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diff --git a/src/librbd/migration/QCOW.h b/src/librbd/migration/QCOW.h
new file mode 100644
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+++ b/src/librbd/migration/QCOW.h
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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+/* Based on QEMU block/qcow.cc and block/qcow2.h, which has this license: */
+
+/*
+ * Block driver for the QCOW version 2 format
+ *
+ * Copyright (c) 2004-2006 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.
+ */
+
+#ifndef CEPH_LIBRBD_MIGRATION_QCOW2_H
+#define CEPH_LIBRBD_MIGRATION_QCOW2_H
+
+#include "include/ceph_assert.h"
+#include "include/int_types.h"
+#include "librbd/migration/QCOW.h"
+
+#define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
+
+#define QCOW_CRYPT_NONE 0
+#define QCOW_CRYPT_AES  1
+#define QCOW_CRYPT_LUKS 2
+
+#define QCOW_MAX_CRYPT_CLUSTERS 32
+#define QCOW_MAX_SNAPSHOTS 65536
+
+/* Field widths in qcow2 mean normal cluster offsets cannot reach
+ * 64PB; depending on cluster size, compressed clusters can have a
+ * smaller limit (64PB for up to 16k clusters, then ramps down to
+ * 512TB for 2M clusters).  */
+#define QCOW_MAX_CLUSTER_OFFSET ((1ULL << 56) - 1)
+
+/* 8 MB refcount table is enough for 2 PB images at 64k cluster size
+ * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+#define QCOW_MAX_REFTABLE_SIZE (1ULL << 23)
+
+/* 32 MB L1 table is enough for 2 PB images at 64k cluster size
+ * (128 GB for 512 byte clusters, 2 EB for 2 MB clusters) */
+#define QCOW_MAX_L1_SIZE (1ULL << 25)
+
+/* Allow for an average of 1k per snapshot table entry, should be plenty of
+ * space for snapshot names and IDs */
+#define QCOW_MAX_SNAPSHOTS_SIZE (1024 * QCOW_MAX_SNAPSHOTS)
+
+/* Maximum amount of extra data per snapshot table entry to accept */
+#define QCOW_MAX_SNAPSHOT_EXTRA_DATA 1024
+
+/* Bitmap header extension constraints */
+#define QCOW2_MAX_BITMAPS 65535
+#define QCOW2_MAX_BITMAP_DIRECTORY_SIZE (1024 * QCOW2_MAX_BITMAPS)
+
+/* Maximum of parallel sub-request per guest request */
+#define QCOW2_MAX_WORKERS 8
+
+/* indicate that the refcount of the referenced cluster is exactly one. */
+#define QCOW_OFLAG_COPIED     (1ULL << 63)
+/* indicate that the cluster is compressed (they never have the copied flag) */
+#define QCOW_OFLAG_COMPRESSED (1ULL << 62)
+/* The cluster reads as all zeros */
+#define QCOW_OFLAG_ZERO (1ULL << 0)
+
+#define QCOW_EXTL2_SUBCLUSTERS_PER_CLUSTER 32
+
+/* The subcluster X [0..31] is allocated */
+#define QCOW_OFLAG_SUB_ALLOC(X)   (1ULL << (X))
+/* The subcluster X [0..31] reads as zeroes */
+#define QCOW_OFLAG_SUB_ZERO(X)    (QCOW_OFLAG_SUB_ALLOC(X) << 32)
+/* Subclusters [X, Y) (0 <= X <= Y <= 32) are allocated */
+#define QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) \
+    (QCOW_OFLAG_SUB_ALLOC(Y) - QCOW_OFLAG_SUB_ALLOC(X))
+/* Subclusters [X, Y) (0 <= X <= Y <= 32) read as zeroes */
+#define QCOW_OFLAG_SUB_ZERO_RANGE(X, Y) \
+    (QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) << 32)
+/* L2 entry bitmap with all allocation bits set */
+#define QCOW_L2_BITMAP_ALL_ALLOC  (QCOW_OFLAG_SUB_ALLOC_RANGE(0, 32))
+/* L2 entry bitmap with all "read as zeroes" bits set */
+#define QCOW_L2_BITMAP_ALL_ZEROES (QCOW_OFLAG_SUB_ZERO_RANGE(0, 32))
+
+/* Size of normal and extended L2 entries */
+#define QCOW_L2E_SIZE_NORMAL   (sizeof(uint64_t))
+#define QCOW_L2E_SIZE_EXTENDED (sizeof(uint64_t) * 2)
+
+/* Size of L1 table entries */
+#define QCOW_L1E_SIZE (sizeof(uint64_t))
+
+/* Size of reftable entries */
+#define QCOW_REFTABLE_ENTRY_SIZE (sizeof(uint64_t))
+
+#define QCOW_MIN_CLUSTER_BITS 9
+#define QCOW_MAX_CLUSTER_BITS 21
+
+/* Defined in the qcow2 spec (compressed cluster descriptor) */
+#define QCOW2_COMPRESSED_SECTOR_SIZE 512U
+#define QCOW2_COMPRESSED_SECTOR_MASK (~(QCOW2_COMPRESSED_SECTOR_SIZE - 1ULL))
+
+#define QCOW_L2_CACHE_SIZE 16
+
+/* Must be at least 2 to cover COW */
+#define QCOW_MIN_L2_CACHE_SIZE 2 /* cache entries */
+
+/* Must be at least 4 to cover all cases of refcount table growth */
+#define QCOW_MIN_REFCOUNT_CACHE_SIZE 4 /* clusters */
+
+#define QCOW_DEFAULT_L2_CACHE_MAX_SIZE (1ULL << 25)
+#define QCOW_DEFAULT_CACHE_CLEAN_INTERVAL 600  /* seconds */
+
+#define QCOW_DEFAULT_CLUSTER_SIZE 65536
+
+#define QCOW2_OPT_DATA_FILE "data-file"
+#define QCOW2_OPT_LAZY_REFCOUNTS "lazy-refcounts"
+#define QCOW2_OPT_DISCARD_REQUEST "pass-discard-request"
+#define QCOW2_OPT_DISCARD_SNAPSHOT "pass-discard-snapshot"
+#define QCOW2_OPT_DISCARD_OTHER "pass-discard-other"
+#define QCOW2_OPT_OVERLAP "overlap-check"
+#define QCOW2_OPT_OVERLAP_TEMPLATE "overlap-check.template"
+#define QCOW2_OPT_OVERLAP_MAIN_HEADER "overlap-check.main-header"
+#define QCOW2_OPT_OVERLAP_ACTIVE_L1 "overlap-check.active-l1"
+#define QCOW2_OPT_OVERLAP_ACTIVE_L2 "overlap-check.active-l2"
+#define QCOW2_OPT_OVERLAP_REFCOUNT_TABLE "overlap-check.refcount-table"
+#define QCOW2_OPT_OVERLAP_REFCOUNT_BLOCK "overlap-check.refcount-block"
+#define QCOW2_OPT_OVERLAP_SNAPSHOT_TABLE "overlap-check.snapshot-table"
+#define QCOW2_OPT_OVERLAP_INACTIVE_L1 "overlap-check.inactive-l1"
+#define QCOW2_OPT_OVERLAP_INACTIVE_L2 "overlap-check.inactive-l2"
+#define QCOW2_OPT_OVERLAP_BITMAP_DIRECTORY "overlap-check.bitmap-directory"
+#define QCOW2_OPT_CACHE_SIZE "cache-size"
+#define QCOW2_OPT_L2_CACHE_SIZE "l2-cache-size"
+#define QCOW2_OPT_L2_CACHE_ENTRY_SIZE "l2-cache-entry-size"
+#define QCOW2_OPT_REFCOUNT_CACHE_SIZE "refcount-cache-size"
+#define QCOW2_OPT_CACHE_CLEAN_INTERVAL "cache-clean-interval"
+
+typedef struct QCowHeaderProbe {
+    uint32_t magic;
+    uint32_t version;
+} __attribute__((__packed__)) QCowHeaderProbe;
+
+typedef struct QCowHeaderV1
+{
+    uint32_t magic;
+    uint32_t version;
+    uint64_t backing_file_offset;
+    uint32_t backing_file_size;
+    uint32_t mtime;
+    uint64_t size; /* in bytes */
+    uint8_t cluster_bits;
+    uint8_t l2_bits;
+    uint16_t padding;
+    uint32_t crypt_method;
+    uint64_t l1_table_offset;
+} __attribute__((__packed__)) QCowHeaderV1;
+
+typedef struct QCowHeader {
+    uint32_t magic;
+    uint32_t version;
+    uint64_t backing_file_offset;
+    uint32_t backing_file_size;
+    uint32_t cluster_bits;
+    uint64_t size; /* in bytes */
+    uint32_t crypt_method;
+    uint32_t l1_size; /* XXX: save number of clusters instead ? */
+    uint64_t l1_table_offset;
+    uint64_t refcount_table_offset;
+    uint32_t refcount_table_clusters;
+    uint32_t nb_snapshots;
+    uint64_t snapshots_offset;
+
+    /* The following fields are only valid for version >= 3 */
+    uint64_t incompatible_features;
+    uint64_t compatible_features;
+    uint64_t autoclear_features;
+
+    uint32_t refcount_order;
+    uint32_t header_length;
+
+    /* Additional fields */
+    uint8_t compression_type;
+
+    /* header must be a multiple of 8 */
+    uint8_t padding[7];
+} __attribute__((__packed__)) QCowHeader;
+
+typedef struct QCowSnapshotHeader {
+    /* header is 8 byte aligned */
+    uint64_t l1_table_offset;
+
+    uint32_t l1_size;
+    uint16_t id_str_size;
+    uint16_t name_size;
+
+    uint32_t date_sec;
+    uint32_t date_nsec;
+
+    uint64_t vm_clock_nsec;
+
+    uint32_t vm_state_size;
+    uint32_t extra_data_size; /* for extension */
+    /* extra data follows */
+    /* id_str follows */
+    /* name follows  */
+} __attribute__((__packed__)) QCowSnapshotHeader;
+
+typedef struct QCowSnapshotExtraData {
+    uint64_t vm_state_size_large;
+    uint64_t disk_size;
+    uint64_t icount;
+} __attribute__((__packed__)) QCowSnapshotExtraData;
+
+
+typedef struct QCowSnapshot {
+    uint64_t l1_table_offset;
+    uint32_t l1_size;
+    char *id_str;
+    char *name;
+    uint64_t disk_size;
+    uint64_t vm_state_size;
+    uint32_t date_sec;
+    uint32_t date_nsec;
+    uint64_t vm_clock_nsec;
+    /* icount value for the moment when snapshot was taken */
+    uint64_t icount;
+    /* Size of all extra data, including QCowSnapshotExtraData if available */
+    uint32_t extra_data_size;
+    /* Data beyond QCowSnapshotExtraData, if any */
+    void *unknown_extra_data;
+} QCowSnapshot;
+
+typedef struct Qcow2CryptoHeaderExtension {
+    uint64_t offset;
+    uint64_t length;
+} __attribute__((__packed__)) Qcow2CryptoHeaderExtension;
+
+typedef struct Qcow2UnknownHeaderExtension {
+    uint32_t magic;
+    uint32_t len;
+    uint8_t data[];
+} Qcow2UnknownHeaderExtension;
+
+enum {
+    QCOW2_FEAT_TYPE_INCOMPATIBLE    = 0,
+    QCOW2_FEAT_TYPE_COMPATIBLE      = 1,
+    QCOW2_FEAT_TYPE_AUTOCLEAR       = 2,
+};
+
+/* Incompatible feature bits */
+enum {
+    QCOW2_INCOMPAT_DIRTY_BITNR      = 0,
+    QCOW2_INCOMPAT_CORRUPT_BITNR    = 1,
+    QCOW2_INCOMPAT_DATA_FILE_BITNR  = 2,
+    QCOW2_INCOMPAT_COMPRESSION_BITNR = 3,
+    QCOW2_INCOMPAT_EXTL2_BITNR      = 4,
+    QCOW2_INCOMPAT_DIRTY            = 1 << QCOW2_INCOMPAT_DIRTY_BITNR,
+    QCOW2_INCOMPAT_CORRUPT          = 1 << QCOW2_INCOMPAT_CORRUPT_BITNR,
+    QCOW2_INCOMPAT_DATA_FILE        = 1 << QCOW2_INCOMPAT_DATA_FILE_BITNR,
+    QCOW2_INCOMPAT_COMPRESSION      = 1 << QCOW2_INCOMPAT_COMPRESSION_BITNR,
+    QCOW2_INCOMPAT_EXTL2            = 1 << QCOW2_INCOMPAT_EXTL2_BITNR,
+
+    QCOW2_INCOMPAT_MASK             = QCOW2_INCOMPAT_DIRTY
+                                    | QCOW2_INCOMPAT_CORRUPT
+                                    | QCOW2_INCOMPAT_DATA_FILE
+                                    | QCOW2_INCOMPAT_COMPRESSION
+                                    | QCOW2_INCOMPAT_EXTL2,
+};
+
+/* Compatible feature bits */
+enum {
+    QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR = 0,
+    QCOW2_COMPAT_LAZY_REFCOUNTS       = 1 << QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR,
+
+    QCOW2_COMPAT_FEAT_MASK            = QCOW2_COMPAT_LAZY_REFCOUNTS,
+};
+
+/* Autoclear feature bits */
+enum {
+    QCOW2_AUTOCLEAR_BITMAPS_BITNR       = 0,
+    QCOW2_AUTOCLEAR_DATA_FILE_RAW_BITNR = 1,
+    QCOW2_AUTOCLEAR_BITMAPS             = 1 << QCOW2_AUTOCLEAR_BITMAPS_BITNR,
+    QCOW2_AUTOCLEAR_DATA_FILE_RAW       = 1 << QCOW2_AUTOCLEAR_DATA_FILE_RAW_BITNR,
+
+    QCOW2_AUTOCLEAR_MASK                = QCOW2_AUTOCLEAR_BITMAPS
+                                        | QCOW2_AUTOCLEAR_DATA_FILE_RAW,
+};
+
+enum qcow2_discard_type {
+    QCOW2_DISCARD_NEVER = 0,
+    QCOW2_DISCARD_ALWAYS,
+    QCOW2_DISCARD_REQUEST,
+    QCOW2_DISCARD_SNAPSHOT,
+    QCOW2_DISCARD_OTHER,
+    QCOW2_DISCARD_MAX
+};
+
+typedef struct Qcow2Feature {
+    uint8_t type;
+    uint8_t bit;
+    char    name[46];
+} __attribute__((__packed__)) Qcow2Feature;
+
+typedef struct Qcow2DiscardRegion {
+    uint64_t offset;
+    uint64_t bytes;
+} Qcow2DiscardRegion;
+
+typedef uint64_t Qcow2GetRefcountFunc(const void *refcount_array,
+                                      uint64_t index);
+typedef void Qcow2SetRefcountFunc(void *refcount_array,
+                                  uint64_t index, uint64_t value);
+
+typedef struct Qcow2BitmapHeaderExt {
+    uint32_t nb_bitmaps;
+    uint32_t reserved32;
+    uint64_t bitmap_directory_size;
+    uint64_t bitmap_directory_offset;
+} __attribute__((__packed__)) Qcow2BitmapHeaderExt;
+
+#define QCOW_RC_CACHE_SIZE QCOW_L2_CACHE_SIZE;
+
+typedef struct Qcow2COWRegion {
+    /**
+     * Offset of the COW region in bytes from the start of the first cluster
+     * touched by the request.
+     */
+    unsigned    offset;
+
+    /** Number of bytes to copy */
+    unsigned    nb_bytes;
+} Qcow2COWRegion;
+
+/**
+ * Describes an in-flight (part of a) write request that writes to clusters
+ * that are not referenced in their L2 table yet.
+ */
+typedef struct QCowL2Meta
+{
+    /** Guest offset of the first newly allocated cluster */
+    uint64_t offset;
+
+    /** Host offset of the first newly allocated cluster */
+    uint64_t alloc_offset;
+
+    /** Number of newly allocated clusters */
+    int nb_clusters;
+
+    /** Do not free the old clusters */
+    bool keep_old_clusters;
+
+    /**
+     * The COW Region between the start of the first allocated cluster and the
+     * area the guest actually writes to.
+     */
+    Qcow2COWRegion cow_start;
+
+    /**
+     * The COW Region between the area the guest actually writes to and the
+     * end of the last allocated cluster.
+     */
+    Qcow2COWRegion cow_end;
+
+    /*
+     * Indicates that COW regions are already handled and do not require
+     * any more processing.
+     */
+    bool skip_cow;
+
+    /**
+     * Indicates that this is not a normal write request but a preallocation.
+     * If the image has extended L2 entries this means that no new individual
+     * subclusters will be marked as allocated in the L2 bitmap (but any
+     * existing contents of that bitmap will be kept).
+     */
+    bool prealloc;
+
+    /** Pointer to next L2Meta of the same write request */
+    struct QCowL2Meta *next;
+} QCowL2Meta;
+
+typedef enum QCow2ClusterType {
+    QCOW2_CLUSTER_UNALLOCATED,
+    QCOW2_CLUSTER_ZERO_PLAIN,
+    QCOW2_CLUSTER_ZERO_ALLOC,
+    QCOW2_CLUSTER_NORMAL,
+    QCOW2_CLUSTER_COMPRESSED,
+} QCow2ClusterType;
+
+typedef enum QCow2MetadataOverlap {
+    QCOW2_OL_MAIN_HEADER_BITNR      = 0,
+    QCOW2_OL_ACTIVE_L1_BITNR        = 1,
+    QCOW2_OL_ACTIVE_L2_BITNR        = 2,
+    QCOW2_OL_REFCOUNT_TABLE_BITNR   = 3,
+    QCOW2_OL_REFCOUNT_BLOCK_BITNR   = 4,
+    QCOW2_OL_SNAPSHOT_TABLE_BITNR   = 5,
+    QCOW2_OL_INACTIVE_L1_BITNR      = 6,
+    QCOW2_OL_INACTIVE_L2_BITNR      = 7,
+    QCOW2_OL_BITMAP_DIRECTORY_BITNR = 8,
+
+    QCOW2_OL_MAX_BITNR              = 9,
+
+    QCOW2_OL_NONE             = 0,
+    QCOW2_OL_MAIN_HEADER      = (1 << QCOW2_OL_MAIN_HEADER_BITNR),
+    QCOW2_OL_ACTIVE_L1        = (1 << QCOW2_OL_ACTIVE_L1_BITNR),
+    QCOW2_OL_ACTIVE_L2        = (1 << QCOW2_OL_ACTIVE_L2_BITNR),
+    QCOW2_OL_REFCOUNT_TABLE   = (1 << QCOW2_OL_REFCOUNT_TABLE_BITNR),
+    QCOW2_OL_REFCOUNT_BLOCK   = (1 << QCOW2_OL_REFCOUNT_BLOCK_BITNR),
+    QCOW2_OL_SNAPSHOT_TABLE   = (1 << QCOW2_OL_SNAPSHOT_TABLE_BITNR),
+    QCOW2_OL_INACTIVE_L1      = (1 << QCOW2_OL_INACTIVE_L1_BITNR),
+    /* NOTE: Checking overlaps with inactive L2 tables will result in bdrv
+     * reads. */
+    QCOW2_OL_INACTIVE_L2      = (1 << QCOW2_OL_INACTIVE_L2_BITNR),
+    QCOW2_OL_BITMAP_DIRECTORY = (1 << QCOW2_OL_BITMAP_DIRECTORY_BITNR),
+} QCow2MetadataOverlap;
+
+/* Perform all overlap checks which can be done in constant time */
+#define QCOW2_OL_CONSTANT \
+    (QCOW2_OL_MAIN_HEADER | QCOW2_OL_ACTIVE_L1 | QCOW2_OL_REFCOUNT_TABLE | \
+     QCOW2_OL_SNAPSHOT_TABLE | QCOW2_OL_BITMAP_DIRECTORY)
+
+/* Perform all overlap checks which don't require disk access */
+#define QCOW2_OL_CACHED \
+    (QCOW2_OL_CONSTANT | QCOW2_OL_ACTIVE_L2 | QCOW2_OL_REFCOUNT_BLOCK | \
+     QCOW2_OL_INACTIVE_L1)
+
+/* Perform all overlap checks */
+#define QCOW2_OL_ALL \
+    (QCOW2_OL_CACHED | QCOW2_OL_INACTIVE_L2)
+
+#define QCOW_L1E_OFFSET_MASK 0x00fffffffffffe00ULL
+#define QCOW_L2E_OFFSET_MASK 0x00fffffffffffe00ULL
+#define QCOW_L2E_COMPRESSED_OFFSET_SIZE_MASK 0x3fffffffffffffffULL
+
+#define REFT_OFFSET_MASK 0xfffffffffffffe00ULL
+
+#define INV_OFFSET (-1ULL)
+
+static inline uint64_t l2meta_cow_start(QCowL2Meta *m)
+{
+    return m->offset + m->cow_start.offset;
+}
+
+static inline uint64_t l2meta_cow_end(QCowL2Meta *m)
+{
+    return m->offset + m->cow_end.offset + m->cow_end.nb_bytes;
+}
+
+static inline uint64_t refcount_diff(uint64_t r1, uint64_t r2)
+{
+    return r1 > r2 ? r1 - r2 : r2 - r1;
+}
+
+#endif // CEPH_LIBRBD_MIGRATION_QCOW2_H