Re: [Libguestfs] [PATCH nbdkit v5 FINAL 12/19] truncate: Implement extents for beyond end of truncated region.

On 3/28/19 11:18 AM, Richard W.M. Jones wrote: > --- > filters/truncate/truncate.c | 55 +++++++++++++++++++++++++++++++++++++ > 1 file changed, 55 insertions(+) > > + > + /* If the entire request is beyond the end of the underlying plugin > + * then this is the easy case: return a hole. > + */ > + if (offset >= real_size_copy) > + return nbdkit_add_extent (extents, offset, (uint64_t) count, > + NBDKIT_EXTENT_ZERO|NBDKIT_EXTENT_HOLE); Why not return a hole up to the end of the file, rather than limiting things at the end of the client's request?

> + /* We're asked first for extents information about the plugin, then > + * possibly (if truncating larger) for the hole after the plugin. > + * Since we're not required to provide all of this information, the > + * easiest thing is to only return data from the plugin. We will be > + * called later about the hole. However we do need to make sure > + * that the extents array is truncated to the real size, hence we > + * have to create a new extents array, ask the plugin, then copy the > + * returned data to the original array. > + */ > + extents2 = nbdkit_extents_new (0, real_size_copy); Why 0 for start instead of offset? You get the same result either way (since the copying code ignores the prefix), but it's probably a lot more efficient to not have to copy the extents for the prefix of the file.