /* ENOMEM, find what's available+try that */
                if (ioctl(infd, SG_GET_RESERVED_SIZE, &buf_sz) < 0) {
                    perror("RESERVED_SIZE ioctls failed");
                    break;
                }
                if (buf_sz < MIN_RESERVED_SIZE)
                    buf_sz = MIN_RESERVED_SIZE;
                blocks_per = (buf_sz + bs - 1) / bs;
                blocks = blocks_per;
                fprintf(stderr,
                        "Reducing read to %d blocks per loop\n", blocks_per);
                res = sg_bread(infd, wrkPos, blocks, skip, bs, scsi_cdbsz,
                               fua, dpo, &dio_tmp, do_mmap, no_dxfer);
            } else if (2 == res) {
                fprintf(stderr,
                        "Unit attention, try again (r)\n");
                res = sg_bread(infd, wrkPos, blocks, skip, bs, scsi_cdbsz,
                               fua, dpo, &dio_tmp, do_mmap, no_dxfer);
            }
            if (0 != res) {
                switch (res) {
                case -3:
                    ret = SG_LIB_CAT_MEDIUM_HARD;
                    fprintf(stderr, ME "SCSI READ medium/hardware error\n");
                    break;
                case -2:
                    ret = SG_LIB_CAT_NOT_READY;
                    fprintf(stderr, ME "device not ready\n");
                    break;
                case 2:
                    ret = SG_LIB_CAT_UNIT_ATTENTION;
                    fprintf(stderr, ME "SCSI READ unit attention\n");
                    break;
                case 3:
                    ret = SG_LIB_CAT_ABORTED_COMMAND;
                    fprintf(stderr, ME "SCSI READ aborted command\n");
                    break;
                default:
                    ret = SG_LIB_CAT_OTHER;
                    fprintf(stderr, ME "SCSI READ failed\n");
                    break;
                }
                break;
            } else {
                in_full += blocks;
                if (do_dio && (0 == dio_tmp))
                    dio_incomplete++;
            }
        } else {
            if (iters > 0) { /* subsequent iteration reset skip position */
                off64_t offset = skip;

                offset *= bs;       /* could exceed 32 bits here! */
                if (lseek64(infd, offset, SEEK_SET) < 0) {
                    perror(ME "could not reset skip position");
                    break;
                }
            }
            while (((res = read(infd, wrkPos, blocks * bs)) < 0) &&
                   (EINTR == errno))
                ;
            if (res < 0) {
                snprintf(ebuff, EBUFF_SZ, ME "reading, skip=%" PRId64 " ",
                         skip);
                perror(ebuff);
                break;
            } else if (res < blocks * bs) {
                fprintf(stderr, ME "short read: wanted/got=%d/%d bytes"
                        ", stop\n", blocks * bs, res);
                blocks = res / bs;
                if ((res % bs) > 0) {
                    blocks++;
                    in_partial++;
                }
                dd_count -= blocks;
                in_full += blocks;
                break;
            }
            in_full += blocks;
        }
        if (dd_count > 0)
            dd_count -= blocks;
        else if (dd_count < 0)
            ++dd_count;
    }
    read_str = (FT_SG & in_type) ? "SCSI READ" : "read";
    if (do_time > 0) {
        gettimeofday(&end_tm, NULL);
        if (start_tm.tv_sec || start_tm.tv_usec) {
            struct timeval res_tm;
            double a, b, c;

            res_tm.tv_sec = end_tm.tv_sec - start_tm.tv_sec;
            res_tm.tv_usec = end_tm.tv_usec - start_tm.tv_usec;
            if (res_tm.tv_usec < 0) {
                --res_tm.tv_sec;
                res_tm.tv_usec += 1000000;
            }
            a = res_tm.tv_sec;
            a += (0.000001 * res_tm.tv_usec);
            if (orig_count > 0) {
                b = (double)bs * (orig_count - dd_count);
                if (do_time > 1)
                    c = b - ((double)bs * ((do_time - 1.0) * bpt));
                else
                    c = 0.0;
            } else {
                b = 0.0;
                c = 0.0;
            }

            if (1 == do_time) {
                fprintf(stderr, "Time for all %s commands was "
                        "%d.%06d secs", read_str, (int)res_tm.tv_sec,
                        (int)res_tm.tv_usec);
                if ((orig_count > 0) && (a > 0.00001) && (b > 511))
                    fprintf(stderr, ", %.2f MB/sec\n", b / (a * 1000000.0));
                else
                    fprintf(stderr, "\n");
            } else if (2 == do_time) {
                fprintf(stderr, "Time from second %s command to end "
                        "was %d.%06d secs", read_str, (int)res_tm.tv_sec,
                        (int)res_tm.tv_usec);
                if ((orig_count > 0) && (a > 0.00001) && (c > 511))
                    fprintf(stderr, ", %.2f MB/sec\n", c / (a * 1000000.0));
                else
                    fprintf(stderr, "\n");
            } else {
                fprintf(stderr, "Time from start of %s command "
                        "#%d to end was %d.%06d secs", read_str, do_time,
                        (int)res_tm.tv_sec, (int)res_tm.tv_usec);
                if ((orig_count > 0) && (a > 0.00001) && (c > 511))
                    fprintf(stderr, ", %.2f MB/sec\n", c / (a * 1000000.0));
                else
                    fprintf(stderr, "\n");
            }
            if ((iters > 0) && (a > 0.00001))
                fprintf(stderr, "Average number of %s commands per "
                        "second was %.2f\n", read_str, (double)iters / a);
        }
    }

    if (wrkBuff)
        free(wrkBuff);

    close(infd);
    res = 0;
    if (0 != dd_count) {
        fprintf(stderr, "Some error occurred,");
        if (0 == ret)
            ret = SG_LIB_CAT_OTHER;
    }
    print_stats(iters, read_str);

    if (dio_incomplete) {
        int fd;
        char c;

        fprintf(stderr, ">> Direct IO requested but incomplete %d times\n",
                dio_incomplete);
        if ((fd = open(proc_allow_dio, O_RDONLY)) >= 0) {
            if (1 == read(fd, &c, 1)) {
                if ('0' == c)
                    fprintf(stderr, ">>> %s set to '0' but should be set "
                            "to '1' for direct IO\n", proc_allow_dio);
            }
            close(fd);
        }
    }
    if (sum_of_resids)
        fprintf(stderr, ">> Non-zero sum of residual counts=%d\n",
                sum_of_resids);
    return (ret >= 0) ? ret : SG_LIB_CAT_OTHER;
}
