[Qemu-devel] [PATCH] specs/qcow2: Fix documentation of the compressed cluster descriptor

[Alberto Garcia]

The documentation claims that the cluster descriptor contains the
number of sectors used to store the compressed data, but what it
actually contains is the number of sectors *minus one*.

That can be easily seen in qcow2_decompress_cluster(), that adds one
to the value stored in that field:

  nb_csectors = ((cluster_offset >> s->csize_shift) & s->csize_mask) + 1;

Signed-off-by: Alberto Garcia <address@hidden>
---
 docs/interop/qcow2.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index d7fdb1fee3..b12972be82 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -429,7 +429,8 @@ Compressed Clusters Descriptor (x = 62 - (cluster_bits - 
8)):
     Bit  0 -  x:    Host cluster offset. This is usually _not_ aligned to a
                     cluster boundary!
 
-       x+1 - 61:    Compressed size of the images in sectors of 512 bytes
+       x+1 - 61:    Size of the compressed data in sectors of 512 bytes,
+                    minus one (that is, a value of n here means n+1 sectors).
 
 If a cluster is unallocated, read requests shall read the data from the backing
 file (except if bit 0 in the Standard Cluster Descriptor is set). If there is
-- 
2.11.0