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_int.h"

#include "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 {

    int fd;

    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, const char *filename, int flags)

{

    BDRVCowState *s = bs->opaque;

    int fd;

    struct cow_header_v2 cow_header;

    int bitmap_size;

    int64_t size;

    fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);

    if (fd < 0) {

        fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);

        if (fd < 0)

            return -1;

    }

    s->fd = fd;

    /* see if it is a cow image */

    if (pread(fd, &cow_header, sizeof(cow_header), 0) != sizeof(cow_header)) {

        goto fail;

    }

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

        be32_to_cpu(cow_header.version) != COW_VERSION) {

        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;

    return 0;

 fail:

    close(fd);

    return -1;

}

/*

 * XXX(hch): right now these functions are extremly ineffcient.

 * 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)

{

    BDRVCowState *s = bs->opaque;

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

    uint8_t bitmap;

    if (pread(s->fd, &bitmap, sizeof(bitmap), offset) !=

            sizeof(bitmap)) {

       return -errno;

    }

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

    if (pwrite(s->fd, &bitmap, sizeof(bitmap), offset) !=

            sizeof(bitmap)) {

       return -errno;

    }

    return 0;

}

static inline int is_bit_set(BlockDriverState *bs, int64_t bitnum)

{

    BDRVCowState *s = bs->opaque;

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

    uint8_t bitmap;

    if (pread(s->fd, &bitmap, sizeof(bitmap), offset) !=

            sizeof(bitmap)) {

       return -errno;

    }

    return !!(bitmap & (1 << (bitnum % 8)));

}

/* 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 cow_is_allocated(BlockDriverState *bs, int64_t sector_num,

        int nb_sectors, int *num_same)

{

    int changed;

    if (nb_sectors == 0) {

        *num_same = nb_sectors;

        return 0;

    }

    changed = is_bit_set(bs, sector_num);

    if (changed < 0) {

        return 0; /* XXX: how to return I/O errors? */

    }

    for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {

        if (is_bit_set(bs, sector_num + *num_same) != changed)

            break;

    }

    return changed;

}

static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,

        int nb_sectors)

{

    int error = 0;

    int i;

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

        error = cow_set_bit(bs, sector_num + i);

        if (error) {

            break;

        }

    }

    return error;

}

static int 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) {

        if (cow_is_allocated(bs, sector_num, nb_sectors, &n)) {

            ret = pread(s->fd, buf, n * 512,

                        s->cow_sectors_offset + sector_num * 512);

            if (ret != n * 512)

                return -1;

        } else {

            if (bs->backing_hd) {

                /* read from the base image */

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

                if (ret < 0)

                    return -1;

            } else {

            memset(buf, 0, n * 512);

        }

        }

        nb_sectors -= n;

        sector_num += n;

        buf += n * 512;

    }

    return 0;

}

static int cow_write(BlockDriverState *bs, int64_t sector_num,

                     const uint8_t *buf, int nb_sectors)

{

    BDRVCowState *s = bs->opaque;

    int ret;

    ret = pwrite(s->fd, buf, nb_sectors * 512,

                 s->cow_sectors_offset + sector_num * 512);

    if (ret != nb_sectors * 512)

        return -1;

    return cow_update_bitmap(bs, sector_num, nb_sectors);

}

static void cow_close(BlockDriverState *bs)

{

    BDRVCowState *s = bs->opaque;

    close(s->fd);

}

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

{

    int fd, cow_fd;

    struct cow_header_v2 cow_header;

    struct stat st;

    int64_t image_sectors = 0;

    const char *image_filename = NULL;

    int ret;

    /* 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++;

    }

    cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,

              0644);

    if (cow_fd < 0)

        return -errno;

    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);

        fd = open(image_filename, O_RDONLY | O_BINARY);

        if (fd < 0) {

            close(cow_fd);

            goto mtime_fail;

        }

        if (fstat(fd, &st) != 0) {

            close(fd);

            goto mtime_fail;

        }

        close(fd);

        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 = qemu_write_full(cow_fd, &cow_header, sizeof(cow_header));

    if (ret != sizeof(cow_header)) {

        ret = -errno;

        goto exit;

    }

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

    ret = ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));

    if (ret) {

        ret = -errno;

        goto exit;

    }

exit:

    close(cow_fd);

    return ret;

}

static void cow_flush(BlockDriverState *bs)

{

    BDRVCowState *s = bs->opaque;

    qemu_fdatasync(s->fd);

}

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_file_open        = cow_open,

    .bdrv_read                = cow_read,

    .bdrv_write                = cow_write,

    .bdrv_close                = cow_close,

    .bdrv_create        = cow_create,

    .bdrv_flush                = cow_flush,

    .bdrv_is_allocated        = cow_is_allocated,

    .create_options = cow_create_options,

};

static void bdrv_cow_init(void)

{

    bdrv_register(&bdrv_cow);

}

block_init(bdrv_cow_init);