Patchwork [V20,7/8] add-cow file format core code

login
register
mail settings
Submitter Robert Wang
Date Aug. 25, 2013, 4:06 p.m.
Message ID <1377446780-15360-8-git-send-email-wdongxu@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/269714/
State New
Headers show

Comments

Robert Wang - Aug. 25, 2013, 4:06 p.m.
add-cow file format core code. It use block-cache.c as cache code.
It lacks of snapshot_blkdev support.

v18->v19:
1) add aio parallel write support.
2) fix flush method.

v17-v18:
1) use error_report, not fprintf.
2) remove version field from header.
3) header_size is MAX(cluster_size, 4096).
4) introduce s->cluster_sectors.
5) use BLKDBG_L2_LOAD/UPDATE.

v16->v17:
1) Use stringify.

v15->v16:
1) Judge if opts is null in add_cow_create function.

Signed-off-by: Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
---
 block/Makefile.objs       |   1 +
 block/add-cow.c           | 824 ++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h |   2 +
 3 files changed, 827 insertions(+)
 create mode 100644 block/add-cow.c

Patch

diff --git a/block/Makefile.objs b/block/Makefile.objs
index 69e5584..7f56d71 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -1,6 +1,7 @@ 
 block-obj-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
 block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o
 block-obj-y += block-cache.o
+block-obj-y += add-cow.o
 block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
 block-obj-y += qed-check.o
 block-obj-y += vhdx.o
diff --git a/block/add-cow.c b/block/add-cow.c
new file mode 100644
index 0000000..af766543
--- /dev/null
+++ b/block/add-cow.c
@@ -0,0 +1,824 @@ 
+/*
+ * QEMU ADD-COW Disk Format
+ *
+ * Copyright IBM, Corp. 2012
+ *
+ * Authors:
+ *  Dong Xu Wang <wdongxu@linux.vnet.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "block/block_int.h"
+#include "qemu/module.h"
+#include "block/block-cache.h"
+
+#define ACOW_CLUSTER_SIZE 65536
+
+typedef struct AddCowMeta {
+    uint64_t start_sector;
+    int remaining_sectors;
+    CoQueue dependent_requests;
+    struct AddCowMeta *next;
+
+    QLIST_ENTRY(AddCowMeta) next_in_flight;
+} AddCowMeta;
+
+enum {
+    /* compat_features bit */
+    ACOW_F_ALL_ALLOCATED    = 0X01,
+
+    /* none feature bit used now */
+    ACOW_FEATURE_MASK       = 0,
+
+    ACOW_MAGIC              = 'A' | 'C' << 8 | 'O' << 16 | 'W' << 24,
+    ACOW_CACHE_SIZE         = 16,
+    DEFAULT_HEADER_SIZE     = 4096,
+    MIN_CLUSTER_BITS        = 12,
+    MAX_CLUSTER_BITS        = 21,
+};
+
+typedef struct AddCowHeader {
+    uint32_t    magic;
+
+    uint32_t    backing_offset;
+    uint32_t    backing_size;
+    uint32_t    image_offset;
+    uint32_t    image_size;
+
+    uint32_t    cluster_bits;
+    uint64_t    features;
+    uint64_t    compat_features;
+    uint32_t    header_size;
+
+    char        backing_fmt[16];
+    char        image_fmt[16];
+} QEMU_PACKED AddCowHeader;
+
+typedef struct BDRVAddCowState {
+    BlockDriverState    *image_hd;
+    CoMutex             lock;
+    int                 cluster_size;
+    int                 cluster_sectors;
+    BlockCache          *bitmap_cache;
+    uint64_t            bitmap_size;
+    AddCowHeader        header;
+    char                backing_fmt[16];
+    char                image_fmt[16];
+    BlockCache          *image_hd_cache;
+    QLIST_HEAD(AddCowAlloc, AddCowMeta) cluster_allocs;
+} BDRVAddCowState;
+
+/* Convert sector_num to offset in bitmap */
+static inline int64_t offset_in_bitmap(int64_t sector_num,
+                                       int64_t cluster_sectors)
+{
+    int64_t cluster_num = sector_num / cluster_sectors;
+    return cluster_num / 8;
+}
+
+static inline bool is_cluster_head(int64_t sector_num,
+                                   int64_t cluster_sectors)
+{
+    return sector_num % cluster_sectors == 0;
+}
+
+static inline bool is_cluster_tail(int64_t sector_num,
+                                   int64_t cluster_sectors)
+{
+    return (sector_num + 1) % cluster_sectors == 0;
+}
+
+static void add_cow_header_le_to_cpu(const AddCowHeader *le, AddCowHeader *cpu)
+{
+    cpu->magic              = le32_to_cpu(le->magic);
+
+    cpu->backing_offset     = le32_to_cpu(le->backing_offset);
+    cpu->backing_size       = le32_to_cpu(le->backing_size);
+    cpu->image_offset       = le32_to_cpu(le->image_offset);
+    cpu->image_size         = le32_to_cpu(le->image_size);
+
+    cpu->cluster_bits       = le32_to_cpu(le->cluster_bits);
+    cpu->features           = le64_to_cpu(le->features);
+    cpu->compat_features    = le64_to_cpu(le->compat_features);
+    cpu->header_size        = le32_to_cpu(le->header_size);
+
+    memcpy(cpu->backing_fmt, le->backing_fmt, sizeof(cpu->backing_fmt));
+    memcpy(cpu->image_fmt, le->image_fmt, sizeof(cpu->image_fmt));
+}
+
+static void add_cow_header_cpu_to_le(const AddCowHeader *cpu, AddCowHeader *le)
+{
+    le->magic               = cpu_to_le32(cpu->magic);
+
+    le->backing_offset      = cpu_to_le32(cpu->backing_offset);
+    le->backing_size        = cpu_to_le32(cpu->backing_size);
+    le->image_offset        = cpu_to_le32(cpu->image_offset);
+    le->image_size          = cpu_to_le32(cpu->image_size);
+
+    le->cluster_bits        = cpu_to_le32(cpu->cluster_bits);
+    le->features            = cpu_to_le64(cpu->features);
+    le->compat_features     = cpu_to_le64(cpu->compat_features);
+    le->header_size         = cpu_to_le32(cpu->header_size);
+    memcpy(le->backing_fmt, cpu->backing_fmt, sizeof(le->backing_fmt));
+    memcpy(le->image_fmt, cpu->image_fmt, sizeof(le->image_fmt));
+}
+
+static int add_cow_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    const AddCowHeader *header = (const AddCowHeader *)buf;
+
+    if (buf_size < sizeof(*header)) {
+        return 0;
+    }
+    if (le32_to_cpu(header->magic) == ACOW_MAGIC) {
+        return 100;
+    }
+    return 0;
+}
+
+static int add_cow_create(const char *filename, QemuOpts *opts)
+{
+    AddCowHeader header = {
+        .magic      = ACOW_MAGIC,
+        .features   = 0,
+        .compat_features = 0,
+    };
+    AddCowHeader le_header;
+    int64_t image_len = 0;
+    const char *backing_filename = NULL, *backing_fmt = NULL;
+    const char *image_filename = NULL, *image_format = NULL;
+    size_t cluster_size = ACOW_CLUSTER_SIZE;
+    BlockDriverState *bs, *backing_bs;
+    BlockDriver *drv = bdrv_find_format("add-cow");
+    int ret;
+
+    image_len = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
+    backing_filename = qemu_opt_get_del(opts, BLOCK_OPT_BACKING_FILE);
+    backing_fmt = qemu_opt_get_del(opts, BLOCK_OPT_BACKING_FMT);
+    image_filename = qemu_opt_get_del(opts, BLOCK_OPT_IMAGE_FILE);
+    image_format = qemu_opt_get_del(opts, BLOCK_OPT_IMAGE_FMT);
+    cluster_size = qemu_opt_get_size_del(opts, BLOCK_OPT_CLUSTER_SIZE,
+                                         ACOW_CLUSTER_SIZE);
+
+    header.cluster_bits = ffs(cluster_size) - 1;
+    if (header.cluster_bits < MIN_CLUSTER_BITS ||
+        header.cluster_bits > MAX_CLUSTER_BITS ||
+        (1 << header.cluster_bits) != cluster_size) {
+        error_report(
+            "Cluster size must be a power of two between %d and %dk",
+            1 << MIN_CLUSTER_BITS, 1 << (MAX_CLUSTER_BITS - 10));
+        return -EINVAL;
+    }
+
+    header.header_size = MAX(cluster_size, DEFAULT_HEADER_SIZE);
+    if (backing_filename) {
+        header.backing_offset = sizeof(header);
+        header.backing_size = strlen(backing_filename);
+
+        if (!backing_fmt) {
+            backing_bs = bdrv_new("image");
+            ret = bdrv_open(backing_bs, backing_filename, NULL,
+                            BDRV_O_RDWR | BDRV_O_CACHE_WB, NULL);
+            if (ret < 0) {
+                bdrv_delete(backing_bs);
+                return ret;
+            }
+            backing_fmt = bdrv_get_format_name(backing_bs);
+            bdrv_delete(backing_bs);
+        }
+    } else {
+        header.compat_features |= ACOW_F_ALL_ALLOCATED;
+    }
+
+    if (image_filename) {
+        header.image_offset = sizeof(header) + header.backing_size;
+        header.image_size = strlen(image_filename);
+    } else {
+        error_report("Error: image_file should be given.");
+        return -EINVAL;
+    }
+
+    if (backing_filename && !strcmp(backing_filename, image_filename)) {
+        error_report("Error: Trying to create an image with the "
+                     "same backing file name as the image file name");
+        return -EINVAL;
+    }
+
+    if (!strcmp(filename, image_filename)) {
+        error_report("Error: Trying to create an image with the "
+                     "same filename as the image file name");
+        return -EINVAL;
+    }
+
+    if (header.image_offset + header.image_size > header.header_size) {
+        error_report("image_file name or backing_file name too long.");
+        return -ENOSPC;
+    }
+
+    ret = bdrv_file_open(&bs, image_filename, NULL, 0);
+    if (ret < 0) {
+        return ret;
+    }
+    bdrv_close(bs);
+
+    ret = bdrv_create_file(filename, NULL);
+    if (ret < 0) {
+        return ret;
+    }
+
+    ret = bdrv_file_open(&bs, filename, NULL, BDRV_O_RDWR);
+    if (ret < 0) {
+        return ret;
+    }
+    assert(strlen(backing_fmt ? backing_fmt : "") < sizeof(header.backing_fmt));
+    strncpy(header.backing_fmt, backing_fmt ? backing_fmt : "",
+            sizeof(header.backing_fmt));
+    assert(strlen(image_format ? image_format : "raw")
+           < sizeof(header.image_fmt));
+    strncpy(header.image_fmt, image_format ? image_format : "raw",
+            sizeof(header.image_fmt));
+    add_cow_header_cpu_to_le(&header, &le_header);
+    ret = bdrv_pwrite(bs, 0, &le_header, sizeof(le_header));
+    if (ret < 0) {
+        bdrv_delete(bs);
+        return ret;
+    }
+
+    ret = bdrv_pwrite(bs, header.image_offset, image_filename,
+                      header.image_size);
+    if (ret < 0) {
+        bdrv_delete(bs);
+        return ret;
+    }
+
+    if (backing_filename) {
+        ret = bdrv_pwrite(bs, header.backing_offset, backing_filename,
+                          header.backing_size);
+        if (ret < 0) {
+            bdrv_delete(bs);
+            return ret;
+        }
+    }
+    bdrv_close(bs);
+
+    ret = bdrv_open(bs, filename, NULL, BDRV_O_RDWR | BDRV_O_NO_FLUSH, drv);
+    if (ret < 0) {
+        bdrv_delete(bs);
+        return ret;
+    }
+
+    ret = bdrv_truncate(bs, image_len);
+    bdrv_delete(bs);
+    return ret;
+}
+
+static int add_cow_open(BlockDriverState *bs, QDict *options, int flags)
+{
+    char                image_filename[PATH_MAX];
+    char                tmp_name[PATH_MAX];
+    int                 ret;
+    int                 sector_per_byte;
+    BDRVAddCowState     *s = bs->opaque;
+    AddCowHeader        le_header;
+    char backing_filename[PATH_MAX];
+
+    ret = bdrv_pread(bs->file, 0, &le_header, sizeof(le_header));
+    if (ret < 0) {
+        goto fail;
+    }
+
+    add_cow_header_le_to_cpu(&le_header, &s->header);
+
+    if (s->header.magic != ACOW_MAGIC) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    if (s->header.features & ~ACOW_FEATURE_MASK) {
+        char buf[64];
+        snprintf(buf, sizeof(buf), "Feature Flags: %" PRIx64,
+                 s->header.features & ~ACOW_FEATURE_MASK);
+        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
+                      bs->device_name, "add-cow", buf);
+        return -ENOTSUP;
+    }
+
+    if ((s->header.compat_features & ACOW_F_ALL_ALLOCATED) == 0) {
+        snprintf(bs->backing_format, sizeof(bs->backing_format),
+                 "%s", s->header.backing_fmt);
+    }
+
+    if (s->header.cluster_bits < MIN_CLUSTER_BITS ||
+        s->header.cluster_bits > MAX_CLUSTER_BITS) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    s->cluster_size = 1 << s->header.cluster_bits;
+    if (s->header.header_size != MAX(s->cluster_size, DEFAULT_HEADER_SIZE)) {
+        char buf[64];
+        snprintf(buf, sizeof(buf), "Header size: %u",
+                 s->header.header_size);
+        qerror_report(QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
+                      bs->device_name, "add-cow", buf);
+        return -ENOTSUP;
+    }
+
+    if ((s->header.compat_features & ACOW_F_ALL_ALLOCATED) == 0) {
+        ret = bdrv_read_string(bs->file, s->header.backing_offset,
+                               s->header.backing_size,
+                               bs->backing_file,
+                               sizeof(bs->backing_file));
+        if (ret < 0) {
+            goto fail;
+        }
+    }
+
+    ret = bdrv_read_string(bs->file, s->header.image_offset,
+                           s->header.image_size, tmp_name,
+                           sizeof(tmp_name));
+    if (ret < 0) {
+        goto fail;
+    }
+
+    if (path_has_protocol(tmp_name)) {
+        pstrcpy(image_filename, sizeof(image_filename), tmp_name);
+    } else {
+        path_combine(image_filename, sizeof(image_filename),
+                     bs->filename, tmp_name);
+    }
+    bdrv_get_full_backing_filename(bs, backing_filename,
+                                   sizeof(backing_filename));
+    if (!strcmp(backing_filename, image_filename)) {
+        error_report("Error: backing file and image file are same: %s\n",
+                     backing_filename);
+        ret = EINVAL;
+        goto fail;
+    }
+    s->image_hd = bdrv_new("");
+    ret = bdrv_open(s->image_hd, image_filename, NULL, flags,
+                    bdrv_find_format(s->header.image_fmt));
+    if (ret < 0) {
+        bdrv_delete(s->image_hd);
+        goto fail;
+    }
+
+    bs->total_sectors = bdrv_getlength(s->image_hd) / BDRV_SECTOR_SIZE;
+    s->cluster_sectors = s->cluster_size / BDRV_SECTOR_SIZE;
+    sector_per_byte = s->cluster_sectors * 8;
+    s->bitmap_size =
+        (bs->total_sectors + sector_per_byte - 1) / sector_per_byte;
+    s->bitmap_cache =  block_cache_create(bs, ACOW_CACHE_SIZE,
+                                          s->cluster_size,
+                                          BLOCK_TABLE_BITMAP);
+    s->image_hd_cache = block_cache_create(s->image_hd, 0, 0, 0);
+    block_cache_depends_on_flush(s->image_hd_cache);
+    qemu_co_mutex_init(&s->lock);
+    QLIST_INIT(&s->cluster_allocs);
+    return 0;
+fail:
+    return ret;
+}
+
+static void add_cow_close(BlockDriverState *bs)
+{
+    BDRVAddCowState *s = bs->opaque;
+    if (s->bitmap_cache) {
+        block_cache_destroy(bs, s->bitmap_cache);
+    }
+    if (s->image_hd_cache) {
+        block_cache_destroy(s->image_hd, s->image_hd_cache);
+    }
+    bdrv_delete(s->image_hd);
+}
+
+static bool is_allocated(BlockDriverState *bs, int64_t sector_num)
+{
+    BDRVAddCowState *s  = bs->opaque;
+    int64_t cluster_num = sector_num / s->cluster_sectors;
+    uint8_t *table      = NULL;
+    bool val = false;
+    int ret;
+
+    uint64_t offset = s->header.header_size +
+        (offset_in_bitmap(sector_num, s->cluster_sectors)
+            & (~(s->cluster_size - 1)));
+    ret = block_cache_get(bs, s->bitmap_cache, offset, (void **)&table);
+    if (ret < 0) {
+        return ret;
+    }
+
+    val = table[cluster_num / 8 % s->cluster_size] & (1 << (cluster_num % 8));
+    ret = block_cache_put(bs, s->bitmap_cache, (void **)&table);
+    if (ret < 0) {
+        return ret;
+    }
+    return val;
+}
+
+static coroutine_fn int add_cow_is_allocated(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors, int *num_same)
+{
+    BDRVAddCowState *s = bs->opaque;
+    int changed;
+
+    if (nb_sectors == 0) {
+        *num_same = 0;
+        return 0;
+    }
+
+    if (s->header.compat_features & ACOW_F_ALL_ALLOCATED) {
+        *num_same = nb_sectors;
+        return 1;
+    }
+    changed = is_allocated(bs, sector_num);
+
+    for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
+        if (is_allocated(bs, sector_num + *num_same) != changed) {
+            break;
+        }
+    }
+    return changed;
+}
+
+static int add_cow_backing_read(BlockDriverState *bs, QEMUIOVector *qiov,
+                                int64_t sector_num, int nb_sectors)
+{
+    int n1;
+    if ((sector_num + nb_sectors) <= bs->total_sectors) {
+        return nb_sectors;
+    }
+    if (sector_num >= bs->total_sectors) {
+        n1 = 0;
+    } else {
+        n1 = bs->total_sectors - sector_num;
+    }
+
+    qemu_iovec_memset(qiov, BDRV_SECTOR_SIZE * n1,
+                      0, BDRV_SECTOR_SIZE * (nb_sectors - n1));
+
+    return n1;
+}
+
+static coroutine_fn int add_cow_co_readv(BlockDriverState *bs,
+                                         int64_t sector_num,
+                                         int remaining_sectors,
+                                         QEMUIOVector *qiov)
+{
+    BDRVAddCowState *s  = bs->opaque;
+    int cur_nr_sectors;
+    uint64_t bytes_done = 0;
+    QEMUIOVector hd_qiov;
+    int n1, ret = 0;
+
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+    qemu_co_mutex_lock(&s->lock);
+    while (remaining_sectors != 0) {
+        cur_nr_sectors = remaining_sectors;
+        if (add_cow_is_allocated(bs, sector_num, cur_nr_sectors,
+                                 &cur_nr_sectors)) {
+            qemu_iovec_reset(&hd_qiov);
+            qemu_iovec_concat(&hd_qiov, qiov, bytes_done,
+                              cur_nr_sectors * BDRV_SECTOR_SIZE);
+            qemu_co_mutex_unlock(&s->lock);
+            ret = bdrv_co_readv(s->image_hd, sector_num,
+                                cur_nr_sectors, &hd_qiov);
+            qemu_co_mutex_lock(&s->lock);
+            if (ret < 0) {
+                goto fail;
+            }
+        } else {
+            if (bs->backing_hd) {
+                qemu_iovec_reset(&hd_qiov);
+                qemu_iovec_concat(&hd_qiov, qiov, bytes_done,
+                                  cur_nr_sectors * BDRV_SECTOR_SIZE);
+                n1 = add_cow_backing_read(bs->backing_hd, &hd_qiov,
+                                          sector_num, cur_nr_sectors);
+                if (n1 > 0) {
+                    qemu_co_mutex_unlock(&s->lock);
+                    ret = bdrv_co_readv(bs->backing_hd, sector_num,
+                                        cur_nr_sectors, &hd_qiov);
+                    qemu_co_mutex_lock(&s->lock);
+                    if (ret < 0) {
+                        goto fail;
+                    }
+                }
+            } else {
+                qemu_iovec_memset(&hd_qiov, 0, 0,
+                                  BDRV_SECTOR_SIZE * cur_nr_sectors);
+            }
+        }
+        remaining_sectors -= cur_nr_sectors;
+        sector_num += cur_nr_sectors;
+        bytes_done += cur_nr_sectors * BDRV_SECTOR_SIZE;
+    }
+fail:
+    qemu_co_mutex_unlock(&s->lock);
+    qemu_iovec_destroy(&hd_qiov);
+    return ret;
+}
+
+static int coroutine_fn copy_sectors(BlockDriverState *bs,
+                                     int n_start, int n_end)
+{
+    BDRVAddCowState *s = bs->opaque;
+    QEMUIOVector qiov;
+    struct iovec iov;
+    int n, ret;
+
+    n = n_end - n_start;
+    if (n <= 0) {
+        return 0;
+    }
+
+    iov.iov_len = n * BDRV_SECTOR_SIZE;
+    iov.iov_base = qemu_blockalign(bs, iov.iov_len);
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    ret = bdrv_co_readv(bs->backing_hd, n_start, n, &qiov);
+    if (ret < 0) {
+        goto out;
+    }
+    ret = bdrv_co_writev(s->image_hd, n_start, n, &qiov);
+    if (ret < 0) {
+        goto out;
+    }
+
+    ret = 0;
+out:
+    qemu_vfree(iov.iov_base);
+    return ret;
+}
+
+static int handle_dependencies(BlockDriverState *bs, uint64_t sector_num,
+                               int remaining_sectors)
+{
+    BDRVAddCowState *s = bs->opaque;
+    AddCowMeta *old_alloc;
+    QLIST_FOREACH(old_alloc, &s->cluster_allocs, next_in_flight) {
+        uint64_t start = sector_num;
+        uint64_t end = sector_num + remaining_sectors;
+        uint64_t old_start = old_alloc->start_sector;
+        uint64_t old_end =
+            old_alloc->start_sector + old_alloc->remaining_sectors;
+        if (end <= old_start || start >= old_end) {
+            /* No intersection */
+        } else {
+            qemu_co_mutex_unlock(&s->lock);
+            qemu_co_queue_wait(&old_alloc->dependent_requests);
+            qemu_co_mutex_lock(&s->lock);
+            return -EAGAIN;
+        }
+    }
+    return 0;
+}
+
+static coroutine_fn int add_cow_co_writev(BlockDriverState *bs,
+                                          int64_t sector_num,
+                                          int remaining_sectors,
+                                          QEMUIOVector *qiov)
+{
+    BDRVAddCowState *s = bs->opaque;
+    int ret = 0, i;
+    QEMUIOVector hd_qiov;
+    uint8_t *table;
+    uint64_t offset;
+    int mask = s->cluster_sectors - 1;
+    int cluster_mask = s->cluster_size - 1;
+    AddCowMeta *meta = NULL;
+
+    if (remaining_sectors == 0) {
+        return ret;
+    }
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+
+    qemu_co_mutex_lock(&s->lock);
+
+    meta = g_malloc0(sizeof(*meta));
+again:
+    *meta = (AddCowMeta) {
+        .next           = QLIST_FIRST(&s->cluster_allocs),
+        .start_sector   = sector_num,
+        .remaining_sectors  = remaining_sectors,
+    };
+    if (handle_dependencies(bs, sector_num, remaining_sectors) == -EAGAIN) {
+        goto again;
+    }
+    qemu_co_queue_init(&meta->dependent_requests);
+    QLIST_INSERT_HEAD(&s->cluster_allocs, meta, next_in_flight);
+    ret = bdrv_co_writev(s->image_hd, sector_num, remaining_sectors, qiov);
+
+    if (ret == 0 && !s->image_hd->enable_write_cache) {
+        ret = bdrv_co_flush(s->image_hd);
+    }
+    if (ret < 0) {
+        goto fail;
+    }
+    if ((s->header.compat_features & ACOW_F_ALL_ALLOCATED) == 0) {
+        /* Copy content of unmodified sectors */
+        if (!is_cluster_head(sector_num, s->cluster_sectors)
+            && !is_allocated(bs, sector_num)) {
+            ret = copy_sectors(bs, sector_num & ~mask, sector_num);
+            if (ret < 0) {
+                goto fail;
+            }
+        }
+
+        if (!is_cluster_tail(sector_num + remaining_sectors - 1,
+                             s->cluster_sectors)
+            && !is_allocated(bs, sector_num + remaining_sectors - 1)) {
+            ret = copy_sectors(bs, sector_num + remaining_sectors,
+                               ((sector_num + remaining_sectors) | mask) + 1);
+            if (ret < 0) {
+                goto fail;
+            }
+        }
+
+        for (i = sector_num / s->cluster_sectors;
+            i <= (sector_num + remaining_sectors - 1) / s->cluster_sectors;
+            i++) {
+            offset = s->header.header_size
+                + (offset_in_bitmap(i * s->cluster_sectors,
+                s->cluster_sectors) & (~cluster_mask));
+            ret = block_cache_get(bs, s->bitmap_cache, offset, (void **)&table);
+            if (ret < 0) {
+                goto fail;
+            }
+
+            block_cache_set_dependency_two_bs(bs, s->bitmap_cache,
+                                              s->image_hd, s->image_hd_cache);
+            if (!(table[(i / 8) & (s->cluster_size - 1)] & (1 << (i % 8)))) {
+                table[(i / 8) & (s->cluster_size - 1)] |= (1 << (i % 8));
+                block_cache_entry_mark_dirty(s->bitmap_cache, table);
+            }
+
+            ret = block_cache_put(bs, s->bitmap_cache, (void **) &table);
+            if (ret < 0) {
+                goto fail;
+            }
+        }
+    }
+    ret = 0;
+fail:
+    while (meta != NULL) {
+        AddCowMeta *next;
+
+        if (meta->remaining_sectors != 0) {
+            QLIST_REMOVE(meta, next_in_flight);
+        }
+        qemu_co_queue_restart_all(&meta->dependent_requests);
+
+        next = meta->next;
+        g_free(meta);
+        meta = next;
+    }
+
+    qemu_co_mutex_unlock(&s->lock);
+    qemu_iovec_destroy(&hd_qiov);
+    return ret;
+}
+
+static int bdrv_add_cow_truncate(BlockDriverState *bs, int64_t size)
+{
+    BDRVAddCowState *s = bs->opaque;
+    int sector_per_byte = s->cluster_sectors * 8;
+    int ret;
+    int64_t bitmap_size =
+        (size / BDRV_SECTOR_SIZE + sector_per_byte - 1) / sector_per_byte;
+    bitmap_size = (bitmap_size + s->cluster_size - 1)
+        & (~(s->cluster_size - 1));
+
+    ret = bdrv_truncate(bs->file, s->header.header_size + bitmap_size);
+    if (ret < 0) {
+        return ret;
+    }
+
+    ret = bdrv_truncate(s->image_hd, size);
+    if (ret < 0) {
+        return ret;
+    }
+    return 0;
+}
+
+static int add_cow_reopen_prepare(BDRVReopenState *state,
+                                  BlockReopenQueue *queue, Error **errp)
+{
+    BDRVAddCowState *s;
+    int ret = -1;
+
+    assert(state != NULL);
+    assert(state->bs != NULL);
+
+    if (queue == NULL) {
+        error_set(errp, ERROR_CLASS_GENERIC_ERROR,
+                  "No reopen queue for add-cow");
+        goto exit;
+    }
+
+    s = state->bs->opaque;
+
+    assert(s != NULL);
+
+
+    bdrv_reopen_queue(queue, s->image_hd, state->flags);
+    ret = 0;
+
+exit:
+    return ret;
+}
+
+
+static coroutine_fn int add_cow_co_flush(BlockDriverState *bs)
+{
+    BDRVAddCowState *s = bs->opaque;
+    int ret = 0;
+
+    qemu_co_mutex_lock(&s->lock);
+    if (s->image_hd_cache) {
+        ret = block_cache_flush(s->image_hd, s->image_hd_cache);
+        if (ret < 0) {
+            qemu_co_mutex_unlock(&s->lock);
+            return ret;
+        }
+    }
+    if (s->bitmap_cache) {
+        ret = block_cache_flush(bs, s->bitmap_cache);
+    }
+    qemu_co_mutex_unlock(&s->lock);
+    return ret;
+}
+
+static int add_cow_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
+{
+    BDRVAddCowState *s = bs->opaque;
+    bdi->cluster_size = s->cluster_size;
+    return 0;
+}
+
+static QemuOptsList add_cow_create_opts = {
+    .name = "add-cow-create-opts",
+    .head = QTAILQ_HEAD_INITIALIZER(add_cow_create_opts.head),
+    .desc = {
+        {
+            .name = BLOCK_OPT_SIZE,
+            .type = QEMU_OPT_SIZE,
+            .help = "Virtual disk size"
+        },
+        {
+            .name = BLOCK_OPT_BACKING_FILE,
+            .type = QEMU_OPT_STRING,
+            .help = "File name of a base image"
+        },
+        {
+            .name = BLOCK_OPT_BACKING_FMT,
+            .type = QEMU_OPT_STRING,
+            .help = "Image format of the base image"
+        },
+        {
+            .name = BLOCK_OPT_IMAGE_FILE,
+            .type = QEMU_OPT_STRING,
+            .help = "File name of a image file"
+        },
+        {
+            .name = BLOCK_OPT_IMAGE_FMT,
+            .type = QEMU_OPT_STRING,
+            .help = "Image format of the image file"
+        },
+        {
+            .name = BLOCK_OPT_CLUSTER_SIZE,
+            .type = QEMU_OPT_SIZE,
+            .help = "add-cow cluster size",
+            .def_value_str = stringify(ACOW_CLUSTER_SIZE)
+        },
+        { /* end of list */ }
+    }
+};
+
+static BlockDriver bdrv_add_cow = {
+    .format_name                = "add-cow",
+    .instance_size              = sizeof(BDRVAddCowState),
+    .bdrv_probe                 = add_cow_probe,
+    .bdrv_open                  = add_cow_open,
+    .bdrv_close                 = add_cow_close,
+    .bdrv_create                = add_cow_create,
+    .bdrv_co_readv              = add_cow_co_readv,
+    .bdrv_co_writev             = add_cow_co_writev,
+    .bdrv_truncate              = bdrv_add_cow_truncate,
+    .bdrv_co_is_allocated       = add_cow_is_allocated,
+    .bdrv_reopen_prepare        = add_cow_reopen_prepare,
+    .bdrv_get_info              = add_cow_get_info,
+
+    .bdrv_create_opts           = &add_cow_create_opts,
+    .bdrv_co_flush_to_os        = add_cow_co_flush,
+};
+
+static void bdrv_add_cow_init(void)
+{
+    bdrv_register(&bdrv_add_cow);
+}
+
+block_init(bdrv_add_cow_init);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 09bf260..3cbfa84 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -58,6 +58,8 @@ 
 #define BLOCK_OPT_COMPAT_LEVEL      "compat"
 #define BLOCK_OPT_LAZY_REFCOUNTS    "lazy_refcounts"
 #define BLOCK_OPT_ADAPTER_TYPE      "adapter_type"
+#define BLOCK_OPT_IMAGE_FILE        "image_file"
+#define BLOCK_OPT_IMAGE_FMT         "image_fmt"
 
 typedef struct BdrvTrackedRequest {
     BlockDriverState *bs;