/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright 2015 Nexenta Systems, Inc. All rights reserved.
 * Copyright (c) 2015, 2018 by Delphix. All rights reserved.
 * Copyright 2016 Joyent, Inc.
 * Copyright 2016 Igor Kozhukhov <ikozhukhov@gmail.com>
 */

/*
 * zfs diff support
 */
#include <ctype.h>
#include <errno.h>
#include <libintl.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <attr.h>
#include <stddef.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stropts.h>
#include <pthread.h>
#include <sys/zfs_ioctl.h>
#include <libzfs.h>
#include "libzfs_impl.h"

#define ZDIFF_SNAPDIR           "/.zfs/snapshot/"
#define ZDIFF_SHARESDIR         "/.zfs/shares/"
#define ZDIFF_PREFIX            "zfs-diff-%d"

#define ZDIFF_ADDED     '+'
#define ZDIFF_MODIFIED  'M'
#define ZDIFF_REMOVED   '-'
#define ZDIFF_RENAMED   'R'

typedef struct differ_info {
        zfs_handle_t *zhp;
        char *fromsnap;
        char *frommnt;
        char *tosnap;
        char *tomnt;
        char *ds;
        char *dsmnt;
        char *tmpsnap;
        char errbuf[1024];
        boolean_t isclone;
        boolean_t scripted;
        boolean_t classify;
        boolean_t timestamped;
        uint64_t shares;
        int zerr;
        int cleanupfd;
        int outputfd;
        int datafd;
} differ_info_t;

/*
 * Given a {dsname, object id}, get the object path
 */
static int
get_stats_for_obj(differ_info_t *di, const char *dsname, uint64_t obj,
    char *pn, int maxlen, zfs_stat_t *sb)
{
        zfs_cmd_t zc = { 0 };
        int error;

        (void) strlcpy(zc.zc_name, dsname, sizeof (zc.zc_name));
        zc.zc_obj = obj;

        errno = 0;
        error = ioctl(di->zhp->zfs_hdl->libzfs_fd, ZFS_IOC_OBJ_TO_STATS, &zc);
        di->zerr = errno;

        /* we can get stats even if we failed to get a path */
        (void) memcpy(sb, &zc.zc_stat, sizeof (zfs_stat_t));
        if (error == 0) {
                ASSERT(di->zerr == 0);
                (void) strlcpy(pn, zc.zc_value, maxlen);
                return (0);
        }

        if (di->zerr == ESTALE) {
                (void) snprintf(pn, maxlen, "(on_delete_queue)");
                return (0);
        } else if (di->zerr == EPERM) {
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN,
                    "The sys_config privilege or diff delegated permission "
                    "is needed\nto discover path names"));
                return (-1);
        } else if (di->zerr == EACCES) {
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN,
                    "Key must be loaded to discover path names"));
                return (-1);
        } else {
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN,
                    "Unable to determine path or stats for "
                    "object %lld in %s"), obj, dsname);
                return (-1);
        }
}

/*
 * stream_bytes
 *
 * Prints a file name out a character at a time.  If the character is
 * not in the range of what we consider "printable" ASCII, display it
 * as an escaped 3-digit octal value.  ASCII values less than a space
 * are all control characters and we declare the upper end as the
 * DELete character.  This also is the last 7-bit ASCII character.
 * We choose to treat all 8-bit ASCII as not printable for this
 * application.
 */
static void
stream_bytes(FILE *fp, const char *string)
{
        char c;

        while ((c = *string++) != '\0') {
                if (c > ' ' && c != '\\' && c < '\177') {
                        (void) fprintf(fp, "%c", c);
                } else {
                        (void) fprintf(fp, "\\%03o", (uint8_t)c);
                }
        }
}

static void
print_what(FILE *fp, mode_t what)
{
        char symbol;

        switch (what & S_IFMT) {
        case S_IFBLK:
                symbol = 'B';
                break;
        case S_IFCHR:
                symbol = 'C';
                break;
        case S_IFDIR:
                symbol = '/';
                break;
        case S_IFDOOR:
                symbol = '>';
                break;
        case S_IFIFO:
                symbol = '|';
                break;
        case S_IFLNK:
                symbol = '@';
                break;
        case S_IFPORT:
                symbol = 'P';
                break;
        case S_IFSOCK:
                symbol = '=';
                break;
        case S_IFREG:
                symbol = 'F';
                break;
        default:
                symbol = '?';
                break;
        }
        (void) fprintf(fp, "%c", symbol);
}

static void
print_cmn(FILE *fp, differ_info_t *di, const char *file)
{
        stream_bytes(fp, di->dsmnt);
        stream_bytes(fp, file);
}

static void
print_rename(FILE *fp, differ_info_t *di, const char *old, const char *new,
    zfs_stat_t *isb)
{
        if (di->timestamped)
                (void) fprintf(fp, "%10lld.%09lld\t",
                    (longlong_t)isb->zs_ctime[0],
                    (longlong_t)isb->zs_ctime[1]);
        (void) fprintf(fp, "%c\t", ZDIFF_RENAMED);
        if (di->classify) {
                print_what(fp, isb->zs_mode);
                (void) fprintf(fp, "\t");
        }
        print_cmn(fp, di, old);
        if (di->scripted)
                (void) fprintf(fp, "\t");
        else
                (void) fprintf(fp, " -> ");
        print_cmn(fp, di, new);
        (void) fprintf(fp, "\n");
}

static void
print_link_change(FILE *fp, differ_info_t *di, int delta, const char *file,
    zfs_stat_t *isb)
{
        if (di->timestamped)
                (void) fprintf(fp, "%10lld.%09lld\t",
                    (longlong_t)isb->zs_ctime[0],
                    (longlong_t)isb->zs_ctime[1]);
        (void) fprintf(fp, "%c\t", ZDIFF_MODIFIED);
        if (di->classify) {
                print_what(fp, isb->zs_mode);
                (void) fprintf(fp, "\t");
        }
        print_cmn(fp, di, file);
        (void) fprintf(fp, "\t(%+d)", delta);
        (void) fprintf(fp, "\n");
}

static void
print_file(FILE *fp, differ_info_t *di, char type, const char *file,
    zfs_stat_t *isb)
{
        if (di->timestamped)
                (void) fprintf(fp, "%10lld.%09lld\t",
                    (longlong_t)isb->zs_ctime[0],
                    (longlong_t)isb->zs_ctime[1]);
        (void) fprintf(fp, "%c\t", type);
        if (di->classify) {
                print_what(fp, isb->zs_mode);
                (void) fprintf(fp, "\t");
        }
        print_cmn(fp, di, file);
        (void) fprintf(fp, "\n");
}

static int
write_inuse_diffs_one(FILE *fp, differ_info_t *di, uint64_t dobj)
{
        struct zfs_stat fsb, tsb;
        mode_t fmode, tmode;
        char fobjname[MAXPATHLEN], tobjname[MAXPATHLEN];
        int fobjerr, tobjerr;
        int change;

        if (dobj == di->shares)
                return (0);

        /*
         * Check the from and to snapshots for info on the object. If
         * we get ENOENT, then the object just didn't exist in that
         * snapshot.  If we get ENOTSUP, then we tried to get
         * info on a non-ZPL object, which we don't care about anyway.
         */
        fobjerr = get_stats_for_obj(di, di->fromsnap, dobj, fobjname,
            MAXPATHLEN, &fsb);
        if (fobjerr && di->zerr != ENOENT && di->zerr != ENOTSUP)
                return (-1);

        tobjerr = get_stats_for_obj(di, di->tosnap, dobj, tobjname,
            MAXPATHLEN, &tsb);
        if (tobjerr && di->zerr != ENOENT && di->zerr != ENOTSUP)
                return (-1);

        /*
         * Unallocated object sharing the same meta dnode block
         */
        if (fobjerr && tobjerr) {
                ASSERT(di->zerr == ENOENT || di->zerr == ENOTSUP);
                di->zerr = 0;
                return (0);
        }

        di->zerr = 0; /* negate get_stats_for_obj() from side that failed */
        fmode = fsb.zs_mode & S_IFMT;
        tmode = tsb.zs_mode & S_IFMT;
        if (fmode == S_IFDIR || tmode == S_IFDIR || fsb.zs_links == 0 ||
            tsb.zs_links == 0)
                change = 0;
        else
                change = tsb.zs_links - fsb.zs_links;

        if (fobjerr) {
                if (change) {
                        print_link_change(fp, di, change, tobjname, &tsb);
                        return (0);
                }
                print_file(fp, di, ZDIFF_ADDED, tobjname, &tsb);
                return (0);
        } else if (tobjerr) {
                if (change) {
                        print_link_change(fp, di, change, fobjname, &fsb);
                        return (0);
                }
                print_file(fp, di, ZDIFF_REMOVED, fobjname, &fsb);
                return (0);
        }

        if (fmode != tmode && fsb.zs_gen == tsb.zs_gen)
                tsb.zs_gen++;   /* Force a generational difference */

        /* Simple modification or no change */
        if (fsb.zs_gen == tsb.zs_gen) {
                /* No apparent changes.  Could we assert !this?  */
                if (fsb.zs_ctime[0] == tsb.zs_ctime[0] &&
                    fsb.zs_ctime[1] == tsb.zs_ctime[1])
                        return (0);
                if (change) {
                        print_link_change(fp, di, change,
                            change > 0 ? fobjname : tobjname, &tsb);
                } else if (strcmp(fobjname, tobjname) == 0) {
                        print_file(fp, di, ZDIFF_MODIFIED, fobjname, &tsb);
                } else {
                        print_rename(fp, di, fobjname, tobjname, &tsb);
                }
                return (0);
        } else {
                /* file re-created or object re-used */
                print_file(fp, di, ZDIFF_REMOVED, fobjname, &fsb);
                print_file(fp, di, ZDIFF_ADDED, tobjname, &tsb);
                return (0);
        }
}

static int
write_inuse_diffs(FILE *fp, differ_info_t *di, dmu_diff_record_t *dr)
{
        uint64_t o;
        int err;

        for (o = dr->ddr_first; o <= dr->ddr_last; o++) {
                if ((err = write_inuse_diffs_one(fp, di, o)) != 0)
                        return (err);
        }
        return (0);
}

static int
describe_free(FILE *fp, differ_info_t *di, uint64_t object, char *namebuf,
    int maxlen)
{
        struct zfs_stat sb;

        if (get_stats_for_obj(di, di->fromsnap, object, namebuf,
            maxlen, &sb) != 0) {
                return (-1);
        }
        /* Don't print if in the delete queue on from side */
        if (di->zerr == ESTALE) {
                di->zerr = 0;
                return (0);
        }

        print_file(fp, di, ZDIFF_REMOVED, namebuf, &sb);
        return (0);
}

static int
write_free_diffs(FILE *fp, differ_info_t *di, dmu_diff_record_t *dr)
{
        zfs_cmd_t zc = { 0 };
        libzfs_handle_t *lhdl = di->zhp->zfs_hdl;
        char fobjname[MAXPATHLEN];

        (void) strlcpy(zc.zc_name, di->fromsnap, sizeof (zc.zc_name));
        zc.zc_obj = dr->ddr_first - 1;

        ASSERT(di->zerr == 0);

        while (zc.zc_obj < dr->ddr_last) {
                int err;

                err = ioctl(lhdl->libzfs_fd, ZFS_IOC_NEXT_OBJ, &zc);
                if (err == 0) {
                        if (zc.zc_obj == di->shares) {
                                zc.zc_obj++;
                                continue;
                        }
                        if (zc.zc_obj > dr->ddr_last) {
                                break;
                        }
                        err = describe_free(fp, di, zc.zc_obj, fobjname,
                            MAXPATHLEN);
                        if (err)
                                break;
                } else if (errno == ESRCH) {
                        break;
                } else {
                        (void) snprintf(di->errbuf, sizeof (di->errbuf),
                            dgettext(TEXT_DOMAIN,
                            "next allocated object (> %lld) find failure"),
                            zc.zc_obj);
                        di->zerr = errno;
                        break;
                }
        }
        if (di->zerr)
                return (-1);
        return (0);
}

static void *
differ(void *arg)
{
        differ_info_t *di = arg;
        dmu_diff_record_t dr;
        FILE *ofp;
        int err = 0;

        if ((ofp = fdopen(di->outputfd, "w")) == NULL) {
                di->zerr = errno;
                (void) strerror_r(errno, di->errbuf, sizeof (di->errbuf));
                (void) close(di->datafd);
                return ((void *)-1);
        }

        for (;;) {
                char *cp = (char *)&dr;
                int len = sizeof (dr);
                int rv;

                do {
                        rv = read(di->datafd, cp, len);
                        cp += rv;
                        len -= rv;
                } while (len > 0 && rv > 0);

                if (rv < 0 || (rv == 0 && len != sizeof (dr))) {
                        di->zerr = EPIPE;
                        break;
                } else if (rv == 0) {
                        /* end of file at a natural breaking point */
                        break;
                }

                switch (dr.ddr_type) {
                case DDR_FREE:
                        err = write_free_diffs(ofp, di, &dr);
                        break;
                case DDR_INUSE:
                        err = write_inuse_diffs(ofp, di, &dr);
                        break;
                default:
                        di->zerr = EPIPE;
                        break;
                }

                if (err || di->zerr)
                        break;
        }

        (void) fclose(ofp);
        (void) close(di->datafd);
        if (err)
                return ((void *)-1);
        if (di->zerr) {
                ASSERT(di->zerr == EINVAL);
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN,
                    "Internal error: bad data from diff IOCTL"));
                return ((void *)-1);
        }
        return ((void *)0);
}

static int
find_shares_object(differ_info_t *di)
{
        char fullpath[MAXPATHLEN];
        struct stat64 sb = { 0 };

        (void) strlcpy(fullpath, di->dsmnt, MAXPATHLEN);
        (void) strlcat(fullpath, ZDIFF_SHARESDIR, MAXPATHLEN);

        if (stat64(fullpath, &sb) != 0) {
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN, "Cannot stat %s"), fullpath);
                return (zfs_error(di->zhp->zfs_hdl, EZFS_DIFF, di->errbuf));
        }

        di->shares = (uint64_t)sb.st_ino;
        return (0);
}

static int
make_temp_snapshot(differ_info_t *di)
{
        libzfs_handle_t *hdl = di->zhp->zfs_hdl;
        zfs_cmd_t zc = { 0 };

        (void) snprintf(zc.zc_value, sizeof (zc.zc_value),
            ZDIFF_PREFIX, getpid());
        (void) strlcpy(zc.zc_name, di->ds, sizeof (zc.zc_name));
        zc.zc_cleanup_fd = di->cleanupfd;

        if (ioctl(hdl->libzfs_fd, ZFS_IOC_TMP_SNAPSHOT, &zc) != 0) {
                int err = errno;
                if (err == EPERM) {
                        (void) snprintf(di->errbuf, sizeof (di->errbuf),
                            dgettext(TEXT_DOMAIN, "The diff delegated "
                            "permission is needed in order\nto create a "
                            "just-in-time snapshot for diffing\n"));
                        return (zfs_error(hdl, EZFS_DIFF, di->errbuf));
                } else {
                        (void) snprintf(di->errbuf, sizeof (di->errbuf),
                            dgettext(TEXT_DOMAIN, "Cannot create just-in-time "
                            "snapshot of '%s'"), zc.zc_name);
                        return (zfs_standard_error(hdl, err, di->errbuf));
                }
        }

        di->tmpsnap = zfs_strdup(hdl, zc.zc_value);
        di->tosnap = zfs_asprintf(hdl, "%s@%s", di->ds, di->tmpsnap);
        return (0);
}

static void
teardown_differ_info(differ_info_t *di)
{
        free(di->ds);
        free(di->dsmnt);
        free(di->fromsnap);
        free(di->frommnt);
        free(di->tosnap);
        free(di->tmpsnap);
        free(di->tomnt);
        (void) close(di->cleanupfd);
}

static int
get_snapshot_names(differ_info_t *di, const char *fromsnap,
    const char *tosnap)
{
        libzfs_handle_t *hdl = di->zhp->zfs_hdl;
        char *atptrf = NULL;
        char *atptrt = NULL;
        int fdslen, fsnlen;
        int tdslen, tsnlen;

        /*
         * Can accept
         *    dataset@snap1
         *    dataset@snap1 dataset@snap2
         *    dataset@snap1 @snap2
         *    dataset@snap1 dataset
         *    @snap1 dataset@snap2
         */
        if (tosnap == NULL) {
                /* only a from snapshot given, must be valid */
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN,
                    "Badly formed snapshot name %s"), fromsnap);

                if (!zfs_validate_name(hdl, fromsnap, ZFS_TYPE_SNAPSHOT,
                    B_FALSE)) {
                        return (zfs_error(hdl, EZFS_INVALIDNAME,
                            di->errbuf));
                }

                atptrf = strchr(fromsnap, '@');
                ASSERT(atptrf != NULL);
                fdslen = atptrf - fromsnap;

                di->fromsnap = zfs_strdup(hdl, fromsnap);
                di->ds = zfs_strdup(hdl, fromsnap);
                di->ds[fdslen] = '\0';

                /* the to snap will be a just-in-time snap of the head */
                return (make_temp_snapshot(di));
        }

        (void) snprintf(di->errbuf, sizeof (di->errbuf),
            dgettext(TEXT_DOMAIN,
            "Unable to determine which snapshots to compare"));

        atptrf = strchr(fromsnap, '@');
        atptrt = strchr(tosnap, '@');
        fdslen = atptrf ? atptrf - fromsnap : strlen(fromsnap);
        tdslen = atptrt ? atptrt - tosnap : strlen(tosnap);
        fsnlen = strlen(fromsnap) - fdslen;     /* includes @ sign */
        tsnlen = strlen(tosnap) - tdslen;       /* includes @ sign */

        if (fsnlen <= 1 || tsnlen == 1 || (fdslen == 0 && tdslen == 0) ||
            (fsnlen == 0 && tsnlen == 0)) {
                return (zfs_error(hdl, EZFS_INVALIDNAME, di->errbuf));
        } else if ((fdslen > 0 && tdslen > 0) &&
            ((tdslen != fdslen || strncmp(fromsnap, tosnap, fdslen) != 0))) {
                /*
                 * not the same dataset name, might be okay if
                 * tosnap is a clone of a fromsnap descendant.
                 */
                char origin[ZFS_MAX_DATASET_NAME_LEN];
                zprop_source_t src;
                zfs_handle_t *zhp;

                di->ds = zfs_alloc(di->zhp->zfs_hdl, tdslen + 1);
                (void) strncpy(di->ds, tosnap, tdslen);
                di->ds[tdslen] = '\0';

                zhp = zfs_open(hdl, di->ds, ZFS_TYPE_FILESYSTEM);
                while (zhp != NULL) {
                        if (zfs_prop_get(zhp, ZFS_PROP_ORIGIN, origin,
                            sizeof (origin), &src, NULL, 0, B_FALSE) != 0) {
                                (void) zfs_close(zhp);
                                zhp = NULL;
                                break;
                        }
                        if (strncmp(origin, fromsnap, fsnlen) == 0)
                                break;

                        (void) zfs_close(zhp);
                        zhp = zfs_open(hdl, origin, ZFS_TYPE_FILESYSTEM);
                }

                if (zhp == NULL) {
                        (void) snprintf(di->errbuf, sizeof (di->errbuf),
                            dgettext(TEXT_DOMAIN,
                            "Not an earlier snapshot from the same fs"));
                        return (zfs_error(hdl, EZFS_INVALIDNAME, di->errbuf));
                } else {
                        (void) zfs_close(zhp);
                }

                di->isclone = B_TRUE;
                di->fromsnap = zfs_strdup(hdl, fromsnap);
                if (tsnlen) {
                        di->tosnap = zfs_strdup(hdl, tosnap);
                } else {
                        return (make_temp_snapshot(di));
                }
        } else {
                int dslen = fdslen ? fdslen : tdslen;

                di->ds = zfs_alloc(hdl, dslen + 1);
                (void) strncpy(di->ds, fdslen ? fromsnap : tosnap, dslen);
                di->ds[dslen] = '\0';

                di->fromsnap = zfs_asprintf(hdl, "%s%s", di->ds, atptrf);
                if (tsnlen) {
                        di->tosnap = zfs_asprintf(hdl, "%s%s", di->ds, atptrt);
                } else {
                        return (make_temp_snapshot(di));
                }
        }
        return (0);
}

static int
get_mountpoint(differ_info_t *di, char *dsnm, char **mntpt)
{
        boolean_t mounted;

        mounted = is_mounted(di->zhp->zfs_hdl, dsnm, mntpt);
        if (mounted == B_FALSE) {
                (void) snprintf(di->errbuf, sizeof (di->errbuf),
                    dgettext(TEXT_DOMAIN,
                    "Cannot diff an unmounted snapshot"));
                return (zfs_error(di->zhp->zfs_hdl, EZFS_BADTYPE, di->errbuf));
        }

        /* Avoid a double slash at the beginning of root-mounted datasets */
        if (**mntpt == '/' && *(*mntpt + 1) == '\0')
                **mntpt = '\0';
        return (0);
}

static int
get_mountpoints(differ_info_t *di)
{
        char *strptr;
        char *frommntpt;

        /*
         * first get the mountpoint for the parent dataset
         */
        if (get_mountpoint(di, di->ds, &di->dsmnt) != 0)
                return (-1);

        strptr = strchr(di->tosnap, '@');
        ASSERT3P(strptr, !=, NULL);
        di->tomnt = zfs_asprintf(di->zhp->zfs_hdl, "%s%s%s", di->dsmnt,
            ZDIFF_SNAPDIR, ++strptr);

        strptr = strchr(di->fromsnap, '@');
        ASSERT3P(strptr, !=, NULL);

        frommntpt = di->dsmnt;
        if (di->isclone) {
                char *mntpt;
                int err;

                *strptr = '\0';
                err = get_mountpoint(di, di->fromsnap, &mntpt);
                *strptr = '@';
                if (err != 0)
                        return (-1);
                frommntpt = mntpt;
        }

        di->frommnt = zfs_asprintf(di->zhp->zfs_hdl, "%s%s%s", frommntpt,
            ZDIFF_SNAPDIR, ++strptr);

        if (di->isclone)
                free(frommntpt);

        return (0);
}

static int
setup_differ_info(zfs_handle_t *zhp, const char *fromsnap,
    const char *tosnap, differ_info_t *di)
{
        di->zhp = zhp;

        di->cleanupfd = open(ZFS_DEV, O_RDWR|O_EXCL);
        VERIFY(di->cleanupfd >= 0);

        if (get_snapshot_names(di, fromsnap, tosnap) != 0)
                return (-1);

        if (get_mountpoints(di) != 0)
                return (-1);

        if (find_shares_object(di) != 0)
                return (-1);

        return (0);
}

int
zfs_show_diffs(zfs_handle_t *zhp, int outfd, const char *fromsnap,
    const char *tosnap, int flags)
{
        zfs_cmd_t zc = { 0 };
        char errbuf[1024];
        differ_info_t di = { 0 };
        pthread_t tid;
        int pipefd[2];
        int iocerr;

        (void) snprintf(errbuf, sizeof (errbuf),
            dgettext(TEXT_DOMAIN, "zfs diff failed"));

        if (setup_differ_info(zhp, fromsnap, tosnap, &di)) {
                teardown_differ_info(&di);
                return (-1);
        }

        if (pipe(pipefd)) {
                zfs_error_aux(zhp->zfs_hdl, strerror(errno));
                teardown_differ_info(&di);
                return (zfs_error(zhp->zfs_hdl, EZFS_PIPEFAILED, errbuf));
        }

        di.scripted = (flags & ZFS_DIFF_PARSEABLE);
        di.classify = (flags & ZFS_DIFF_CLASSIFY);
        di.timestamped = (flags & ZFS_DIFF_TIMESTAMP);

        di.outputfd = outfd;
        di.datafd = pipefd[0];

        if (pthread_create(&tid, NULL, differ, &di)) {
                zfs_error_aux(zhp->zfs_hdl, strerror(errno));
                (void) close(pipefd[0]);
                (void) close(pipefd[1]);
                teardown_differ_info(&di);
                return (zfs_error(zhp->zfs_hdl,
                    EZFS_THREADCREATEFAILED, errbuf));
        }

        /* do the ioctl() */
        (void) strlcpy(zc.zc_value, di.fromsnap, strlen(di.fromsnap) + 1);
        (void) strlcpy(zc.zc_name, di.tosnap, strlen(di.tosnap) + 1);
        zc.zc_cookie = pipefd[1];

        iocerr = ioctl(zhp->zfs_hdl->libzfs_fd, ZFS_IOC_DIFF, &zc);
        if (iocerr != 0) {
                (void) snprintf(errbuf, sizeof (errbuf),
                    dgettext(TEXT_DOMAIN, "Unable to obtain diffs"));
                if (errno == EPERM) {
                        zfs_error_aux(zhp->zfs_hdl, dgettext(TEXT_DOMAIN,
                            "\n   The sys_mount privilege or diff delegated "
                            "permission is needed\n   to execute the "
                            "diff ioctl"));
                } else if (errno == EXDEV) {
                        zfs_error_aux(zhp->zfs_hdl, dgettext(TEXT_DOMAIN,
                            "\n   Not an earlier snapshot from the same fs"));
                } else if (errno != EPIPE || di.zerr == 0) {
                        zfs_error_aux(zhp->zfs_hdl, strerror(errno));
                }
                (void) close(pipefd[1]);
                (void) pthread_cancel(tid);
                (void) pthread_join(tid, NULL);
                teardown_differ_info(&di);
                if (di.zerr != 0 && di.zerr != EPIPE) {
                        zfs_error_aux(zhp->zfs_hdl, strerror(di.zerr));
                        return (zfs_error(zhp->zfs_hdl, EZFS_DIFF, di.errbuf));
                } else {
                        return (zfs_error(zhp->zfs_hdl, EZFS_DIFFDATA, errbuf));
                }
        }

        (void) close(pipefd[1]);
        (void) pthread_join(tid, NULL);

        if (di.zerr != 0) {
                zfs_error_aux(zhp->zfs_hdl, strerror(di.zerr));
                return (zfs_error(zhp->zfs_hdl, EZFS_DIFF, di.errbuf));
        }
        teardown_differ_info(&di);
        return (0);
}