Re: [Qemu-devel] [PATCH v3 2/3] qcow2: Implement bdrv_amend_options

[Fam Zheng]

On Fri, 08/30 12:27, Max Reitz wrote:
> Implement bdrv_amend_options for compat, size, backing_file, backing_fmt
> and lazy_refcounts.
> 
> Downgrading images from compat=1.1 to compat=0.10 is achieved through
> handling all incompatible flags accordingly, clearing all compatible and
> autoclear flags and expanding all zero clusters.
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/qcow2-cluster.c | 165 ++++++++++++++++++++++++++++++++++++++++++
>  block/qcow2.c         | 194 
> +++++++++++++++++++++++++++++++++++++++++++++++++-
>  block/qcow2.h         |   3 +
>  3 files changed, 361 insertions(+), 1 deletion(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index cca76d4..e0ca104 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1476,3 +1476,168 @@ fail:
>  
>      return ret;
>  }
> +
> +/*
> + * Expands all zero clusters in a specific L1 table (or deallocates them, for
> + * non-backed non-pre-allocated zero clusters).
> + */
> +static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t 
> *l1_table,
> +                                      int l1_size)
> +{
> +    BDRVQcowState *s = bs->opaque;
> +    bool is_active_l1 = (l1_table == s->l1_table);
> +    uint64_t *l2_table;
> +    int ret;
> +    int i, j;
> +
> +    if (!is_active_l1) {
> +        /* inactive L2 tables require a buffer to be stored in when loading
> +         * them from disk */
> +        l2_table = qemu_blockalign(bs, s->cluster_size);
> +    }
> +
> +    for (i = 0; i < l1_size; i++) {
> +        uint64_t l2_offset = l1_table[i] & L1E_OFFSET_MASK;
> +        bool l2_dirty = false;
> +
> +        if (!l2_offset) {
> +            /* unallocated */
> +            continue;
> +        }
> +
> +        if (is_active_l1) {
> +            /* get active L2 tables from cache */
> +            ret = qcow2_cache_get(bs, s->l2_table_cache, l2_offset,
> +                    (void **)&l2_table);
> +        } else {
> +            /* load inactive L2 tables from disk */
> +            ret = bdrv_read(bs->file, l2_offset / BDRV_SECTOR_SIZE,
> +                    (void *)l2_table, s->cluster_sectors);
> +        }
> +        if (ret < 0) {
> +            goto fail;
> +        }
> +
> +        for (j = 0; j < s->l2_size; j++) {
> +            uint64_t l2_entry = be64_to_cpu(l2_table[j]);
> +            int64_t offset;
> +
> +            if (qcow2_get_cluster_type(l2_entry) != QCOW2_CLUSTER_ZERO) {
> +                continue;
> +            }
> +
> +            offset = l2_entry & L2E_OFFSET_MASK;
> +            if (!offset) {
> +                /* not preallocated */
> +                if (!bs->backing_hd) {
> +                    /* not backed; therefore we can simply deallocate the
> +                     * cluster */
> +                    l2_table[j] = 0;
> +                    l2_dirty = true;
> +                    continue;
> +                }
> +
> +                offset = qcow2_alloc_clusters(bs, s->cluster_size);
> +                if (offset < 0) {
> +                    ret = offset;
> +                    goto fail;
> +                }
> +            }
> +
> +            ret = bdrv_write_zeroes(bs->file, offset / BDRV_SECTOR_SIZE,
> +                                    s->cluster_sectors);
> +            if (ret < 0) {
> +                qcow2_free_clusters(bs, offset, s->cluster_size,
> +                        QCOW2_DISCARD_ALWAYS);
> +                goto fail;
> +            }
> +
> +            l2_table[j] = cpu_to_be64(offset | QCOW_OFLAG_COPIED);
> +            l2_dirty = true;
> +        }
> +
> +        if (is_active_l1) {
> +            if (l2_dirty) {
> +                qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
> +                qcow2_cache_depends_on_flush(s->l2_table_cache);
> +            }
> +            ret = qcow2_cache_put(bs, s->l2_table_cache, (void **)&l2_table);
> +            if (ret < 0) {
> +                l2_table = NULL;
> +                goto fail;
> +            }
> +        } else {
> +            if (l2_dirty) {
> +                ret = bdrv_write(bs->file, l2_offset / BDRV_SECTOR_SIZE,
> +                        (void *)l2_table, s->cluster_sectors);
> +                if (ret < 0) {
> +                    goto fail;
> +                }
> +            }
> +        }
> +    }
> +
> +    ret = 0;
> +
> +fail:
> +    if (l2_table) {
> +        if (!is_active_l1) {
> +            qemu_vfree(l2_table);
> +        } else {
> +            if (ret < 0) {
> +                qcow2_cache_put(bs, s->l2_table_cache, (void **)&l2_table);
> +            } else {
> +                ret = qcow2_cache_put(bs, s->l2_table_cache,
> +                        (void **)&l2_table);
> +            }
> +        }
> +    }
> +    return ret;
> +}
> +
> +/*
> + * For backed images, expands all zero clusters on the image. For non-backed
> + * images, deallocates all non-pre-allocated zero clusters (and claims the
> + * allocation for pre-allocated ones). This is important for downgrading to a
> + * qcow2 version which doesn't yet support metadata zero clusters.
> + */
> +int qcow2_expand_zero_clusters(BlockDriverState *bs)
> +{
> +    BDRVQcowState *s = bs->opaque;
> +    uint64_t *l1_table = NULL;
> +    int ret;
> +    int i, j;
> +
> +    ret = expand_zero_clusters_in_l1(bs, s->l1_table, s->l1_size);
> +    if (ret < 0) {
> +        goto fail;
> +    }
> +
> +    for (i = 0; i < s->nb_snapshots; i++) {
> +        int l1_sectors = (s->snapshots[i].l1_size * sizeof(uint64_t) +
> +                BDRV_SECTOR_SIZE - 1) / BDRV_SECTOR_SIZE;
> +
> +        l1_table = g_realloc(l1_table, l1_sectors * BDRV_SECTOR_SIZE);
> +
> +        ret = bdrv_read(bs->file, s->snapshots[i].l1_table_offset /
> +                BDRV_SECTOR_SIZE, (void *)l1_table, l1_sectors);
> +        if (ret < 0) {
> +            goto fail;
> +        }
> +
> +        for (j = 0; j < s->snapshots[i].l1_size; j++) {
> +            be64_to_cpus(&l1_table[j]);
> +        }
> +
> +        ret = expand_zero_clusters_in_l1(bs, l1_table, 
> s->snapshots[i].l1_size);
> +        if (ret < 0) {
> +            goto fail;
> +        }
> +    }
> +
> +    ret = 0;
> +
> +fail:
> +    g_free(l1_table);
> +    return ret;
> +}
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 78097e5..a8eaf45 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -409,6 +409,7 @@ static int qcow2_open(BlockDriverState *bs, QDict 
> *options, int flags)
>          ret = -ENOTSUP;
>          goto fail;
>      }
> +    s->refcount_order = header.refcount_order;
>  
>      if (header.cluster_bits < MIN_CLUSTER_BITS ||
>          header.cluster_bits > MAX_CLUSTER_BITS) {
> @@ -1076,7 +1077,7 @@ int qcow2_update_header(BlockDriverState *bs)
>          .incompatible_features  = cpu_to_be64(s->incompatible_features),
>          .compatible_features    = cpu_to_be64(s->compatible_features),
>          .autoclear_features     = cpu_to_be64(s->autoclear_features),
> -        .refcount_order         = cpu_to_be32(3 + REFCOUNT_SHIFT),
> +        .refcount_order         = cpu_to_be32(s->refcount_order),
>          .header_length          = cpu_to_be32(header_length),
>      };
>  
> @@ -1735,6 +1736,196 @@ static int qcow2_load_vmstate(BlockDriverState *bs, 
> uint8_t *buf,
>      return ret;
>  }
>  
> +/*
> + * Downgrades an image's version. To achieve this, any incompatible features
> + * have to be removed.
> + */
> +static int qcow2_downgrade(BlockDriverState *bs, int target_version)
> +{
> +    BDRVQcowState *s = bs->opaque;
> +    int current_version = s->qcow_version;
> +    int ret;
> +
> +    if (target_version == current_version) {
> +        return 0;
> +    } else if (target_version > current_version) {
> +        return -EINVAL;
> +    } else if (target_version != 2) {
> +        return -EINVAL;
> +    }
> +
> +    if (s->refcount_order != 4) {
> +        /* we would have to convert the image to a refcount_order == 4 image
> +         * here; however, since qemu (at the time of writing this) does not
> +         * support anything different than 4 anyway, there is no point in 
> doing
> +         * so right now; however, we should error out (if qemu supports this 
> in
> +         * the future and this code has not been adapted) */
> +        error_report("qcow2_downgrade: Image refcount orders other than 4 
> are"
> +                     "currently not supported.");
> +        return -ENOTSUP;
> +    }
> +
> +    /* clear incompatible features */
> +    if (s->incompatible_features & QCOW2_INCOMPAT_DIRTY) {
> +        ret = qcow2_mark_clean(bs);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    if (s->incompatible_features) {
> +        return -ENOTSUP;
> +    }
> +
> +    /* since we can ignore compatible features, we can set them to 0 as well 
> */
> +    s->compatible_features = 0;
> +    /* if lazy refcounts have been used, they have already been fixed through
> +     * clearing the dirty flag */
> +
> +    /* clearing autoclear features is trivial */
> +    s->autoclear_features = 0;
> +
> +    ret = qcow2_expand_zero_clusters(bs);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    s->qcow_version = target_version;
> +    ret = qcow2_update_header(bs);
> +    if (ret < 0) {
> +        s->qcow_version = current_version;
> +        return ret;
> +    }
> +    return 0;
> +}
> +
> +static int qcow2_amend_options(BlockDriverState *bs,
> +                               QEMUOptionParameter *options)
> +{
> +    BDRVQcowState *s = bs->opaque;
> +    int old_version = s->qcow_version, new_version = old_version;
> +    uint64_t new_size = 0;
> +    const char *backing_file = NULL, *backing_format = NULL;
> +    bool lazy_refcounts = s->use_lazy_refcounts;
> +    int ret;
> +    int i;
> +
> +    for (i = 0; options[i].name; i++)
> +    {
> +        if (!strcmp(options[i].name, "compat")) {
> +            if (!options[i].value.s) {
> +                /* preserve default */
> +            } else if (!strcmp(options[i].value.s, "0.10")) {
> +                new_version = 2;
> +            } else if (!strcmp(options[i].value.s, "1.1")) {
> +                new_version = 3;
> +            } else {
> +                fprintf(stderr, "Unknown compatibility level %s.\n",
> +                        options[i].value.s);
> +                return -EINVAL;
> +            }
> +        } else if (!strcmp(options[i].name, "preallocation")) {
> +            if (options[i].assigned) {

For encryption flag and cluster_size, you checked the original value and only
error out on actual change, should check the original preallocation value here
as well?

> +                fprintf(stderr, "Cannot change preallocation mode.\n");
> +                return -ENOTSUP;
> +            }
> +        } else if (!strcmp(options[i].name, "size")) {
> +            new_size = options[i].value.n;
> +        } else if (!strcmp(options[i].name, "backing_file")) {
> +            backing_file = options[i].value.s;
> +        } else if (!strcmp(options[i].name, "backing_fmt")) {
> +            backing_format = options[i].value.s;
> +        } else if (!strcmp(options[i].name, "encryption")) {
> +            if (options[i].assigned &&
> +                (options[i].value.n != !!s->crypt_method)) {
> +                fprintf(stderr, "Changing the encryption flag is not "
> +                        "supported.\n");
> +                return -ENOTSUP;
> +            }
> +        } else if (!strcmp(options[i].name, "cluster_size")) {
> +            if (options[i].assigned && (options[i].value.n != 
> s->cluster_size))
> +            {
> +                fprintf(stderr, "Changing the cluster size is not "
> +                        "supported.\n");
> +                return -ENOTSUP;
> +            }
> +        } else if (!strcmp(options[i].name, "lazy_refcounts")) {
> +            if (options[i].assigned) {
> +                lazy_refcounts = options[i].value.n;
> +            }
> +        } else {
> +            /* if this assertion fails, this probably means a new option was
> +             * added without having it covered here */
> +            assert(false);

A unknown option reported as -ENOTSUP with a proper message is good enough,
it's not that critical for an assert.

> +        }
> +    }
> +
> +    if (new_version != old_version) {
> +        if (new_version > old_version) {
> +            /* Upgrade */
> +            s->qcow_version = new_version;
> +            ret = qcow2_update_header(bs);
> +            if (ret < 0) {
> +                s->qcow_version = old_version;
> +                return ret;
> +            }
> +        } else {
> +            ret = qcow2_downgrade(bs, new_version);
> +            if (ret < 0) {
> +                return ret;
> +            }
> +        }
> +    }
> +
> +    if (new_size) {
> +        ret = qcow2_truncate(bs, new_size);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    if (backing_file || backing_format) {
> +        ret = qcow2_change_backing_file(bs, backing_file ?: bs->backing_file,
> +                                        backing_format ?: 
> bs->backing_format);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    if (s->use_lazy_refcounts != lazy_refcounts) {
> +        if (lazy_refcounts) {
> +            if (s->qcow_version < 3) {
> +                fprintf(stderr, "Lazy refcounts only supported with 
> compatibility "
> +                        "level 1.1 and above (use compat=1.1 or greater)\n");
> +                return -EINVAL;
> +            }
> +            s->compatible_features |= QCOW2_COMPAT_LAZY_REFCOUNTS;
> +            ret = qcow2_update_header(bs);
> +            if (ret < 0) {
> +                s->compatible_features &= ~QCOW2_COMPAT_LAZY_REFCOUNTS;
> +                return ret;
> +            }
> +            s->use_lazy_refcounts = true;
> +        } else {
> +            /* make image clean first */
> +            ret = qcow2_mark_clean(bs);
> +            if (ret < 0) {
> +                return ret;
> +            }
> +            /* now disallow lazy refcounts */
> +            s->compatible_features &= ~QCOW2_COMPAT_LAZY_REFCOUNTS;
> +            ret = qcow2_update_header(bs);
> +            if (ret < 0) {
> +                s->compatible_features |= QCOW2_COMPAT_LAZY_REFCOUNTS;
> +                return ret;
> +            }
> +            s->use_lazy_refcounts = false;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  static QEMUOptionParameter qcow2_create_options[] = {
>      {
>          .name = BLOCK_OPT_SIZE,
> @@ -1818,6 +2009,7 @@ static BlockDriver bdrv_qcow2 = {
>  
>      .create_options = qcow2_create_options,
>      .bdrv_check = qcow2_check,
> +    .bdrv_amend_options = qcow2_amend_options,
>  };
>  
>  static void bdrv_qcow2_init(void)
> diff --git a/block/qcow2.h b/block/qcow2.h
> index dba9771..ad3fd21 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -196,6 +196,7 @@ typedef struct BDRVQcowState {
>      int flags;
>      int qcow_version;
>      bool use_lazy_refcounts;
> +    int refcount_order;
>  
>      bool discard_passthrough[QCOW2_DISCARD_MAX];
>  
> @@ -408,6 +409,8 @@ int qcow2_discard_clusters(BlockDriverState *bs, uint64_t 
> offset,
>      int nb_sectors);
>  int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int 
> nb_sectors);
>  
> +int qcow2_expand_zero_clusters(BlockDriverState *bs);
> +
>  /* qcow2-snapshot.c functions */
>  int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info);
>  int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id);
> -- 
> 1.8.3.1
> 
>