qcow2: introduce compression type feature

The patch adds some preparation parts for incompatible compression type
feature to qcow2 allowing the use different compression methods for
image clusters (de)compressing.

It is implied that the compression type is set on the image creation and
can be changed only later by image conversion, thus compression type
defines the only compression algorithm used for the image, and thus,
for all image clusters.

The goal of the feature is to add support of other compression methods
to qcow2. For example, ZSTD which is more effective on compression than ZLIB.

The default compression is ZLIB. Images created with ZLIB compression type
are backward compatible with older qemu versions.

Adding of the compression type breaks a number of tests because now the
compression type is reported on image creation and there are some changes
in the qcow2 header in size and offsets.

The tests are fixed in the following ways:
    * filter out compression_type for many tests
    * fix header size, feature table size and backing file offset
      affected tests: 031, 036, 061, 080
      header_size +=8: 1 byte compression type
                       7 bytes padding
      feature_table += 48: incompatible feature compression type
      backing_file_offset += 56 (8 + 48 -> header_change + feature_table_change)
    * add "compression type" for test output matching when it isn't filtered
      affected tests: 049, 060, 061, 065, 082, 085, 144, 182, 185, 198, 206,
                      242, 255, 274, 280

Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
QAPI part:
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200507082521.29210-2-dplotnikov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

2 files changed, 132 insertions, 1 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index 1ad95ff..b878a6a 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1242,6 +1242,39 @@ static int qcow2_update_options(BlockDriverState *bs, QDict *options,
     return ret;
 }
 
+static int validate_compression_type(BDRVQcow2State *s, Error **errp)
+{
+    switch (s->compression_type) {
+    case QCOW2_COMPRESSION_TYPE_ZLIB:
+        break;
+
+    default:
+        error_setg(errp, "qcow2: unknown compression type: %u",
+                   s->compression_type);
+        return -ENOTSUP;
+    }
+
+    /*
+     * if the compression type differs from QCOW2_COMPRESSION_TYPE_ZLIB
+     * the incompatible feature flag must be set
+     */
+    if (s->compression_type == QCOW2_COMPRESSION_TYPE_ZLIB) {
+        if (s->incompatible_features & QCOW2_INCOMPAT_COMPRESSION) {
+            error_setg(errp, "qcow2: Compression type incompatible feature "
+                             "bit must not be set");
+            return -EINVAL;
+        }
+    } else {
+        if (!(s->incompatible_features & QCOW2_INCOMPAT_COMPRESSION)) {
+            error_setg(errp, "qcow2: Compression type incompatible feature "
+                             "bit must be set");
+            return -EINVAL;
+        }
+    }
+
+    return 0;
+}
+
 /* Called with s->lock held.  */
 static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
                                       int flags, Error **errp)
@@ -1357,6 +1390,23 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
     s->compatible_features      = header.compatible_features;
     s->autoclear_features       = header.autoclear_features;
 
+    /*
+     * Handle compression type
+     * Older qcow2 images don't contain the compression type header.
+     * Distinguish them by the header length and use
+     * the only valid (default) compression type in that case
+     */
+    if (header.header_length > offsetof(QCowHeader, compression_type)) {
+        s->compression_type = header.compression_type;
+    } else {
+        s->compression_type = QCOW2_COMPRESSION_TYPE_ZLIB;
+    }
+
+    ret = validate_compression_type(s, errp);
+    if (ret) {
+        goto fail;
+    }
+
     if (s->incompatible_features & ~QCOW2_INCOMPAT_MASK) {
         void *feature_table = NULL;
         qcow2_read_extensions(bs, header.header_length, ext_end,
@@ -2728,6 +2778,11 @@ int qcow2_update_header(BlockDriverState *bs)
     total_size = bs->total_sectors * BDRV_SECTOR_SIZE;
     refcount_table_clusters = s->refcount_table_size >> (s->cluster_bits - 3);
 
+    ret = validate_compression_type(s, NULL);
+    if (ret) {
+        goto fail;
+    }
+
     *header = (QCowHeader) {
         /* Version 2 fields */
         .magic                  = cpu_to_be32(QCOW_MAGIC),
@@ -2750,6 +2805,7 @@ int qcow2_update_header(BlockDriverState *bs)
         .autoclear_features     = cpu_to_be64(s->autoclear_features),
         .refcount_order         = cpu_to_be32(s->refcount_order),
         .header_length          = cpu_to_be32(header_length),
+        .compression_type       = s->compression_type,
     };
 
     /* For older versions, write a shorter header */
@@ -2850,6 +2906,11 @@ int qcow2_update_header(BlockDriverState *bs)
                 .name = "external data file",
             },
             {
+                .type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
+                .bit  = QCOW2_INCOMPAT_COMPRESSION_BITNR,
+                .name = "compression type",
+            },
+            {
                 .type = QCOW2_FEAT_TYPE_COMPATIBLE,
                 .bit  = QCOW2_COMPAT_LAZY_REFCOUNTS_BITNR,
                 .name = "lazy refcounts",
@@ -3287,6 +3348,7 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
     uint64_t* refcount_table;
     Error *local_err = NULL;
     int ret;
+    uint8_t compression_type = QCOW2_COMPRESSION_TYPE_ZLIB;
 
     assert(create_options->driver == BLOCKDEV_DRIVER_QCOW2);
     qcow2_opts = &create_options->u.qcow2;
@@ -3404,6 +3466,27 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
         }
     }
 
+    if (qcow2_opts->has_compression_type &&
+        qcow2_opts->compression_type != QCOW2_COMPRESSION_TYPE_ZLIB) {
+
+        ret = -EINVAL;
+
+        if (version < 3) {
+            error_setg(errp, "Non-zlib compression type is only supported with "
+                       "compatibility level 1.1 and above (use version=v3 or "
+                       "greater)");
+            goto out;
+        }
+
+        switch (qcow2_opts->compression_type) {
+        default:
+            error_setg(errp, "Unknown compression type");
+            goto out;
+        }
+
+        compression_type = qcow2_opts->compression_type;
+    }
+
     /* Create BlockBackend to write to the image */
     blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
                           errp);
@@ -3426,6 +3509,8 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
         .refcount_table_offset      = cpu_to_be64(cluster_size),
         .refcount_table_clusters    = cpu_to_be32(1),
         .refcount_order             = cpu_to_be32(refcount_order),
+        /* don't deal with endianness since compression_type is 1 byte long */
+        .compression_type           = compression_type,
         .header_length              = cpu_to_be32(sizeof(*header)),
     };
 
@@ -3444,6 +3529,10 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
         header->autoclear_features |=
             cpu_to_be64(QCOW2_AUTOCLEAR_DATA_FILE_RAW);
     }
+    if (compression_type != QCOW2_COMPRESSION_TYPE_ZLIB) {
+        header->incompatible_features |=
+            cpu_to_be64(QCOW2_INCOMPAT_COMPRESSION);
+    }
 
     ret = blk_pwrite(blk, 0, header, cluster_size, 0);
     g_free(header);
@@ -3629,6 +3718,7 @@ static int coroutine_fn qcow2_co_create_opts(BlockDriver *drv,
         { BLOCK_OPT_ENCRYPT,            BLOCK_OPT_ENCRYPT_FORMAT },
         { BLOCK_OPT_COMPAT_LEVEL,       "version" },
         { BLOCK_OPT_DATA_FILE_RAW,      "data-file-raw" },
+        { BLOCK_OPT_COMPRESSION_TYPE,   "compression-type" },
         { NULL, NULL },
     };
 
@@ -4925,6 +5015,7 @@ static ImageInfoSpecific *qcow2_get_specific_info(BlockDriverState *bs,
             .data_file          = g_strdup(s->image_data_file),
             .has_data_file_raw  = has_data_file(bs),
             .data_file_raw      = data_file_is_raw(bs),
+            .compression_type   = s->compression_type,
         };
     } else {
         /* if this assertion fails, this probably means a new version was
@@ -5330,6 +5421,22 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
                                  "images");
                 return -EINVAL;
             }
+        } else if (!strcmp(desc->name, BLOCK_OPT_COMPRESSION_TYPE)) {
+            const char *ct_name =
+                qemu_opt_get(opts, BLOCK_OPT_COMPRESSION_TYPE);
+            int compression_type =
+                qapi_enum_parse(&Qcow2CompressionType_lookup, ct_name, -1,
+                                NULL);
+            if (compression_type == -1) {
+                error_setg(errp, "Unknown compression type: %s", ct_name);
+                return -ENOTSUP;
+            }
+
+            if (compression_type != s->compression_type) {
+                error_setg(errp, "Changing the compression type "
+                                 "is not supported");
+                return -ENOTSUP;
+            }
         } else {
             /* if this point is reached, this probably means a new option was
              * added without having it covered here */
@@ -5596,6 +5703,12 @@ static QemuOptsList qcow2_create_opts = {
             .help = "Width of a reference count entry in bits",
             .def_value_str = "16"
         },
+        {
+            .name = BLOCK_OPT_COMPRESSION_TYPE,
+            .type = QEMU_OPT_STRING,
+            .help = "Compression method used for image cluster compression",
+            .def_value_str = "zlib"
+        },
         { /* end of list */ }
     }
 };
diff --git a/block/qcow2.h b/block/qcow2.h
index f4de0a2..6a8b82e 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -146,8 +146,16 @@ typedef struct QCowHeader {
 
     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];
 } QEMU_PACKED QCowHeader;
 
+QEMU_BUILD_BUG_ON(!QEMU_IS_ALIGNED(sizeof(QCowHeader), 8));
+
 typedef struct QEMU_PACKED QCowSnapshotHeader {
     /* header is 8 byte aligned */
     uint64_t l1_table_offset;
@@ -216,13 +224,16 @@ enum {
     QCOW2_INCOMPAT_DIRTY_BITNR      = 0,
     QCOW2_INCOMPAT_CORRUPT_BITNR    = 1,
     QCOW2_INCOMPAT_DATA_FILE_BITNR  = 2,
+    QCOW2_INCOMPAT_COMPRESSION_BITNR = 3,
     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_MASK             = QCOW2_INCOMPAT_DIRTY
                                     | QCOW2_INCOMPAT_CORRUPT
-                                    | QCOW2_INCOMPAT_DATA_FILE,
+                                    | QCOW2_INCOMPAT_DATA_FILE
+                                    | QCOW2_INCOMPAT_COMPRESSION,
 };
 
 /* Compatible feature bits */
@@ -366,6 +377,13 @@ typedef struct BDRVQcow2State {
 
     bool metadata_preallocation_checked;
     bool metadata_preallocation;
+    /*
+     * Compression type used for the image. Default: 0 - ZLIB
+     * The image compression type is set on image creation.
+     * For now, the only way to change the compression type
+     * is to convert the image with the desired compression type set.
+     */
+    Qcow2CompressionType compression_type;
 } BDRVQcow2State;
 
 typedef struct Qcow2COWRegion {