On 06/07/2017 09:08 AM, Alberto Garcia wrote: > Qcow2COWRegion has two attributes: > > - The offset of the COW region from the start of the first cluster > touched by the I/O request. Since it's always going to be positive > and the maximum request size is at most INT_MAX, we can use a > regular unsigned int to store this offset.
I don't know if we will ever get to the point that we allow a 64-bit request at the block layer (and then the block layer guarantees it is split down to the driver's limits, which works when a driver is still bound by 32-bit limits). But we ALSO know that a cluster is at most 2M (in our current implementation of qcow2), so the offset of where the COW region starts in relation to the start of a cluster is < 2M. > > - The size of the COW region in bytes. This is guaranteed to be >= 0, > so we should use an unsigned type instead. And likewise, since a COW region is a sub-cluster, and clusters are bounded at 2M, we also have a sub-int upper bound on the size of the region. > > In x86_64 this reduces the size of Qcow2COWRegion from 16 to 8 bytes. > It will also help keep some assertions simpler now that we know that > there are no negative numbers. > > The prototype of do_perform_cow() is also updated to reflect these > changes. > > Signed-off-by: Alberto Garcia <be...@igalia.com> > --- > block/qcow2-cluster.c | 4 ++-- > block/qcow2.h | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index d1c419f52b..a86c5a75a9 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -406,8 +406,8 @@ int qcow2_encrypt_sectors(BDRVQcow2State *s, int64_t > sector_num, > static int coroutine_fn do_perform_cow(BlockDriverState *bs, > uint64_t src_cluster_offset, > uint64_t cluster_offset, > - int offset_in_cluster, > - int bytes) > + unsigned offset_in_cluster, > + unsigned bytes) I don't know if the code base has a strong preference for 'unsigned int' over 'unsigned', but it doesn't bother me. Reviewed-by: Eric Blake <ebl...@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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