I'd like to recommend a few commas. Denis Plotnikov <dplotni...@virtuozzo.com> writes:
> The patch adds some preparation parts for incompatible compression type > feature to QCOW2 header that indicates that *all* compressed clusters > must be (de)compressed using a certain compression type. > > 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. > > The goal of the feature is to add support of other compression algorithms > to qcow2. For example, ZSTD which is more effective on compression than ZLIB. > It works roughly x2 faster than ZLIB providing a comparable compression ratio > and therefore provide a performance advantage in backup scenarios. > > The default compression is ZLIB. Images created with ZLIB compression type > is backward compatible with older qemu versions. > > Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com> [...] > diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt > index af5711e533..5b8a8d15fe 100644 > --- a/docs/interop/qcow2.txt > +++ b/docs/interop/qcow2.txt > @@ -109,7 +109,12 @@ in the description of a field. > An External Data File Name header extension > may > be present if this bit is set. > > - Bits 3-63: Reserved (set to 0) > + Bit 3: Compression type bit. The bit must be set if > + the compression type differs from default: > zlib. > + If the compression type is default the bit > must > + be unset. > + > + Bits 4-63: Reserved (set to 0) > > 80 - 87: compatible_features > Bitmask of compatible features. An implementation can > @@ -165,6 +170,21 @@ in the description of a field. > Length of the header structure in bytes. For version 2 > images, the length is always assumed to be 72 bytes. > > + 104 - 107: compression_type > + Defines the compression method used for compressed > clusters. > + A single compression type is applied to all compressed > image > + clusters. > + The compression type is set on image creation only. > + The default compression type is zlib. > + When the deafult compression type is used the compression Comma after used, please. > + type bit (incompatible feature bit 3) must be unset. > + When any other compression type is used the compression Likewise. > + type bit must be set. > + Qemu versions older than 4.1 can use images created with > + the default compression type without any additional > + preparations and cannot use images created with any other Comma after preparations, please. > + compression type. > + > Directly after the image header, optional sections called header extensions > can > be stored. Each extension has a structure like the following: > [...]