btrfs-progs: import ulist

[btrfs-progs-unstable/devel.git] / cmds-scrub.c

/*
 * Copyright (C) 2011 STRATO.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include "kerncompat.h"

#include <sys/ioctl.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/syscall.h>
#include <poll.h>
#include <sys/file.h>
#include <uuid/uuid.h>
#include <fcntl.h>
#include <unistd.h>
#include <pthread.h>
#include <ctype.h>
#include <signal.h>
#include <stdarg.h>

#include "ctree.h"
#include "ioctl.h"
#include "utils.h"
#include "volumes.h"
#include "disk-io.h"

#include "commands.h"

static const char * const scrub_cmd_group_usage[] = {
        "btrfs scrub <command> [options] <path>|<device>",
        NULL
};

#define SCRUB_DATA_FILE "/var/lib/btrfs/scrub.status"
#define SCRUB_PROGRESS_SOCKET_PATH "/var/lib/btrfs/scrub.progress"
#define SCRUB_FILE_VERSION_PREFIX "scrub status"
#define SCRUB_FILE_VERSION "1"

struct scrub_stats {
        time_t t_start;
        time_t t_resumed;
        u64 duration;
        u64 finished;
        u64 canceled;
};

/* TBD: replace with #include "linux/ioprio.h" in some years */
#if !defined (IOPRIO_H)
#define IOPRIO_WHO_PROCESS 1
#define IOPRIO_CLASS_SHIFT 13
#define IOPRIO_PRIO_VALUE(class, data) \
                (((class) << IOPRIO_CLASS_SHIFT) | (data))
#define IOPRIO_CLASS_IDLE 3
#endif

struct scrub_progress {
        struct btrfs_ioctl_scrub_args scrub_args;
        int fd;
        int ret;
        int skip;
        struct scrub_stats stats;
        struct scrub_file_record *resumed;
        int ioctl_errno;
        pthread_mutex_t progress_mutex;
        int ioprio_class;
        int ioprio_classdata;
};

struct scrub_file_record {
        u8 fsid[BTRFS_FSID_SIZE];
        u64 devid;
        struct scrub_stats stats;
        struct btrfs_scrub_progress p;
};

struct scrub_progress_cycle {
        int fdmnt;
        int prg_fd;
        int do_record;
        struct btrfs_ioctl_fs_info_args *fi;
        struct scrub_progress *progress;
        struct scrub_progress *shared_progress;
        pthread_mutex_t *write_mutex;
};

struct scrub_fs_stat {
        struct btrfs_scrub_progress p;
        struct scrub_stats s;
        int i;
};

static void print_scrub_full(struct btrfs_scrub_progress *sp)
{
        printf("\tdata_extents_scrubbed: %lld\n", sp->data_extents_scrubbed);
        printf("\ttree_extents_scrubbed: %lld\n", sp->tree_extents_scrubbed);
        printf("\tdata_bytes_scrubbed: %lld\n", sp->data_bytes_scrubbed);
        printf("\ttree_bytes_scrubbed: %lld\n", sp->tree_bytes_scrubbed);
        printf("\tread_errors: %lld\n", sp->read_errors);
        printf("\tcsum_errors: %lld\n", sp->csum_errors);
        printf("\tverify_errors: %lld\n", sp->verify_errors);
        printf("\tno_csum: %lld\n", sp->no_csum);
        printf("\tcsum_discards: %lld\n", sp->csum_discards);
        printf("\tsuper_errors: %lld\n", sp->super_errors);
        printf("\tmalloc_errors: %lld\n", sp->malloc_errors);
        printf("\tuncorrectable_errors: %lld\n", sp->uncorrectable_errors);
        printf("\tunverified_errors: %lld\n", sp->unverified_errors);
        printf("\tcorrected_errors: %lld\n", sp->corrected_errors);
        printf("\tlast_physical: %lld\n", sp->last_physical);
}

#define ERR(test, ...) do {                     \
        if (test)                               \
                fprintf(stderr, __VA_ARGS__);   \
} while (0)

#define PRINT_SCRUB_ERROR(test, desc) do {      \
        if (test)                               \
                printf(" %s=%llu", desc, test); \
} while (0)

static void print_scrub_summary(struct btrfs_scrub_progress *p)
{
        u64 err_cnt;
        u64 err_cnt2;

        err_cnt = p->read_errors +
                        p->csum_errors +
                        p->verify_errors +
                        p->super_errors;

        err_cnt2 = p->corrected_errors + p->uncorrectable_errors;

        if (p->malloc_errors)
                printf("*** WARNING: memory allocation failed while scrubbing. "
                       "results may be inaccurate\n");

        printf("\ttotal bytes scrubbed: %s with %llu errors\n",
                pretty_size(p->data_bytes_scrubbed + p->tree_bytes_scrubbed),
                max(err_cnt, err_cnt2));

        if (err_cnt || err_cnt2) {
                printf("\terror details:");
                PRINT_SCRUB_ERROR(p->read_errors, "read");
                PRINT_SCRUB_ERROR(p->super_errors, "super");
                PRINT_SCRUB_ERROR(p->verify_errors, "verify");
                PRINT_SCRUB_ERROR(p->csum_errors, "csum");
                printf("\n");
                printf("\tcorrected errors: %llu, uncorrectable errors: %llu, "
                        "unverified errors: %llu\n", p->corrected_errors,
                        p->uncorrectable_errors, p->unverified_errors);
        }
}

#define _SCRUB_FS_STAT(p, name, fs_stat) do {   \
        fs_stat->p.name += p->name;             \
} while (0)

#define _SCRUB_FS_STAT_MIN(ss, name, fs_stat)   \
do {                                            \
        if (fs_stat->s.name > ss->name) {       \
                fs_stat->s.name = ss->name;     \
        }                                       \
} while (0)

#define _SCRUB_FS_STAT_ZMIN(ss, name, fs_stat)                  \
do {                                                            \
        if (!fs_stat->s.name || fs_stat->s.name > ss->name) {   \
                fs_stat->s.name = ss->name;                     \
        }                                                       \
} while (0)

#define _SCRUB_FS_STAT_ZMAX(ss, name, fs_stat)                          \
do {                                                                    \
        if (!(fs_stat)->s.name || (fs_stat)->s.name < (ss)->name) {     \
                (fs_stat)->s.name = (ss)->name;                         \
        }                                                               \
} while (0)

static void add_to_fs_stat(struct btrfs_scrub_progress *p,
                                struct scrub_stats *ss,
                                struct scrub_fs_stat *fs_stat)
{
        _SCRUB_FS_STAT(p, data_extents_scrubbed, fs_stat);
        _SCRUB_FS_STAT(p, tree_extents_scrubbed, fs_stat);
        _SCRUB_FS_STAT(p, data_bytes_scrubbed, fs_stat);
        _SCRUB_FS_STAT(p, tree_bytes_scrubbed, fs_stat);
        _SCRUB_FS_STAT(p, read_errors, fs_stat);
        _SCRUB_FS_STAT(p, csum_errors, fs_stat);
        _SCRUB_FS_STAT(p, verify_errors, fs_stat);
        _SCRUB_FS_STAT(p, no_csum, fs_stat);
        _SCRUB_FS_STAT(p, csum_discards, fs_stat);
        _SCRUB_FS_STAT(p, super_errors, fs_stat);
        _SCRUB_FS_STAT(p, malloc_errors, fs_stat);
        _SCRUB_FS_STAT(p, uncorrectable_errors, fs_stat);
        _SCRUB_FS_STAT(p, corrected_errors, fs_stat);
        _SCRUB_FS_STAT(p, last_physical, fs_stat);
        _SCRUB_FS_STAT_ZMIN(ss, t_start, fs_stat);
        _SCRUB_FS_STAT_ZMIN(ss, t_resumed, fs_stat);
        _SCRUB_FS_STAT_ZMAX(ss, duration, fs_stat);
        _SCRUB_FS_STAT_ZMAX(ss, canceled, fs_stat);
        _SCRUB_FS_STAT_MIN(ss, finished, fs_stat);
}

static void init_fs_stat(struct scrub_fs_stat *fs_stat)
{
        memset(fs_stat, 0, sizeof(*fs_stat));
        fs_stat->s.finished = 1;
}

static void _print_scrub_ss(struct scrub_stats *ss)
{
        char t[4096];
        struct tm tm;

        if (!ss || !ss->t_start) {
                printf("\tno stats available\n");
                return;
        }
        if (ss->t_resumed) {
                localtime_r(&ss->t_resumed, &tm);
                strftime(t, sizeof(t), "%c", &tm);
                t[sizeof(t) - 1] = '\0';
                printf("\tscrub resumed at %s", t);
        } else {
                localtime_r(&ss->t_start, &tm);
                strftime(t, sizeof(t), "%c", &tm);
                t[sizeof(t) - 1] = '\0';
                printf("\tscrub started at %s", t);
        }
        if (ss->finished && !ss->canceled) {
                printf(" and finished after %llu seconds\n",
                       ss->duration);
        } else if (ss->canceled) {
                printf(" and was aborted after %llu seconds\n",
                       ss->duration);
        } else {
                printf(", running for %llu seconds\n", ss->duration);
        }
}

static void print_scrub_dev(struct btrfs_ioctl_dev_info_args *di,
                                struct btrfs_scrub_progress *p, int raw,
                                const char *append, struct scrub_stats *ss)
{
        printf("scrub device %s (id %llu) %s\n", di->path, di->devid,
               append ? append : "");

        _print_scrub_ss(ss);

        if (p) {
                if (raw)
                        print_scrub_full(p);
                else
                        print_scrub_summary(p);
        }
}

static void print_fs_stat(struct scrub_fs_stat *fs_stat, int raw)
{
        _print_scrub_ss(&fs_stat->s);

        if (raw)
                print_scrub_full(&fs_stat->p);
        else
                print_scrub_summary(&fs_stat->p);
}

static void free_history(struct scrub_file_record **last_scrubs)
{
        struct scrub_file_record **l = last_scrubs;
        if (!l || IS_ERR(l))
                return;
        while (*l)
                free(*l++);
        free(last_scrubs);
}

/*
 * cancels a running scrub and makes the master process record the current
 * progress status before exiting.
 */
static int cancel_fd = -1;
static void scrub_sigint_record_progress(int signal)
{
        int ret;

        ret = ioctl(cancel_fd, BTRFS_IOC_SCRUB_CANCEL, NULL);
        if (ret < 0)
                perror("Scrub cancel failed");
}

static int scrub_handle_sigint_parent(void)
{
        struct sigaction sa = {
                .sa_handler = SIG_IGN,
                .sa_flags = SA_RESTART,
        };

        return sigaction(SIGINT, &sa, NULL);
}

static int scrub_handle_sigint_child(int fd)
{
        struct sigaction sa = {
                .sa_handler = fd == -1 ? SIG_DFL : scrub_sigint_record_progress,
        };

        cancel_fd = fd;
        return sigaction(SIGINT, &sa, NULL);
}

static int scrub_datafile(const char *fn_base, const char *fn_local,
                                const char *fn_tmp, char *datafile, int size)
{
        int ret;
        int end = size - 2;

        datafile[end + 1] = '\0';
        strncpy(datafile, fn_base, end);
        ret = strlen(datafile);

        if (ret + 1 > end)
                return -EOVERFLOW;

        datafile[ret] = '.';
        strncpy(datafile + ret + 1, fn_local, end - ret - 1);
        ret = strlen(datafile);

        if (ret + 1 > end)
                return -EOVERFLOW;

        if (fn_tmp) {
                datafile[ret] = '_';
                strncpy(datafile + ret + 1, fn_tmp, end - ret - 1);
                ret = strlen(datafile);

                if (ret > end)
                        return -EOVERFLOW;
        }

        return 0;
}

static int scrub_open_file(const char *datafile, int m)
{
        int fd;
        int ret;

        fd = open(datafile, m, 0600);
        if (fd < 0)
                return -errno;

        ret = flock(fd, LOCK_EX|LOCK_NB);
        if (ret) {
                ret = errno;
                close(fd);
                return -ret;
        }

        return fd;
}

static int scrub_open_file_r(const char *fn_base, const char *fn_local)
{
        int ret;
        char datafile[BTRFS_PATH_NAME_MAX + 1];
        ret = scrub_datafile(fn_base, fn_local, NULL,
                                datafile, sizeof(datafile));
        if (ret < 0)
                return ret;
        return scrub_open_file(datafile, O_RDONLY);
}

static int scrub_open_file_w(const char *fn_base, const char *fn_local,
                                const char *tmp)
{
        int ret;
        char datafile[BTRFS_PATH_NAME_MAX + 1];
        ret = scrub_datafile(fn_base, fn_local, tmp,
                                datafile, sizeof(datafile));
        if (ret < 0)
                return ret;
        return scrub_open_file(datafile, O_WRONLY|O_CREAT);
}

static int scrub_rename_file(const char *fn_base, const char *fn_local,
                                const char *tmp)
{
        int ret;
        char datafile_old[BTRFS_PATH_NAME_MAX + 1];
        char datafile_new[BTRFS_PATH_NAME_MAX + 1];
        ret = scrub_datafile(fn_base, fn_local, tmp,
                                datafile_old, sizeof(datafile_old));
        if (ret < 0)
                return ret;
        ret = scrub_datafile(fn_base, fn_local, NULL,
                                datafile_new, sizeof(datafile_new));
        if (ret < 0)
                return ret;
        ret = rename(datafile_old, datafile_new);
        return ret ? -errno : 0;
}

#define _SCRUB_KVREAD(ret, i, name, avail, l, dest) if (ret == 0) {       \
        ret = scrub_kvread(i, sizeof(#name), avail, l, #name, dest.name); \
}

/*
 * returns 0 if the key did not match (nothing was read)
 *         1 if the key did match (success)
 *        -1 if the key did match and an error occured
 */
static int scrub_kvread(int *i, int len, int avail, const char *buf,
                        const char *key, u64 *dest)
{
        int j;

        if (*i + len + 1 < avail && strncmp(&buf[*i], key, len - 1) == 0) {
                *i += len - 1;
                if (buf[*i] != ':')
                        return -1;
                *i += 1;
                for (j = 0; isdigit(buf[*i + j]) && *i + j < avail; ++j)
                        ;
                if (*i + j >= avail)
                        return -1;
                *dest = atoll(&buf[*i]);
                *i += j;
                return 1;
        }

        return 0;
}

#define _SCRUB_INVALID do {                                             \
        if (report_errors)                                              \
                fprintf(stderr, "WARNING: invalid data in line %d pos " \
                        "%d state %d (near \"%.*s\") at %s:%d\n",       \
                        lineno, i, state, 20 > avail ? avail : 20,      \
                        l + i,  __FILE__, __LINE__);                    \
        goto skip;                                                      \
} while (0)

static struct scrub_file_record **scrub_read_file(int fd, int report_errors)
{
        int avail = 0;
        int old_avail = 0;
        char l[16 * 1024];
        int state = 0;
        int curr = -1;
        int i = 0;
        int j;
        int ret;
        int eof = 0;
        int lineno = 0;
        u64 version;
        char empty_uuid[BTRFS_FSID_SIZE] = {0};
        struct scrub_file_record **p = NULL;

        if (fd < 0)
                return ERR_PTR(-EINVAL);

again:
        old_avail = avail - i;
        BUG_ON(old_avail < 0);
        if (old_avail)
                memmove(l, l + i, old_avail);
        avail = read(fd, l + old_avail, sizeof(l) - old_avail);
        if (avail == 0)
                eof = 1;
        if (avail == 0 && old_avail == 0) {
                if (curr >= 0 &&
                    memcmp(p[curr]->fsid, empty_uuid, BTRFS_FSID_SIZE) == 0) {
                        p[curr] = NULL;
                } else if (curr == -1) {
                        p = ERR_PTR(-ENODATA);
                }
                return p;
        }
        if (avail == -1)
                return ERR_PTR(-errno);
        avail += old_avail;

        i = 0;
        while (i < avail) {
                switch (state) {
                case 0: /* start of file */
                        ret = scrub_kvread(&i,
                                sizeof(SCRUB_FILE_VERSION_PREFIX), avail, l,
                                SCRUB_FILE_VERSION_PREFIX, &version);
                        if (ret != 1)
                                _SCRUB_INVALID;
                        if (version != atoll(SCRUB_FILE_VERSION))
                                return ERR_PTR(-ENOTSUP);
                        state = 6;
                        continue;
                case 1: /* start of line, alloc */
                        /*
                         * this state makes sure we have a complete line in
                         * further processing, so we don't need wrap-tracking
                         * everywhere.
                         */
                        if (!eof && !memchr(l + i, '\n', avail - i))
                                goto again;
                        ++lineno;
                        if (curr > -1 && memcmp(p[curr]->fsid, empty_uuid,
                                                BTRFS_FSID_SIZE) == 0) {
                                state = 2;
                                continue;
                        }
                        ++curr;
                        p = realloc(p, (curr + 2) * sizeof(*p));
                        if (p)
                                p[curr] = malloc(sizeof(**p));
                        if (!p || !p[curr])
                                return ERR_PTR(-errno);
                        memset(p[curr], 0, sizeof(**p));
                        p[curr + 1] = NULL;
                        ++state;
                        /* fall through */
                case 2: /* start of line, skip space */
                        while (isspace(l[i]) && i < avail) {
                                if (l[i] == '\n')
                                        ++lineno;
                                ++i;
                        }
                        if (i >= avail ||
                            (!eof && !memchr(l + i, '\n', avail - i)))
                                goto again;
                        ++state;
                        /* fall through */
                case 3: /* read fsid */
                        if (i == avail)
                                continue;
                        for (j = 0; l[i + j] != ':' && i + j < avail; ++j)
                                ;
                        if (i + j + 1 >= avail)
                                _SCRUB_INVALID;
                        if (j != 36)
                                _SCRUB_INVALID;
                        l[i + j] = '\0';
                        ret = uuid_parse(l + i, p[curr]->fsid);
                        if (ret)
                                _SCRUB_INVALID;
                        i += j + 1;
                        ++state;
                        /* fall through */
                case 4: /* read dev id */
                        for (j = 0; isdigit(l[i + j]) && i+j < avail; ++j)
                                ;
                        if (j == 0 || i + j + 1 >= avail)
                                _SCRUB_INVALID;
                        p[curr]->devid = atoll(&l[i]);
                        i += j + 1;
                        ++state;
                        /* fall through */
                case 5: /* read key/value pair */
                        ret = 0;
                        _SCRUB_KVREAD(ret, &i, data_extents_scrubbed, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, data_extents_scrubbed, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, tree_extents_scrubbed, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, data_bytes_scrubbed, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, tree_bytes_scrubbed, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, read_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, csum_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, verify_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, no_csum, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, csum_discards, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, super_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, malloc_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, uncorrectable_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, corrected_errors, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, last_physical, avail, l,
                                        &p[curr]->p);
                        _SCRUB_KVREAD(ret, &i, finished, avail, l,
                                        &p[curr]->stats);
                        _SCRUB_KVREAD(ret, &i, t_start, avail, l,
                                        (u64 *)&p[curr]->stats);
                        _SCRUB_KVREAD(ret, &i, t_resumed, avail, l,
                                        (u64 *)&p[curr]->stats);
                        _SCRUB_KVREAD(ret, &i, duration, avail, l,
                                        (u64 *)&p[curr]->stats);
                        _SCRUB_KVREAD(ret, &i, canceled, avail, l,
                                        &p[curr]->stats);
                        if (ret != 1)
                                _SCRUB_INVALID;
                        ++state;
                        /* fall through */
                case 6: /* after number */
                        if (l[i] == '|')
                                state = 5;
                        else if (l[i] == '\n')
                                state = 1;
                        else
                                _SCRUB_INVALID;
                        ++i;
                        continue;
                case 99: /* skip rest of line */
skip:
                        state = 99;
                        do {
                                ++i;
                                if (l[i - 1] == '\n') {
                                        state = 1;
                                        break;
                                }
                        } while (i < avail);
                        continue;
                }
                BUG();
        }
        goto again;
}

static int scrub_write_buf(int fd, const void *data, int len)
{
        int ret;
        ret = write(fd, data, len);
        return ret - len;
}

static int scrub_writev(int fd, char *buf, int max, const char *fmt, ...)
                                __attribute__ ((format (printf, 4, 5)));
static int scrub_writev(int fd, char *buf, int max, const char *fmt, ...)
{
        int ret;
        va_list args;

        va_start(args, fmt);
        ret = vsnprintf(buf, max, fmt, args);
        va_end(args);
        if (ret >= max)
                return ret - max;
        return scrub_write_buf(fd, buf, ret);
}

#define _SCRUB_SUM(dest, data, name) dest->scrub_args.progress.name =   \
                        data->resumed->p.name + data->scrub_args.progress.name

static struct scrub_progress *scrub_resumed_stats(struct scrub_progress *data,
                                                  struct scrub_progress *dest)
{
        if (!data->resumed || data->skip)
                return data;

        _SCRUB_SUM(dest, data, data_extents_scrubbed);
        _SCRUB_SUM(dest, data, tree_extents_scrubbed);
        _SCRUB_SUM(dest, data, data_bytes_scrubbed);
        _SCRUB_SUM(dest, data, tree_bytes_scrubbed);
        _SCRUB_SUM(dest, data, read_errors);
        _SCRUB_SUM(dest, data, csum_errors);
        _SCRUB_SUM(dest, data, verify_errors);
        _SCRUB_SUM(dest, data, no_csum);
        _SCRUB_SUM(dest, data, csum_discards);
        _SCRUB_SUM(dest, data, super_errors);
        _SCRUB_SUM(dest, data, malloc_errors);
        _SCRUB_SUM(dest, data, uncorrectable_errors);
        _SCRUB_SUM(dest, data, corrected_errors);
        _SCRUB_SUM(dest, data, last_physical);
        dest->stats.canceled = data->stats.canceled;
        dest->stats.finished = data->stats.finished;
        dest->stats.t_resumed = data->stats.t_start;
        dest->stats.t_start = data->resumed->stats.t_start;
        dest->stats.duration = data->resumed->stats.duration +
                                                        data->stats.duration;
        dest->scrub_args.devid = data->scrub_args.devid;
        return dest;
}

#define _SCRUB_KVWRITE(fd, buf, name, use)              \
        scrub_kvwrite(fd, buf, sizeof(buf), #name,      \
                        use->scrub_args.progress.name)

#define _SCRUB_KVWRITE_STATS(fd, buf, name, use)        \
        scrub_kvwrite(fd, buf, sizeof(buf), #name,      \
                        use->stats.name)

static int scrub_kvwrite(int fd, char *buf, int max, const char *key, u64 val)
{
        return scrub_writev(fd, buf, max, "|%s:%lld", key, val);
}

static int scrub_write_file(int fd, const char *fsid,
                                struct scrub_progress *data, int n)
{
        int ret = 0;
        int i;
        char buf[1024];
        struct scrub_progress local;
        struct scrub_progress *use;

        if (n < 1)
                return -EINVAL;

        /* each -1 is to subtract one \0 byte, the + 2 is for ':' and '\n' */
        ret = scrub_write_buf(fd, SCRUB_FILE_VERSION_PREFIX ":"
                                SCRUB_FILE_VERSION "\n",
                                (sizeof(SCRUB_FILE_VERSION_PREFIX) - 1) +
                                (sizeof(SCRUB_FILE_VERSION) - 1) + 2);
        if (ret)
                return -EOVERFLOW;

        for (i = 0; i < n; ++i) {
                use = scrub_resumed_stats(&data[i], &local);
                if (scrub_write_buf(fd, fsid, strlen(fsid)) ||
                    scrub_write_buf(fd, ":", 1) ||
                    scrub_writev(fd, buf, sizeof(buf), "%lld",
                                        use->scrub_args.devid) ||
                    scrub_write_buf(fd, buf, ret) ||
                    _SCRUB_KVWRITE(fd, buf, data_extents_scrubbed, use) ||
                    _SCRUB_KVWRITE(fd, buf, tree_extents_scrubbed, use) ||
                    _SCRUB_KVWRITE(fd, buf, data_bytes_scrubbed, use) ||
                    _SCRUB_KVWRITE(fd, buf, tree_bytes_scrubbed, use) ||
                    _SCRUB_KVWRITE(fd, buf, read_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, csum_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, verify_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, no_csum, use) ||
                    _SCRUB_KVWRITE(fd, buf, csum_discards, use) ||
                    _SCRUB_KVWRITE(fd, buf, super_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, malloc_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, uncorrectable_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, corrected_errors, use) ||
                    _SCRUB_KVWRITE(fd, buf, last_physical, use) ||
                    _SCRUB_KVWRITE_STATS(fd, buf, t_start, use) ||
                    _SCRUB_KVWRITE_STATS(fd, buf, t_resumed, use) ||
                    _SCRUB_KVWRITE_STATS(fd, buf, duration, use) ||
                    _SCRUB_KVWRITE_STATS(fd, buf, canceled, use) ||
                    _SCRUB_KVWRITE_STATS(fd, buf, finished, use) ||
                    scrub_write_buf(fd, "\n", 1)) {
                        return -EOVERFLOW;
                }
        }

        return 0;
}

static int scrub_write_progress(pthread_mutex_t *m, const char *fsid,
                                struct scrub_progress *data, int n)
{
        int ret;
        int err;
        int fd = -1;
        int old;

        ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &old);
        if (ret) {
                err = -ret;
                goto out3;
        }

        ret = pthread_mutex_lock(m);
        if (ret) {
                err = -ret;
                goto out2;
        }

        fd = scrub_open_file_w(SCRUB_DATA_FILE, fsid, "tmp");
        if (fd < 0) {
                err = fd;
                goto out1;
        }
        err = scrub_write_file(fd, fsid, data, n);
        if (err)
                goto out1;
        err = scrub_rename_file(SCRUB_DATA_FILE, fsid, "tmp");
        if (err)
                goto out1;

out1:
        if (fd >= 0) {
                ret = close(fd);
                if (ret)
                        err = -errno;
        }

        ret = pthread_mutex_unlock(m);
        if (ret && !err)
                err = -ret;

out2:
        ret = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &old);
        if (ret && !err)
                err = -ret;

out3:
        return err;
}

static void *scrub_one_dev(void *ctx)
{
        struct scrub_progress *sp = ctx;
        int ret;
        struct timeval tv;

        sp->stats.canceled = 0;
        sp->stats.duration = 0;
        sp->stats.finished = 0;

        ret = syscall(SYS_ioprio_set, IOPRIO_WHO_PROCESS, 0,
                      IOPRIO_PRIO_VALUE(sp->ioprio_class,
                                        sp->ioprio_classdata));
        if (ret)
                fprintf(stderr,
                        "WARNING: setting ioprio failed: %s (ignored).\n",
                        strerror(errno));

        ret = ioctl(sp->fd, BTRFS_IOC_SCRUB, &sp->scrub_args);
        gettimeofday(&tv, NULL);
        sp->ret = ret;
        sp->stats.duration = tv.tv_sec - sp->stats.t_start;
        sp->stats.canceled = !!ret;
        sp->ioctl_errno = errno;
        ret = pthread_mutex_lock(&sp->progress_mutex);
        if (ret)
                return ERR_PTR(-ret);
        sp->stats.finished = 1;
        ret = pthread_mutex_unlock(&sp->progress_mutex);
        if (ret)
                return ERR_PTR(-ret);

        return NULL;
}

static void *progress_one_dev(void *ctx)
{
        struct scrub_progress *sp = ctx;

        sp->ret = ioctl(sp->fd, BTRFS_IOC_SCRUB_PROGRESS, &sp->scrub_args);
        sp->ioctl_errno = errno;

        return NULL;
}

/* nb: returns a negative errno via ERR_PTR */
static void *scrub_progress_cycle(void *ctx)
{
        int ret = 0;
        int  perr = 0;  /* positive / pthread error returns */
        int old;
        int i;
        char fsid[BTRFS_UUID_UNPARSED_SIZE];
        struct scrub_progress *sp;
        struct scrub_progress *sp_last;
        struct scrub_progress *sp_shared;
        struct timeval tv;
        struct scrub_progress_cycle *spc = ctx;
        int ndev = spc->fi->num_devices;
        int this = 1;
        int last = 0;
        int peer_fd = -1;
        struct pollfd accept_poll_fd = {
                .fd = spc->prg_fd,
                .events = POLLIN,
                .revents = 0,
        };
        struct pollfd write_poll_fd = {
                .events = POLLOUT,
                .revents = 0,
        };
        struct sockaddr_un peer;
        socklen_t peer_size = sizeof(peer);

        perr = pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &old);
        if (perr)
                goto out;

        uuid_unparse(spc->fi->fsid, fsid);

        for (i = 0; i < ndev; ++i) {
                sp = &spc->progress[i];
                sp_last = &spc->progress[i + ndev];
                sp_shared = &spc->shared_progress[i];
                sp->scrub_args.devid = sp_last->scrub_args.devid =
                                                sp_shared->scrub_args.devid;
                sp->fd = sp_last->fd = spc->fdmnt;
                sp->stats.t_start = sp_last->stats.t_start =
                                                sp_shared->stats.t_start;
                sp->resumed = sp_last->resumed = sp_shared->resumed;
                sp->skip = sp_last->skip = sp_shared->skip;
                sp->stats.finished = sp_last->stats.finished =
                                                sp_shared->stats.finished;
        }

        while (1) {
                ret = poll(&accept_poll_fd, 1, 5 * 1000);
                if (ret == -1) {
                        ret = -errno;
                        goto out;
                }
                if (ret)
                        peer_fd = accept(spc->prg_fd, (struct sockaddr *)&peer,
                                         &peer_size);
                gettimeofday(&tv, NULL);
                this = (this + 1)%2;
                last = (last + 1)%2;
                for (i = 0; i < ndev; ++i) {
                        sp = &spc->progress[this * ndev + i];
                        sp_last = &spc->progress[last * ndev + i];
                        sp_shared = &spc->shared_progress[i];
                        if (sp->stats.finished)
                                continue;
                        progress_one_dev(sp);
                        sp->stats.duration = tv.tv_sec - sp->stats.t_start;
                        if (!sp->ret)
                                continue;
                        if (sp->ioctl_errno != ENOTCONN &&
                            sp->ioctl_errno != ENODEV) {
                                ret = -sp->ioctl_errno;
                                goto out;
                        }
                        /*
                         * scrub finished or device removed, check the
                         * finished flag. if unset, just use the last
                         * result we got for the current write and go
                         * on. flag should be set on next cycle, then.
                         */
                        perr = pthread_setcancelstate(
                                        PTHREAD_CANCEL_DISABLE, &old);
                        if (perr)
                                goto out;
                        perr = pthread_mutex_lock(&sp_shared->progress_mutex);
                        if (perr)
                                goto out;
                        if (!sp_shared->stats.finished) {
                                perr = pthread_mutex_unlock(
                                                &sp_shared->progress_mutex);
                                if (perr)
                                        goto out;
                                perr = pthread_setcancelstate(
                                                PTHREAD_CANCEL_ENABLE, &old);
                                if (perr)
                                        goto out;
                                memcpy(sp, sp_last, sizeof(*sp));
                                continue;
                        }
                        perr = pthread_mutex_unlock(&sp_shared->progress_mutex);
                        if (perr)
                                goto out;
                        perr = pthread_setcancelstate(
                                        PTHREAD_CANCEL_ENABLE, &old);
                        if (perr)
                                goto out;
                        memcpy(sp, sp_shared, sizeof(*sp));
                        memcpy(sp_last, sp_shared, sizeof(*sp));
                }
                if (peer_fd != -1) {
                        write_poll_fd.fd = peer_fd;
                        ret = poll(&write_poll_fd, 1, 0);
                        if (ret == -1) {
                                ret = -errno;
                                goto out;
                        }
                        if (ret) {
                                ret = scrub_write_file(
                                        peer_fd, fsid,
                                        &spc->progress[this * ndev], ndev);
                                if (ret)
                                        goto out;
                        }
                        close(peer_fd);
                        peer_fd = -1;
                }
                if (!spc->do_record)
                        continue;
                ret = scrub_write_progress(spc->write_mutex, fsid,
                                           &spc->progress[this * ndev], ndev);
                if (ret)
                        goto out;
        }
out:
        if (peer_fd != -1)
                close(peer_fd);
        if (perr)
                ret = -perr;
        return ERR_PTR(ret);
}

static struct scrub_file_record *last_dev_scrub(
                struct scrub_file_record *const *const past_scrubs, u64 devid)
{
        int i;

        if (!past_scrubs || IS_ERR(past_scrubs))
                return NULL;

        for (i = 0; past_scrubs[i]; ++i)
                if (past_scrubs[i]->devid == devid)
                        return past_scrubs[i];

        return NULL;
}

static int mkdir_p(char *path)
{
        int i;
        int ret;

        for (i = 1; i < strlen(path); ++i) {
                if (path[i] != '/')
                        continue;
                path[i] = '\0';
                ret = mkdir(path, 0777);
                if (ret && errno != EEXIST)
                        return -errno;
                path[i] = '/';
        }

        return 0;
}

static int is_scrub_running_on_fs(struct btrfs_ioctl_fs_info_args *fi_args,
                                  struct btrfs_ioctl_dev_info_args *di_args,
                                  struct scrub_file_record **past_scrubs)
{
        int i;

        if (!fi_args || !di_args || !past_scrubs)
                return 0;

        for (i = 0; i < fi_args->num_devices; i++) {
                struct scrub_file_record *sfr =
                        last_dev_scrub(past_scrubs, di_args[i].devid);

                if (!sfr)
                        continue;
                if (!(sfr->stats.finished || sfr->stats.canceled))
                        return 1;
        }
        return 0;
}

static const char * const cmd_scrub_start_usage[];
static const char * const cmd_scrub_resume_usage[];

static int scrub_start(int argc, char **argv, int resume)
{
        int fdmnt;
        int prg_fd = -1;
        int fdres = -1;
        int ret;
        pid_t pid;
        int c;
        int i;
        int err = 0;
        int e_uncorrectable = 0;
        int e_correctable = 0;
        int print_raw = 0;
        char *path;
        int do_background = 1;
        int do_wait = 0;
        int do_print = 0;
        int do_quiet = 0;
        int do_record = 1;
        int readonly = 0;
        int do_stats_per_dev = 0;
        int ioprio_class = IOPRIO_CLASS_IDLE;
        int ioprio_classdata = 0;
        int n_start = 0;
        int n_skip = 0;
        int n_resume = 0;
        struct btrfs_ioctl_fs_info_args fi_args;
        struct btrfs_ioctl_dev_info_args *di_args = NULL;
        struct scrub_progress *sp = NULL;
        struct scrub_fs_stat fs_stat;
        struct timeval tv;
        struct sockaddr_un addr = {
                .sun_family = AF_UNIX,
        };
        pthread_t *t_devs = NULL;
        pthread_t t_prog;
        struct scrub_file_record **past_scrubs = NULL;
        struct scrub_file_record *last_scrub = NULL;
        char *datafile = strdup(SCRUB_DATA_FILE);
        char fsid[BTRFS_UUID_UNPARSED_SIZE];
        char sock_path[BTRFS_PATH_NAME_MAX + 1] = "";
        struct scrub_progress_cycle spc;
        pthread_mutex_t spc_write_mutex = PTHREAD_MUTEX_INITIALIZER;
        void *terr;
        u64 devid;
        DIR *dirstream = NULL;
        int force = 0;
        int nothing_to_resume = 0;

        optind = 1;
        while ((c = getopt(argc, argv, "BdqrRc:n:f")) != -1) {
                switch (c) {
                case 'B':
                        do_background = 0;
                        do_wait = 1;
                        do_print = 1;
                        break;
                case 'd':
                        do_stats_per_dev = 1;
                        break;
                case 'q':
                        do_quiet = 1;
                        break;
                case 'r':
                        readonly = 1;
                        break;
                case 'R':
                        print_raw = 1;
                        break;
                case 'c':
                        ioprio_class = (int)strtol(optarg, NULL, 10);
                        break;
                case 'n':
                        ioprio_classdata = (int)strtol(optarg, NULL, 10);
                        break;
                case 'f':
                        force = 1;
                        break;
                case '?':
                default:
                        usage(resume ? cmd_scrub_resume_usage :
                                                cmd_scrub_start_usage);
                }
        }

        /* try to catch most error cases before forking */

        if (check_argc_exact(argc - optind, 1)) {
                usage(resume ? cmd_scrub_resume_usage :
                                        cmd_scrub_start_usage);
        }

        spc.progress = NULL;
        if (do_quiet && do_print)
                do_print = 0;

        if (mkdir_p(datafile)) {
                ERR(!do_quiet, "WARNING: cannot create scrub data "
                               "file, mkdir %s failed: %s. Status recording "
                               "disabled\n", datafile, strerror(errno));
                do_record = 0;
        }
        free(datafile);

        path = argv[optind];

        fdmnt = open_path_or_dev_mnt(path, &dirstream);

        if (fdmnt < 0) {
                if (errno == EINVAL)
                        ERR(!do_quiet,
                            "ERROR: '%s' is not a mounted btrfs device\n",
                            path);
                else
                        ERR(!do_quiet, "ERROR: can't access '%s': %s\n",
                            path, strerror(errno));
                return 1;
        }

        ret = get_fs_info(path, &fi_args, &di_args);
        if (ret) {
                ERR(!do_quiet, "ERROR: getting dev info for scrub failed: "
                    "%s\n", strerror(-ret));
                err = 1;
                goto out;
        }
        if (!fi_args.num_devices) {
                ERR(!do_quiet, "ERROR: no devices found\n");
                err = 1;
                goto out;
        }

        uuid_unparse(fi_args.fsid, fsid);
        fdres = scrub_open_file_r(SCRUB_DATA_FILE, fsid);
        if (fdres < 0 && fdres != -ENOENT) {
                ERR(!do_quiet, "WARNING: failed to open status file: "
                    "%s\n", strerror(-fdres));
        } else if (fdres >= 0) {
                past_scrubs = scrub_read_file(fdres, !do_quiet);
                if (IS_ERR(past_scrubs))
                        ERR(!do_quiet, "WARNING: failed to read status file: "
                            "%s\n", strerror(-PTR_ERR(past_scrubs)));
                close(fdres);
        }

        /*
         * check whether any involved device is already busy running a
         * scrub. This would cause damaged status messages and the state
         * "aborted" without the explanation that a scrub was already
         * running. Therefore check it first, prevent it and give some
         * feedback to the user if scrub is already running.
         * Note that if scrub is started with a block device as the
         * parameter, only that particular block device is checked. It
         * is a normal mode of operation to start scrub on multiple
         * single devices, there is no reason to prevent this.
         */
        if (!force && is_scrub_running_on_fs(&fi_args, di_args, past_scrubs)) {
                ERR(!do_quiet,
                    "ERROR: scrub is already running.\n"
                    "To cancel use 'btrfs scrub cancel %s'.\n"
                    "To see the status use 'btrfs scrub status [-d] %s'.\n",
                    path, path);
                err = 1;
                goto out;
        }

        t_devs = malloc(fi_args.num_devices * sizeof(*t_devs));
        sp = calloc(fi_args.num_devices, sizeof(*sp));
        spc.progress = calloc(fi_args.num_devices * 2, sizeof(*spc.progress));

        if (!t_devs || !sp || !spc.progress) {
                ERR(!do_quiet, "ERROR: scrub failed: %s", strerror(errno));
                err = 1;
                goto out;
        }

        for (i = 0; i < fi_args.num_devices; ++i) {
                devid = di_args[i].devid;
                ret = pthread_mutex_init(&sp[i].progress_mutex, NULL);
                if (ret) {
                        ERR(!do_quiet, "ERROR: pthread_mutex_init failed: "
                            "%s\n", strerror(ret));
                        err = 1;
                        goto out;
                }
                last_scrub = last_dev_scrub(past_scrubs, devid);
                sp[i].scrub_args.devid = devid;
                sp[i].fd = fdmnt;
                if (resume && last_scrub && (last_scrub->stats.canceled ||
                                             !last_scrub->stats.finished)) {
                        ++n_resume;
                        sp[i].scrub_args.start = last_scrub->p.last_physical;
                        sp[i].resumed = last_scrub;
                } else if (resume) {
                        ++n_skip;
                        sp[i].skip = 1;
                        sp[i].resumed = last_scrub;
                        continue;
                } else {
                        ++n_start;
                        sp[i].scrub_args.start = 0ll;
                        sp[i].resumed = NULL;
                }
                sp[i].skip = 0;
                sp[i].scrub_args.end = (u64)-1ll;
                sp[i].scrub_args.flags = readonly ? BTRFS_SCRUB_READONLY : 0;
                sp[i].ioprio_class = ioprio_class;
                sp[i].ioprio_classdata = ioprio_classdata;
        }

        if (!n_start && !n_resume) {
                if (!do_quiet)
                        printf("scrub: nothing to resume for %s, fsid %s\n",
                               path, fsid);
                nothing_to_resume = 1;
                goto out;
        }

        ret = prg_fd = socket(AF_UNIX, SOCK_STREAM, 0);
        while (ret != -1) {
                ret = scrub_datafile(SCRUB_PROGRESS_SOCKET_PATH, fsid, NULL,
                                        sock_path, sizeof(sock_path));
                /* ignore EOVERFLOW, try using a shorter path for the socket */
                addr.sun_path[sizeof(addr.sun_path) - 1] = '\0';
                strncpy(addr.sun_path, sock_path, sizeof(addr.sun_path) - 1);
                ret = bind(prg_fd, (struct sockaddr *)&addr, sizeof(addr));
                if (ret != -1 || errno != EADDRINUSE)
                        break;
                /*
                 * bind failed with EADDRINUSE. so let's see if anyone answers
                 * when we make a call to the socket ...
                 */
                ret = connect(prg_fd, (struct sockaddr *)&addr, sizeof(addr));
                if (!ret || errno != ECONNREFUSED) {
                        /* ... yes, so scrub must be running. error out */
                        fprintf(stderr, "ERROR: scrub already running\n");
                        close(prg_fd);
                        prg_fd = -1;
                        goto out;
                }
                /*
                 * ... no, this means someone left us alone with an unused
                 * socket in the file system. remove it and try again.
                 */
                ret = unlink(sock_path);
        }
        if (ret != -1)
                ret = listen(prg_fd, 100);
        if (ret == -1) {
                ERR(!do_quiet, "WARNING: failed to open the progress status "
                    "socket at %s: %s. Progress cannot be queried\n",
                    sock_path[0] ? sock_path : SCRUB_PROGRESS_SOCKET_PATH,
                    strerror(errno));
                if (prg_fd != -1) {
                        close(prg_fd);
                        prg_fd = -1;
                        if (sock_path[0])
                                unlink(sock_path);
                }
        }

        if (do_record) {
                /* write all-zero progress file for a start */
                ret = scrub_write_progress(&spc_write_mutex, fsid, sp,
                                           fi_args.num_devices);
                if (ret) {
                        ERR(!do_quiet, "WARNING: failed to write the progress "
                            "status file: %s. Status recording disabled\n",
                            strerror(-ret));
                        do_record = 0;
                }
        }

        if (do_background) {
                pid = fork();
                if (pid == -1) {
                        ERR(!do_quiet, "ERROR: cannot scrub, fork failed: "
                                        "%s\n", strerror(errno));
                        err = 1;
                        goto out;
                }

                if (pid) {
                        int stat;
                        scrub_handle_sigint_parent();
                        if (!do_quiet)
                                printf("scrub %s on %s, fsid %s (pid=%d)\n",
                                       n_start ? "started" : "resumed",
                                       path, fsid, pid);
                        if (!do_wait) {
                                err = 0;
                                goto out;
                        }
                        ret = wait(&stat);
                        if (ret != pid) {
                                ERR(!do_quiet, "ERROR: wait failed: (ret=%d) "
                                    "%s\n", ret, strerror(errno));
                                err = 1;
                                goto out;
                        }
                        if (!WIFEXITED(stat) || WEXITSTATUS(stat)) {
                                ERR(!do_quiet, "ERROR: scrub process failed\n");
                                err = WIFEXITED(stat) ? WEXITSTATUS(stat) : -1;
                                goto out;
                        }
                        err = 0;
                        goto out;
                }
        }

        scrub_handle_sigint_child(fdmnt);

        for (i = 0; i < fi_args.num_devices; ++i) {
                if (sp[i].skip) {
                        sp[i].scrub_args.progress = sp[i].resumed->p;
                        sp[i].stats = sp[i].resumed->stats;
                        sp[i].ret = 0;
                        sp[i].stats.finished = 1;
                        continue;
                }
                devid = di_args[i].devid;
                gettimeofday(&tv, NULL);
                sp[i].stats.t_start = tv.tv_sec;
                ret = pthread_create(&t_devs[i], NULL,
                                        scrub_one_dev, &sp[i]);
                if (ret) {
                        if (do_print)
                                fprintf(stderr, "ERROR: creating "
                                        "scrub_one_dev[%llu] thread failed: "
                                        "%s\n", devid, strerror(ret));
                        err = 1;
                        goto out;
                }
        }

        spc.fdmnt = fdmnt;
        spc.prg_fd = prg_fd;
        spc.do_record = do_record;
        spc.write_mutex = &spc_write_mutex;
        spc.shared_progress = sp;
        spc.fi = &fi_args;
        ret = pthread_create(&t_prog, NULL, scrub_progress_cycle, &spc);
        if (ret) {
                if (do_print)
                        fprintf(stderr, "ERROR: creating progress thread "
                                "failed: %s\n", strerror(ret));
                err = 1;
                goto out;
        }

        err = 0;
        for (i = 0; i < fi_args.num_devices; ++i) {
                if (sp[i].skip)
                        continue;
                devid = di_args[i].devid;
                ret = pthread_join(t_devs[i], NULL);
                if (ret) {
                        if (do_print)
                                fprintf(stderr, "ERROR: pthread_join failed "
                                        "for scrub_one_dev[%llu]: %s\n", devid,
                                        strerror(ret));
                        ++err;
                        continue;
                }
                if (sp[i].ret && sp[i].ioctl_errno == ENODEV) {
                        if (do_print)
                                fprintf(stderr, "WARNING: device %lld not "
                                        "present\n", devid);
                        continue;
                }
                if (sp[i].ret && sp[i].ioctl_errno == ECANCELED) {
                        ++err;
                } else if (sp[i].ret) {
                        if (do_print)
                                fprintf(stderr, "ERROR: scrubbing %s failed "
                                        "for device id %lld (%s)\n", path,
                                        devid, strerror(sp[i].ioctl_errno));
                        ++err;
                        continue;
                }
                if (sp[i].scrub_args.progress.uncorrectable_errors > 0)
                        e_uncorrectable++;
                if (sp[i].scrub_args.progress.corrected_errors > 0
                    || sp[i].scrub_args.progress.unverified_errors > 0)
                        e_correctable++;
        }

        if (do_print) {
                const char *append = "done";
                if (!do_stats_per_dev)
                        init_fs_stat(&fs_stat);
                for (i = 0; i < fi_args.num_devices; ++i) {
                        if (do_stats_per_dev) {
                                print_scrub_dev(&di_args[i],
                                                &sp[i].scrub_args.progress,
                                                print_raw,
                                                sp[i].ret ? "canceled" : "done",
                                                &sp[i].stats);
                        } else {
                                if (sp[i].ret)
                                        append = "canceled";
                                add_to_fs_stat(&sp[i].scrub_args.progress,
                                                &sp[i].stats, &fs_stat);
                        }
                }
                if (!do_stats_per_dev) {
                        printf("scrub %s for %s\n", append, fsid);
                        print_fs_stat(&fs_stat, print_raw);
                }
        }

        ret = pthread_cancel(t_prog);
        if (!ret)
                ret = pthread_join(t_prog, &terr);

        /* check for errors from the handling of the progress thread */
        if (do_print && ret) {
                fprintf(stderr, "ERROR: progress thread handling failed: %s\n",
                        strerror(ret));
        }

        /* check for errors returned from the progress thread itself */
        if (do_print && terr && terr != PTHREAD_CANCELED) {
                fprintf(stderr, "ERROR: recording progress "
                        "failed: %s\n", strerror(-PTR_ERR(terr)));
        }

        if (do_record) {
                ret = scrub_write_progress(&spc_write_mutex, fsid, sp,
                                           fi_args.num_devices);
                if (ret && do_print) {
                        fprintf(stderr, "ERROR: failed to record the result: "
                                "%s\n", strerror(-ret));
                }
        }

        scrub_handle_sigint_child(-1);

out:
        free_history(past_scrubs);
        free(di_args);
        free(t_devs);
        free(sp);
        free(spc.progress);
        if (prg_fd > -1) {
                close(prg_fd);
                if (sock_path[0])
                        unlink(sock_path);
        }
        close_file_or_dir(fdmnt, dirstream);

        if (nothing_to_resume)
                return 2;
        if (err)
                return 1;
        if (e_correctable)
                return 3;
        if (e_uncorrectable)
                return 4;
        return 0;
}

static const char * const cmd_scrub_start_usage[] = {
        "btrfs scrub start [-BdqrRf] [-c ioprio_class -n ioprio_classdata] <path>|<device>",
        "Start a new scrub",
        "",
        "-B     do not background",
        "-d     stats per device (-B only)",
        "-q     be quiet",
        "-r     read only mode",
        "-R     raw print mode, print full data instead of summary"
        "-c     set ioprio class (see ionice(1) manpage)",
        "-n     set ioprio classdata (see ionice(1) manpage)",
        "-f     force to skip checking whether scrub has started/resumed in userspace ",
        "       this is useful when scrub stats record file is damaged",
        NULL
};

static int cmd_scrub_start(int argc, char **argv)
{
        return scrub_start(argc, argv, 0);
}

static const char * const cmd_scrub_cancel_usage[] = {
        "btrfs scrub cancel <path>|<device>",
        "Cancel a running scrub",
        NULL
};

static int cmd_scrub_cancel(int argc, char **argv)
{
        char *path;
        int ret;
        int fdmnt = -1;
        DIR *dirstream = NULL;

        if (check_argc_exact(argc, 2))
                usage(cmd_scrub_cancel_usage);

        path = argv[1];

        fdmnt = open_path_or_dev_mnt(path, &dirstream);
        if (fdmnt < 0) {
                if (errno == EINVAL)
                        fprintf(stderr,
                                "ERROR: '%s' is not a mounted btrfs device\n",
                                path);
                else
                        fprintf(stderr, "ERROR: can't access '%s': %s\n",
                                path, strerror(errno));
                ret = 1;
                goto out;
        }

        ret = ioctl(fdmnt, BTRFS_IOC_SCRUB_CANCEL, NULL);

        if (ret < 0) {
                fprintf(stderr, "ERROR: scrub cancel failed on %s: %s\n", path,
                        errno == ENOTCONN ? "not running" : strerror(errno));
                if (errno == ENOTCONN)
                        ret = 2;
                else
                        ret = 1;
                goto out;
        }

        ret = 0;
        printf("scrub cancelled\n");

out:
        close_file_or_dir(fdmnt, dirstream);
        return ret;
}

static const char * const cmd_scrub_resume_usage[] = {
        "btrfs scrub resume [-BdqrR] [-c ioprio_class -n ioprio_classdata] <path>|<device>",
        "Resume previously canceled or interrupted scrub",
        "",
        "-B     do not background",
        "-d     stats per device (-B only)",
        "-q     be quiet",
        "-r     read only mode",
        "-c     set ioprio class (see ionice(1) manpage)",
        "-n     set ioprio classdata (see ionice(1) manpage)",
        NULL
};

static int cmd_scrub_resume(int argc, char **argv)
{
        return scrub_start(argc, argv, 1);
}

static const char * const cmd_scrub_status_usage[] = {
        "btrfs scrub status [-dR] <path>|<device>",
        "Show status of running or finished scrub",
        "",
        "-d     stats per device",
        "-R     print raw stats",
        NULL
};

static int cmd_scrub_status(int argc, char **argv)
{
        char *path;
        struct btrfs_ioctl_fs_info_args fi_args;
        struct btrfs_ioctl_dev_info_args *di_args = NULL;
        struct scrub_file_record **past_scrubs = NULL;
        struct scrub_file_record *last_scrub;
        struct scrub_fs_stat fs_stat;
        struct sockaddr_un addr = {
                .sun_family = AF_UNIX,
        };
        int ret;
        int i;
        int fdmnt;
        int print_raw = 0;
        int do_stats_per_dev = 0;
        int c;
        char fsid[BTRFS_UUID_UNPARSED_SIZE];
        int fdres = -1;
        int err = 0;
        DIR *dirstream = NULL;

        optind = 1;
        while ((c = getopt(argc, argv, "dR")) != -1) {
                switch (c) {
                case 'd':
                        do_stats_per_dev = 1;
                        break;
                case 'R':
                        print_raw = 1;
                        break;
                case '?':
                default:
                        usage(cmd_scrub_status_usage);
                }
        }

        if (check_argc_exact(argc - optind, 1))
                usage(cmd_scrub_status_usage);

        path = argv[optind];

        fdmnt = open_path_or_dev_mnt(path, &dirstream);

        if (fdmnt < 0) {
                if (errno == EINVAL)
                        fprintf(stderr,
                                "ERROR: '%s' is not a mounted btrfs device\n",
                                path);
                else
                        fprintf(stderr, "ERROR: can't access '%s': %s\n",
                                path, strerror(errno));
                return 1;
        }

        ret = get_fs_info(path, &fi_args, &di_args);
        if (ret) {
                fprintf(stderr, "ERROR: getting dev info for scrub failed: "
                                "%s\n", strerror(-ret));
                err = 1;
                goto out;
        }
        if (!fi_args.num_devices) {
                fprintf(stderr, "ERROR: no devices found\n");
                err = 1;
                goto out;
        }

        uuid_unparse(fi_args.fsid, fsid);

        fdres = socket(AF_UNIX, SOCK_STREAM, 0);
        if (fdres == -1) {
                fprintf(stderr, "ERROR: failed to create socket to "
                        "receive progress information: %s\n",
                        strerror(errno));
                err = 1;
                goto out;
        }
        scrub_datafile(SCRUB_PROGRESS_SOCKET_PATH, fsid,
                        NULL, addr.sun_path, sizeof(addr.sun_path));
        /* ignore EOVERFLOW, just use shorter name and hope for the best */
        addr.sun_path[sizeof(addr.sun_path) - 1] = '\0';
        ret = connect(fdres, (struct sockaddr *)&addr, sizeof(addr));
        if (ret == -1) {
                close(fdres);
                fdres = scrub_open_file_r(SCRUB_DATA_FILE, fsid);
                if (fdres < 0 && fdres != -ENOENT) {
                        fprintf(stderr, "WARNING: failed to open status file: "
                                "%s\n", strerror(-fdres));
                        err = 1;
                        goto out;
                }
        }

        if (fdres >= 0) {
                past_scrubs = scrub_read_file(fdres, 1);
                if (IS_ERR(past_scrubs))
                        fprintf(stderr, "WARNING: failed to read status: %s\n",
                                strerror(-PTR_ERR(past_scrubs)));
        }

        printf("scrub status for %s\n", fsid);

        if (do_stats_per_dev) {
                for (i = 0; i < fi_args.num_devices; ++i) {
                        last_scrub = last_dev_scrub(past_scrubs,
                                                        di_args[i].devid);
                        if (!last_scrub) {
                                print_scrub_dev(&di_args[i], NULL, print_raw,
                                                NULL, NULL);
                                continue;
                        }
                        print_scrub_dev(&di_args[i], &last_scrub->p, print_raw,
                                        last_scrub->stats.finished ?
                                                        "history" : "status",
                                        &last_scrub->stats);
                }
        } else {
                init_fs_stat(&fs_stat);
                for (i = 0; i < fi_args.num_devices; ++i) {
                        last_scrub = last_dev_scrub(past_scrubs,
                                                        di_args[i].devid);
                        if (!last_scrub)
                                continue;
                        add_to_fs_stat(&last_scrub->p, &last_scrub->stats,
                                        &fs_stat);
                }
                print_fs_stat(&fs_stat, print_raw);
        }

out:
        free_history(past_scrubs);
        free(di_args);
        if (fdres > -1)
                close(fdres);
        close_file_or_dir(fdmnt, dirstream);

        return !!err;
}

const struct cmd_group scrub_cmd_group = {
        scrub_cmd_group_usage, NULL, {
                { "start", cmd_scrub_start, cmd_scrub_start_usage, NULL, 0 },
                { "cancel", cmd_scrub_cancel, cmd_scrub_cancel_usage, NULL, 0 },
                { "resume", cmd_scrub_resume, cmd_scrub_resume_usage, NULL, 0 },
                { "status", cmd_scrub_status, cmd_scrub_status_usage, NULL, 0 },
                NULL_CMD_STRUCT
        }
};

int cmd_scrub(int argc, char **argv)
{
        return handle_command_group(&scrub_cmd_group, argc, argv);
}