Re: [PATCH v11 2/2] docs: qcow2: introduce compression type feature

[Alberto Garcia]

On Fri 31 Jan 2020 03:46:12 PM CET, Eric Blake wrote:
>> +                    If the incompatible bit "Compression type" is set: the 
>> field
>> +                    must be present and non-zero (which means non-zlib
>> +                    compression type). Otherwise, this field must not be 
>> present
>> +                    or must be zero (which means zlib).
>
>             If the incompatible bit "Compression type" is set: the field
>             must be present. Otherwise, this field must not be present
>             or must be zero (which means zlib).

But "not being present" and "being zero" is equivalent (as described in
the previous commit).

And if the incompatible bit is not present then the field can be safely
ignored (i.e. whether it is zero or not is irrelevant).

Let's try again:

   Defines the compression method used for compressed clusters. All
   compressed clusters in an image use the same type.

   The value of this field should only be used when the incompatible bit
   "Compression type" is set. If that bit is unset then this field is
   not used and the compression method is zlib.

Berto