block-vpc: Write support (Kevin Wolf)

[qemu] / block-vpc.c

/*
 * Block driver for Conectix/Microsoft Virtual PC images
 *
 * Copyright (c) 2005 Alex Beregszaszi
 * Copyright (c) 2009 Kevin Wolf <kwolf@suse.de>
 *
 * 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"

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

#define HEADER_SIZE 512

//#define CACHE

enum vhd_type {
    VHD_FIXED           = 2,
    VHD_DYNAMIC         = 3,
    VHD_DIFFERENCING    = 4,
};

// always big-endian
struct vhd_footer {
    char        creator[8]; // "conectix"
    uint32_t    features;
    uint32_t    version;

    // Offset of next header structure, 0xFFFFFFFF if none
    uint64_t    data_offset;

    // Seconds since Jan 1, 2000 0:00:00 (UTC)
    uint32_t    timestamp;

    char        creator_app[4]; // "vpc "
    uint16_t    major;
    uint16_t    minor;
    char        creator_os[4]; // "Wi2k"

    uint64_t    orig_size;
    uint64_t    size;

    uint16_t    cyls;
    uint8_t     heads;
    uint8_t     secs_per_cyl;

    uint32_t    type;

    // Checksum of the Hard Disk Footer ("one's complement of the sum of all
    // the bytes in the footer without the checksum field")
    uint32_t    checksum;

    // UUID used to identify a parent hard disk (backing file)
    uint8_t     uuid[16];

    uint8_t     in_saved_state;
};

struct vhd_dyndisk_header {
    char        magic[8]; // "cxsparse"

    // Offset of next header structure, 0xFFFFFFFF if none
    uint64_t    data_offset;

    // Offset of the Block Allocation Table (BAT)
    uint64_t    table_offset;

    uint32_t    version;
    uint32_t    max_table_entries; // 32bit/entry

    // 2 MB by default, must be a power of two
    uint32_t    block_size;

    uint32_t    checksum;
    uint8_t     parent_uuid[16];
    uint32_t    parent_timestamp;
    uint32_t    reserved;

    // Backing file name (in UTF-16)
    uint8_t     parent_name[512];

    struct {
        uint32_t    platform;
        uint32_t    data_space;
        uint32_t    data_length;
        uint32_t    reserved;
        uint64_t    data_offset;
    } parent_locator[8];
};

typedef struct BDRVVPCState {
    BlockDriverState *hd;

    uint8_t footer_buf[HEADER_SIZE];
    uint64_t free_data_block_offset;
    int max_table_entries;
    uint32_t *pagetable;
    uint64_t bat_offset;
    uint64_t last_bitmap_offset;

    uint32_t block_size;
    uint32_t bitmap_size;

#ifdef CACHE
    uint8_t *pageentry_u8;
    uint32_t *pageentry_u32;
    uint16_t *pageentry_u16;

    uint64_t last_bitmap;
#endif
} BDRVVPCState;

static int vpc_probe(const uint8_t *buf, int buf_size, const char *filename)
{
    if (buf_size >= 8 && !strncmp((char *)buf, "conectix", 8))
        return 100;
    return 0;
}

static int vpc_open(BlockDriverState *bs, const char *filename, int flags)
{
    BDRVVPCState *s = bs->opaque;
    int ret, i;
    struct vhd_footer* footer;
    struct vhd_dyndisk_header* dyndisk_header;
    uint8_t buf[HEADER_SIZE];

    ret = bdrv_file_open(&s->hd, filename, flags);
    if (ret < 0)
        return ret;

    if (bdrv_pread(s->hd, 0, s->footer_buf, HEADER_SIZE) != HEADER_SIZE)
        goto fail;

    footer = (struct vhd_footer*) s->footer_buf;
    if (strncmp(footer->creator, "conectix", 8))
        goto fail;

    // The visible size of a image in Virtual PC depends on the geometry
    // rather than on the size stored in the footer (the size in the footer
    // is too large usually)
    bs->total_sectors = (int64_t)
        be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl;

    if (bdrv_pread(s->hd, be64_to_cpu(footer->data_offset), buf, HEADER_SIZE)
            != HEADER_SIZE)
        goto fail;

    dyndisk_header = (struct vhd_dyndisk_header*) buf;

    if (strncmp(dyndisk_header->magic, "cxsparse", 8))
        goto fail;


    s->block_size = be32_to_cpu(dyndisk_header->block_size);
    s->bitmap_size = ((s->block_size / (8 * 512)) + 511) & ~511;

    s->max_table_entries = be32_to_cpu(dyndisk_header->max_table_entries);
    s->pagetable = qemu_malloc(s->max_table_entries * 4);
    if (!s->pagetable)
        goto fail;

    s->bat_offset = be64_to_cpu(dyndisk_header->table_offset);
    if (bdrv_pread(s->hd, s->bat_offset, s->pagetable,
            s->max_table_entries * 4) != s->max_table_entries * 4)
            goto fail;

    s->free_data_block_offset =
        (s->bat_offset + (s->max_table_entries * 4) + 511) & ~511;

    for (i = 0; i < s->max_table_entries; i++) {
        be32_to_cpus(&s->pagetable[i]);
        if (s->pagetable[i] != 0xFFFFFFFF) {
            int64_t next = (512 * (int64_t) s->pagetable[i]) +
                s->bitmap_size + s->block_size;

            if (next> s->free_data_block_offset)
                s->free_data_block_offset = next;
        }
    }

    s->last_bitmap_offset = (int64_t) -1;

#ifdef CACHE
    s->pageentry_u8 = qemu_malloc(512);
    if (!s->pageentry_u8)
        goto fail;
    s->pageentry_u32 = s->pageentry_u8;
    s->pageentry_u16 = s->pageentry_u8;
    s->last_pagetable = -1;
#endif

    return 0;
 fail:
    bdrv_delete(s->hd);
    return -1;
}

/*
 * Returns the absolute byte offset of the given sector in the image file.
 * If the sector is not allocated, -1 is returned instead.
 *
 * The parameter write must be 1 if the offset will be used for a write
 * operation (the block bitmaps is updated then), 0 otherwise.
 */
static inline int64_t get_sector_offset(BlockDriverState *bs,
    int64_t sector_num, int write)
{
    BDRVVPCState *s = bs->opaque;
    uint64_t offset = sector_num * 512;
    uint64_t bitmap_offset, block_offset;
    uint32_t pagetable_index, pageentry_index;

    pagetable_index = offset / s->block_size;
    pageentry_index = (offset % s->block_size) / 512;

    if (pagetable_index >= s->max_table_entries || s->pagetable[pagetable_index] == 0xffffffff)
        return -1; // not allocated

    bitmap_offset = 512 * s->pagetable[pagetable_index];
    block_offset = bitmap_offset + s->bitmap_size + (512 * pageentry_index);

    // We must ensure that we don't write to any sectors which are marked as
    // unused in the bitmap. We get away with setting all bits in the block
    // bitmap each time we write to a new block. This might cause Virtual PC to
    // miss sparse read optimization, but it's not a problem in terms of
    // correctness.
    if (write && (s->last_bitmap_offset != bitmap_offset)) {
        uint8_t bitmap[s->bitmap_size];

        s->last_bitmap_offset = bitmap_offset;
        memset(bitmap, 0xff, s->bitmap_size);
        bdrv_pwrite(s->hd, bitmap_offset, bitmap, s->bitmap_size);
    }

//    printf("sector: %" PRIx64 ", index: %x, offset: %x, bioff: %" PRIx64 ", bloff: %" PRIx64 "\n",
//      sector_num, pagetable_index, pageentry_index,
//      bitmap_offset, block_offset);

// disabled by reason
#if 0
#ifdef CACHE
    if (bitmap_offset != s->last_bitmap)
    {
        lseek(s->fd, bitmap_offset, SEEK_SET);

        s->last_bitmap = bitmap_offset;

        // Scary! Bitmap is stored as big endian 32bit entries,
        // while we used to look it up byte by byte
        read(s->fd, s->pageentry_u8, 512);
        for (i = 0; i < 128; i++)
            be32_to_cpus(&s->pageentry_u32[i]);
    }

    if ((s->pageentry_u8[pageentry_index / 8] >> (pageentry_index % 8)) & 1)
        return -1;
#else
    lseek(s->fd, bitmap_offset + (pageentry_index / 8), SEEK_SET);

    read(s->fd, &bitmap_entry, 1);

    if ((bitmap_entry >> (pageentry_index % 8)) & 1)
        return -1; // not allocated
#endif
#endif

    return block_offset;
}

/*
 * Writes the footer to the end of the image file. This is needed when the
 * file grows as it overwrites the old footer
 *
 * Returns 0 on success and < 0 on error
 */
static int rewrite_footer(BlockDriverState* bs)
{
    int ret;
    BDRVVPCState *s = bs->opaque;
    int64_t offset = s->free_data_block_offset;

    ret = bdrv_pwrite(s->hd, offset, s->footer_buf, HEADER_SIZE);
    if (ret < 0)
        return ret;

    return 0;
}

/*
 * Allocates a new block. This involves writing a new footer and updating
 * the Block Allocation Table to use the space at the old end of the image
 * file (overwriting the old footer)
 *
 * Returns the sectors' offset in the image file on success and < 0 on error
 */
static int64_t alloc_block(BlockDriverState* bs, int64_t sector_num)
{
    BDRVVPCState *s = bs->opaque;
    int64_t bat_offset;
    uint32_t index, bat_value;
    int ret;
    uint8_t bitmap[s->bitmap_size];

    // Check if sector_num is valid
    if ((sector_num < 0) || (sector_num > bs->total_sectors))
        return -1;

    // Write entry into in-memory BAT
    index = (sector_num * 512) / s->block_size;
    if (s->pagetable[index] != 0xFFFFFFFF)
        return -1;

    s->pagetable[index] = s->free_data_block_offset / 512;

    // Initialize the block's bitmap
    memset(bitmap, 0xff, s->bitmap_size);
    bdrv_pwrite(s->hd, s->free_data_block_offset, bitmap, s->bitmap_size);

    // Write new footer (the old one will be overwritten)
    s->free_data_block_offset += s->block_size + s->bitmap_size;
    ret = rewrite_footer(bs);
    if (ret < 0)
        goto fail;

    // Write BAT entry to disk
    bat_offset = s->bat_offset + (4 * index);
    bat_value = be32_to_cpu(s->pagetable[index]);
    ret = bdrv_pwrite(s->hd, bat_offset, &bat_value, 4);
    if (ret < 0)
        goto fail;

    return get_sector_offset(bs, sector_num, 0);

fail:
    s->free_data_block_offset -= (s->block_size + s->bitmap_size);
    return -1;
}

static int vpc_read(BlockDriverState *bs, int64_t sector_num,
                    uint8_t *buf, int nb_sectors)
{
    BDRVVPCState *s = bs->opaque;
    int ret;
    int64_t offset;

    while (nb_sectors > 0) {
        offset = get_sector_offset(bs, sector_num, 0);

        if (offset == -1) {
            memset(buf, 0, 512);
        } else {
            ret = bdrv_pread(s->hd, offset, buf, 512);
            if (ret != 512)
                return -1;
        }

        nb_sectors--;
        sector_num++;
        buf += 512;
    }
    return 0;
}

static int vpc_write(BlockDriverState *bs, int64_t sector_num,
    const uint8_t *buf, int nb_sectors)
{
    BDRVVPCState *s = bs->opaque;
    int64_t offset;
    int ret;

    while (nb_sectors > 0) {
        offset = get_sector_offset(bs, sector_num, 1);

        if (offset == -1) {
            offset = alloc_block(bs, sector_num);
            if (offset < 0)
                return -1;
        }

        ret = bdrv_pwrite(s->hd, offset, buf, 512);
        if (ret != 512)
            return -1;

        nb_sectors--;
        sector_num++;
        buf += 512;
    }

    return 0;
}

static void vpc_close(BlockDriverState *bs)
{
    BDRVVPCState *s = bs->opaque;
    qemu_free(s->pagetable);
#ifdef CACHE
    qemu_free(s->pageentry_u8);
#endif
    bdrv_delete(s->hd);
}

BlockDriver bdrv_vpc = {
    "vpc",
    sizeof(BDRVVPCState),
    vpc_probe,
    vpc_open,
    vpc_read,
    vpc_write,
    vpc_close,
};