Can we please fix this to take a flags parameter? I want to make it easier
for callers to request BDRV_REQ_NO_FALLBACK for distinguishing between
callers where the image must be made empty (read as all zeroes) regardless
of time spent, vs. made empty quickly (including if it is already all zero)
but where the caller is prepared for the operation to fail and will write
zeroes itself if fast bulk zeroing was not possible.
bdrv_make_empty() is not for making an image read as all zeroes, but to
make it fully unallocated so that the backing file becomes visible.
Are you confusing it with bdrv_make_zero(), which is just a wrapper
around bdrv_pwrite_zeroes() and does take flags?