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Diffstat (limited to 'docs/interop/qcow2.txt')
| -rw-r--r-- | docs/interop/qcow2.txt | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index 823cc266e0..5597e24474 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -109,7 +109,12 @@ the next fields through header_length. An External Data File Name header extension may be present if this bit is set. - Bits 3-63: Reserved (set to 0) + Bit 3: Compression type bit. If this bit is set, + a non-default compression is used for compressed + clusters. The compression_type field must be + present and not zero. + + Bits 4-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can @@ -190,7 +195,19 @@ present*, if not altered by a specific incompatible bit. to the field's offset. Also, all additional fields are not present for version 2. - < ... No additional fields in the header currently ... > + 104: compression_type + + Defines the compression method used for compressed clusters. + All compressed clusters in an image use the same compression + type. + + 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). + + Available compression type values: + 0: zlib <https://www.zlib.net/> === Header padding === |