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

[Max Reitz]

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 |  66 ++++++++++++++++++
 block/qcow2.c         | 182 ++++++++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2.h         |   2 +
 3 files changed, 250 insertions(+)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index cca76d4..ac50db2 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1476,3 +1476,69 @@ fail:
 
     return ret;
 }
+
+/*
+ * Expands all zero clusters on the image; 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;
+    int ret;
+    int i;
+
+    for (i = 0; i < s->l1_size; i++) {
+        uint64_t *l2_table;
+        int l2_index;
+        int j;
+        bool l2_dirty = false;
+
+        ret = get_cluster_table(bs, (uint64_t)i << (s->l2_bits +
+                s->cluster_bits), &l2_table, &l2_index);
+        if (ret < 0) {
+            return ret;
+        }
+
+        for (j = 0; j < s->l2_size; j++) {
+            uint64_t l2_entry = be64_to_cpu(l2_table[j]);
+            if (!(l2_entry & QCOW_OFLAG_COMPRESSED) &&
+                (l2_entry & QCOW_OFLAG_ZERO)) {
+                /* uncompressed zero cluster */
+                int64_t offset = qcow2_alloc_clusters(bs, s->cluster_size);
+                if (offset < 0) {
+                    ret = offset;
+                    goto fail;
+                }
+
+                ret = bdrv_write_zeroes(bs->file, offset >> BDRV_SECTOR_BITS,
+                                        s->cluster_size >> BDRV_SECTOR_BITS);
+                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;
+            }
+        }
+
+        ret = 0;
+
+fail:
+        if (l2_dirty) {
+            qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
+        }
+
+        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);
+        }
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    return 0;
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index 78097e5..47cd5ad 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1735,6 +1735,187 @@ 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;
+    }
+
+    /* clear incompatible features */
+    if (s->incompatible_features & QCOW2_INCOMPAT_DIRTY) {
+        BdrvCheckResult result;
+        ret = qcow2_check(bs, &result, BDRV_FIX_ERRORS);
+        if (ret < 0) {
+            return ret;
+        }
+        qcow2_mark_clean(bs);
+    }
+
+    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;
+
+    /* the refcount order might be different in newer images - however, qemu
+     * doesn't support anything different than 4 anyway, so nothing to fix
+     * there */
+
+    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].value.s) {
+                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].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].value.n && (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")) {
+            /* TODO: detect whether this flag was indeed explicitly given */
+            lazy_refcounts = options[i].value.n;
+        } else {
+            fprintf(stderr, "Unknown option '%s'.\n", options[i].name);
+        }
+    }
+
+    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 {
+            qcow2_downgrade(bs, new_version);
+        }
+    }
+
+    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 */
+            if (s->incompatible_features & QCOW2_INCOMPAT_DIRTY) {
+                BdrvCheckResult result;
+                ret = qcow2_check(bs, &result, BDRV_FIX_ERRORS);
+                if (ret < 0) {
+                    return ret;
+                }
+            }
+            qcow2_mark_clean(bs);
+            /* 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 +1999,7 @@ 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..84109de 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -408,6 +408,8 @@ 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