Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 764 insertions, 0 deletions

diff --git a/block/dmg.c b/block/dmg.c
new file mode 100644
index 000000000..447901fbb
--- /dev/null
+++ b/block/dmg.c
@@ -0,0 +1,764 @@
+/*
+ * QEMU Block driver for DMG images
+ *
+ * Copyright (c) 2004 Johannes E. Schindelin
+ *
+ * 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/osdep.h"
+#include "qapi/error.h"
+#include "block/block_int.h"
+#include "qemu/bswap.h"
+#include "qemu/error-report.h"
+#include "qemu/module.h"
+#include "dmg.h"
+
+int (*dmg_uncompress_bz2)(char *next_in, unsigned int avail_in,
+                          char *next_out, unsigned int avail_out);
+
+int (*dmg_uncompress_lzfse)(char *next_in, unsigned int avail_in,
+                            char *next_out, unsigned int avail_out);
+
+enum {
+    /* Limit chunk sizes to prevent unreasonable amounts of memory being used
+     * or truncating when converting to 32-bit types
+     */
+    DMG_LENGTHS_MAX = 64 * 1024 * 1024, /* 64 MB */
+    DMG_SECTORCOUNTS_MAX = DMG_LENGTHS_MAX / 512,
+};
+
+enum {
+    /* DMG Block Type */
+    UDZE = 0, /* Zeroes */
+    UDRW,     /* RAW type */
+    UDIG,     /* Ignore */
+    UDCO = 0x80000004,
+    UDZO,
+    UDBZ,
+    ULFO,
+    UDCM = 0x7ffffffe, /* Comments */
+    UDLE = 0xffffffff  /* Last Entry */
+};
+
+static int dmg_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    int len;
+
+    if (!filename) {
+        return 0;
+    }
+
+    len = strlen(filename);
+    if (len > 4 && !strcmp(filename + len - 4, ".dmg")) {
+        return 2;
+    }
+    return 0;
+}
+
+static int read_uint64(BlockDriverState *bs, int64_t offset, uint64_t *result)
+{
+    uint64_t buffer;
+    int ret;
+
+    ret = bdrv_pread(bs->file, offset, &buffer, 8);
+    if (ret < 0) {
+        return ret;
+    }
+
+    *result = be64_to_cpu(buffer);
+    return 0;
+}
+
+static int read_uint32(BlockDriverState *bs, int64_t offset, uint32_t *result)
+{
+    uint32_t buffer;
+    int ret;
+
+    ret = bdrv_pread(bs->file, offset, &buffer, 4);
+    if (ret < 0) {
+        return ret;
+    }
+
+    *result = be32_to_cpu(buffer);
+    return 0;
+}
+
+static inline uint64_t buff_read_uint64(const uint8_t *buffer, int64_t offset)
+{
+    return be64_to_cpu(*(uint64_t *)&buffer[offset]);
+}
+
+static inline uint32_t buff_read_uint32(const uint8_t *buffer, int64_t offset)
+{
+    return be32_to_cpu(*(uint32_t *)&buffer[offset]);
+}
+
+/* Increase max chunk sizes, if necessary.  This function is used to calculate
+ * the buffer sizes needed for compressed/uncompressed chunk I/O.
+ */
+static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
+                                  uint32_t *max_compressed_size,
+                                  uint32_t *max_sectors_per_chunk)
+{
+    uint32_t compressed_size = 0;
+    uint32_t uncompressed_sectors = 0;
+
+    switch (s->types[chunk]) {
+    case UDZO: /* zlib compressed */
+    case UDBZ: /* bzip2 compressed */
+    case ULFO: /* lzfse compressed */
+        compressed_size = s->lengths[chunk];
+        uncompressed_sectors = s->sectorcounts[chunk];
+        break;
+    case UDRW: /* copy */
+        uncompressed_sectors = DIV_ROUND_UP(s->lengths[chunk], 512);
+        break;
+    case UDZE: /* zero */
+    case UDIG: /* ignore */
+        /* as the all-zeroes block may be large, it is treated specially: the
+         * sector is not copied from a large buffer, a simple memset is used
+         * instead. Therefore uncompressed_sectors does not need to be set. */
+        break;
+    }
+
+    if (compressed_size > *max_compressed_size) {
+        *max_compressed_size = compressed_size;
+    }
+    if (uncompressed_sectors > *max_sectors_per_chunk) {
+        *max_sectors_per_chunk = uncompressed_sectors;
+    }
+}
+
+static int64_t dmg_find_koly_offset(BdrvChild *file, Error **errp)
+{
+    BlockDriverState *file_bs = file->bs;
+    int64_t length;
+    int64_t offset = 0;
+    uint8_t buffer[515];
+    int i, ret;
+
+    /* bdrv_getlength returns a multiple of block size (512), rounded up. Since
+     * dmg images can have odd sizes, try to look for the "koly" magic which
+     * marks the begin of the UDIF trailer (512 bytes). This magic can be found
+     * in the last 511 bytes of the second-last sector or the first 4 bytes of
+     * the last sector (search space: 515 bytes) */
+    length = bdrv_getlength(file_bs);
+    if (length < 0) {
+        error_setg_errno(errp, -length,
+            "Failed to get file size while reading UDIF trailer");
+        return length;
+    } else if (length < 512) {
+        error_setg(errp, "dmg file must be at least 512 bytes long");
+        return -EINVAL;
+    }
+    if (length > 511 + 512) {
+        offset = length - 511 - 512;
+    }
+    length = length < 515 ? length : 515;
+    ret = bdrv_pread(file, offset, buffer, length);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Failed while reading UDIF trailer");
+        return ret;
+    }
+    for (i = 0; i < length - 3; i++) {
+        if (buffer[i] == 'k' && buffer[i+1] == 'o' &&
+            buffer[i+2] == 'l' && buffer[i+3] == 'y') {
+            return offset + i;
+        }
+    }
+    error_setg(errp, "Could not locate UDIF trailer in dmg file");
+    return -EINVAL;
+}
+
+/* used when building the sector table */
+typedef struct DmgHeaderState {
+    /* used internally by dmg_read_mish_block to remember offsets of blocks
+     * across calls */
+    uint64_t data_fork_offset;
+    /* exported for dmg_open */
+    uint32_t max_compressed_size;
+    uint32_t max_sectors_per_chunk;
+} DmgHeaderState;
+
+static bool dmg_is_known_block_type(uint32_t entry_type)
+{
+    switch (entry_type) {
+    case UDZE:    /* zeros */
+    case UDRW:    /* uncompressed */
+    case UDIG:    /* ignore */
+    case UDZO:    /* zlib */
+        return true;
+    case UDBZ:    /* bzip2 */
+        return !!dmg_uncompress_bz2;
+    case ULFO:    /* lzfse */
+        return !!dmg_uncompress_lzfse;
+    default:
+        return false;
+    }
+}
+
+static int dmg_read_mish_block(BDRVDMGState *s, DmgHeaderState *ds,
+                               uint8_t *buffer, uint32_t count)
+{
+    uint32_t type, i;
+    int ret;
+    size_t new_size;
+    uint32_t chunk_count;
+    int64_t offset = 0;
+    uint64_t data_offset;
+    uint64_t in_offset = ds->data_fork_offset;
+    uint64_t out_offset;
+
+    type = buff_read_uint32(buffer, offset);
+    /* skip data that is not a valid MISH block (invalid magic or too small) */
+    if (type != 0x6d697368 || count < 244) {
+        /* assume success for now */
+        return 0;
+    }
+
+    /* chunk offsets are relative to this sector number */
+    out_offset = buff_read_uint64(buffer, offset + 8);
+
+    /* location in data fork for (compressed) blob (in bytes) */
+    data_offset = buff_read_uint64(buffer, offset + 0x18);
+    in_offset += data_offset;
+
+    /* move to begin of chunk entries */
+    offset += 204;
+
+    chunk_count = (count - 204) / 40;
+    new_size = sizeof(uint64_t) * (s->n_chunks + chunk_count);
+    s->types = g_realloc(s->types, new_size / 2);
+    s->offsets = g_realloc(s->offsets, new_size);
+    s->lengths = g_realloc(s->lengths, new_size);
+    s->sectors = g_realloc(s->sectors, new_size);
+    s->sectorcounts = g_realloc(s->sectorcounts, new_size);
+
+    for (i = s->n_chunks; i < s->n_chunks + chunk_count; i++) {
+        s->types[i] = buff_read_uint32(buffer, offset);
+        if (!dmg_is_known_block_type(s->types[i])) {
+            chunk_count--;
+            i--;
+            offset += 40;
+            continue;
+        }
+
+        /* sector number */
+        s->sectors[i] = buff_read_uint64(buffer, offset + 8);
+        s->sectors[i] += out_offset;
+
+        /* sector count */
+        s->sectorcounts[i] = buff_read_uint64(buffer, offset + 0x10);
+
+        /* all-zeroes sector (type UDZE and UDIG) does not need to be
+         * "uncompressed" and can therefore be unbounded. */
+        if (s->types[i] != UDZE && s->types[i] != UDIG
+            && s->sectorcounts[i] > DMG_SECTORCOUNTS_MAX) {
+            error_report("sector count %" PRIu64 " for chunk %" PRIu32
+                         " is larger than max (%u)",
+                         s->sectorcounts[i], i, DMG_SECTORCOUNTS_MAX);
+            ret = -EINVAL;
+            goto fail;
+        }
+
+        /* offset in (compressed) data fork */
+        s->offsets[i] = buff_read_uint64(buffer, offset + 0x18);
+        s->offsets[i] += in_offset;
+
+        /* length in (compressed) data fork */
+        s->lengths[i] = buff_read_uint64(buffer, offset + 0x20);
+
+        if (s->lengths[i] > DMG_LENGTHS_MAX) {
+            error_report("length %" PRIu64 " for chunk %" PRIu32
+                         " is larger than max (%u)",
+                         s->lengths[i], i, DMG_LENGTHS_MAX);
+            ret = -EINVAL;
+            goto fail;
+        }
+
+        update_max_chunk_size(s, i, &ds->max_compressed_size,
+                              &ds->max_sectors_per_chunk);
+        offset += 40;
+    }
+    s->n_chunks += chunk_count;
+    return 0;
+
+fail:
+    return ret;
+}
+
+static int dmg_read_resource_fork(BlockDriverState *bs, DmgHeaderState *ds,
+                                  uint64_t info_begin, uint64_t info_length)
+{
+    BDRVDMGState *s = bs->opaque;
+    int ret;
+    uint32_t count, rsrc_data_offset;
+    uint8_t *buffer = NULL;
+    uint64_t info_end;
+    uint64_t offset;
+
+    /* read offset from begin of resource fork (info_begin) to resource data */
+    ret = read_uint32(bs, info_begin, &rsrc_data_offset);
+    if (ret < 0) {
+        goto fail;
+    } else if (rsrc_data_offset > info_length) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* read length of resource data */
+    ret = read_uint32(bs, info_begin + 8, &count);
+    if (ret < 0) {
+        goto fail;
+    } else if (count == 0 || rsrc_data_offset + count > info_length) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* begin of resource data (consisting of one or more resources) */
+    offset = info_begin + rsrc_data_offset;
+
+    /* end of resource data (there is possibly a following resource map
+     * which will be ignored). */
+    info_end = offset + count;
+
+    /* read offsets (mish blocks) from one or more resources in resource data */
+    while (offset < info_end) {
+        /* size of following resource */
+        ret = read_uint32(bs, offset, &count);
+        if (ret < 0) {
+            goto fail;
+        } else if (count == 0 || count > info_end - offset) {
+            ret = -EINVAL;
+            goto fail;
+        }
+        offset += 4;
+
+        buffer = g_realloc(buffer, count);
+        ret = bdrv_pread(bs->file, offset, buffer, count);
+        if (ret < 0) {
+            goto fail;
+        }
+
+        ret = dmg_read_mish_block(s, ds, buffer, count);
+        if (ret < 0) {
+            goto fail;
+        }
+        /* advance offset by size of resource */
+        offset += count;
+    }
+    ret = 0;
+
+fail:
+    g_free(buffer);
+    return ret;
+}
+
+static int dmg_read_plist_xml(BlockDriverState *bs, DmgHeaderState *ds,
+                              uint64_t info_begin, uint64_t info_length)
+{
+    BDRVDMGState *s = bs->opaque;
+    int ret;
+    uint8_t *buffer = NULL;
+    char *data_begin, *data_end;
+
+    /* Have at least some length to avoid NULL for g_malloc. Attempt to set a
+     * safe upper cap on the data length. A test sample had a XML length of
+     * about 1 MiB. */
+    if (info_length == 0 || info_length > 16 * 1024 * 1024) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    buffer = g_malloc(info_length + 1);
+    buffer[info_length] = '\0';
+    ret = bdrv_pread(bs->file, info_begin, buffer, info_length);
+    if (ret != info_length) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* look for <data>...</data>. The data is 284 (0x11c) bytes after base64
+     * decode. The actual data element has 431 (0x1af) bytes which includes tabs
+     * and line feeds. */
+    data_end = (char *)buffer;
+    while ((data_begin = strstr(data_end, "<data>")) != NULL) {
+        guchar *mish;
+        gsize out_len = 0;
+
+        data_begin += 6;
+        data_end = strstr(data_begin, "</data>");
+        /* malformed XML? */
+        if (data_end == NULL) {
+            ret = -EINVAL;
+            goto fail;
+        }
+        *data_end++ = '\0';
+        mish = g_base64_decode(data_begin, &out_len);
+        ret = dmg_read_mish_block(s, ds, mish, (uint32_t)out_len);
+        g_free(mish);
+        if (ret < 0) {
+            goto fail;
+        }
+    }
+    ret = 0;
+
+fail:
+    g_free(buffer);
+    return ret;
+}
+
+static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
+                    Error **errp)
+{
+    BDRVDMGState *s = bs->opaque;
+    DmgHeaderState ds;
+    uint64_t rsrc_fork_offset, rsrc_fork_length;
+    uint64_t plist_xml_offset, plist_xml_length;
+    int64_t offset;
+    int ret;
+
+    ret = bdrv_apply_auto_read_only(bs, NULL, errp);
+    if (ret < 0) {
+        return ret;
+    }
+
+    bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
+                               BDRV_CHILD_IMAGE, false, errp);
+    if (!bs->file) {
+        return -EINVAL;
+    }
+
+    block_module_load_one("dmg-bz2");
+    block_module_load_one("dmg-lzfse");
+
+    s->n_chunks = 0;
+    s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
+    /* used by dmg_read_mish_block to keep track of the current I/O position */
+    ds.data_fork_offset = 0;
+    ds.max_compressed_size = 1;
+    ds.max_sectors_per_chunk = 1;
+
+    /* locate the UDIF trailer */
+    offset = dmg_find_koly_offset(bs->file, errp);
+    if (offset < 0) {
+        ret = offset;
+        goto fail;
+    }
+
+    /* offset of data fork (DataForkOffset) */
+    ret = read_uint64(bs, offset + 0x18, &ds.data_fork_offset);
+    if (ret < 0) {
+        goto fail;
+    } else if (ds.data_fork_offset > offset) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* offset of resource fork (RsrcForkOffset) */
+    ret = read_uint64(bs, offset + 0x28, &rsrc_fork_offset);
+    if (ret < 0) {
+        goto fail;
+    }
+    ret = read_uint64(bs, offset + 0x30, &rsrc_fork_length);
+    if (ret < 0) {
+        goto fail;
+    }
+    if (rsrc_fork_offset >= offset ||
+        rsrc_fork_length > offset - rsrc_fork_offset) {
+        ret = -EINVAL;
+        goto fail;
+    }
+    /* offset of property list (XMLOffset) */
+    ret = read_uint64(bs, offset + 0xd8, &plist_xml_offset);
+    if (ret < 0) {
+        goto fail;
+    }
+    ret = read_uint64(bs, offset + 0xe0, &plist_xml_length);
+    if (ret < 0) {
+        goto fail;
+    }
+    if (plist_xml_offset >= offset ||
+        plist_xml_length > offset - plist_xml_offset) {
+        ret = -EINVAL;
+        goto fail;
+    }
+    ret = read_uint64(bs, offset + 0x1ec, (uint64_t *)&bs->total_sectors);
+    if (ret < 0) {
+        goto fail;
+    }
+    if (bs->total_sectors < 0) {
+        ret = -EINVAL;
+        goto fail;
+    }
+    if (rsrc_fork_length != 0) {
+        ret = dmg_read_resource_fork(bs, &ds,
+                                     rsrc_fork_offset, rsrc_fork_length);
+        if (ret < 0) {
+            goto fail;
+        }
+    } else if (plist_xml_length != 0) {
+        ret = dmg_read_plist_xml(bs, &ds, plist_xml_offset, plist_xml_length);
+        if (ret < 0) {
+            goto fail;
+        }
+    } else {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    /* initialize zlib engine */
+    s->compressed_chunk = qemu_try_blockalign(bs->file->bs,
+                                              ds.max_compressed_size + 1);
+    s->uncompressed_chunk = qemu_try_blockalign(bs->file->bs,
+                                                512 * ds.max_sectors_per_chunk);
+    if (s->compressed_chunk == NULL || s->uncompressed_chunk == NULL) {
+        ret = -ENOMEM;
+        goto fail;
+    }
+
+    if (inflateInit(&s->zstream) != Z_OK) {
+        ret = -EINVAL;
+        goto fail;
+    }
+
+    s->current_chunk = s->n_chunks;
+
+    qemu_co_mutex_init(&s->lock);
+    return 0;
+
+fail:
+    g_free(s->types);
+    g_free(s->offsets);
+    g_free(s->lengths);
+    g_free(s->sectors);
+    g_free(s->sectorcounts);
+    qemu_vfree(s->compressed_chunk);
+    qemu_vfree(s->uncompressed_chunk);
+    return ret;
+}
+
+static void dmg_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+    bs->bl.request_alignment = BDRV_SECTOR_SIZE; /* No sub-sector I/O */
+}
+
+static inline int is_sector_in_chunk(BDRVDMGState *s,
+                uint32_t chunk_num, uint64_t sector_num)
+{
+    if (chunk_num >= s->n_chunks || s->sectors[chunk_num] > sector_num ||
+            s->sectors[chunk_num] + s->sectorcounts[chunk_num] <= sector_num) {
+        return 0;
+    } else {
+        return -1;
+    }
+}
+
+static inline uint32_t search_chunk(BDRVDMGState *s, uint64_t sector_num)
+{
+    /* binary search */
+    uint32_t chunk1 = 0, chunk2 = s->n_chunks, chunk3;
+    while (chunk1 <= chunk2) {
+        chunk3 = (chunk1 + chunk2) / 2;
+        if (s->sectors[chunk3] > sector_num) {
+            if (chunk3 == 0) {
+                goto err;
+            }
+            chunk2 = chunk3 - 1;
+        } else if (s->sectors[chunk3] + s->sectorcounts[chunk3] > sector_num) {
+            return chunk3;
+        } else {
+            chunk1 = chunk3 + 1;
+        }
+    }
+err:
+    return s->n_chunks; /* error */
+}
+
+static inline int dmg_read_chunk(BlockDriverState *bs, uint64_t sector_num)
+{
+    BDRVDMGState *s = bs->opaque;
+
+    if (!is_sector_in_chunk(s, s->current_chunk, sector_num)) {
+        int ret;
+        uint32_t chunk = search_chunk(s, sector_num);
+
+        if (chunk >= s->n_chunks) {
+            return -1;
+        }
+
+        s->current_chunk = s->n_chunks;
+        switch (s->types[chunk]) { /* block entry type */
+        case UDZO: { /* zlib compressed */
+            /* we need to buffer, because only the chunk as whole can be
+             * inflated. */
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
+                             s->compressed_chunk, s->lengths[chunk]);
+            if (ret != s->lengths[chunk]) {
+                return -1;
+            }
+
+            s->zstream.next_in = s->compressed_chunk;
+            s->zstream.avail_in = s->lengths[chunk];
+            s->zstream.next_out = s->uncompressed_chunk;
+            s->zstream.avail_out = 512 * s->sectorcounts[chunk];
+            ret = inflateReset(&s->zstream);
+            if (ret != Z_OK) {
+                return -1;
+            }
+            ret = inflate(&s->zstream, Z_FINISH);
+            if (ret != Z_STREAM_END ||
+                s->zstream.total_out != 512 * s->sectorcounts[chunk]) {
+                return -1;
+            }
+            break; }
+        case UDBZ: /* bzip2 compressed */
+            if (!dmg_uncompress_bz2) {
+                break;
+            }
+            /* we need to buffer, because only the chunk as whole can be
+             * inflated. */
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
+                             s->compressed_chunk, s->lengths[chunk]);
+            if (ret != s->lengths[chunk]) {
+                return -1;
+            }
+
+            ret = dmg_uncompress_bz2((char *)s->compressed_chunk,
+                                     (unsigned int) s->lengths[chunk],
+                                     (char *)s->uncompressed_chunk,
+                                     (unsigned int)
+                                         (512 * s->sectorcounts[chunk]));
+            if (ret < 0) {
+                return ret;
+            }
+            break;
+        case ULFO:
+            if (!dmg_uncompress_lzfse) {
+                break;
+            }
+            /* we need to buffer, because only the chunk as whole can be
+             * inflated. */
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
+                             s->compressed_chunk, s->lengths[chunk]);
+            if (ret != s->lengths[chunk]) {
+                return -1;
+            }
+
+            ret = dmg_uncompress_lzfse((char *)s->compressed_chunk,
+                                       (unsigned int) s->lengths[chunk],
+                                       (char *)s->uncompressed_chunk,
+                                       (unsigned int)
+                                           (512 * s->sectorcounts[chunk]));
+            if (ret < 0) {
+                return ret;
+            }
+            break;
+        case UDRW: /* copy */
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
+                             s->uncompressed_chunk, s->lengths[chunk]);
+            if (ret != s->lengths[chunk]) {
+                return -1;
+            }
+            break;
+        case UDZE: /* zeros */
+        case UDIG: /* ignore */
+            /* see dmg_read, it is treated specially. No buffer needs to be
+             * pre-filled, the zeroes can be set directly. */
+            break;
+        }
+        s->current_chunk = chunk;
+    }
+    return 0;
+}
+
+static int coroutine_fn
+dmg_co_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
+              QEMUIOVector *qiov, BdrvRequestFlags flags)
+{
+    BDRVDMGState *s = bs->opaque;
+    uint64_t sector_num = offset >> BDRV_SECTOR_BITS;
+    int nb_sectors = bytes >> BDRV_SECTOR_BITS;
+    int ret, i;
+
+    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
+    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
+
+    qemu_co_mutex_lock(&s->lock);
+
+    for (i = 0; i < nb_sectors; i++) {
+        uint32_t sector_offset_in_chunk;
+        void *data;
+
+        if (dmg_read_chunk(bs, sector_num + i) != 0) {
+            ret = -EIO;
+            goto fail;
+        }
+        /* Special case: current chunk is all zeroes. Do not perform a memcpy as
+         * s->uncompressed_chunk may be too small to cover the large all-zeroes
+         * section. dmg_read_chunk is called to find s->current_chunk */
+        if (s->types[s->current_chunk] == UDZE
+            || s->types[s->current_chunk] == UDIG) { /* all zeroes block entry */
+            qemu_iovec_memset(qiov, i * 512, 0, 512);
+            continue;
+        }
+        sector_offset_in_chunk = sector_num + i - s->sectors[s->current_chunk];
+        data = s->uncompressed_chunk + sector_offset_in_chunk * 512;
+        qemu_iovec_from_buf(qiov, i * 512, data, 512);
+    }
+
+    ret = 0;
+fail:
+    qemu_co_mutex_unlock(&s->lock);
+    return ret;
+}
+
+static void dmg_close(BlockDriverState *bs)
+{
+    BDRVDMGState *s = bs->opaque;
+
+    g_free(s->types);
+    g_free(s->offsets);
+    g_free(s->lengths);
+    g_free(s->sectors);
+    g_free(s->sectorcounts);
+    qemu_vfree(s->compressed_chunk);
+    qemu_vfree(s->uncompressed_chunk);
+
+    inflateEnd(&s->zstream);
+}
+
+static BlockDriver bdrv_dmg = {
+    .format_name    = "dmg",
+    .instance_size  = sizeof(BDRVDMGState),
+    .bdrv_probe     = dmg_probe,
+    .bdrv_open      = dmg_open,
+    .bdrv_refresh_limits = dmg_refresh_limits,
+    .bdrv_child_perm     = bdrv_default_perms,
+    .bdrv_co_preadv = dmg_co_preadv,
+    .bdrv_close     = dmg_close,
+    .is_format      = true,
+};
+
+static void bdrv_dmg_init(void)
+{
+    bdrv_register(&bdrv_dmg);
+}
+
+block_init(bdrv_dmg_init);