Archipelago » qemu

/*

 * Block driver for the COW format

 *

 * Copyright (c) 2004 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 "qemu-common.h"

#include "block/block_int.h"

#include "qemu/module.h"

/**************************************************************/

/* COW block driver using file system holes */

/* user mode linux compatible COW file */

#define COW_MAGIC 0x4f4f4f4d  /* MOOO */

#define COW_VERSION 2

struct cow_header_v2 {

    uint32_t magic;

    uint32_t version;

    char backing_file[1024];

    int32_t mtime;

    uint64_t size;

    uint32_t sectorsize;

};

typedef struct BDRVCowState {

    CoMutex lock;

    int64_t cow_sectors_offset;

} BDRVCowState;

static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)

{

    const struct cow_header_v2 *cow_header = (const void *)buf;

    if (buf_size >= sizeof(struct cow_header_v2) &&

        be32_to_cpu(cow_header->magic) == COW_MAGIC &&

        be32_to_cpu(cow_header->version) == COW_VERSION)

        return 100;

    else

        return 0;

}

static int cow_open(BlockDriverState *bs, QDict *options, int flags,

                    Error **errp)

{

    BDRVCowState *s = bs->opaque;

    struct cow_header_v2 cow_header;

    int bitmap_size;

    int64_t size;

    int ret;

    /* see if it is a cow image */

    ret = bdrv_pread(bs->file, 0, &cow_header, sizeof(cow_header));

    if (ret < 0) {

        goto fail;

    }

    if (be32_to_cpu(cow_header.magic) != COW_MAGIC) {

        ret = -EMEDIUMTYPE;

        goto fail;

    }

    if (be32_to_cpu(cow_header.version) != COW_VERSION) {

        char version[64];

        snprintf(version, sizeof(version),

               "COW version %d", cow_header.version);

        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,

            bs->device_name, "cow", version);

        ret = -ENOTSUP;

        goto fail;

    }

    /* cow image found */

    size = be64_to_cpu(cow_header.size);

    bs->total_sectors = size / 512;

    pstrcpy(bs->backing_file, sizeof(bs->backing_file),

            cow_header.backing_file);

    bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);

    s->cow_sectors_offset = (bitmap_size + 511) & ~511;

    qemu_co_mutex_init(&s->lock);

    return 0;

 fail:

    return ret;

}

/*

 * XXX(hch): right now these functions are extremely inefficient.

 * We should just read the whole bitmap we'll need in one go instead.

 */

static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)

{

    uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;

    uint8_t bitmap;

    int ret;

    ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));

    if (ret < 0) {

       return ret;

    }

    if (bitmap & (1 << (bitnum % 8))) {

        return 0;

    }

    if (*first) {

        ret = bdrv_flush(bs->file);

        if (ret < 0) {

            return ret;

        }

        *first = false;

    }

    bitmap |= (1 << (bitnum % 8));

    ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));

    if (ret < 0) {

       return ret;

    }

    return 0;

}

#define BITS_PER_BITMAP_SECTOR (512 * 8)

/* Cannot use bitmap.c on big-endian machines.  */

static int cow_test_bit(int64_t bitnum, const uint8_t *bitmap)

{

    return (bitmap[bitnum / 8] & (1 << (bitnum & 7))) != 0;

}

static int cow_find_streak(const uint8_t *bitmap, int value, int start, int nb_sectors)

{

    int streak_value = value ? 0xFF : 0;

    int last = MIN(start + nb_sectors, BITS_PER_BITMAP_SECTOR);

    int bitnum = start;

    while (bitnum < last) {

        if ((bitnum & 7) == 0 && bitmap[bitnum / 8] == streak_value) {

            bitnum += 8;

            continue;

        }

        if (cow_test_bit(bitnum, bitmap) == value) {

            bitnum++;

            continue;

        }

        break;

    }

    return MIN(bitnum, last) - start;

}

/* Return true if first block has been changed (ie. current version is

 * in COW file).  Set the number of continuous blocks for which that

 * is true. */

static int coroutine_fn cow_co_is_allocated(BlockDriverState *bs,

        int64_t sector_num, int nb_sectors, int *num_same)

{

    int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8;

    uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE;

    uint8_t bitmap[BDRV_SECTOR_SIZE];

    int ret;

    int changed;

    ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap));

    if (ret < 0) {

        return ret;

    }

    bitnum &= BITS_PER_BITMAP_SECTOR - 1;

    changed = cow_test_bit(bitnum, bitmap);

    *num_same = cow_find_streak(bitmap, changed, bitnum, nb_sectors);

    return changed;

}

static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs,

        int64_t sector_num, int nb_sectors, int *num_same)

{

    BDRVCowState *s = bs->opaque;

    int ret = cow_co_is_allocated(bs, sector_num, nb_sectors, num_same);

    int64_t offset = s->cow_sectors_offset + (sector_num << BDRV_SECTOR_BITS);

    if (ret < 0) {

        return ret;

    }

    return (ret ? BDRV_BLOCK_DATA : 0) | offset | BDRV_BLOCK_OFFSET_VALID;

}

static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,

        int nb_sectors)

{

    int error = 0;

    int i;

    bool first = true;

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

        error = cow_set_bit(bs, sector_num + i, &first);

        if (error) {

            break;

        }

    }

    return error;

}

static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num,

                                 uint8_t *buf, int nb_sectors)

{

    BDRVCowState *s = bs->opaque;

    int ret, n;

    while (nb_sectors > 0) {

        ret = cow_co_is_allocated(bs, sector_num, nb_sectors, &n);

        if (ret < 0) {

            return ret;

        }

        if (ret) {

            ret = bdrv_pread(bs->file,

                        s->cow_sectors_offset + sector_num * 512,

                        buf, n * 512);

            if (ret < 0) {

                return ret;

            }

        } else {

            if (bs->backing_hd) {

                /* read from the base image */

                ret = bdrv_read(bs->backing_hd, sector_num, buf, n);

                if (ret < 0) {

                    return ret;

                }

            } else {

                memset(buf, 0, n * 512);

            }

        }

        nb_sectors -= n;

        sector_num += n;

        buf += n * 512;

    }

    return 0;

}

static coroutine_fn int cow_co_read(BlockDriverState *bs, int64_t sector_num,

                                    uint8_t *buf, int nb_sectors)

{

    int ret;

    BDRVCowState *s = bs->opaque;

    qemu_co_mutex_lock(&s->lock);

    ret = cow_read(bs, sector_num, buf, nb_sectors);

    qemu_co_mutex_unlock(&s->lock);

    return ret;

}

static int cow_write(BlockDriverState *bs, int64_t sector_num,

                     const uint8_t *buf, int nb_sectors)

{

    BDRVCowState *s = bs->opaque;

    int ret;

    ret = bdrv_pwrite(bs->file, s->cow_sectors_offset + sector_num * 512,

                      buf, nb_sectors * 512);

    if (ret < 0) {

        return ret;

    }

    return cow_update_bitmap(bs, sector_num, nb_sectors);

}

static coroutine_fn int cow_co_write(BlockDriverState *bs, int64_t sector_num,

                                     const uint8_t *buf, int nb_sectors)

{

    int ret;

    BDRVCowState *s = bs->opaque;

    qemu_co_mutex_lock(&s->lock);

    ret = cow_write(bs, sector_num, buf, nb_sectors);

    qemu_co_mutex_unlock(&s->lock);

    return ret;

}

static void cow_close(BlockDriverState *bs)

{

}

static int cow_create(const char *filename, QEMUOptionParameter *options,

                      Error **errp)

{

    struct cow_header_v2 cow_header;

    struct stat st;

    int64_t image_sectors = 0;

    const char *image_filename = NULL;

    int ret;

    BlockDriverState *cow_bs;

    /* Read out options */

    while (options && options->name) {

        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {

            image_sectors = options->value.n / 512;

        } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {

            image_filename = options->value.s;

        }

        options++;

    }

    ret = bdrv_create_file(filename, options);

    if (ret < 0) {

        return ret;

    }

    ret = bdrv_file_open(&cow_bs, filename, NULL, BDRV_O_RDWR);

    if (ret < 0) {

        return ret;

    }

    memset(&cow_header, 0, sizeof(cow_header));

    cow_header.magic = cpu_to_be32(COW_MAGIC);

    cow_header.version = cpu_to_be32(COW_VERSION);

    if (image_filename) {

        /* Note: if no file, we put a dummy mtime */

        cow_header.mtime = cpu_to_be32(0);

        if (stat(image_filename, &st) != 0) {

            goto mtime_fail;

        }

        cow_header.mtime = cpu_to_be32(st.st_mtime);

    mtime_fail:

        pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),

                image_filename);

    }

    cow_header.sectorsize = cpu_to_be32(512);

    cow_header.size = cpu_to_be64(image_sectors * 512);

    ret = bdrv_pwrite(cow_bs, 0, &cow_header, sizeof(cow_header));

    if (ret < 0) {

        goto exit;

    }

    /* resize to include at least all the bitmap */

    ret = bdrv_truncate(cow_bs,

        sizeof(cow_header) + ((image_sectors + 7) >> 3));

    if (ret < 0) {

        goto exit;

    }

exit:

    bdrv_unref(cow_bs);

    return ret;

}

static QEMUOptionParameter cow_create_options[] = {

    {

        .name = BLOCK_OPT_SIZE,

        .type = OPT_SIZE,

        .help = "Virtual disk size"

    },

    {

        .name = BLOCK_OPT_BACKING_FILE,

        .type = OPT_STRING,

        .help = "File name of a base image"

    },

    { NULL }

};

static BlockDriver bdrv_cow = {

    .format_name    = "cow",

    .instance_size  = sizeof(BDRVCowState),

    .bdrv_probe     = cow_probe,

    .bdrv_open      = cow_open,

    .bdrv_close     = cow_close,

    .bdrv_create    = cow_create,

    .bdrv_has_zero_init     = bdrv_has_zero_init_1,

    .bdrv_read              = cow_co_read,

    .bdrv_write             = cow_co_write,

    .bdrv_co_get_block_status   = cow_co_get_block_status,

    .create_options = cow_create_options,

};

static void bdrv_cow_init(void)

{

    bdrv_register(&bdrv_cow);

}

block_init(bdrv_cow_init);