On Mon, Mar 13, 2017 at 10:41:14PM +0100, Max Reitz wrote: > This patch extends qcow2_calc_size_usage() so it can calculate the > additional space needed for preallocating image growth. > > Signed-off-by: Max Reitz <mre...@redhat.com> > --- > block/qcow2.c | 137 > +++++++++++++++++++++++++++++++++++++++++----------------- > 1 file changed, 98 insertions(+), 39 deletions(-) > > diff --git a/block/qcow2.c b/block/qcow2.c > index 21b2b3cd53..80fb815b15 100644 > --- a/block/qcow2.c > +++ b/block/qcow2.c > @@ -2101,7 +2101,15 @@ done: > return ret; > } > > -static uint64_t qcow2_calc_size_usage(uint64_t new_size, > +/** > + * Returns the number of bytes that must be allocated in the underlying file > + * to accomodate an image growth from @current_size to @new_size. > + * > + * @current_size must be 0 when creating a new image. In that case, @bs is > + * ignored; otherwise it must be valid. > + */ > +static uint64_t qcow2_calc_size_usage(BlockDriverState *bs, > + uint64_t current_size, uint64_t > new_size, > int cluster_bits, int refcount_order) > { > size_t cluster_size = 1u << cluster_bits; > @@ -2122,47 +2130,97 @@ static uint64_t qcow2_calc_size_usage(uint64_t > new_size, > refblock_bits = cluster_bits - (refcount_order - 3); > refblock_size = 1 << refblock_bits; > > - /* header: 1 cluster */ > - meta_size += cluster_size; > - > - /* total size of L2 tables */ > - nl2e = aligned_total_size / cluster_size; > - nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t)); > - meta_size += nl2e * sizeof(uint64_t); > + if (!current_size) {
This massive if statement effectively makes two functions: the old qcow2_calc_size_usage() and the new qcow2_calc_size_change(bs) function. It might be nicer to split the two functions.
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