Archipelago » qemu

/*

 * QEMU System Emulator block driver

 *

 * Copyright (c) 2003 Fabrice Bellard

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL

 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

 * THE SOFTWARE.

 */

#include "config-host.h"

#include "qemu-common.h"

#include "monitor.h"

#include "block_int.h"

#include "module.h"

#ifdef CONFIG_BSD

#include <sys/types.h>

#include <sys/stat.h>

#include <sys/ioctl.h>

#include <sys/queue.h>

#ifndef __DragonFly__

#include <sys/disk.h>

#endif

#endif

#ifdef _WIN32

#include <windows.h>

#endif

#define SECTOR_BITS 9

#define SECTOR_SIZE (1 << SECTOR_BITS)

static BlockDriverAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,

        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,

        BlockDriverCompletionFunc *cb, void *opaque);

static BlockDriverAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,

        int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,

        BlockDriverCompletionFunc *cb, void *opaque);

static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,

        BlockDriverCompletionFunc *cb, void *opaque);

static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,

                        uint8_t *buf, int nb_sectors);

static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,

                         const uint8_t *buf, int nb_sectors);

BlockDriverState *bdrv_first;

static BlockDriver *first_drv;

/* If non-zero, use only whitelisted block drivers */

static int use_bdrv_whitelist;

int path_is_absolute(const char *path)

{

    const char *p;

#ifdef _WIN32

    /* specific case for names like: "\\.\d:" */

    if (*path == '/' || *path == '\\')

        return 1;

#endif

    p = strchr(path, ':');

    if (p)

        p++;

    else

        p = path;

#ifdef _WIN32

    return (*p == '/' || *p == '\\');

#else

    return (*p == '/');

#endif

}

/* if filename is absolute, just copy it to dest. Otherwise, build a

   path to it by considering it is relative to base_path. URL are

   supported. */

void path_combine(char *dest, int dest_size,

                  const char *base_path,

                  const char *filename)

{

    const char *p, *p1;

    int len;

    if (dest_size <= 0)

        return;

    if (path_is_absolute(filename)) {

        pstrcpy(dest, dest_size, filename);

    } else {

        p = strchr(base_path, ':');

        if (p)

            p++;

        else

            p = base_path;

        p1 = strrchr(base_path, '/');

#ifdef _WIN32

        {

            const char *p2;

            p2 = strrchr(base_path, '\\');

            if (!p1 || p2 > p1)

                p1 = p2;

        }

#endif

        if (p1)

            p1++;

        else

            p1 = base_path;

        if (p1 > p)

            p = p1;

        len = p - base_path;

        if (len > dest_size - 1)

            len = dest_size - 1;

        memcpy(dest, base_path, len);

        dest[len] = '\0';

        pstrcat(dest, dest_size, filename);

    }

}

void bdrv_register(BlockDriver *bdrv)

{

    if (!bdrv->bdrv_aio_readv) {

        /* add AIO emulation layer */

        bdrv->bdrv_aio_readv = bdrv_aio_readv_em;

        bdrv->bdrv_aio_writev = bdrv_aio_writev_em;

    } else if (!bdrv->bdrv_read) {

        /* add synchronous IO emulation layer */

        bdrv->bdrv_read = bdrv_read_em;

        bdrv->bdrv_write = bdrv_write_em;

    }

    if (!bdrv->bdrv_aio_flush)

        bdrv->bdrv_aio_flush = bdrv_aio_flush_em;

    bdrv->next = first_drv;

    first_drv = bdrv;

}

/* create a new block device (by default it is empty) */

BlockDriverState *bdrv_new(const char *device_name)

{

    BlockDriverState **pbs, *bs;

    bs = qemu_mallocz(sizeof(BlockDriverState));

    pstrcpy(bs->device_name, sizeof(bs->device_name), device_name);

    if (device_name[0] != '\0') {

        /* insert at the end */

        pbs = &bdrv_first;

        while (*pbs != NULL)

            pbs = &(*pbs)->next;

        *pbs = bs;

    }

    return bs;

}

BlockDriver *bdrv_find_format(const char *format_name)

{

    BlockDriver *drv1;

    for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {

        if (!strcmp(drv1->format_name, format_name))

            return drv1;

    }

    return NULL;

}

static int bdrv_is_whitelisted(BlockDriver *drv)

{

    static const char *whitelist[] = {

        CONFIG_BDRV_WHITELIST

    };

    const char **p;

    if (!whitelist[0])

        return 1;               /* no whitelist, anything goes */

    for (p = whitelist; *p; p++) {

        if (!strcmp(drv->format_name, *p)) {

            return 1;

        }

    }

    return 0;

}

BlockDriver *bdrv_find_whitelisted_format(const char *format_name)

{

    BlockDriver *drv = bdrv_find_format(format_name);

    return drv && bdrv_is_whitelisted(drv) ? drv : NULL;

}

int bdrv_create(BlockDriver *drv, const char* filename,

    QEMUOptionParameter *options)

{

    if (!drv->bdrv_create)

        return -ENOTSUP;

    return drv->bdrv_create(filename, options);

}

#ifdef _WIN32

void get_tmp_filename(char *filename, int size)

{

    char temp_dir[MAX_PATH];

    GetTempPath(MAX_PATH, temp_dir);

    GetTempFileName(temp_dir, "qem", 0, filename);

}

#else

void get_tmp_filename(char *filename, int size)

{

    int fd;

    const char *tmpdir;

    /* XXX: race condition possible */

    tmpdir = getenv("TMPDIR");

    if (!tmpdir)

        tmpdir = "/tmp";

    snprintf(filename, size, "%s/vl.XXXXXX", tmpdir);

    fd = mkstemp(filename);

    close(fd);

}

#endif

#ifdef _WIN32

static int is_windows_drive_prefix(const char *filename)

{

    return (((filename[0] >= 'a' && filename[0] <= 'z') ||

             (filename[0] >= 'A' && filename[0] <= 'Z')) &&

            filename[1] == ':');

}

int is_windows_drive(const char *filename)

{

    if (is_windows_drive_prefix(filename) &&

        filename[2] == '\0')

        return 1;

    if (strstart(filename, "\\\\.\\", NULL) ||

        strstart(filename, "//./", NULL))

        return 1;

    return 0;

}

#endif

static BlockDriver *find_protocol(const char *filename)

{

    BlockDriver *drv1;

    char protocol[128];

    int len;

    const char *p;

#ifdef _WIN32

    if (is_windows_drive(filename) ||

        is_windows_drive_prefix(filename))

        return bdrv_find_format("raw");

#endif

    p = strchr(filename, ':');

    if (!p)

        return bdrv_find_format("raw");

    len = p - filename;

    if (len > sizeof(protocol) - 1)

        len = sizeof(protocol) - 1;

    memcpy(protocol, filename, len);

    protocol[len] = '\0';

    for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {

        if (drv1->protocol_name &&

            !strcmp(drv1->protocol_name, protocol))

            return drv1;

    }

    return NULL;

}

/*

 * Detect host devices. By convention, /dev/cdrom[N] is always

 * recognized as a host CDROM.

 */

static BlockDriver *find_hdev_driver(const char *filename)

{

    int score_max = 0, score;

    BlockDriver *drv = NULL, *d;

    for (d = first_drv; d; d = d->next) {

        if (d->bdrv_probe_device) {

            score = d->bdrv_probe_device(filename);

            if (score > score_max) {

                score_max = score;

                drv = d;

            }

        }

    }

    return drv;

}

static BlockDriver *find_image_format(const char *filename)

{

    int ret, score, score_max;

    BlockDriver *drv1, *drv;

    uint8_t buf[2048];

    BlockDriverState *bs;

    drv = find_protocol(filename);

    /* no need to test disk image formats for vvfat */

    if (drv && strcmp(drv->format_name, "vvfat") == 0)

        return drv;

    ret = bdrv_file_open(&bs, filename, BDRV_O_RDONLY);

    if (ret < 0)

        return NULL;

    ret = bdrv_pread(bs, 0, buf, sizeof(buf));

    bdrv_delete(bs);

    if (ret < 0) {

        return NULL;

    }

    score_max = 0;

    for(drv1 = first_drv; drv1 != NULL; drv1 = drv1->next) {

        if (drv1->bdrv_probe) {

            score = drv1->bdrv_probe(buf, ret, filename);

            if (score > score_max) {

                score_max = score;

                drv = drv1;

            }

        }

    }

    return drv;

}

int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags)

{

    BlockDriverState *bs;

    int ret;

    bs = bdrv_new("");

    ret = bdrv_open2(bs, filename, flags | BDRV_O_FILE, NULL);

    if (ret < 0) {

        bdrv_delete(bs);

        return ret;

    }

    bs->growable = 1;

    *pbs = bs;

    return 0;

}

int bdrv_open(BlockDriverState *bs, const char *filename, int flags)

{

    return bdrv_open2(bs, filename, flags, NULL);

}

int bdrv_open2(BlockDriverState *bs, const char *filename, int flags,

               BlockDriver *drv)

{

    int ret, open_flags, try_rw;

    char tmp_filename[PATH_MAX];

    char backing_filename[PATH_MAX];

    bs->is_temporary = 0;

    bs->encrypted = 0;

    bs->valid_key = 0;

    /* buffer_alignment defaulted to 512, drivers can change this value */

    bs->buffer_alignment = 512;

    if (flags & BDRV_O_SNAPSHOT) {

        BlockDriverState *bs1;

        int64_t total_size;

        int is_protocol = 0;

        BlockDriver *bdrv_qcow2;

        QEMUOptionParameter *options;

        /* if snapshot, we create a temporary backing file and open it

           instead of opening 'filename' directly */

        /* if there is a backing file, use it */

        bs1 = bdrv_new("");

        ret = bdrv_open2(bs1, filename, 0, drv);

        if (ret < 0) {

            bdrv_delete(bs1);

            return ret;

        }

        total_size = bdrv_getlength(bs1) >> SECTOR_BITS;

        if (bs1->drv && bs1->drv->protocol_name)

            is_protocol = 1;

        bdrv_delete(bs1);

        get_tmp_filename(tmp_filename, sizeof(tmp_filename));

        /* Real path is meaningless for protocols */

        if (is_protocol)

            snprintf(backing_filename, sizeof(backing_filename),

                     "%s", filename);

        else

            realpath(filename, backing_filename);

        bdrv_qcow2 = bdrv_find_format("qcow2");

        options = parse_option_parameters("", bdrv_qcow2->create_options, NULL);

        set_option_parameter_int(options, BLOCK_OPT_SIZE, total_size * 512);

        set_option_parameter(options, BLOCK_OPT_BACKING_FILE, backing_filename);

        if (drv) {

            set_option_parameter(options, BLOCK_OPT_BACKING_FMT,

                drv->format_name);

        }

        ret = bdrv_create(bdrv_qcow2, tmp_filename, options);

        if (ret < 0) {

            return ret;

        }

        filename = tmp_filename;

        drv = bdrv_qcow2;

        bs->is_temporary = 1;

    }

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

    if (flags & BDRV_O_FILE) {

        drv = find_protocol(filename);

    } else if (!drv) {

        drv = find_hdev_driver(filename);

        if (!drv) {

            drv = find_image_format(filename);

        }

    }

    if (!drv) {

        ret = -ENOENT;

        goto unlink_and_fail;

    }

    bs->drv = drv;

    bs->opaque = qemu_mallocz(drv->instance_size);

    /*

     * Yes, BDRV_O_NOCACHE aka O_DIRECT means we have to present a

     * write cache to the guest.  We do need the fdatasync to flush

     * out transactions for block allocations, and we maybe have a

     * volatile write cache in our backing device to deal with.

     */

    if (flags & (BDRV_O_CACHE_WB|BDRV_O_NOCACHE))

        bs->enable_write_cache = 1;

    /* Note: for compatibility, we open disk image files as RDWR, and

       RDONLY as fallback */

    try_rw = !bs->read_only || bs->is_temporary;

    if (!(flags & BDRV_O_FILE))

        open_flags = (try_rw ? BDRV_O_RDWR : 0) |

            (flags & (BDRV_O_CACHE_MASK|BDRV_O_NATIVE_AIO));

    else

        open_flags = flags & ~(BDRV_O_FILE | BDRV_O_SNAPSHOT);

    if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv))

        ret = -ENOTSUP;

    else

        ret = drv->bdrv_open(bs, filename, open_flags);

    if ((ret == -EACCES || ret == -EPERM) && !(flags & BDRV_O_FILE)) {

        ret = drv->bdrv_open(bs, filename, open_flags & ~BDRV_O_RDWR);

        bs->read_only = 1;

    }

    if (ret < 0) {

        qemu_free(bs->opaque);

        bs->opaque = NULL;

        bs->drv = NULL;

    unlink_and_fail:

        if (bs->is_temporary)

            unlink(filename);

        return ret;

    }

    if (drv->bdrv_getlength) {

        bs->total_sectors = bdrv_getlength(bs) >> SECTOR_BITS;

    }

#ifndef _WIN32

    if (bs->is_temporary) {

        unlink(filename);

    }

#endif

    if (bs->backing_file[0] != '\0') {

        /* if there is a backing file, use it */

        BlockDriver *back_drv = NULL;

        bs->backing_hd = bdrv_new("");

        /* pass on read_only property to the backing_hd */

        bs->backing_hd->read_only = bs->read_only;

        path_combine(backing_filename, sizeof(backing_filename),

                     filename, bs->backing_file);

        if (bs->backing_format[0] != '\0')

            back_drv = bdrv_find_format(bs->backing_format);

        ret = bdrv_open2(bs->backing_hd, backing_filename, open_flags,

                         back_drv);

        if (ret < 0) {

            bdrv_close(bs);

            return ret;

        }

    }

    if (!bdrv_key_required(bs)) {

        /* call the change callback */

        bs->media_changed = 1;

        if (bs->change_cb)

            bs->change_cb(bs->change_opaque);

    }

    return 0;

}

void bdrv_close(BlockDriverState *bs)

{

    if (bs->drv) {

        if (bs->backing_hd)

            bdrv_delete(bs->backing_hd);

        bs->drv->bdrv_close(bs);

        qemu_free(bs->opaque);

#ifdef _WIN32

        if (bs->is_temporary) {

            unlink(bs->filename);

        }

#endif

        bs->opaque = NULL;

        bs->drv = NULL;

        /* call the change callback */

        bs->media_changed = 1;

        if (bs->change_cb)

            bs->change_cb(bs->change_opaque);

    }

}

void bdrv_delete(BlockDriverState *bs)

{

    BlockDriverState **pbs;

    pbs = &bdrv_first;

    while (*pbs != bs && *pbs != NULL)

        pbs = &(*pbs)->next;

    if (*pbs == bs)

        *pbs = bs->next;

    bdrv_close(bs);

    qemu_free(bs);

}

/*

 * Run consistency checks on an image

 *

 * Returns the number of errors or -errno when an internal error occurs

 */

int bdrv_check(BlockDriverState *bs)

{

    if (bs->drv->bdrv_check == NULL) {

        return -ENOTSUP;

    }

    return bs->drv->bdrv_check(bs);

}

/* commit COW file into the raw image */

int bdrv_commit(BlockDriverState *bs)

{

    BlockDriver *drv = bs->drv;

    int64_t i, total_sectors;

    int n, j;

    unsigned char sector[512];

    if (!drv)

        return -ENOMEDIUM;

    if (bs->read_only) {

        return -EACCES;

    }

    if (!bs->backing_hd) {

        return -ENOTSUP;

    }

    total_sectors = bdrv_getlength(bs) >> SECTOR_BITS;

    for (i = 0; i < total_sectors;) {

        if (drv->bdrv_is_allocated(bs, i, 65536, &n)) {

            for(j = 0; j < n; j++) {

                if (bdrv_read(bs, i, sector, 1) != 0) {

                    return -EIO;

                }

                if (bdrv_write(bs->backing_hd, i, sector, 1) != 0) {

                    return -EIO;

                }

                i++;

            }

        } else {

            i += n;

        }

    }

    if (drv->bdrv_make_empty)

        return drv->bdrv_make_empty(bs);

    return 0;

}

static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,

                                   size_t size)

{

    int64_t len;

    if (!bdrv_is_inserted(bs))

        return -ENOMEDIUM;

    if (bs->growable)

        return 0;

    len = bdrv_getlength(bs);

    if (offset < 0)

        return -EIO;

    if ((offset > len) || (len - offset < size))

        return -EIO;

    return 0;

}

static int bdrv_check_request(BlockDriverState *bs, int64_t sector_num,

                              int nb_sectors)

{

    return bdrv_check_byte_request(bs, sector_num * 512, nb_sectors * 512);

}

/* return < 0 if error. See bdrv_write() for the return codes */

int bdrv_read(BlockDriverState *bs, int64_t sector_num,

              uint8_t *buf, int nb_sectors)

{

    BlockDriver *drv = bs->drv;

    if (!drv)

        return -ENOMEDIUM;

    if (bdrv_check_request(bs, sector_num, nb_sectors))

        return -EIO;

    return drv->bdrv_read(bs, sector_num, buf, nb_sectors);

}

/* Return < 0 if error. Important errors are:

  -EIO         generic I/O error (may happen for all errors)

  -ENOMEDIUM   No media inserted.

  -EINVAL      Invalid sector number or nb_sectors

  -EACCES      Trying to write a read-only device

*/

int bdrv_write(BlockDriverState *bs, int64_t sector_num,

               const uint8_t *buf, int nb_sectors)

{

    BlockDriver *drv = bs->drv;

    if (!bs->drv)

        return -ENOMEDIUM;

    if (bs->read_only)

        return -EACCES;

    if (bdrv_check_request(bs, sector_num, nb_sectors))

        return -EIO;

    return drv->bdrv_write(bs, sector_num, buf, nb_sectors);

}

int bdrv_pread(BlockDriverState *bs, int64_t offset,

               void *buf, int count1)

{

    uint8_t tmp_buf[SECTOR_SIZE];

    int len, nb_sectors, count;

    int64_t sector_num;

    count = count1;

    /* first read to align to sector start */

    len = (SECTOR_SIZE - offset) & (SECTOR_SIZE - 1);

    if (len > count)

        len = count;

    sector_num = offset >> SECTOR_BITS;

    if (len > 0) {

        if (bdrv_read(bs, sector_num, tmp_buf, 1) < 0)

            return -EIO;

        memcpy(buf, tmp_buf + (offset & (SECTOR_SIZE - 1)), len);

        count -= len;

        if (count == 0)

            return count1;

        sector_num++;

        buf += len;

    }

    /* read the sectors "in place" */

    nb_sectors = count >> SECTOR_BITS;

    if (nb_sectors > 0) {

        if (bdrv_read(bs, sector_num, buf, nb_sectors) < 0)

            return -EIO;

        sector_num += nb_sectors;

        len = nb_sectors << SECTOR_BITS;

        buf += len;

        count -= len;

    }

    /* add data from the last sector */

    if (count > 0) {

        if (bdrv_read(bs, sector_num, tmp_buf, 1) < 0)

            return -EIO;

        memcpy(buf, tmp_buf, count);

    }

    return count1;

}

int bdrv_pwrite(BlockDriverState *bs, int64_t offset,

                const void *buf, int count1)

{

    uint8_t tmp_buf[SECTOR_SIZE];

    int len, nb_sectors, count;

    int64_t sector_num;

    count = count1;

    /* first write to align to sector start */

    len = (SECTOR_SIZE - offset) & (SECTOR_SIZE - 1);

    if (len > count)

        len = count;

    sector_num = offset >> SECTOR_BITS;

    if (len > 0) {

        if (bdrv_read(bs, sector_num, tmp_buf, 1) < 0)

            return -EIO;

        memcpy(tmp_buf + (offset & (SECTOR_SIZE - 1)), buf, len);

        if (bdrv_write(bs, sector_num, tmp_buf, 1) < 0)

            return -EIO;

        count -= len;

        if (count == 0)

            return count1;

        sector_num++;

        buf += len;

    }

    /* write the sectors "in place" */

    nb_sectors = count >> SECTOR_BITS;

    if (nb_sectors > 0) {

        if (bdrv_write(bs, sector_num, buf, nb_sectors) < 0)

            return -EIO;

        sector_num += nb_sectors;

        len = nb_sectors << SECTOR_BITS;

        buf += len;

        count -= len;

    }

    /* add data from the last sector */

    if (count > 0) {

        if (bdrv_read(bs, sector_num, tmp_buf, 1) < 0)

            return -EIO;

        memcpy(tmp_buf, buf, count);

        if (bdrv_write(bs, sector_num, tmp_buf, 1) < 0)

            return -EIO;

    }

    return count1;

}

/**

 * Truncate file to 'offset' bytes (needed only for file protocols)

 */

int bdrv_truncate(BlockDriverState *bs, int64_t offset)

{

    BlockDriver *drv = bs->drv;

    if (!drv)

        return -ENOMEDIUM;

    if (!drv->bdrv_truncate)

        return -ENOTSUP;

    if (bs->read_only)

        return -EACCES;

    return drv->bdrv_truncate(bs, offset);

}

/**

 * Length of a file in bytes. Return < 0 if error or unknown.

 */

int64_t bdrv_getlength(BlockDriverState *bs)

{

    BlockDriver *drv = bs->drv;

    if (!drv)

        return -ENOMEDIUM;

    if (!drv->bdrv_getlength) {

        /* legacy mode */

        return bs->total_sectors * SECTOR_SIZE;

    }

    return drv->bdrv_getlength(bs);

}

/* return 0 as number of sectors if no device present or error */

void bdrv_get_geometry(BlockDriverState *bs, uint64_t *nb_sectors_ptr)

{

    int64_t length;

    length = bdrv_getlength(bs);

    if (length < 0)

        length = 0;

    else

        length = length >> SECTOR_BITS;

    *nb_sectors_ptr = length;

}

struct partition {

        uint8_t boot_ind;           /* 0x80 - active */

        uint8_t head;               /* starting head */

        uint8_t sector;             /* starting sector */

        uint8_t cyl;                /* starting cylinder */

        uint8_t sys_ind;            /* What partition type */

        uint8_t end_head;           /* end head */

        uint8_t end_sector;         /* end sector */

        uint8_t end_cyl;            /* end cylinder */

        uint32_t start_sect;        /* starting sector counting from 0 */

        uint32_t nr_sects;          /* nr of sectors in partition */

} __attribute__((packed));

/* try to guess the disk logical geometry from the MSDOS partition table. Return 0 if OK, -1 if could not guess */

static int guess_disk_lchs(BlockDriverState *bs,

                           int *pcylinders, int *pheads, int *psectors)

{

    uint8_t buf[512];

    int ret, i, heads, sectors, cylinders;

    struct partition *p;

    uint32_t nr_sects;

    uint64_t nb_sectors;

    bdrv_get_geometry(bs, &nb_sectors);

    ret = bdrv_read(bs, 0, buf, 1);

    if (ret < 0)

        return -1;

    /* test msdos magic */

    if (buf[510] != 0x55 || buf[511] != 0xaa)

        return -1;

    for(i = 0; i < 4; i++) {

        p = ((struct partition *)(buf + 0x1be)) + i;

        nr_sects = le32_to_cpu(p->nr_sects);

        if (nr_sects && p->end_head) {

            /* We make the assumption that the partition terminates on

               a cylinder boundary */

            heads = p->end_head + 1;

            sectors = p->end_sector & 63;

            if (sectors == 0)

                continue;

            cylinders = nb_sectors / (heads * sectors);

            if (cylinders < 1 || cylinders > 16383)

                continue;

            *pheads = heads;

            *psectors = sectors;

            *pcylinders = cylinders;

#if 0

            printf("guessed geometry: LCHS=%d %d %d\n",

                   cylinders, heads, sectors);

#endif

            return 0;

        }

    }

    return -1;

}

void bdrv_guess_geometry(BlockDriverState *bs, int *pcyls, int *pheads, int *psecs)

{

    int translation, lba_detected = 0;

    int cylinders, heads, secs;

    uint64_t nb_sectors;

    /* if a geometry hint is available, use it */

    bdrv_get_geometry(bs, &nb_sectors);

    bdrv_get_geometry_hint(bs, &cylinders, &heads, &secs);

    translation = bdrv_get_translation_hint(bs);

    if (cylinders != 0) {

        *pcyls = cylinders;

        *pheads = heads;

        *psecs = secs;

    } else {

        if (guess_disk_lchs(bs, &cylinders, &heads, &secs) == 0) {

            if (heads > 16) {

                /* if heads > 16, it means that a BIOS LBA

                   translation was active, so the default

                   hardware geometry is OK */

                lba_detected = 1;

                goto default_geometry;

            } else {

                *pcyls = cylinders;

                *pheads = heads;

                *psecs = secs;

                /* disable any translation to be in sync with

                   the logical geometry */

                if (translation == BIOS_ATA_TRANSLATION_AUTO) {

                    bdrv_set_translation_hint(bs,

                                              BIOS_ATA_TRANSLATION_NONE);

                }

            }

        } else {

        default_geometry:

            /* if no geometry, use a standard physical disk geometry */

            cylinders = nb_sectors / (16 * 63);

            if (cylinders > 16383)

                cylinders = 16383;

            else if (cylinders < 2)

                cylinders = 2;