Re: [Libguestfs] [nbdkit PATCH 2/3] extents: Add nbdkit_extents_aligned()

+/* 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; + }

+ /* 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;