block: add I/O throttling algorithm

[mirror_qemu.git] / blockdev.c

/*
 * QEMU host block devices
 *
 * Copyright (c) 2003-2008 Fabrice Bellard
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or
 * later.  See the COPYING file in the top-level directory.
 */

#include "block.h"
#include "blockdev.h"
#include "monitor.h"
#include "qerror.h"
#include "qemu-option.h"
#include "qemu-config.h"
#include "sysemu.h"
#include "block_int.h"

static QTAILQ_HEAD(drivelist, DriveInfo) drives = QTAILQ_HEAD_INITIALIZER(drives);

static const char *const if_name[IF_COUNT] = {
    [IF_NONE] = "none",
    [IF_IDE] = "ide",
    [IF_SCSI] = "scsi",
    [IF_FLOPPY] = "floppy",
    [IF_PFLASH] = "pflash",
    [IF_MTD] = "mtd",
    [IF_SD] = "sd",
    [IF_VIRTIO] = "virtio",
    [IF_XEN] = "xen",
};

static const int if_max_devs[IF_COUNT] = {
    /*
     * Do not change these numbers!  They govern how drive option
     * index maps to unit and bus.  That mapping is ABI.
     *
     * All controllers used to imlement if=T drives need to support
     * if_max_devs[T] units, for any T with if_max_devs[T] != 0.
     * Otherwise, some index values map to "impossible" bus, unit
     * values.
     *
     * For instance, if you change [IF_SCSI] to 255, -drive
     * if=scsi,index=12 no longer means bus=1,unit=5, but
     * bus=0,unit=12.  With an lsi53c895a controller (7 units max),
     * the drive can't be set up.  Regression.
     */
    [IF_IDE] = 2,
    [IF_SCSI] = 7,
};

/*
 * We automatically delete the drive when a device using it gets
 * unplugged.  Questionable feature, but we can't just drop it.
 * Device models call blockdev_mark_auto_del() to schedule the
 * automatic deletion, and generic qdev code calls blockdev_auto_del()
 * when deletion is actually safe.
 */
void blockdev_mark_auto_del(BlockDriverState *bs)
{
    DriveInfo *dinfo = drive_get_by_blockdev(bs);

    if (dinfo) {
        dinfo->auto_del = 1;
    }
}

void blockdev_auto_del(BlockDriverState *bs)
{
    DriveInfo *dinfo = drive_get_by_blockdev(bs);

    if (dinfo && dinfo->auto_del) {
        drive_put_ref(dinfo);
    }
}

static int drive_index_to_bus_id(BlockInterfaceType type, int index)
{
    int max_devs = if_max_devs[type];
    return max_devs ? index / max_devs : 0;
}

static int drive_index_to_unit_id(BlockInterfaceType type, int index)
{
    int max_devs = if_max_devs[type];
    return max_devs ? index % max_devs : index;
}

QemuOpts *drive_def(const char *optstr)
{
    return qemu_opts_parse(qemu_find_opts("drive"), optstr, 0);
}

QemuOpts *drive_add(BlockInterfaceType type, int index, const char *file,
                    const char *optstr)
{
    QemuOpts *opts;
    char buf[32];

    opts = drive_def(optstr);
    if (!opts) {
        return NULL;
    }
    if (type != IF_DEFAULT) {
        qemu_opt_set(opts, "if", if_name[type]);
    }
    if (index >= 0) {
        snprintf(buf, sizeof(buf), "%d", index);
        qemu_opt_set(opts, "index", buf);
    }
    if (file)
        qemu_opt_set(opts, "file", file);
    return opts;
}

DriveInfo *drive_get(BlockInterfaceType type, int bus, int unit)
{
    DriveInfo *dinfo;

    /* seek interface, bus and unit */

    QTAILQ_FOREACH(dinfo, &drives, next) {
        if (dinfo->type == type &&
	    dinfo->bus == bus &&
	    dinfo->unit == unit)
            return dinfo;
    }

    return NULL;
}

DriveInfo *drive_get_by_index(BlockInterfaceType type, int index)
{
    return drive_get(type,
                     drive_index_to_bus_id(type, index),
                     drive_index_to_unit_id(type, index));
}

int drive_get_max_bus(BlockInterfaceType type)
{
    int max_bus;
    DriveInfo *dinfo;

    max_bus = -1;
    QTAILQ_FOREACH(dinfo, &drives, next) {
        if(dinfo->type == type &&
           dinfo->bus > max_bus)
            max_bus = dinfo->bus;
    }
    return max_bus;
}

/* Get a block device.  This should only be used for single-drive devices
   (e.g. SD/Floppy/MTD).  Multi-disk devices (scsi/ide) should use the
   appropriate bus.  */
DriveInfo *drive_get_next(BlockInterfaceType type)
{
    static int next_block_unit[IF_COUNT];

    return drive_get(type, 0, next_block_unit[type]++);
}

DriveInfo *drive_get_by_blockdev(BlockDriverState *bs)
{
    DriveInfo *dinfo;

    QTAILQ_FOREACH(dinfo, &drives, next) {
        if (dinfo->bdrv == bs) {
            return dinfo;
        }
    }
    return NULL;
}

static void bdrv_format_print(void *opaque, const char *name)
{
    error_printf(" %s", name);
}

static void drive_uninit(DriveInfo *dinfo)
{
    qemu_opts_del(dinfo->opts);
    bdrv_delete(dinfo->bdrv);
    g_free(dinfo->id);
    QTAILQ_REMOVE(&drives, dinfo, next);
    g_free(dinfo);
}

void drive_put_ref(DriveInfo *dinfo)
{
    assert(dinfo->refcount);
    if (--dinfo->refcount == 0) {
        drive_uninit(dinfo);
    }
}

void drive_get_ref(DriveInfo *dinfo)
{
    dinfo->refcount++;
}

static int parse_block_error_action(const char *buf, int is_read)
{
    if (!strcmp(buf, "ignore")) {
        return BLOCK_ERR_IGNORE;
    } else if (!is_read && !strcmp(buf, "enospc")) {
        return BLOCK_ERR_STOP_ENOSPC;
    } else if (!strcmp(buf, "stop")) {
        return BLOCK_ERR_STOP_ANY;
    } else if (!strcmp(buf, "report")) {
        return BLOCK_ERR_REPORT;
    } else {
        error_report("'%s' invalid %s error action",
                     buf, is_read ? "read" : "write");
        return -1;
    }
}

static bool do_check_io_limits(BlockIOLimit *io_limits)
{
    bool bps_flag;
    bool iops_flag;

    assert(io_limits);

    bps_flag  = (io_limits->bps[BLOCK_IO_LIMIT_TOTAL] != 0)
                 && ((io_limits->bps[BLOCK_IO_LIMIT_READ] != 0)
                 || (io_limits->bps[BLOCK_IO_LIMIT_WRITE] != 0));
    iops_flag = (io_limits->iops[BLOCK_IO_LIMIT_TOTAL] != 0)
                 && ((io_limits->iops[BLOCK_IO_LIMIT_READ] != 0)
                 || (io_limits->iops[BLOCK_IO_LIMIT_WRITE] != 0));
    if (bps_flag || iops_flag) {
        return false;
    }

    return true;
}

DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
{
    const char *buf;
    const char *file = NULL;
    char devname[128];
    const char *serial;
    const char *mediastr = "";
    BlockInterfaceType type;
    enum { MEDIA_DISK, MEDIA_CDROM } media;
    int bus_id, unit_id;
    int cyls, heads, secs, translation;
    BlockDriver *drv = NULL;
    int max_devs;
    int index;
    int ro = 0;
    int bdrv_flags = 0;
    int on_read_error, on_write_error;
    const char *devaddr;
    DriveInfo *dinfo;
    BlockIOLimit io_limits;
    int snapshot = 0;
    int ret;

    translation = BIOS_ATA_TRANSLATION_AUTO;
    media = MEDIA_DISK;

    /* extract parameters */
    bus_id  = qemu_opt_get_number(opts, "bus", 0);
    unit_id = qemu_opt_get_number(opts, "unit", -1);
    index   = qemu_opt_get_number(opts, "index", -1);

    cyls  = qemu_opt_get_number(opts, "cyls", 0);
    heads = qemu_opt_get_number(opts, "heads", 0);
    secs  = qemu_opt_get_number(opts, "secs", 0);

    snapshot = qemu_opt_get_bool(opts, "snapshot", 0);
    ro = qemu_opt_get_bool(opts, "readonly", 0);

    file = qemu_opt_get(opts, "file");
    serial = qemu_opt_get(opts, "serial");

    if ((buf = qemu_opt_get(opts, "if")) != NULL) {
        pstrcpy(devname, sizeof(devname), buf);
        for (type = 0; type < IF_COUNT && strcmp(buf, if_name[type]); type++)
            ;
        if (type == IF_COUNT) {
            error_report("unsupported bus type '%s'", buf);
            return NULL;
	}
    } else {
        type = default_to_scsi ? IF_SCSI : IF_IDE;
        pstrcpy(devname, sizeof(devname), if_name[type]);
    }

    max_devs = if_max_devs[type];

    if (cyls || heads || secs) {
        if (cyls < 1 || (type == IF_IDE && cyls > 16383)) {
            error_report("invalid physical cyls number");
	    return NULL;
	}
        if (heads < 1 || (type == IF_IDE && heads > 16)) {
            error_report("invalid physical heads number");
	    return NULL;
	}
        if (secs < 1 || (type == IF_IDE && secs > 63)) {
            error_report("invalid physical secs number");
	    return NULL;
	}
    }

    if ((buf = qemu_opt_get(opts, "trans")) != NULL) {
        if (!cyls) {
            error_report("'%s' trans must be used with cyls, heads and secs",
                         buf);
            return NULL;
        }
        if (!strcmp(buf, "none"))
            translation = BIOS_ATA_TRANSLATION_NONE;
        else if (!strcmp(buf, "lba"))
            translation = BIOS_ATA_TRANSLATION_LBA;
        else if (!strcmp(buf, "auto"))
            translation = BIOS_ATA_TRANSLATION_AUTO;
	else {
            error_report("'%s' invalid translation type", buf);
	    return NULL;
	}
    }

    if ((buf = qemu_opt_get(opts, "media")) != NULL) {
        if (!strcmp(buf, "disk")) {
	    media = MEDIA_DISK;
	} else if (!strcmp(buf, "cdrom")) {
            if (cyls || secs || heads) {
                error_report("CHS can't be set with media=%s", buf);
	        return NULL;
            }
	    media = MEDIA_CDROM;
	} else {
	    error_report("'%s' invalid media", buf);
	    return NULL;
	}
    }

    if ((buf = qemu_opt_get(opts, "cache")) != NULL) {
        if (bdrv_parse_cache_flags(buf, &bdrv_flags) != 0) {
            error_report("invalid cache option");
            return NULL;
        }
    }

#ifdef CONFIG_LINUX_AIO
    if ((buf = qemu_opt_get(opts, "aio")) != NULL) {
        if (!strcmp(buf, "native")) {
            bdrv_flags |= BDRV_O_NATIVE_AIO;
        } else if (!strcmp(buf, "threads")) {
            /* this is the default */
        } else {
           error_report("invalid aio option");
           return NULL;
        }
    }
#endif

    if ((buf = qemu_opt_get(opts, "format")) != NULL) {
       if (strcmp(buf, "?") == 0) {
           error_printf("Supported formats:");
           bdrv_iterate_format(bdrv_format_print, NULL);
           error_printf("\n");
           return NULL;
        }
        drv = bdrv_find_whitelisted_format(buf);
        if (!drv) {
            error_report("'%s' invalid format", buf);
            return NULL;
        }
    }

    /* disk I/O throttling */
    io_limits.bps[BLOCK_IO_LIMIT_TOTAL]  =
                           qemu_opt_get_number(opts, "bps", 0);
    io_limits.bps[BLOCK_IO_LIMIT_READ]   =
                           qemu_opt_get_number(opts, "bps_rd", 0);
    io_limits.bps[BLOCK_IO_LIMIT_WRITE]  =
                           qemu_opt_get_number(opts, "bps_wr", 0);
    io_limits.iops[BLOCK_IO_LIMIT_TOTAL] =
                           qemu_opt_get_number(opts, "iops", 0);
    io_limits.iops[BLOCK_IO_LIMIT_READ]  =
                           qemu_opt_get_number(opts, "iops_rd", 0);
    io_limits.iops[BLOCK_IO_LIMIT_WRITE] =
                           qemu_opt_get_number(opts, "iops_wr", 0);

    if (!do_check_io_limits(&io_limits)) {
        error_report("bps(iops) and bps_rd/bps_wr(iops_rd/iops_wr) "
                     "cannot be used at the same time");
        return NULL;
    }

    on_write_error = BLOCK_ERR_STOP_ENOSPC;
    if ((buf = qemu_opt_get(opts, "werror")) != NULL) {
        if (type != IF_IDE && type != IF_SCSI && type != IF_VIRTIO && type != IF_NONE) {
            error_report("werror is not supported by this bus type");
            return NULL;
        }

        on_write_error = parse_block_error_action(buf, 0);
        if (on_write_error < 0) {
            return NULL;
        }
    }

    on_read_error = BLOCK_ERR_REPORT;
    if ((buf = qemu_opt_get(opts, "rerror")) != NULL) {
        if (type != IF_IDE && type != IF_VIRTIO && type != IF_SCSI && type != IF_NONE) {
            error_report("rerror is not supported by this bus type");
            return NULL;
        }

        on_read_error = parse_block_error_action(buf, 1);
        if (on_read_error < 0) {
            return NULL;
        }
    }

    if ((devaddr = qemu_opt_get(opts, "addr")) != NULL) {
        if (type != IF_VIRTIO) {
            error_report("addr is not supported by this bus type");
            return NULL;
        }
    }

    /* compute bus and unit according index */

    if (index != -1) {
        if (bus_id != 0 || unit_id != -1) {
            error_report("index cannot be used with bus and unit");
            return NULL;
        }
        bus_id = drive_index_to_bus_id(type, index);
        unit_id = drive_index_to_unit_id(type, index);
    }

    /* if user doesn't specify a unit_id,
     * try to find the first free
     */

    if (unit_id == -1) {
       unit_id = 0;
       while (drive_get(type, bus_id, unit_id) != NULL) {
           unit_id++;
           if (max_devs && unit_id >= max_devs) {
               unit_id -= max_devs;
               bus_id++;
           }
       }
    }

    /* check unit id */

    if (max_devs && unit_id >= max_devs) {
        error_report("unit %d too big (max is %d)",
                     unit_id, max_devs - 1);
        return NULL;
    }

    /*
     * catch multiple definitions
     */

    if (drive_get(type, bus_id, unit_id) != NULL) {
        error_report("drive with bus=%d, unit=%d (index=%d) exists",
                     bus_id, unit_id, index);
        return NULL;
    }

    /* init */

    dinfo = g_malloc0(sizeof(*dinfo));
    if ((buf = qemu_opts_id(opts)) != NULL) {
        dinfo->id = g_strdup(buf);
    } else {
        /* no id supplied -> create one */
        dinfo->id = g_malloc0(32);
        if (type == IF_IDE || type == IF_SCSI)
            mediastr = (media == MEDIA_CDROM) ? "-cd" : "-hd";
        if (max_devs)
            snprintf(dinfo->id, 32, "%s%i%s%i",
                     devname, bus_id, mediastr, unit_id);
        else
            snprintf(dinfo->id, 32, "%s%s%i",
                     devname, mediastr, unit_id);
    }
    dinfo->bdrv = bdrv_new(dinfo->id);
    dinfo->devaddr = devaddr;
    dinfo->type = type;
    dinfo->bus = bus_id;
    dinfo->unit = unit_id;
    dinfo->opts = opts;
    dinfo->refcount = 1;
    if (serial)
        strncpy(dinfo->serial, serial, sizeof(dinfo->serial) - 1);
    QTAILQ_INSERT_TAIL(&drives, dinfo, next);

    bdrv_set_on_error(dinfo->bdrv, on_read_error, on_write_error);

    /* disk I/O throttling */
    bdrv_set_io_limits(dinfo->bdrv, &io_limits);

    switch(type) {
    case IF_IDE:
    case IF_SCSI:
    case IF_XEN:
    case IF_NONE:
        switch(media) {
	case MEDIA_DISK:
            if (cyls != 0) {
                bdrv_set_geometry_hint(dinfo->bdrv, cyls, heads, secs);
                bdrv_set_translation_hint(dinfo->bdrv, translation);
            }
	    break;
	case MEDIA_CDROM:
            dinfo->media_cd = 1;
	    break;
	}
        break;
    case IF_SD:
    case IF_FLOPPY:
    case IF_PFLASH:
    case IF_MTD:
        break;
    case IF_VIRTIO:
        /* add virtio block device */
        opts = qemu_opts_create(qemu_find_opts("device"), NULL, 0);
        qemu_opt_set(opts, "driver", "virtio-blk");
        qemu_opt_set(opts, "drive", dinfo->id);
        if (devaddr)
            qemu_opt_set(opts, "addr", devaddr);
        break;
    default:
        abort();
    }
    if (!file || !*file) {
        return dinfo;
    }
    if (snapshot) {
        /* always use cache=unsafe with snapshot */
        bdrv_flags &= ~BDRV_O_CACHE_MASK;
        bdrv_flags |= (BDRV_O_SNAPSHOT|BDRV_O_CACHE_WB|BDRV_O_NO_FLUSH);
    }

    if (media == MEDIA_CDROM) {
        /* CDROM is fine for any interface, don't check.  */
        ro = 1;
    } else if (ro == 1) {
        if (type != IF_SCSI && type != IF_VIRTIO && type != IF_FLOPPY && type != IF_NONE) {
            error_report("readonly not supported by this bus type");
            goto err;
        }
    }

    bdrv_flags |= ro ? 0 : BDRV_O_RDWR;

    ret = bdrv_open(dinfo->bdrv, file, bdrv_flags, drv);
    if (ret < 0) {
        error_report("could not open disk image %s: %s",
                     file, strerror(-ret));
        goto err;
    }

    if (bdrv_key_required(dinfo->bdrv))
        autostart = 0;
    return dinfo;

err:
    bdrv_delete(dinfo->bdrv);
    g_free(dinfo->id);
    QTAILQ_REMOVE(&drives, dinfo, next);
    g_free(dinfo);
    return NULL;
}

void do_commit(Monitor *mon, const QDict *qdict)
{
    const char *device = qdict_get_str(qdict, "device");
    BlockDriverState *bs;

    if (!strcmp(device, "all")) {
        bdrv_commit_all();
    } else {
        bs = bdrv_find(device);
        if (!bs) {
            qerror_report(QERR_DEVICE_NOT_FOUND, device);
            return;
        }
        bdrv_commit(bs);
    }
}

int do_snapshot_blkdev(Monitor *mon, const QDict *qdict, QObject **ret_data)
{
    const char *device = qdict_get_str(qdict, "device");
    const char *filename = qdict_get_try_str(qdict, "snapshot-file");
    const char *format = qdict_get_try_str(qdict, "format");
    BlockDriverState *bs;
    BlockDriver *drv, *old_drv, *proto_drv;
    int ret = 0;
    int flags;
    char old_filename[1024];

    if (!filename) {
        qerror_report(QERR_MISSING_PARAMETER, "snapshot-file");
        ret = -1;
        goto out;
    }

    bs = bdrv_find(device);
    if (!bs) {
        qerror_report(QERR_DEVICE_NOT_FOUND, device);
        ret = -1;
        goto out;
    }

    pstrcpy(old_filename, sizeof(old_filename), bs->filename);

    old_drv = bs->drv;
    flags = bs->open_flags;

    if (!format) {
        format = "qcow2";
    }

    drv = bdrv_find_format(format);
    if (!drv) {
        qerror_report(QERR_INVALID_BLOCK_FORMAT, format);
        ret = -1;
        goto out;
    }

    proto_drv = bdrv_find_protocol(filename);
    if (!proto_drv) {
        qerror_report(QERR_INVALID_BLOCK_FORMAT, format);
        ret = -1;
        goto out;
    }

    ret = bdrv_img_create(filename, format, bs->filename,
                          bs->drv->format_name, NULL, -1, flags);
    if (ret) {
        goto out;
    }

    qemu_aio_flush();
    bdrv_flush(bs);

    bdrv_close(bs);
    ret = bdrv_open(bs, filename, flags, drv);
    /*
     * If reopening the image file we just created fails, fall back
     * and try to re-open the original image. If that fails too, we
     * are in serious trouble.
     */
    if (ret != 0) {
        ret = bdrv_open(bs, old_filename, flags, old_drv);
        if (ret != 0) {
            qerror_report(QERR_OPEN_FILE_FAILED, old_filename);
        } else {
            qerror_report(QERR_OPEN_FILE_FAILED, filename);
        }
    }
out:
    if (ret) {
        ret = -1;
    }

    return ret;
}

static int eject_device(Monitor *mon, BlockDriverState *bs, int force)
{
    if (!bdrv_dev_has_removable_media(bs)) {
        qerror_report(QERR_DEVICE_NOT_REMOVABLE, bdrv_get_device_name(bs));
        return -1;
    }
    if (bdrv_dev_is_medium_locked(bs) && !bdrv_dev_is_tray_open(bs)) {
        bdrv_dev_eject_request(bs, force);
        if (!force) {
            qerror_report(QERR_DEVICE_LOCKED, bdrv_get_device_name(bs));
            return -1;
        }
    }
    bdrv_close(bs);
    return 0;
}

int do_eject(Monitor *mon, const QDict *qdict, QObject **ret_data)
{
    BlockDriverState *bs;
    int force = qdict_get_try_bool(qdict, "force", 0);
    const char *filename = qdict_get_str(qdict, "device");

    bs = bdrv_find(filename);
    if (!bs) {
        qerror_report(QERR_DEVICE_NOT_FOUND, filename);
        return -1;
    }
    return eject_device(mon, bs, force);
}

int do_block_set_passwd(Monitor *mon, const QDict *qdict,
                        QObject **ret_data)
{
    BlockDriverState *bs;
    int err;

    bs = bdrv_find(qdict_get_str(qdict, "device"));
    if (!bs) {
        qerror_report(QERR_DEVICE_NOT_FOUND, qdict_get_str(qdict, "device"));
        return -1;
    }

    err = bdrv_set_key(bs, qdict_get_str(qdict, "password"));
    if (err == -EINVAL) {
        qerror_report(QERR_DEVICE_NOT_ENCRYPTED, bdrv_get_device_name(bs));
        return -1;
    } else if (err < 0) {
        qerror_report(QERR_INVALID_PASSWORD);
        return -1;
    }

    return 0;
}

int do_change_block(Monitor *mon, const char *device,
                    const char *filename, const char *fmt)
{
    BlockDriverState *bs;
    BlockDriver *drv = NULL;
    int bdrv_flags;

    bs = bdrv_find(device);
    if (!bs) {
        qerror_report(QERR_DEVICE_NOT_FOUND, device);
        return -1;
    }
    if (fmt) {
        drv = bdrv_find_whitelisted_format(fmt);
        if (!drv) {
            qerror_report(QERR_INVALID_BLOCK_FORMAT, fmt);
            return -1;
        }
    }
    if (eject_device(mon, bs, 0) < 0) {
        return -1;
    }
    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
    bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
    if (bdrv_open(bs, filename, bdrv_flags, drv) < 0) {
        qerror_report(QERR_OPEN_FILE_FAILED, filename);
        return -1;
    }
    return monitor_read_bdrv_key_start(mon, bs, NULL, NULL);
}

int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
{
    const char *id = qdict_get_str(qdict, "id");
    BlockDriverState *bs;

    bs = bdrv_find(id);
    if (!bs) {
        qerror_report(QERR_DEVICE_NOT_FOUND, id);
        return -1;
    }
    if (bdrv_in_use(bs)) {
        qerror_report(QERR_DEVICE_IN_USE, id);
        return -1;
    }

    /* quiesce block driver; prevent further io */
    qemu_aio_flush();
    bdrv_flush(bs);
    bdrv_close(bs);

    /* if we have a device attached to this BlockDriverState
     * then we need to make the drive anonymous until the device
     * can be removed.  If this is a drive with no device backing
     * then we can just get rid of the block driver state right here.
     */
    if (bdrv_get_attached_dev(bs)) {
        bdrv_make_anon(bs);
    } else {
        drive_uninit(drive_get_by_blockdev(bs));
    }

    return 0;
}

/*
 * XXX: replace the QERR_UNDEFINED_ERROR errors with real values once the
 * existing QERR_ macro mess is cleaned up.  A good example for better
 * error reports can be found in the qemu-img resize code.
 */
int do_block_resize(Monitor *mon, const QDict *qdict, QObject **ret_data)
{
    const char *device = qdict_get_str(qdict, "device");
    int64_t size = qdict_get_int(qdict, "size");
    BlockDriverState *bs;

    bs = bdrv_find(device);
    if (!bs) {
        qerror_report(QERR_DEVICE_NOT_FOUND, device);
        return -1;
    }

    if (size < 0) {
        qerror_report(QERR_UNDEFINED_ERROR);
        return -1;
    }

    if (bdrv_truncate(bs, size)) {
        qerror_report(QERR_UNDEFINED_ERROR);
        return -1;
    }

    return 0;
}