On 02/29/2016 08:46 AM, Max Reitz wrote: >>> 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: Bits 9-(x+9) of host cluster offset. This is >> >> I'd rather use one of "9..(x+9)", "[9, x+9]", "9 - (x+9)", "9—(x+9)" in >> order to clarify that this is not a minus but a range. > > ...unless, of course, this is actually a byte offset, which it seems to > be, judging from qcow2_get_cluster_offset() (and > qcow2_decompress_cluster(), as Kevin said on IRC).
Hmm, then I may be totally wrong. (Serves me right for trying to write a spec patch without testing actual behavior). At the least, we may want to say that things are usually not aligned to even a _sector_ boundary (not just cluster boundary), and also clarify whether the sector length is truncated or rounded up (zlib doesn't care about trailing garbage during decompression, but you DO need to know how many sectors to read to ensure that you are supplying zlib with trailing garbage, rather than a truncated stream). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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