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由 Max Reitz 提交于
Currently, qemu-img convert writes zeroes when it reads zeroes. Sometimes it does not because the target is initialized to zeroes anyway, so we do not need to overwrite (and thus potentially allocate) it. This is never the case for targets with backing files, though. But even they may have an area that is initialized to zeroes, and that is the area past the end of the backing file (if that is shorter than the overlay). So if the target format's unallocated blocks are zero and there is a gap between the target's backing file's end and the target's end, we do not have to explicitly write zeroes there. Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1527898Signed-off-by: NMax Reitz <mreitz@redhat.com> Message-id: 20180501165750.19242-2-mreitz@redhat.com Reviewed-by: NEric Blake <eblake@redhat.com> Signed-off-by: NMax Reitz <mreitz@redhat.com>
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