Add conversion to VHDX - #77
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Add vhdx.Writer, an io.WriterAt for a dynamic VHDX image that plugs into convert.Convert. Payload blocks are allocated on the first non-zero write, so zero and unallocated extents of the source become PAYLOAD_BLOCK_ZERO entries. Unwritten parts of the file are kept as holes by extending the file with Truncate when the target supports it. The default block size is 1 MiB for disks up to 1 TiB (doubling beyond that to keep the BAT at or under 8 MiB), smaller than the 8-32 MiB used by qemu-img, since file systems that do not support sparse files, or that fill small holes (APFS), allocate the unwritten part of every touched block. The example command gains `convert -O vhdx [-block-size N]`, and hack/compare-with-qemu-img.sh gains a phase converting to VHDX and comparing with qemu-img. Spec: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-vhdx/83e061f8-f6e2-4de1-91bd-5d518a43d477 Assisted-by: Claude Fable 5.1 <noreply@anthropic.com> Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
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What This PR Changes
Add
vhdx.Writerfor converting raw/qcow2 to vhdx:Spec: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-vhdx/83e061f8-f6e2-4de1-91bd-5d518a43d477
Linked Issue (Required in most cases)
For:
qemu-img.exe(used for converting qcow2/raw to vhdx) lima#5466How I Tested This
Used
hack/compare-with-qemu-img.sh.The script converts a qcow2 image to raw and vhdx, and compares them.
AI Usage
Assisted-by: Claude Fable 5.1 noreply@anthropic.com