docs: Grammar and spelling fixes

[qemu.git] / docs / interop / qcow2.txt

diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index 886a546825ea0297fdf327f9b77f4b26fcf02d2f..845d40a086d505b4ef6ee96ee78dfddf87d7cd13 100644 (file)
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -203,7 +203,7 @@ The fields of the bitmaps extension are:
 
           8 - 15:  bitmap_directory_size
                    Size of the bitmap directory in bytes. It is the cumulative
-                   size of all (nb_bitmaps) bitmap headers.
+                   size of all (nb_bitmaps) bitmap directory entries.
 
          16 - 23:  bitmap_directory_offset
                    Offset into the image file at which the bitmap directory
@@ -326,8 +326,8 @@ in the image file.
 It contains pointers to the second level structures which are called refcount
 blocks and are exactly one cluster in size.
 
-Given a offset into the image file, the refcount of its cluster can be obtained
-as follows:
+Given an offset into the image file, the refcount of its cluster can be
+obtained as follows:
 
     refcount_block_entries = (cluster_size * 8 / refcount_bits)
 
@@ -365,7 +365,7 @@ The L1 table has a variable size (stored in the header) and may use multiple
 clusters, however it must be contiguous in the image file. L2 tables are
 exactly one cluster in size.
 
-Given a offset into the virtual disk, the offset into the image file can be
+Given an offset into the virtual disk, the offset into the image file can be
 obtained as follows:
 
     l2_entries = (cluster_size / sizeof(uint64_t))
@@ -400,10 +400,10 @@ L2 table entry:
               62:   0 for standard clusters
                     1 for compressed clusters
 
-              63:   0 for a cluster that is unused or requires COW, 1 if its
-                    refcount is exactly one. This information is only accurate
-                    in L2 tables that are reachable from the active L1
-                    table.
+              63:   0 for clusters that are unused, compressed or require COW.
+                    1 for standard clusters whose refcount is exactly one.
+                    This information is only accurate in L2 tables
+                    that are reachable from the active L1 table.
 
 Standard Cluster Descriptor:
 
@@ -426,10 +426,20 @@ 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-1:   Host cluster offset. This is usually _not_ aligned to a
+                    cluster or sector boundary!
+
+         x - 61:    Number of additional 512-byte sectors used for the
+                    compressed data, beyond the sector containing the offset
+                    in the previous field. Some of these sectors may reside
+                    in the next contiguous host cluster.
+
+                    Note that the compressed data does not necessarily occupy
+                    all of the bytes in the final sector; rather, decompression
+                    stops when it has produced a cluster of data.
 
-       x+1 - 61:    Compressed size of the images in sectors of 512 bytes
+                    Another compressed cluster may map to the tail of the final
+                    sector used by this compressed cluster.
 
 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
@@ -529,8 +539,7 @@ Each bitmap saved in the image is described in a bitmap directory entry. The
 bitmap directory is a contiguous area in the image file, whose starting offset
 and length are given by the header extension fields bitmap_directory_offset and
 bitmap_directory_size. The entries of the bitmap directory have variable
-length, depending on the lengths of the bitmap name and extra data. These
-entries are also called bitmap headers.
+length, depending on the lengths of the bitmap name and extra data.
 
 Structure of a bitmap directory entry:
 
@@ -575,8 +584,7 @@ Structure of a bitmap directory entry:
              17:    granularity_bits
                     Granularity bits. Valid values: 0 - 63.
 
-                    Note: Qemu currently doesn't support granularity_bits
-                    greater than 31.
+                    Note: Qemu currently supports only values 9 - 31.
 
                     Granularity is calculated as
                         granularity = 1 << granularity_bits