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, 1073 insertions, 0 deletions

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
new file mode 100644
index 000000000..71ddb08c2
--- /dev/null
+++ b/block/qcow2-snapshot.c
@@ -0,0 +1,1073 @@
+/*
+ * 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.
+ */
+
+#include "qemu/osdep.h"
+#include "sysemu/block-backend.h"
+#include "qapi/error.h"
+#include "qcow2.h"
+#include "qemu/bswap.h"
+#include "qemu/error-report.h"
+#include "qemu/cutils.h"
+
+static void qcow2_free_single_snapshot(BlockDriverState *bs, int i)
+{
+    BDRVQcow2State *s = bs->opaque;
+
+    assert(i >= 0 && i < s->nb_snapshots);
+    g_free(s->snapshots[i].name);
+    g_free(s->snapshots[i].id_str);
+    g_free(s->snapshots[i].unknown_extra_data);
+    memset(&s->snapshots[i], 0, sizeof(s->snapshots[i]));
+}
+
+void qcow2_free_snapshots(BlockDriverState *bs)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int i;
+
+    for(i = 0; i < s->nb_snapshots; i++) {
+        qcow2_free_single_snapshot(bs, i);
+    }
+    g_free(s->snapshots);
+    s->snapshots = NULL;
+    s->nb_snapshots = 0;
+}
+
+/*
+ * If @repair is true, try to repair a broken snapshot table instead
+ * of just returning an error:
+ *
+ * - If the snapshot table was too long, set *nb_clusters_reduced to
+ *   the number of snapshots removed off the end.
+ *   The caller will update the on-disk nb_snapshots accordingly;
+ *   this leaks clusters, but is safe.
+ *   (The on-disk information must be updated before
+ *   qcow2_check_refcounts(), because that function relies on
+ *   s->nb_snapshots to reflect the on-disk value.)
+ *
+ * - If there were snapshots with too much extra metadata, increment
+ *   *extra_data_dropped for each.
+ *   This requires the caller to eventually rewrite the whole snapshot
+ *   table, which requires cluster allocation.  Therefore, this should
+ *   be done only after qcow2_check_refcounts() made sure the refcount
+ *   structures are valid.
+ *   (In the meantime, the image is still valid because
+ *   qcow2_check_refcounts() does not do anything with snapshots'
+ *   extra data.)
+ */
+static int qcow2_do_read_snapshots(BlockDriverState *bs, bool repair,
+                                   int *nb_clusters_reduced,
+                                   int *extra_data_dropped,
+                                   Error **errp)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshotHeader h;
+    QCowSnapshotExtraData extra;
+    QCowSnapshot *sn;
+    int i, id_str_size, name_size;
+    int64_t offset, pre_sn_offset;
+    uint64_t table_length = 0;
+    int ret;
+
+    if (!s->nb_snapshots) {
+        s->snapshots = NULL;
+        s->snapshots_size = 0;
+        return 0;
+    }
+
+    offset = s->snapshots_offset;
+    s->snapshots = g_new0(QCowSnapshot, s->nb_snapshots);
+
+    for(i = 0; i < s->nb_snapshots; i++) {
+        bool truncate_unknown_extra_data = false;
+
+        pre_sn_offset = offset;
+        table_length = ROUND_UP(table_length, 8);
+
+        /* Read statically sized part of the snapshot header */
+        offset = ROUND_UP(offset, 8);
+        ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to read snapshot table");
+            goto fail;
+        }
+
+        offset += sizeof(h);
+        sn = s->snapshots + i;
+        sn->l1_table_offset = be64_to_cpu(h.l1_table_offset);
+        sn->l1_size = be32_to_cpu(h.l1_size);
+        sn->vm_state_size = be32_to_cpu(h.vm_state_size);
+        sn->date_sec = be32_to_cpu(h.date_sec);
+        sn->date_nsec = be32_to_cpu(h.date_nsec);
+        sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
+        sn->extra_data_size = be32_to_cpu(h.extra_data_size);
+
+        id_str_size = be16_to_cpu(h.id_str_size);
+        name_size = be16_to_cpu(h.name_size);
+
+        if (sn->extra_data_size > QCOW_MAX_SNAPSHOT_EXTRA_DATA) {
+            if (!repair) {
+                ret = -EFBIG;
+                error_setg(errp, "Too much extra metadata in snapshot table "
+                           "entry %i", i);
+                error_append_hint(errp, "You can force-remove this extra "
+                                  "metadata with qemu-img check -r all\n");
+                goto fail;
+            }
+
+            fprintf(stderr, "Discarding too much extra metadata in snapshot "
+                    "table entry %i (%" PRIu32 " > %u)\n",
+                    i, sn->extra_data_size, QCOW_MAX_SNAPSHOT_EXTRA_DATA);
+
+            (*extra_data_dropped)++;
+            truncate_unknown_extra_data = true;
+        }
+
+        /* Read known extra data */
+        ret = bdrv_pread(bs->file, offset, &extra,
+                         MIN(sizeof(extra), sn->extra_data_size));
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to read snapshot table");
+            goto fail;
+        }
+        offset += MIN(sizeof(extra), sn->extra_data_size);
+
+        if (sn->extra_data_size >= endof(QCowSnapshotExtraData,
+                                         vm_state_size_large)) {
+            sn->vm_state_size = be64_to_cpu(extra.vm_state_size_large);
+        }
+
+        if (sn->extra_data_size >= endof(QCowSnapshotExtraData, disk_size)) {
+            sn->disk_size = be64_to_cpu(extra.disk_size);
+        } else {
+            sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
+        }
+
+        if (sn->extra_data_size >= endof(QCowSnapshotExtraData, icount)) {
+            sn->icount = be64_to_cpu(extra.icount);
+        } else {
+            sn->icount = -1ULL;
+        }
+
+        if (sn->extra_data_size > sizeof(extra)) {
+            uint64_t extra_data_end;
+            size_t unknown_extra_data_size;
+
+            extra_data_end = offset + sn->extra_data_size - sizeof(extra);
+
+            if (truncate_unknown_extra_data) {
+                sn->extra_data_size = QCOW_MAX_SNAPSHOT_EXTRA_DATA;
+            }
+
+            /* Store unknown extra data */
+            unknown_extra_data_size = sn->extra_data_size - sizeof(extra);
+            sn->unknown_extra_data = g_malloc(unknown_extra_data_size);
+            ret = bdrv_pread(bs->file, offset, sn->unknown_extra_data,
+                             unknown_extra_data_size);
+            if (ret < 0) {
+                error_setg_errno(errp, -ret,
+                                 "Failed to read snapshot table");
+                goto fail;
+            }
+            offset = extra_data_end;
+        }
+
+        /* Read snapshot ID */
+        sn->id_str = g_malloc(id_str_size + 1);
+        ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to read snapshot table");
+            goto fail;
+        }
+        offset += id_str_size;
+        sn->id_str[id_str_size] = '\0';
+
+        /* Read snapshot name */
+        sn->name = g_malloc(name_size + 1);
+        ret = bdrv_pread(bs->file, offset, sn->name, name_size);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to read snapshot table");
+            goto fail;
+        }
+        offset += name_size;
+        sn->name[name_size] = '\0';
+
+        /* Note that the extra data may have been truncated */
+        table_length += sizeof(h) + sn->extra_data_size + id_str_size +
+                        name_size;
+        if (!repair) {
+            assert(table_length == offset - s->snapshots_offset);
+        }
+
+        if (table_length > QCOW_MAX_SNAPSHOTS_SIZE ||
+            offset - s->snapshots_offset > INT_MAX)
+        {
+            if (!repair) {
+                ret = -EFBIG;
+                error_setg(errp, "Snapshot table is too big");
+                error_append_hint(errp, "You can force-remove all %u "
+                                  "overhanging snapshots with qemu-img check "
+                                  "-r all\n", s->nb_snapshots - i);
+                goto fail;
+            }
+
+            fprintf(stderr, "Discarding %u overhanging snapshots (snapshot "
+                    "table is too big)\n", s->nb_snapshots - i);
+
+            *nb_clusters_reduced += (s->nb_snapshots - i);
+
+            /* Discard current snapshot also */
+            qcow2_free_single_snapshot(bs, i);
+
+            /*
+             * This leaks all the rest of the snapshot table and the
+             * snapshots' clusters, but we run in check -r all mode,
+             * so qcow2_check_refcounts() will take care of it.
+             */
+            s->nb_snapshots = i;
+            offset = pre_sn_offset;
+            break;
+        }
+    }
+
+    assert(offset - s->snapshots_offset <= INT_MAX);
+    s->snapshots_size = offset - s->snapshots_offset;
+    return 0;
+
+fail:
+    qcow2_free_snapshots(bs);
+    return ret;
+}
+
+int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
+{
+    return qcow2_do_read_snapshots(bs, false, NULL, NULL, errp);
+}
+
+/* add at the end of the file a new list of snapshots */
+int qcow2_write_snapshots(BlockDriverState *bs)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshot *sn;
+    QCowSnapshotHeader h;
+    QCowSnapshotExtraData extra;
+    int i, name_size, id_str_size, snapshots_size;
+    struct {
+        uint32_t nb_snapshots;
+        uint64_t snapshots_offset;
+    } QEMU_PACKED header_data;
+    int64_t offset, snapshots_offset = 0;
+    int ret;
+
+    /* compute the size of the snapshots */
+    offset = 0;
+    for(i = 0; i < s->nb_snapshots; i++) {
+        sn = s->snapshots + i;
+        offset = ROUND_UP(offset, 8);
+        offset += sizeof(h);
+        offset += MAX(sizeof(extra), sn->extra_data_size);
+        offset += strlen(sn->id_str);
+        offset += strlen(sn->name);
+
+        if (offset > QCOW_MAX_SNAPSHOTS_SIZE) {
+            ret = -EFBIG;
+            goto fail;
+        }
+    }
+
+    assert(offset <= INT_MAX);
+    snapshots_size = offset;
+
+    /* Allocate space for the new snapshot list */
+    snapshots_offset = qcow2_alloc_clusters(bs, snapshots_size);
+    offset = snapshots_offset;
+    if (offset < 0) {
+        ret = offset;
+        goto fail;
+    }
+    ret = bdrv_flush(bs);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    /* The snapshot list position has not yet been updated, so these clusters
+     * must indeed be completely free */
+    ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size, false);
+    if (ret < 0) {
+        goto fail;
+    }
+
+
+    /* Write all snapshots to the new list */
+    for(i = 0; i < s->nb_snapshots; i++) {
+        sn = s->snapshots + i;
+        memset(&h, 0, sizeof(h));
+        h.l1_table_offset = cpu_to_be64(sn->l1_table_offset);
+        h.l1_size = cpu_to_be32(sn->l1_size);
+        /* If it doesn't fit in 32 bit, older implementations should treat it
+         * as a disk-only snapshot rather than truncate the VM state */
+        if (sn->vm_state_size <= 0xffffffff) {
+            h.vm_state_size = cpu_to_be32(sn->vm_state_size);
+        }
+        h.date_sec = cpu_to_be32(sn->date_sec);
+        h.date_nsec = cpu_to_be32(sn->date_nsec);
+        h.vm_clock_nsec = cpu_to_be64(sn->vm_clock_nsec);
+        h.extra_data_size = cpu_to_be32(MAX(sizeof(extra),
+                                            sn->extra_data_size));
+
+        memset(&extra, 0, sizeof(extra));
+        extra.vm_state_size_large = cpu_to_be64(sn->vm_state_size);
+        extra.disk_size = cpu_to_be64(sn->disk_size);
+        extra.icount = cpu_to_be64(sn->icount);
+
+        id_str_size = strlen(sn->id_str);
+        name_size = strlen(sn->name);
+        assert(id_str_size <= UINT16_MAX && name_size <= UINT16_MAX);
+        h.id_str_size = cpu_to_be16(id_str_size);
+        h.name_size = cpu_to_be16(name_size);
+        offset = ROUND_UP(offset, 8);
+
+        ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
+        if (ret < 0) {
+            goto fail;
+        }
+        offset += sizeof(h);
+
+        ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
+        if (ret < 0) {
+            goto fail;
+        }
+        offset += sizeof(extra);
+
+        if (sn->extra_data_size > sizeof(extra)) {
+            size_t unknown_extra_data_size =
+                sn->extra_data_size - sizeof(extra);
+
+            /* qcow2_read_snapshots() ensures no unbounded allocation */
+            assert(unknown_extra_data_size <= BDRV_REQUEST_MAX_BYTES);
+            assert(sn->unknown_extra_data);
+
+            ret = bdrv_pwrite(bs->file, offset, sn->unknown_extra_data,
+                              unknown_extra_data_size);
+            if (ret < 0) {
+                goto fail;
+            }
+            offset += unknown_extra_data_size;
+        }
+
+        ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
+        if (ret < 0) {
+            goto fail;
+        }
+        offset += id_str_size;
+
+        ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
+        if (ret < 0) {
+            goto fail;
+        }
+        offset += name_size;
+    }
+
+    /*
+     * Update the header to point to the new snapshot table. This requires the
+     * new table and its refcounts to be stable on disk.
+     */
+    ret = bdrv_flush(bs);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
+                      endof(QCowHeader, nb_snapshots));
+
+    header_data.nb_snapshots        = cpu_to_be32(s->nb_snapshots);
+    header_data.snapshots_offset    = cpu_to_be64(snapshots_offset);
+
+    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
+                           &header_data, sizeof(header_data));
+    if (ret < 0) {
+        goto fail;
+    }
+
+    /* free the old snapshot table */
+    qcow2_free_clusters(bs, s->snapshots_offset, s->snapshots_size,
+                        QCOW2_DISCARD_SNAPSHOT);
+    s->snapshots_offset = snapshots_offset;
+    s->snapshots_size = snapshots_size;
+    return 0;
+
+fail:
+    if (snapshots_offset > 0) {
+        qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
+                            QCOW2_DISCARD_ALWAYS);
+    }
+    return ret;
+}
+
+int coroutine_fn qcow2_check_read_snapshot_table(BlockDriverState *bs,
+                                                 BdrvCheckResult *result,
+                                                 BdrvCheckMode fix)
+{
+    BDRVQcow2State *s = bs->opaque;
+    Error *local_err = NULL;
+    int nb_clusters_reduced = 0;
+    int extra_data_dropped = 0;
+    int ret;
+    struct {
+        uint32_t nb_snapshots;
+        uint64_t snapshots_offset;
+    } QEMU_PACKED snapshot_table_pointer;
+
+    /* qcow2_do_open() discards this information in check mode */
+    ret = bdrv_pread(bs->file, offsetof(QCowHeader, nb_snapshots),
+                     &snapshot_table_pointer, sizeof(snapshot_table_pointer));
+    if (ret < 0) {
+        result->check_errors++;
+        fprintf(stderr, "ERROR failed to read the snapshot table pointer from "
+                "the image header: %s\n", strerror(-ret));
+        return ret;
+    }
+
+    s->snapshots_offset = be64_to_cpu(snapshot_table_pointer.snapshots_offset);
+    s->nb_snapshots = be32_to_cpu(snapshot_table_pointer.nb_snapshots);
+
+    if (s->nb_snapshots > QCOW_MAX_SNAPSHOTS && (fix & BDRV_FIX_ERRORS)) {
+        fprintf(stderr, "Discarding %u overhanging snapshots\n",
+                s->nb_snapshots - QCOW_MAX_SNAPSHOTS);
+
+        nb_clusters_reduced += s->nb_snapshots - QCOW_MAX_SNAPSHOTS;
+        s->nb_snapshots = QCOW_MAX_SNAPSHOTS;
+    }
+
+    ret = qcow2_validate_table(bs, s->snapshots_offset, s->nb_snapshots,
+                               sizeof(QCowSnapshotHeader),
+                               sizeof(QCowSnapshotHeader) * QCOW_MAX_SNAPSHOTS,
+                               "snapshot table", &local_err);
+    if (ret < 0) {
+        result->check_errors++;
+        error_reportf_err(local_err, "ERROR ");
+
+        if (s->nb_snapshots > QCOW_MAX_SNAPSHOTS) {
+            fprintf(stderr, "You can force-remove all %u overhanging snapshots "
+                    "with qemu-img check -r all\n",
+                    s->nb_snapshots - QCOW_MAX_SNAPSHOTS);
+        }
+
+        /* We did not read the snapshot table, so invalidate this information */
+        s->snapshots_offset = 0;
+        s->nb_snapshots = 0;
+
+        return ret;
+    }
+
+    qemu_co_mutex_unlock(&s->lock);
+    ret = qcow2_do_read_snapshots(bs, fix & BDRV_FIX_ERRORS,
+                                  &nb_clusters_reduced, &extra_data_dropped,
+                                  &local_err);
+    qemu_co_mutex_lock(&s->lock);
+    if (ret < 0) {
+        result->check_errors++;
+        error_reportf_err(local_err,
+                          "ERROR failed to read the snapshot table: ");
+
+        /* We did not read the snapshot table, so invalidate this information */
+        s->snapshots_offset = 0;
+        s->nb_snapshots = 0;
+
+        return ret;
+    }
+    result->corruptions += nb_clusters_reduced + extra_data_dropped;
+
+    if (nb_clusters_reduced) {
+        /*
+         * Update image header now, because:
+         * (1) qcow2_check_refcounts() relies on s->nb_snapshots to be
+         *     the same as what the image header says,
+         * (2) this leaks clusters, but qcow2_check_refcounts() will
+         *     fix that.
+         */
+        assert(fix & BDRV_FIX_ERRORS);
+
+        snapshot_table_pointer.nb_snapshots = cpu_to_be32(s->nb_snapshots);
+        ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
+                               &snapshot_table_pointer.nb_snapshots,
+                               sizeof(snapshot_table_pointer.nb_snapshots));
+        if (ret < 0) {
+            result->check_errors++;
+            fprintf(stderr, "ERROR failed to update the snapshot count in the "
+                    "image header: %s\n", strerror(-ret));
+            return ret;
+        }
+
+        result->corruptions_fixed += nb_clusters_reduced;
+        result->corruptions -= nb_clusters_reduced;
+    }
+
+    /*
+     * All of v3 images' snapshot table entries need to have at least
+     * 16 bytes of extra data.
+     */
+    if (s->qcow_version >= 3) {
+        int i;
+        for (i = 0; i < s->nb_snapshots; i++) {
+            if (s->snapshots[i].extra_data_size <
+                sizeof_field(QCowSnapshotExtraData, vm_state_size_large) +
+                sizeof_field(QCowSnapshotExtraData, disk_size))
+            {
+                result->corruptions++;
+                fprintf(stderr, "%s snapshot table entry %i is incomplete\n",
+                        fix & BDRV_FIX_ERRORS ? "Repairing" : "ERROR", i);
+            }
+        }
+    }
+
+    return 0;
+}
+
+int coroutine_fn qcow2_check_fix_snapshot_table(BlockDriverState *bs,
+                                                BdrvCheckResult *result,
+                                                BdrvCheckMode fix)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int ret;
+
+    if (result->corruptions && (fix & BDRV_FIX_ERRORS)) {
+        qemu_co_mutex_unlock(&s->lock);
+        ret = qcow2_write_snapshots(bs);
+        qemu_co_mutex_lock(&s->lock);
+        if (ret < 0) {
+            result->check_errors++;
+            fprintf(stderr, "ERROR failed to update snapshot table: %s\n",
+                    strerror(-ret));
+            return ret;
+        }
+
+        result->corruptions_fixed += result->corruptions;
+        result->corruptions = 0;
+    }
+
+    return 0;
+}
+
+static void find_new_snapshot_id(BlockDriverState *bs,
+                                 char *id_str, int id_str_size)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshot *sn;
+    int i;
+    unsigned long id, id_max = 0;
+
+    for(i = 0; i < s->nb_snapshots; i++) {
+        sn = s->snapshots + i;
+        id = strtoul(sn->id_str, NULL, 10);
+        if (id > id_max)
+            id_max = id;
+    }
+    snprintf(id_str, id_str_size, "%lu", id_max + 1);
+}
+
+static int find_snapshot_by_id_and_name(BlockDriverState *bs,
+                                        const char *id,
+                                        const char *name)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int i;
+
+    if (id && name) {
+        for (i = 0; i < s->nb_snapshots; i++) {
+            if (!strcmp(s->snapshots[i].id_str, id) &&
+                !strcmp(s->snapshots[i].name, name)) {
+                return i;
+            }
+        }
+    } else if (id) {
+        for (i = 0; i < s->nb_snapshots; i++) {
+            if (!strcmp(s->snapshots[i].id_str, id)) {
+                return i;
+            }
+        }
+    } else if (name) {
+        for (i = 0; i < s->nb_snapshots; i++) {
+            if (!strcmp(s->snapshots[i].name, name)) {
+                return i;
+            }
+        }
+    }
+
+    return -1;
+}
+
+static int find_snapshot_by_id_or_name(BlockDriverState *bs,
+                                       const char *id_or_name)
+{
+    int ret;
+
+    ret = find_snapshot_by_id_and_name(bs, id_or_name, NULL);
+    if (ret >= 0) {
+        return ret;
+    }
+    return find_snapshot_by_id_and_name(bs, NULL, id_or_name);
+}
+
+/* if no id is provided, a new one is constructed */
+int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshot *new_snapshot_list = NULL;
+    QCowSnapshot *old_snapshot_list = NULL;
+    QCowSnapshot sn1, *sn = &sn1;
+    int i, ret;
+    uint64_t *l1_table = NULL;
+    int64_t l1_table_offset;
+
+    if (s->nb_snapshots >= QCOW_MAX_SNAPSHOTS) {
+        return -EFBIG;
+    }
+
+    if (has_data_file(bs)) {
+        return -ENOTSUP;
+    }
+
+    memset(sn, 0, sizeof(*sn));
+
+    /* Generate an ID */
+    find_new_snapshot_id(bs, sn_info->id_str, sizeof(sn_info->id_str));
+
+    /* Populate sn with passed data */
+    sn->id_str = g_strdup(sn_info->id_str);
+    sn->name = g_strdup(sn_info->name);
+
+    sn->disk_size = bs->total_sectors * BDRV_SECTOR_SIZE;
+    sn->vm_state_size = sn_info->vm_state_size;
+    sn->date_sec = sn_info->date_sec;
+    sn->date_nsec = sn_info->date_nsec;
+    sn->vm_clock_nsec = sn_info->vm_clock_nsec;
+    sn->icount = sn_info->icount;
+    sn->extra_data_size = sizeof(QCowSnapshotExtraData);
+
+    /* Allocate the L1 table of the snapshot and copy the current one there. */
+    l1_table_offset = qcow2_alloc_clusters(bs, s->l1_size * L1E_SIZE);
+    if (l1_table_offset < 0) {
+        ret = l1_table_offset;
+        goto fail;
+    }
+
+    sn->l1_table_offset = l1_table_offset;
+    sn->l1_size = s->l1_size;
+
+    l1_table = g_try_new(uint64_t, s->l1_size);
+    if (s->l1_size && l1_table == NULL) {
+        ret = -ENOMEM;
+        goto fail;
+    }
+
+    for(i = 0; i < s->l1_size; i++) {
+        l1_table[i] = cpu_to_be64(s->l1_table[i]);
+    }
+
+    ret = qcow2_pre_write_overlap_check(bs, 0, sn->l1_table_offset,
+                                        s->l1_size * L1E_SIZE, false);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
+                      s->l1_size * L1E_SIZE);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    g_free(l1_table);
+    l1_table = NULL;
+
+    /*
+     * Increase the refcounts of all clusters and make sure everything is
+     * stable on disk before updating the snapshot table to contain a pointer
+     * to the new L1 table.
+     */
+    ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 1);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    /* Append the new snapshot to the snapshot list */
+    new_snapshot_list = g_new(QCowSnapshot, s->nb_snapshots + 1);
+    if (s->snapshots) {
+        memcpy(new_snapshot_list, s->snapshots,
+               s->nb_snapshots * sizeof(QCowSnapshot));
+        old_snapshot_list = s->snapshots;
+    }
+    s->snapshots = new_snapshot_list;
+    s->snapshots[s->nb_snapshots++] = *sn;
+
+    ret = qcow2_write_snapshots(bs);
+    if (ret < 0) {
+        g_free(s->snapshots);
+        s->snapshots = old_snapshot_list;
+        s->nb_snapshots--;
+        goto fail;
+    }
+
+    g_free(old_snapshot_list);
+
+    /* The VM state isn't needed any more in the active L1 table; in fact, it
+     * hurts by causing expensive COW for the next snapshot. */
+    qcow2_cluster_discard(bs, qcow2_vm_state_offset(s),
+                          ROUND_UP(sn->vm_state_size, s->cluster_size),
+                          QCOW2_DISCARD_NEVER, false);
+
+#ifdef DEBUG_ALLOC
+    {
+      BdrvCheckResult result = {0};
+      qcow2_check_refcounts(bs, &result, 0);
+    }
+#endif
+    return 0;
+
+fail:
+    g_free(sn->id_str);
+    g_free(sn->name);
+    g_free(l1_table);
+
+    return ret;
+}
+
+/* copy the snapshot 'snapshot_name' into the current disk image */
+int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshot *sn;
+    Error *local_err = NULL;
+    int i, snapshot_index;
+    int cur_l1_bytes, sn_l1_bytes;
+    int ret;
+    uint64_t *sn_l1_table = NULL;
+
+    if (has_data_file(bs)) {
+        return -ENOTSUP;
+    }
+
+    /* Search the snapshot */
+    snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
+    if (snapshot_index < 0) {
+        return -ENOENT;
+    }
+    sn = &s->snapshots[snapshot_index];
+
+    ret = qcow2_validate_table(bs, sn->l1_table_offset, sn->l1_size,
+                               L1E_SIZE, QCOW_MAX_L1_SIZE,
+                               "Snapshot L1 table", &local_err);
+    if (ret < 0) {
+        error_report_err(local_err);
+        goto fail;
+    }
+
+    if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
+        BlockBackend *blk = blk_new_with_bs(bs, BLK_PERM_RESIZE, BLK_PERM_ALL,
+                                            &local_err);
+        if (!blk) {
+            error_report_err(local_err);
+            ret = -ENOTSUP;
+            goto fail;
+        }
+
+        ret = blk_truncate(blk, sn->disk_size, true, PREALLOC_MODE_OFF, 0,
+                           &local_err);
+        blk_unref(blk);
+        if (ret < 0) {
+            error_report_err(local_err);
+            goto fail;
+        }
+    }
+
+    /*
+     * Make sure that the current L1 table is big enough to contain the whole
+     * L1 table of the snapshot. If the snapshot L1 table is smaller, the
+     * current one must be padded with zeros.
+     */
+    ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    cur_l1_bytes = s->l1_size * L1E_SIZE;
+    sn_l1_bytes = sn->l1_size * L1E_SIZE;
+
+    /*
+     * Copy the snapshot L1 table to the current L1 table.
+     *
+     * Before overwriting the old current L1 table on disk, make sure to
+     * increase all refcounts for the clusters referenced by the new one.
+     * Decrease the refcount referenced by the old one only when the L1
+     * table is overwritten.
+     */
+    sn_l1_table = g_try_malloc0(cur_l1_bytes);
+    if (cur_l1_bytes && sn_l1_table == NULL) {
+        ret = -ENOMEM;
+        goto fail;
+    }
+
+    ret = bdrv_pread(bs->file, sn->l1_table_offset,
+                     sn_l1_table, sn_l1_bytes);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
+                                         sn->l1_size, 1);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
+                                        s->l1_table_offset, cur_l1_bytes,
+                                        false);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
+                           cur_l1_bytes);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    /*
+     * Decrease refcount of clusters of current L1 table.
+     *
+     * At this point, the in-memory s->l1_table points to the old L1 table,
+     * whereas on disk we already have the new one.
+     *
+     * qcow2_update_snapshot_refcount special cases the current L1 table to use
+     * the in-memory data instead of really using the offset to load a new one,
+     * which is why this works.
+     */
+    ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
+                                         s->l1_size, -1);
+
+    /*
+     * Now update the in-memory L1 table to be in sync with the on-disk one. We
+     * need to do this even if updating refcounts failed.
+     */
+    for(i = 0;i < s->l1_size; i++) {
+        s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
+    }
+
+    if (ret < 0) {
+        goto fail;
+    }
+
+    g_free(sn_l1_table);
+    sn_l1_table = NULL;
+
+    /*
+     * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
+     * when we decreased the refcount of the old snapshot.
+     */
+    ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
+    if (ret < 0) {
+        goto fail;
+    }
+
+#ifdef DEBUG_ALLOC
+    {
+        BdrvCheckResult result = {0};
+        qcow2_check_refcounts(bs, &result, 0);
+    }
+#endif
+    return 0;
+
+fail:
+    g_free(sn_l1_table);
+    return ret;
+}
+
+int qcow2_snapshot_delete(BlockDriverState *bs,
+                          const char *snapshot_id,
+                          const char *name,
+                          Error **errp)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshot sn;
+    int snapshot_index, ret;
+
+    if (has_data_file(bs)) {
+        return -ENOTSUP;
+    }
+
+    /* Search the snapshot */
+    snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
+    if (snapshot_index < 0) {
+        error_setg(errp, "Can't find the snapshot");
+        return -ENOENT;
+    }
+    sn = s->snapshots[snapshot_index];
+
+    ret = qcow2_validate_table(bs, sn.l1_table_offset, sn.l1_size,
+                               L1E_SIZE, QCOW_MAX_L1_SIZE,
+                               "Snapshot L1 table", errp);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /* Remove it from the snapshot list */
+    memmove(s->snapshots + snapshot_index,
+            s->snapshots + snapshot_index + 1,
+            (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
+    s->nb_snapshots--;
+    ret = qcow2_write_snapshots(bs);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret,
+                         "Failed to remove snapshot from snapshot list");
+        return ret;
+    }
+
+    /*
+     * The snapshot is now unused, clean up. If we fail after this point, we
+     * won't recover but just leak clusters.
+     */
+    g_free(sn.unknown_extra_data);
+    g_free(sn.id_str);
+    g_free(sn.name);
+
+    /*
+     * Now decrease the refcounts of clusters referenced by the snapshot and
+     * free the L1 table.
+     */
+    ret = qcow2_update_snapshot_refcount(bs, sn.l1_table_offset,
+                                         sn.l1_size, -1);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Failed to free the cluster and L1 table");
+        return ret;
+    }
+    qcow2_free_clusters(bs, sn.l1_table_offset, sn.l1_size * L1E_SIZE,
+                        QCOW2_DISCARD_SNAPSHOT);
+
+    /* must update the copied flag on the current cluster offsets */
+    ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, 0);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret,
+                         "Failed to update snapshot status in disk");
+        return ret;
+    }
+
+#ifdef DEBUG_ALLOC
+    {
+        BdrvCheckResult result = {0};
+        qcow2_check_refcounts(bs, &result, 0);
+    }
+#endif
+    return 0;
+}
+
+int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QEMUSnapshotInfo *sn_tab, *sn_info;
+    QCowSnapshot *sn;
+    int i;
+
+    if (has_data_file(bs)) {
+        return -ENOTSUP;
+    }
+    if (!s->nb_snapshots) {
+        *psn_tab = NULL;
+        return s->nb_snapshots;
+    }
+
+    sn_tab = g_new0(QEMUSnapshotInfo, s->nb_snapshots);
+    for(i = 0; i < s->nb_snapshots; i++) {
+        sn_info = sn_tab + i;
+        sn = s->snapshots + i;
+        pstrcpy(sn_info->id_str, sizeof(sn_info->id_str),
+                sn->id_str);
+        pstrcpy(sn_info->name, sizeof(sn_info->name),
+                sn->name);
+        sn_info->vm_state_size = sn->vm_state_size;
+        sn_info->date_sec = sn->date_sec;
+        sn_info->date_nsec = sn->date_nsec;
+        sn_info->vm_clock_nsec = sn->vm_clock_nsec;
+        sn_info->icount = sn->icount;
+    }
+    *psn_tab = sn_tab;
+    return s->nb_snapshots;
+}
+
+int qcow2_snapshot_load_tmp(BlockDriverState *bs,
+                            const char *snapshot_id,
+                            const char *name,
+                            Error **errp)
+{
+    int i, snapshot_index;
+    BDRVQcow2State *s = bs->opaque;
+    QCowSnapshot *sn;
+    uint64_t *new_l1_table;
+    int new_l1_bytes;
+    int ret;
+
+    assert(bdrv_is_read_only(bs));
+
+    /* Search the snapshot */
+    snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
+    if (snapshot_index < 0) {
+        error_setg(errp,
+                   "Can't find snapshot");
+        return -ENOENT;
+    }
+    sn = &s->snapshots[snapshot_index];
+
+    /* Allocate and read in the snapshot's L1 table */
+    ret = qcow2_validate_table(bs, sn->l1_table_offset, sn->l1_size,
+                               L1E_SIZE, QCOW_MAX_L1_SIZE,
+                               "Snapshot L1 table", errp);
+    if (ret < 0) {
+        return ret;
+    }
+    new_l1_bytes = sn->l1_size * L1E_SIZE;
+    new_l1_table = qemu_try_blockalign(bs->file->bs, new_l1_bytes);
+    if (new_l1_table == NULL) {
+        return -ENOMEM;
+    }
+
+    ret = bdrv_pread(bs->file, sn->l1_table_offset,
+                     new_l1_table, new_l1_bytes);
+    if (ret < 0) {
+        error_setg(errp, "Failed to read l1 table for snapshot");
+        qemu_vfree(new_l1_table);
+        return ret;
+    }
+
+    /* Switch the L1 table */
+    qemu_vfree(s->l1_table);
+
+    s->l1_size = sn->l1_size;
+    s->l1_table_offset = sn->l1_table_offset;
+    s->l1_table = new_l1_table;
+
+    for(i = 0;i < s->l1_size; i++) {
+        be64_to_cpus(&s->l1_table[i]);
+    }
+
+    return 0;
+}