Patchwork [v6,2/5] qed: Add QEMU Enhanced Disk image format

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Submitter Stefan Hajnoczi
Date Dec. 6, 2010, 4:08 p.m.
Message ID <1291651683-11990-3-git-send-email-stefanha@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/74385/
State New
Headers show

Comments

Stefan Hajnoczi - Dec. 6, 2010, 4:08 p.m.
This patch introduces the qed on-disk layout and implements image
creation.  Later patches add read/write and other functionality.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
 Makefile.objs |    1 +
 block/qed.c   |  554 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 block/qed.h   |  148 +++++++++++++++
 block_int.h   |    1 +
 4 files changed, 704 insertions(+), 0 deletions(-)
 create mode 100644 block/qed.c
 create mode 100644 block/qed.h

Patch

diff --git a/Makefile.objs b/Makefile.objs
index 04625eb..f89ce19 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -20,6 +20,7 @@  block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
 
 block-nested-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
 block-nested-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o
+block-nested-y += qed.o
 block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
 block-nested-$(CONFIG_WIN32) += raw-win32.o
 block-nested-$(CONFIG_POSIX) += raw-posix.o
diff --git a/block/qed.c b/block/qed.c
new file mode 100644
index 0000000..1436ac4
--- /dev/null
+++ b/block/qed.c
@@ -0,0 +1,554 @@ 
+/*
+ * QEMU Enhanced Disk Format
+ *
+ * Copyright IBM, Corp. 2010
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
+ *  Anthony Liguori   <aliguori@us.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 "qed.h"
+
+static int bdrv_qed_probe(const uint8_t *buf, int buf_size,
+                          const char *filename)
+{
+    const QEDHeader *header = (const QEDHeader *)buf;
+
+    if (buf_size < sizeof(*header)) {
+        return 0;
+    }
+    if (le32_to_cpu(header->magic) != QED_MAGIC) {
+        return 0;
+    }
+    return 100;
+}
+
+/**
+ * Check whether an image format is raw
+ *
+ * @fmt:    Backing file format, may be NULL
+ */
+static bool qed_fmt_is_raw(const char *fmt)
+{
+    return fmt && strcmp(fmt, "raw") == 0;
+}
+
+static void qed_header_le_to_cpu(const QEDHeader *le, QEDHeader *cpu)
+{
+    cpu->magic = le32_to_cpu(le->magic);
+    cpu->cluster_size = le32_to_cpu(le->cluster_size);
+    cpu->table_size = le32_to_cpu(le->table_size);
+    cpu->header_size = le32_to_cpu(le->header_size);
+    cpu->features = le64_to_cpu(le->features);
+    cpu->compat_features = le64_to_cpu(le->compat_features);
+    cpu->autoclear_features = le64_to_cpu(le->autoclear_features);
+    cpu->l1_table_offset = le64_to_cpu(le->l1_table_offset);
+    cpu->image_size = le64_to_cpu(le->image_size);
+    cpu->backing_filename_offset = le32_to_cpu(le->backing_filename_offset);
+    cpu->backing_filename_size = le32_to_cpu(le->backing_filename_size);
+}
+
+static void qed_header_cpu_to_le(const QEDHeader *cpu, QEDHeader *le)
+{
+    le->magic = cpu_to_le32(cpu->magic);
+    le->cluster_size = cpu_to_le32(cpu->cluster_size);
+    le->table_size = cpu_to_le32(cpu->table_size);
+    le->header_size = cpu_to_le32(cpu->header_size);
+    le->features = cpu_to_le64(cpu->features);
+    le->compat_features = cpu_to_le64(cpu->compat_features);
+    le->autoclear_features = cpu_to_le64(cpu->autoclear_features);
+    le->l1_table_offset = cpu_to_le64(cpu->l1_table_offset);
+    le->image_size = cpu_to_le64(cpu->image_size);
+    le->backing_filename_offset = cpu_to_le32(cpu->backing_filename_offset);
+    le->backing_filename_size = cpu_to_le32(cpu->backing_filename_size);
+}
+
+static int qed_write_header_sync(BDRVQEDState *s)
+{
+    QEDHeader le;
+    int ret;
+
+    qed_header_cpu_to_le(&s->header, &le);
+    ret = bdrv_pwrite(s->bs->file, 0, &le, sizeof(le));
+    if (ret != sizeof(le)) {
+        return ret;
+    }
+    return 0;
+}
+
+static uint64_t qed_max_image_size(uint32_t cluster_size, uint32_t table_size)
+{
+    uint64_t table_entries;
+    uint64_t l2_size;
+
+    table_entries = (table_size * cluster_size) / sizeof(uint64_t);
+    l2_size = table_entries * cluster_size;
+
+    return l2_size * table_entries;
+}
+
+static bool qed_is_cluster_size_valid(uint32_t cluster_size)
+{
+    if (cluster_size < QED_MIN_CLUSTER_SIZE ||
+        cluster_size > QED_MAX_CLUSTER_SIZE) {
+        return false;
+    }
+    if (cluster_size & (cluster_size - 1)) {
+        return false; /* not power of 2 */
+    }
+    return true;
+}
+
+static bool qed_is_table_size_valid(uint32_t table_size)
+{
+    if (table_size < QED_MIN_TABLE_SIZE ||
+        table_size > QED_MAX_TABLE_SIZE) {
+        return false;
+    }
+    if (table_size & (table_size - 1)) {
+        return false; /* not power of 2 */
+    }
+    return true;
+}
+
+static bool qed_is_image_size_valid(uint64_t image_size, uint32_t cluster_size,
+                                    uint32_t table_size)
+{
+    if (image_size % BDRV_SECTOR_SIZE != 0) {
+        return false; /* not multiple of sector size */
+    }
+    if (image_size > qed_max_image_size(cluster_size, table_size)) {
+        return false; /* image is too large */
+    }
+    return true;
+}
+
+/**
+ * Read a string of known length from the image file
+ *
+ * @file:       Image file
+ * @offset:     File offset to start of string, in bytes
+ * @n:          String length in bytes
+ * @buf:        Destination buffer
+ * @buflen:     Destination buffer length in bytes
+ * @ret:        0 on success, -errno on failure
+ *
+ * The string is NUL-terminated.
+ */
+static int qed_read_string(BlockDriverState *file, uint64_t offset, size_t n,
+                           char *buf, size_t buflen)
+{
+    int ret;
+    if (n >= buflen) {
+        return -EINVAL;
+    }
+    ret = bdrv_pread(file, offset, buf, n);
+    if (ret < 0) {
+        return ret;
+    }
+    buf[n] = '\0';
+    return 0;
+}
+
+static int bdrv_qed_open(BlockDriverState *bs, int flags)
+{
+    BDRVQEDState *s = bs->opaque;
+    QEDHeader le_header;
+    int64_t file_size;
+    int ret;
+
+    s->bs = bs;
+
+    ret = bdrv_pread(bs->file, 0, &le_header, sizeof(le_header));
+    if (ret < 0) {
+        return ret;
+    }
+    ret = 0; /* ret should always be 0 or -errno */
+    qed_header_le_to_cpu(&le_header, &s->header);
+
+    if (s->header.magic != QED_MAGIC) {
+        return -EINVAL;
+    }
+    if (s->header.features & ~QED_FEATURE_MASK) {
+        return -ENOTSUP; /* image uses unsupported feature bits */
+    }
+    if (!qed_is_cluster_size_valid(s->header.cluster_size)) {
+        return -EINVAL;
+    }
+
+    /* Round down file size to the last cluster */
+    file_size = bdrv_getlength(bs->file);
+    if (file_size < 0) {
+        return file_size;
+    }
+    s->file_size = qed_start_of_cluster(s, file_size);
+
+    if (!qed_is_table_size_valid(s->header.table_size)) {
+        return -EINVAL;
+    }
+    if (!qed_is_image_size_valid(s->header.image_size,
+                                 s->header.cluster_size,
+                                 s->header.table_size)) {
+        return -EINVAL;
+    }
+    if (!qed_check_table_offset(s, s->header.l1_table_offset)) {
+        return -EINVAL;
+    }
+
+    s->table_nelems = (s->header.cluster_size * s->header.table_size) /
+                      sizeof(uint64_t);
+    s->l2_shift = ffs(s->header.cluster_size) - 1;
+    s->l2_mask = s->table_nelems - 1;
+    s->l1_shift = s->l2_shift + ffs(s->table_nelems) - 1;
+
+    if ((s->header.features & QED_F_BACKING_FILE)) {
+        if ((uint64_t)s->header.backing_filename_offset +
+            s->header.backing_filename_size >
+            s->header.cluster_size * s->header.header_size) {
+            return -EINVAL;
+        }
+
+        ret = qed_read_string(bs->file, s->header.backing_filename_offset,
+                              s->header.backing_filename_size, bs->backing_file,
+                              sizeof(bs->backing_file));
+        if (ret < 0) {
+            return ret;
+        }
+
+        if (s->header.features & QED_F_BACKING_FORMAT_NO_PROBE) {
+            pstrcpy(bs->backing_format, sizeof(bs->backing_format), "raw");
+        }
+    }
+
+    /* Reset unknown autoclear feature bits.  This is a backwards
+     * compatibility mechanism that allows images to be opened by older
+     * programs, which "knock out" unknown feature bits.  When an image is
+     * opened by a newer program again it can detect that the autoclear
+     * feature is no longer valid.
+     */
+    if ((s->header.autoclear_features & ~QED_AUTOCLEAR_FEATURE_MASK) != 0 &&
+        !bdrv_is_read_only(bs->file)) {
+        s->header.autoclear_features &= QED_AUTOCLEAR_FEATURE_MASK;
+
+        ret = qed_write_header_sync(s);
+        if (ret) {
+            return ret;
+        }
+
+        /* From here on only known autoclear feature bits are valid */
+        bdrv_flush(bs->file);
+    }
+
+    return ret;
+}
+
+static void bdrv_qed_close(BlockDriverState *bs)
+{
+}
+
+static int bdrv_qed_flush(BlockDriverState *bs)
+{
+    return bdrv_flush(bs->file);
+}
+
+static int qed_create(const char *filename, uint32_t cluster_size,
+                      uint64_t image_size, uint32_t table_size,
+                      const char *backing_file, const char *backing_fmt)
+{
+    QEDHeader header = {
+        .magic = QED_MAGIC,
+        .cluster_size = cluster_size,
+        .table_size = table_size,
+        .header_size = 1,
+        .features = 0,
+        .compat_features = 0,
+        .l1_table_offset = cluster_size,
+        .image_size = image_size,
+    };
+    QEDHeader le_header;
+    uint8_t *l1_table = NULL;
+    size_t l1_size = header.cluster_size * header.table_size;
+    int ret = 0;
+    BlockDriverState *bs = NULL;
+
+    ret = bdrv_create_file(filename, NULL);
+    if (ret < 0) {
+        return ret;
+    }
+
+    ret = bdrv_file_open(&bs, filename, BDRV_O_RDWR | BDRV_O_CACHE_WB);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (backing_file) {
+        header.features |= QED_F_BACKING_FILE;
+        header.backing_filename_offset = sizeof(le_header);
+        header.backing_filename_size = strlen(backing_file);
+
+        if (qed_fmt_is_raw(backing_fmt)) {
+            header.features |= QED_F_BACKING_FORMAT_NO_PROBE;
+        }
+    }
+
+    qed_header_cpu_to_le(&header, &le_header);
+    ret = bdrv_pwrite(bs, 0, &le_header, sizeof(le_header));
+    if (ret < 0) {
+        goto out;
+    }
+    ret = bdrv_pwrite(bs, sizeof(le_header), backing_file,
+                      header.backing_filename_size);
+    if (ret < 0) {
+        goto out;
+    }
+
+    l1_table = qemu_mallocz(l1_size);
+    ret = bdrv_pwrite(bs, header.l1_table_offset, l1_table, l1_size);
+    if (ret < 0) {
+        goto out;
+    }
+
+    ret = 0; /* success */
+out:
+    qemu_free(l1_table);
+    bdrv_delete(bs);
+    return ret;
+}
+
+static int bdrv_qed_create(const char *filename, QEMUOptionParameter *options)
+{
+    uint64_t image_size = 0;
+    uint32_t cluster_size = QED_DEFAULT_CLUSTER_SIZE;
+    uint32_t table_size = QED_DEFAULT_TABLE_SIZE;
+    const char *backing_file = NULL;
+    const char *backing_fmt = NULL;
+
+    while (options && options->name) {
+        if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
+            image_size = options->value.n;
+        } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
+            backing_file = options->value.s;
+        } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FMT)) {
+            backing_fmt = options->value.s;
+        } else if (!strcmp(options->name, BLOCK_OPT_CLUSTER_SIZE)) {
+            if (options->value.n) {
+                cluster_size = options->value.n;
+            }
+        } else if (!strcmp(options->name, BLOCK_OPT_TABLE_SIZE)) {
+            if (options->value.n) {
+                table_size = options->value.n;
+            }
+        }
+        options++;
+    }
+
+    if (!qed_is_cluster_size_valid(cluster_size)) {
+        fprintf(stderr, "QED cluster size must be within range [%u, %u] and power of 2\n",
+                QED_MIN_CLUSTER_SIZE, QED_MAX_CLUSTER_SIZE);
+        return -EINVAL;
+    }
+    if (!qed_is_table_size_valid(table_size)) {
+        fprintf(stderr, "QED table size must be within range [%u, %u] and power of 2\n",
+                QED_MIN_TABLE_SIZE, QED_MAX_TABLE_SIZE);
+        return -EINVAL;
+    }
+    if (!qed_is_image_size_valid(image_size, cluster_size, table_size)) {
+        fprintf(stderr, "QED image size must be a non-zero multiple of "
+                        "cluster size and less than %" PRIu64 " bytes\n",
+                qed_max_image_size(cluster_size, table_size));
+        return -EINVAL;
+    }
+
+    return qed_create(filename, cluster_size, image_size, table_size,
+                      backing_file, backing_fmt);
+}
+
+static int bdrv_qed_is_allocated(BlockDriverState *bs, int64_t sector_num,
+                                  int nb_sectors, int *pnum)
+{
+    return -ENOTSUP;
+}
+
+static int bdrv_qed_make_empty(BlockDriverState *bs)
+{
+    return -ENOTSUP;
+}
+
+static BlockDriverAIOCB *bdrv_qed_aio_readv(BlockDriverState *bs,
+                                            int64_t sector_num,
+                                            QEMUIOVector *qiov, int nb_sectors,
+                                            BlockDriverCompletionFunc *cb,
+                                            void *opaque)
+{
+    return NULL;
+}
+
+static BlockDriverAIOCB *bdrv_qed_aio_writev(BlockDriverState *bs,
+                                             int64_t sector_num,
+                                             QEMUIOVector *qiov, int nb_sectors,
+                                             BlockDriverCompletionFunc *cb,
+                                             void *opaque)
+{
+    return NULL;
+}
+
+static BlockDriverAIOCB *bdrv_qed_aio_flush(BlockDriverState *bs,
+                                            BlockDriverCompletionFunc *cb,
+                                            void *opaque)
+{
+    return bdrv_aio_flush(bs->file, cb, opaque);
+}
+
+static int bdrv_qed_truncate(BlockDriverState *bs, int64_t offset)
+{
+    return -ENOTSUP;
+}
+
+static int64_t bdrv_qed_getlength(BlockDriverState *bs)
+{
+    BDRVQEDState *s = bs->opaque;
+    return s->header.image_size;
+}
+
+static int bdrv_qed_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
+{
+    BDRVQEDState *s = bs->opaque;
+
+    memset(bdi, 0, sizeof(*bdi));
+    bdi->cluster_size = s->header.cluster_size;
+    return 0;
+}
+
+static int bdrv_qed_change_backing_file(BlockDriverState *bs,
+                                        const char *backing_file,
+                                        const char *backing_fmt)
+{
+    BDRVQEDState *s = bs->opaque;
+    QEDHeader new_header, le_header;
+    void *buffer;
+    size_t buffer_len, backing_file_len;
+    int ret;
+
+    /* Refuse to set backing filename if unknown compat feature bits are
+     * active.  If the image uses an unknown compat feature then we may not
+     * know the layout of data following the header structure and cannot safely
+     * add a new string.
+     */
+    if (backing_file && (s->header.compat_features &
+                         ~QED_COMPAT_FEATURE_MASK)) {
+        return -ENOTSUP;
+    }
+
+    memcpy(&new_header, &s->header, sizeof(new_header));
+
+    new_header.features &= ~(QED_F_BACKING_FILE |
+                             QED_F_BACKING_FORMAT_NO_PROBE);
+
+    /* Adjust feature flags */
+    if (backing_file) {
+        new_header.features |= QED_F_BACKING_FILE;
+
+        if (qed_fmt_is_raw(backing_fmt)) {
+            new_header.features |= QED_F_BACKING_FORMAT_NO_PROBE;
+        }
+    }
+
+    /* Calculate new header size */
+    backing_file_len = 0;
+
+    if (backing_file) {
+        backing_file_len = strlen(backing_file);
+    }
+
+    buffer_len = sizeof(new_header);
+    new_header.backing_filename_offset = buffer_len;
+    new_header.backing_filename_size = backing_file_len;
+    buffer_len += backing_file_len;
+
+    /* Make sure we can rewrite header without failing */
+    if (buffer_len > new_header.header_size * new_header.cluster_size) {
+        return -ENOSPC;
+    }
+
+    /* Prepare new header */
+    buffer = qemu_malloc(buffer_len);
+
+    qed_header_cpu_to_le(&new_header, &le_header);
+    memcpy(buffer, &le_header, sizeof(le_header));
+    buffer_len = sizeof(le_header);
+
+    memcpy(buffer + buffer_len, backing_file, backing_file_len);
+    buffer_len += backing_file_len;
+
+    /* Write new header */
+    ret = bdrv_pwrite_sync(bs->file, 0, buffer, buffer_len);
+    qemu_free(buffer);
+    if (ret == 0) {
+        memcpy(&s->header, &new_header, sizeof(new_header));
+    }
+    return ret;
+}
+
+static int bdrv_qed_check(BlockDriverState *bs, BdrvCheckResult *result)
+{
+    return -ENOTSUP;
+}
+
+static QEMUOptionParameter qed_create_options[] = {
+    {
+        .name = BLOCK_OPT_SIZE,
+        .type = OPT_SIZE,
+        .help = "Virtual disk size (in bytes)"
+    }, {
+        .name = BLOCK_OPT_BACKING_FILE,
+        .type = OPT_STRING,
+        .help = "File name of a base image"
+    }, {
+        .name = BLOCK_OPT_BACKING_FMT,
+        .type = OPT_STRING,
+        .help = "Image format of the base image"
+    }, {
+        .name = BLOCK_OPT_CLUSTER_SIZE,
+        .type = OPT_SIZE,
+        .help = "Cluster size (in bytes)"
+    }, {
+        .name = BLOCK_OPT_TABLE_SIZE,
+        .type = OPT_SIZE,
+        .help = "L1/L2 table size (in clusters)"
+    },
+    { /* end of list */ }
+};
+
+static BlockDriver bdrv_qed = {
+    .format_name              = "qed",
+    .instance_size            = sizeof(BDRVQEDState),
+    .create_options           = qed_create_options,
+
+    .bdrv_probe               = bdrv_qed_probe,
+    .bdrv_open                = bdrv_qed_open,
+    .bdrv_close               = bdrv_qed_close,
+    .bdrv_create              = bdrv_qed_create,
+    .bdrv_flush               = bdrv_qed_flush,
+    .bdrv_is_allocated        = bdrv_qed_is_allocated,
+    .bdrv_make_empty          = bdrv_qed_make_empty,
+    .bdrv_aio_readv           = bdrv_qed_aio_readv,
+    .bdrv_aio_writev          = bdrv_qed_aio_writev,
+    .bdrv_aio_flush           = bdrv_qed_aio_flush,
+    .bdrv_truncate            = bdrv_qed_truncate,
+    .bdrv_getlength           = bdrv_qed_getlength,
+    .bdrv_get_info            = bdrv_qed_get_info,
+    .bdrv_change_backing_file = bdrv_qed_change_backing_file,
+    .bdrv_check               = bdrv_qed_check,
+};
+
+static void bdrv_qed_init(void)
+{
+    bdrv_register(&bdrv_qed);
+}
+
+block_init(bdrv_qed_init);
diff --git a/block/qed.h b/block/qed.h
new file mode 100644
index 0000000..1f8a125
--- /dev/null
+++ b/block/qed.h
@@ -0,0 +1,148 @@ 
+/*
+ * QEMU Enhanced Disk Format
+ *
+ * Copyright IBM, Corp. 2010
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
+ *  Anthony Liguori   <aliguori@us.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.
+ *
+ */
+
+#ifndef BLOCK_QED_H
+#define BLOCK_QED_H
+
+#include "block_int.h"
+
+/* The layout of a QED file is as follows:
+ *
+ * +--------+----------+----------+----------+-----+
+ * | header | L1 table | cluster0 | cluster1 | ... |
+ * +--------+----------+----------+----------+-----+
+ *
+ * There is a 2-level pagetable for cluster allocation:
+ *
+ *                     +----------+
+ *                     | L1 table |
+ *                     +----------+
+ *                ,------'  |  '------.
+ *           +----------+   |    +----------+
+ *           | L2 table |  ...   | L2 table |
+ *           +----------+        +----------+
+ *       ,------'  |  '------.
+ *  +----------+   |    +----------+
+ *  |   Data   |  ...   |   Data   |
+ *  +----------+        +----------+
+ *
+ * The L1 table is fixed size and always present.  L2 tables are allocated on
+ * demand.  The L1 table size determines the maximum possible image size; it
+ * can be influenced using the cluster_size and table_size values.
+ *
+ * All fields are little-endian on disk.
+ */
+
+enum {
+    QED_MAGIC = 'Q' | 'E' << 8 | 'D' << 16 | '\0' << 24,
+
+    /* The image supports a backing file */
+    QED_F_BACKING_FILE = 0x01,
+
+    /* The backing file format must not be probed, treat as raw image */
+    QED_F_BACKING_FORMAT_NO_PROBE = 0x04,
+
+    /* Feature bits must be used when the on-disk format changes */
+    QED_FEATURE_MASK = QED_F_BACKING_FILE | /* supported feature bits */
+                       QED_F_BACKING_FORMAT_NO_PROBE,
+    QED_COMPAT_FEATURE_MASK = 0,            /* supported compat feature bits */
+    QED_AUTOCLEAR_FEATURE_MASK = 0,         /* supported autoclear feature bits */
+
+    /* Data is stored in groups of sectors called clusters.  Cluster size must
+     * be large to avoid keeping too much metadata.  I/O requests that have
+     * sub-cluster size will require read-modify-write.
+     */
+    QED_MIN_CLUSTER_SIZE = 4 * 1024, /* in bytes */
+    QED_MAX_CLUSTER_SIZE = 64 * 1024 * 1024,
+    QED_DEFAULT_CLUSTER_SIZE = 64 * 1024,
+
+    /* Allocated clusters are tracked using a 2-level pagetable.  Table size is
+     * a multiple of clusters so large maximum image sizes can be supported
+     * without jacking up the cluster size too much.
+     */
+    QED_MIN_TABLE_SIZE = 1,        /* in clusters */
+    QED_MAX_TABLE_SIZE = 16,
+    QED_DEFAULT_TABLE_SIZE = 4,
+};
+
+typedef struct {
+    uint32_t magic;                 /* QED\0 */
+
+    uint32_t cluster_size;          /* in bytes */
+    uint32_t table_size;            /* for L1 and L2 tables, in clusters */
+    uint32_t header_size;           /* in clusters */
+
+    uint64_t features;              /* format feature bits */
+    uint64_t compat_features;       /* compatible feature bits */
+    uint64_t autoclear_features;    /* self-resetting feature bits */
+
+    uint64_t l1_table_offset;       /* in bytes */
+    uint64_t image_size;            /* total logical image size, in bytes */
+
+    /* if (features & QED_F_BACKING_FILE) */
+    uint32_t backing_filename_offset; /* in bytes from start of header */
+    uint32_t backing_filename_size;   /* in bytes */
+} QEDHeader;
+
+typedef struct {
+    BlockDriverState *bs;           /* device */
+    uint64_t file_size;             /* length of image file, in bytes */
+
+    QEDHeader header;               /* always cpu-endian */
+    uint32_t table_nelems;
+    uint32_t l1_shift;
+    uint32_t l2_shift;
+    uint32_t l2_mask;
+} BDRVQEDState;
+
+/**
+ * Round down to the start of a cluster
+ */
+static inline uint64_t qed_start_of_cluster(BDRVQEDState *s, uint64_t offset)
+{
+    return offset & ~(uint64_t)(s->header.cluster_size - 1);
+}
+
+/**
+ * Test if a cluster offset is valid
+ */
+static inline bool qed_check_cluster_offset(BDRVQEDState *s, uint64_t offset)
+{
+    uint64_t header_size = (uint64_t)s->header.header_size *
+                           s->header.cluster_size;
+
+    if (offset & (s->header.cluster_size - 1)) {
+        return false;
+    }
+    return offset >= header_size && offset < s->file_size;
+}
+
+/**
+ * Test if a table offset is valid
+ */
+static inline bool qed_check_table_offset(BDRVQEDState *s, uint64_t offset)
+{
+    uint64_t end_offset = offset + (s->header.table_size - 1) *
+                          s->header.cluster_size;
+
+    /* Overflow check */
+    if (end_offset <= offset) {
+        return false;
+    }
+
+    return qed_check_cluster_offset(s, offset) &&
+           qed_check_cluster_offset(s, end_offset);
+}
+
+#endif /* BLOCK_QED_H */
diff --git a/block_int.h b/block_int.h
index 3c3adb5..069d227 100644
--- a/block_int.h
+++ b/block_int.h
@@ -38,6 +38,7 @@ 
 #define BLOCK_OPT_BACKING_FILE  "backing_file"
 #define BLOCK_OPT_BACKING_FMT   "backing_fmt"
 #define BLOCK_OPT_CLUSTER_SIZE  "cluster_size"
+#define BLOCK_OPT_TABLE_SIZE    "table_size"
 #define BLOCK_OPT_PREALLOC      "preallocation"
 
 typedef struct AIOPool {