libzfs/common/libzfs_diff.c

/*
 * 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 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 == 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 {
        (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) {
        /* Let it slide, if in the delete queue on from side */
        if (di->zerr == ENOENT && sb.zs_links == 0) {
            di->zerr = 0;
            return (0);
        }
        return (-1);
    }

    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);
}