Comment 17 for bug 1776920

My hunch is that we're handling zero regions incorrectly and we might be skipping data regions we ought to be copying.

...I'm looking at the `image2.qemu` file you've uploaded and it's empty! we didn't copy *anything* from your source file.

Try converting with '-S 0` to disable sparse protection and see if that might help.

  '-S' indicates the consecutive number of bytes (defaults to 4k) that must
       contain only zeros for qemu-img to create a sparse image during
       conversion. If the number of bytes is 0, the source will not be scanned for
       unallocated or zero sectors, and the destination image will always be
       fully allocated

If that helps, I'd take a look at img_convert in qemu-img.c ...

convert_iteration_sectors looks relevant, it appears to help us know which sectors to copy when called by convert_co_do_copy.

Tracing around "convert_co_read" in the same function might also help us to know which portions of the image we're even deciding to read; and we could probably track backwards from there to figure out which condition(s) are disqualifying us if we're deciding not to copy data.

My current hunch is that bdrv_block_status[_above] is returning something wrong when backed by APFS.