[Libguestfs] [nbdkit PATCH 2/3] extents: Add nbdkit_extents_aligned()
Richard W.M. Jones
rjones at redhat.com
Wed Jul 8 11:28:47 UTC 2020
On Tue, Jul 07, 2020 at 05:22:46PM -0500, Eric Blake wrote:
[...]
> +/* Compute aligned extents on behalf of a filter. */
> +int
> +nbdkit_extents_aligned (struct nbdkit_next_ops *next_ops,
> + nbdkit_backend *nxdata,
> + uint32_t count, uint64_t offset,
> + uint32_t flags, uint32_t align,
> + struct nbdkit_extents *exts, int *err)
> +{
> + size_t i;
> + struct nbdkit_extent e, e2;
> +
> + if (!IS_ALIGNED(count | offset, align)) {
> + nbdkit_error ("nbdkit_extents_aligned: unaligned request");
> + *err = EINVAL;
> + return -1;
> + }
I wonder if this also should be an assert? This is less clear to me
than the vector case however.
> + /* Perform an initial query, then scan for the first unaligned extent. */
> + if (next_ops->extents (nxdata, count, offset, flags, exts, err) == -1)
> + return -1;
> + for (i = 0; i < exts->extents.size; ++i) {
> + e = exts->extents.ptr[i];
> + if (!IS_ALIGNED(e.length, align)) {
> + /* If the unalignment is past align, just truncate and return early */
> + if (e.offset + e.length > offset + align) {
> + e.length = ROUND_DOWN (e.length, align);
> + exts->extents.size = i + !!e.length;
> + exts->next = e.offset + e.length;
> + break;
> + }
> +
> + /* Otherwise, coalesce until we have at least align bytes, which
> + * may require further queries.
> + */
> + assert (i == 0);
> + while (e.length < align) {
> + if (exts->extents.size > 1) {
> + e.length += exts->extents.ptr[1].length;
> + e.type &= exts->extents.ptr[1].type;
> + extents_remove (&exts->extents, 1);
> + }
> + else {
> + /* The plugin needs a fresh extents object each time, but
> + * with care, we can merge it into the callers' extents.
> + */
> + extents tmp;
> + CLEANUP_EXTENTS_FREE struct nbdkit_extents *extents2 = NULL;
> +
> + extents2 = nbdkit_extents_new (e.offset + e.length, offset + align);
> + if (next_ops->extents (nxdata, offset + align - e.length,
> + e.offset + e.length,
> + flags & ~NBDKIT_FLAG_REQ_ONE,
> + extents2, err) == -1)
> + return -1;
> + e2 = extents2->extents.ptr[0];
> + assert (e2.offset == e.offset + e.length);
> + e2.offset = e.offset;
> + e2.length += e.length;
> + e2.type &= e.type;
So we're intersecting (&) the types defined as:
#define NBDKIT_EXTENT_HOLE (1<<0) /* Same as NBD_STATE_HOLE */
#define NBDKIT_EXTENT_ZERO (1<<1) /* Same as NBD_STATE_ZERO */
If all extents are holes, then it's a hole. If all extents are zero,
then it's a zero. Otherwise it's non-zero data.
This seems correct.
All looks good to me, so ACK.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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