Re: [Qemu-devel] [Qemu-block] [PATCH] qcow2: Clarify that compressed cluster offset requires shift

[Max Reitz <mreitz@redhat.com>]

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On 29.02.2016 16:42, Max Reitz wrote:
> On 29.02.2016 16:11, Eric Blake wrote:
>> The specs for the host cluster offset of a compressed cluster
>> were not clear that the offset is in terms of sectors, and requires
>> a shift by 9 to be a byte offset.  Add some more text to make the
>> interpretation obvious.
>>
>> CC: mgreger@cinci.rr.com
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>  docs/specs/qcow2.txt | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
>> index 80cdfd0..7049415 100644
>> --- a/docs/specs/qcow2.txt
>> +++ b/docs/specs/qcow2.txt
>> @@ -323,11 +323,16 @@ Standard Cluster Descriptor:
>>
>>  Compressed Clusters Descriptor (x = 62 - (cluster_bits - 8)):
>>
>> -    Bit  0 -  x:    Host cluster offset. This is usually _not_ aligned to a
>> -                    cluster boundary!
>> +    Bit  0 -  x:    Bits 9-(x+9) of host cluster offset. This is
> 
> I'd rather use one of "9..(x+9)", "[9, x+9]", "9 - (x+9)", "9—(x+9)" in
> order to clarify that this is not a minus but a range.

...unless, of course, this is actually a byte offset, which it seems to
be, judging from qcow2_get_cluster_offset() (and
qcow2_decompress_cluster(), as Kevin said on IRC).

Max


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