If you create a zfs child folder, zfs send returns an error when a recursive
incremental send is done between two snapshots made prior to the folder
creation.
The problem can be reproduced with the following steps.
root@zfs:/# zfs create pool/test
root@zfs:/# zfs snapshot pool/test@snap1
root@zfs:/# zfs snapshot pool/test@snap2
root@zfs:/# zfs create pool/test/child
root@zfs:/# zfs send -R -I pool/test@snap1 pool/test@snap2 > /dev/null
WARNING: could not send pool/test/child@snap2: does not exist
WARNING: could not send pool/test/child@snap2: does not exist
root@zfs:/# echo $?
1
root@zfs:/# zfs snapshot -r pool/test@snap3
root@zfs:/# zfs send -R -I pool/test@snap1 pool/test@snap3 > /dev/null
root@zfs:/# echo $?
0
root@zfs:/# zfs send -R -I pool/test@snap2 pool/test@snap3 > /dev/null
root@zfs:/# echo $?
0
Since pool/test/child was created after snap2, zfs send should not expect snap2
to be in pool/test/child when doing a recursive send. It should examine the
compare the creation time of the snapshot and each child folder to decide if
the folder will be sent. The next incremental send between snap2 and snap3
would properly create the child folder and snap3 which first appears in the
child folder.
The problem is identical if '-i' is used instead of '-I'.