On Tue 05 May 2020 09:35:06 PM CEST, Eric Blake wrote: > On 5/5/20 12:38 PM, Alberto Garcia wrote: >> Subcluster allocation in qcow2 is implemented by extending the >> existing L2 table entries and adding additional information to >> indicate the allocation status of each subcluster. >> >> This patch documents the changes to the qcow2 format and how they >> affect the calculation of the L2 cache size. >> >> Signed-off-by: Alberto Garcia <be...@igalia.com> >> Reviewed-by: Max Reitz <mre...@redhat.com> >> --- >> docs/interop/qcow2.txt | 68 ++++++++++++++++++++++++++++++++++++++++-- >> docs/qcow2-cache.txt | 19 +++++++++++- >> 2 files changed, 83 insertions(+), 4 deletions(-) >> > >> @@ -547,7 +557,8 @@ Standard Cluster Descriptor: >> nor is data read from the backing file if the cluster >> is >> unallocated. >> >> - With version 2, this is always 0. >> + With version 2 or with extended L2 entries (see the next >> + section), this is always 0. > > In your cover letter, you said you changed things to tolerate this bit > being set even with extended L2 entries. Does this sentence need a > tweak?
Not a bad idea. >> +The last 64 bits contain a subcluster allocation bitmap with this format: >> + >> +Subcluster Allocation Bitmap (for standard clusters): >> + >> + Bit 0 - 31: Allocation status (one bit per subcluster) > > Why two spaces after '-'? No reason, I guess I just didn't notice. I'll fix it. Berto
