@
SILdoc(`
"from" can be null, a snapshot, or a bookmark.
If from is null, a full (non-incremental) stream will be estimated. This
is calculated very efficiently.
If from is a snapshot, lzc_send_space uses the deadlists attached to
each snapshot to efficiently estimate the stream size.
If from is a bookmark, the indirect blocks in the destination snapshot
are traversed, looking for blocks with a birth time since the creation TXG of
the snapshot this bookmark was created from. This will result in
significantly more I/O and be less efficient than a send space estimation on
an equivalent snapshot.
`)