Signed-off-by: Peter Lieven <p...@kamp.de> --- docs/interop/qcow2.txt | 51 +++++++++++++++++++++++++++++++++++++++++++++++++- roms/ipxe | 2 +- 2 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt index d7fdb1f..d0d2a8f 100644 --- a/docs/interop/qcow2.txt +++ b/docs/interop/qcow2.txt @@ -86,7 +86,12 @@ in the description of a field. be written to (unless for regaining consistency). - Bits 2-63: Reserved (set to 0) + Bit 2: Compress format bit. If and only if this bit + is set then the compress format extension + MUST be present and MUST be parsed and checked + for compatibility. + + Bits 3-63: Reserved (set to 0) 80 - 87: compatible_features Bitmask of compatible features. An implementation can @@ -137,6 +142,7 @@ be stored. Each extension has a structure like the following: 0x6803f857 - Feature name table 0x23852875 - Bitmaps extension 0x0537be77 - Full disk encryption header pointer + 0xC03183A3 - Compress format extension other - Unknown header extension, can be safely ignored @@ -311,6 +317,49 @@ The algorithms used for encryption vary depending on the method in the LUKS header, with the physical disk sector as the input tweak. + +== Compress format extension == + +The compress format extension is an optional header extension. It provides +the ability to specify the compress algorithm and compress parameters +that are used for compressed clusters. This new header MUST be present if +the incompatible-feature bit "compress format bit" is set and MUST be absent +otherwise. + +The fields of the compress format extension are: + + Byte 0 - 13: compress_format_name (padded with zeros, but not + necessarily null terminated if it has full length). + Valid compression format names currently are: + + deflate: Standard zlib deflate compression without + compression header + + 14: compress_level (uint8_t) + + 0 = default compress level (valid for all formats, default) + + Additional valid compression levels for deflate compression: + + All values between 1 and 9. 1 gives best speed, 9 gives best + compression. The default compression level is defined by zlib + and currently defaults to 6. + + 15: compress_window_size (uint8_t) + + Window or dictionary size used by the compression format. + Currently only used by the deflate compression algorithm. + + Valid window sizes for deflate compression range from 8 to + 15 inclusively. + +Note: Omitting the incompatible "Compress format bit" results in the usage +of deflate compression with default compression level and a window size of 12 +(which was default before QEMU 2.11). If exactly these parameters are choosen +it is free to the implementation to omit the "Compress format bit" and the +compress format extension when updating the QCOW2 header. + + == Host cluster management == qcow2 manages the allocation of host clusters by maintaining a reference count diff --git a/roms/ipxe b/roms/ipxe index 0600d3a..b991c67 160000 --- a/roms/ipxe +++ b/roms/ipxe @@ -1 +1 @@ -Subproject commit 0600d3ae94f93efd10fc6b3c7420a9557a3a1670 +Subproject commit b991c67c1d91574ef22336cc3a5944d1e63230c9 -- 1.9.1