On 04/10/2017 08:17 PM, Eric Blake wrote: > Passing a byte offset, but sector count, when we ultimately > want to operate on cluster granularity, is madness. Clean up > the external interfaces to take both offset and count as bytes, > while still keeping the assertion added previously that the > caller must align the values to a cluster. Then rename things > to make sure backports don't get confused by changed units: > instead of qcow2_discard_clusters() and qcow2_zero_clusters(), > we now have qcow2_cluster_discard() and qcow2_cluster_zeroize(). > > The internal functions still operate on clusters at a time, and > return an int for number of cleared clusters; but on an image > with 2M clusters, a single L2 table holds 256k entries that each > represent a 2M cluster, totalling well over INT_MAX bytes if we > ever had a request for that many bytes at once. All our callers > currently limit themselves to 32-bit bytes (and therefore fewer > clusters), but by making this function 64-bit clean, we have one > less place to clean up if we later improve the block layer to > support 64-bit bytes through all operations (with the block layer > auto-fragmenting on behalf of more-limited drivers), rather than > the current state where some interfaces are artificially limited > to INT_MAX at a time. > > Signed-off-by: Eric Blake <ebl...@redhat.com> >
> +int qcow2_cluster_zeroize(BlockDriverState *bs, uint64_t offset,
> + uint64_t bytes, int flags)
> {
> BDRVQcow2State *s = bs->opaque;
> uint64_t end_offset;
> uint64_t nb_clusters;
> + int64_t cleared;
> int ret;
>
> - end_offset = offset + (nb_sectors << BDRV_SECTOR_BITS);
> + end_offset = offset + bytes;
>
> /* Caller must pass aligned values, except at image end */
> assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
> assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
> end_offset == bs->total_sectors << BDRV_SECTOR_BITS);
> + assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
And I promptly botched my rebasing. qemu-iotests 154 caught my mistake
(the whole point of calculating end_offset is because bytes need not be
cluster-aligned if end_offset is at EOF). I'll send the obvious fixup.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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