Re: [PATCH v8 1/4] qcow2: introduce compression type feature

[Denis Plotnikov]

On 23.03.2020 15:26, Vladimir Sementsov-Ogievskiy wrote:

23.03.2020 15:22, Denis Plotnikov wrote:

On 23.03.2020 11:00, Vladimir Sementsov-Ogievskiy wrote:

21.03.2020 17:34, Denis Plotnikov wrote:

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, 144, 182, 242, 255

Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---

[...]

@@ -4859,6 +4949,7 @@ 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 @@ -5248,6 +5339,22 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,

                                   "images");
                  return -EINVAL;
              }
+        } else if (!strcmp(desc->name, BLOCK_OPT_COMPRESSION_TYPE)) {
+            int compression_type =
+ qapi_enum_parse(&Qcow2CompressionType_lookup,

+                                qemu_opt_get(opts, BLOCK_OPT_COMPRESSION_TYPE),

+                                -1, errp);
+
+            if (compression_type == -EINVAL) {

You should compare to -1, as qapi_enum_parse returns given default on error.

ok

+                error_setg(errp, "Unknown compression type");

and errp is already set (ofcourse, if qemu_opt_get returned non NULL, but I hope it is guaranteed by if (!strcmp(desc->name, BLOCK_OPT_COMPRESSION_TYPE)) condition

I wouldn't propagate the error from qapi_enum_parse because it looks like "invalid parameter value: foo". I think it's better to print "Unknown compression type: foo"

No objections. Then you should pass NULL to qapi_enum_parse instead of errp. (As you can't set errp twice, second try will crash).

ok

+                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 */
@@ -5516,6 +5623,12 @@ 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 */ }
      }
  };

[...]