`zfs send -t <token>` for an incremental send should be able to resume
successfully when sending to the same pool: a subtle issue in
`zfs_iter_children()` doesn't currently allow this.
Because resuming from a token requires "guid" -> "dataset" mapping
(`guid_to_name()`), we have to walk the whole hierarchy to find the right
snapshots to send.
When resuming an incremental send both source and destination live in the same
pool and have the same guid: this is where `zfs_iter_children()` gets confused
and picks up the wrong snapshot, so we end up trying to send an incremental
"destination@snap1 -> source@snap2" stream instead of "source@snap1 ->
source@snap2": this fails with an "Invalid cross-device link" (EXDEV) error.
```
root@openindiana:~# uname -a
SunOS openindiana 5.11 master-0-gb3c0a3b184 i86pc i386 i86pc
root@openindiana:~#
root@openindiana:~#
root@openindiana:~# POOLNAME='testpool'
root@openindiana:~# TMPDIR='/tmp'
root@openindiana:~# zpool destroy -f $POOLNAME
root@openindiana:~# rm -f $TMPDIR/zpool_$POOLNAME.dat
root@openindiana:~# mkfile 128m $TMPDIR/zpool_$POOLNAME.dat
root@openindiana:~# zpool create $POOLNAME $TMPDIR/zpool_$POOLNAME.dat
root@openindiana:~# #
root@openindiana:~# dd if=/dev/urandom of=/$POOLNAME/data.bin bs=1M count=10
10+0 records in
10+0 records out
10485760 bytes transferred in 2.964483 secs (3537130 bytes/sec)
root@openindiana:~# zfs snapshot $POOLNAME@snap1
root@openindiana:~# zfs send $POOLNAME@snap1 | zfs recv -s $POOLNAME/mirror
root@openindiana:~# #
root@openindiana:~# dd if=/dev/urandom of=/$POOLNAME/data.bin bs=1M count=10
10+0 records in
10+0 records out
10485760 bytes transferred in 2.655169 secs (3949188 bytes/sec)
root@openindiana:~# zfs snapshot $POOLNAME@snap2
root@openindiana:~# zfs send -i $POOLNAME@snap1 $POOLNAME@snap2 | dd bs=1M
count=1 | zfs recv -s $POOLNAME/mirror
0+1 records in
0+1 records out
312 bytes transferred in 0.010768 secs (28975 bytes/sec)
cannot receive incremental stream: checksum mismatch or incomplete stream.
Partially received snapshot is saved.
A resuming stream can be generated on the sending system by running:
zfs send -t
1-c12d90fb3-e0-789c636064000310a501c49c50360710a715e5e7a69766a63040814f53c88cd7367f5a14806c762475f94959a9c925103e0860c8a7a515a79630c001489e0d493ea9b224b59801551e597f493ec4155bb5a6a41dccbdd4a08124cf0996cf4bcc4d05d2a9c52505f9f9390ec57989054610b30083501f20
root@openindiana:~# #
root@openindiana:~# TOKEN=$(zfs get -H -o value receive_resume_token
$POOLNAME/mirror)
root@openindiana:~# zfs send -nP -t $TOKEN > /dev/null
resume token contents:
nvlist version: 0
fromguid = 0x84fc3ceb9854824c
object = 0x1
offset = 0x0
bytes = 0x0
toguid = 0x80d26dc166942ab5
toname = testpool@snap2
incremental testpool/mirror@snap1 testpool@snap2
root@openindiana:~# zfs send -t $TOKEN > /dev/null
warning: cannot send 'testpool@snap2': Cross-device link
root@openindiana:~#
```
Illumos issue: https://www.illumos.org/issues/8940
ZFS on Linux PR: https://github.com/zfsonlinux/zfs/pull/6623
NOTE: the original pull request contained also a small fix for another issue
(_zfs send -n -t <token> should dump its output to stdout, not stderr, for
consistency with other dry-run commands_): can we squeeze it in this PR or
should we open a separate Illumos issue?
You can view, comment on, or merge this pull request online at:
https://github.com/openzfs/openzfs/pull/510
-- Commit Summary --
* 8940 Sending an intra-pool resumable send stream may result in EXDEV
-- File Changes --
M usr/src/lib/libzfs/common/libzfs_iter.c (4)
M usr/src/test/zfs-tests/tests/functional/rsend/rsend.kshlib (10)
M usr/src/test/zfs-tests/tests/functional/rsend/rsend_019_pos.ksh (4)
M usr/src/test/zfs-tests/tests/functional/rsend/rsend_020_pos.ksh (2)
M usr/src/test/zfs-tests/tests/functional/rsend/rsend_021_pos.ksh (2)
M usr/src/test/zfs-tests/tests/functional/rsend/rsend_022_pos.ksh (2)
M usr/src/test/zfs-tests/tests/functional/rsend/rsend_024_pos.ksh (2)
M usr/src/test/zfs-tests/tests/functional/rsend/send-c_resume.ksh (2)
-- Patch Links --
https://github.com/openzfs/openzfs/pull/510.patch
https://github.com/openzfs/openzfs/pull/510.diff
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