zfs send -R -i does not fail if source snapshot does not exist

[jvsalo]

In ZFS 0.6.5 (and also older versions) the following command will succeed:

# zfs send -R -i dataset@snapshot_that_never_existed dataset@snapshot_that_exists

Also happens with -I. It appears ZFS does "zfs send -R ..." instead. Without -R, it fails as expected:

incremental source (dataset@snasphot_that_never_existed) does not exist

This can result in confusing error messages with replication, when source snapshot does not exist any more. Then the receiving party gets: "cannot receive new filesystem stream: destination 'pool/dataset' exists". This is because the stream from "zfs send -R -i" is not, in fact, an incremental stream.

[rageagainstthebugs]

This be duplicate #3010 (comment)

[loli10K]

Still an issue here, reproducer needs both -i and -R:

root@linux:~# uname -a
Linux linux 3.16.0-4-amd64 #1 SMP Debian 3.16.51-3 (2017-12-13) x86_64 GNU/Linux
root@linux:~# cat /proc/sys/kernel/spl/gitrev
zfs-0.8.0-rc3-50-g2d76ab9
root@linux:~# 
root@linux:~# 
root@linux:~# POOLNAME='testpool'
root@linux:~# TMPDIR='/var/tmp'
root@linux:~# mountpoint -q $TMPDIR || mount -t tmpfs tmpfs $TMPDIR
root@linux:~# zpool destroy -f $POOLNAME
root@linux:~# rm -f $TMPDIR/zpool.dat
root@linux:~# truncate -s 128m $TMPDIR/zpool.dat
root@linux:~# zpool create -f -O mountpoint=none $POOLNAME $TMPDIR/zpool.dat
root@linux:~# 
root@linux:~# zfs create $POOLNAME/fs
root@linux:~# zfs snap $POOLNAME/fs@snap1
root@linux:~# zfs snap $POOLNAME/fs@snap2
root@linux:~# zfs send -v -R -i $POOLNAME/fs@snap1 $POOLNAME/fs@snap2 > /dev/null
send from @snap1 to testpool/fs@snap2 estimated size is 624B
total estimated size is 624B
TIME        SENT   SNAPSHOT
root@linux:~# zfs send -v -R -i $POOLNAME/fs@does-not-exist $POOLNAME/fs@snap2 > /dev/null
full send of testpool/fs@snap2 estimated size is 12.6K
total estimated size is 12.6K
TIME        SENT   SNAPSHOT
root@linux:~# 

[bunder2015]

Interesting... in theory this should be zero right?

gazelle ~ # zfs create g-pool/temp/testing
gazelle ~ # zfs snap g-pool/temp/testing@snap1
gazelle ~ # zfs snap g-pool/temp/testing@snap2
gazelle ~ # zfs send -v -R -i g-pool/temp/testing@nonexist g-pool/temp/testing@snap2 | zstreamdump -v
BEGIN record
        hdrtype = 2
        features = 4
        magic = 2f5bacbac
        creation_time = 0
        type = 0
        flags = 0x0
        toguid = 0
        fromguid = 0
        toname = g-pool/temp/testing@snap2

nvlist version: 0
        fromsnap = nonexist
        tosnap = snap2
        fss = (embedded nvlist)
        nvlist version: 0
                0xc522601872dc7df0 = (embedded nvlist)
                nvlist version: 0
                        name = g-pool/temp/testing
                        parentfromsnap = 0x0
                        props = (embedded nvlist)
                        nvlist version: 0
                        (end props)

                        snaps = (embedded nvlist)
                        nvlist version: 0
                                snap1 = 0x4dfa86725aba5224
                                snap2 = 0x35dc3d0c098c6004
                        (end snaps)

                        snapprops = (embedded nvlist)
                        nvlist version: 0
                                snap1 = (embedded nvlist)
                                nvlist version: 0
                                (end snap1)

                                snap2 = (embedded nvlist)
                                nvlist version: 0
                                (end snap2)

                        (end snapprops)

                (end 0xc522601872dc7df0)

        (end fss)

END checksum = 15cc51958c/8dbec27e26c/258a07fe0f729/7d8be31f807151
full send of g-pool/temp/testing@snap2 estimated size is 45.1K
total estimated size is 45.1K
TIME        SENT   SNAPSHOT
BEGIN record
        hdrtype = 1
        features = 4
        magic = 2f5bacbac
        creation_time = 5c67c22e
        type = 2
        flags = 0x4
        toguid = 35dc3d0c098c6004
        fromguid = 0
        toname = g-pool/temp/testing@snap2

FREEOBJECTS firstobj = 0 numobjs = 1
OBJECT object = 1 type = 21 bonustype = 0 blksz = 512 bonuslen = 0 dn_slots = 1 raw_bonuslen = 0 flags = 0 maxblkid = 0 indblkshift = 0 nlevels = 0 nblkptr = 0
FREE object = 1 offset = 512 length = -1
FREEOBJECTS firstobj = 2 numobjs = 30
WRITE object = 1 type = 21 checksum type = 7 compression type = 0
    flags = 0 offset = 0 logical_size = 512 compressed_size = 0 payload_size = 512 props = 200000000 salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
FREE object = 1 offset = 512 length = 1024
OBJECT object = 32 type = 45 bonustype = 0 blksz = 512 bonuslen = 0 dn_slots = 1 raw_bonuslen = 0 flags = 0 maxblkid = 0 indblkshift = 0 nlevels = 0 nblkptr = 0
FREE object = 32 offset = 512 length = -1
OBJECT object = 33 type = 22 bonustype = 0 blksz = 512 bonuslen = 0 dn_slots = 1 raw_bonuslen = 0 flags = 0 maxblkid = 0 indblkshift = 0 nlevels = 0 nblkptr = 0
FREE object = 33 offset = 512 length = -1
OBJECT object = 34 type = 20 bonustype = 44 blksz = 512 bonuslen = 168 dn_slots = 1 raw_bonuslen = 0 flags = 0 maxblkid = 0 indblkshift = 0 nlevels = 0 nblkptr = 0
FREE object = 34 offset = 512 length = -1
OBJECT object = 35 type = 46 bonustype = 0 blksz = 1536 bonuslen = 0 dn_slots = 1 raw_bonuslen = 0 flags = 0 maxblkid = 0 indblkshift = 0 nlevels = 0 nblkptr = 0
FREE object = 35 offset = 1536 length = -1
OBJECT object = 36 type = 47 bonustype = 0 blksz = 16384 bonuslen = 0 dn_slots = 1 raw_bonuslen = 0 flags = 0 maxblkid = 0 indblkshift = 0 nlevels = 0 nblkptr = 0
FREE object = 36 offset = 32768 length = -1
FREEOBJECTS firstobj = 37 numobjs = 27
WRITE object = 32 type = 45 checksum type = 7 compression type = 0
    flags = 0 offset = 0 logical_size = 512 compressed_size = 0 payload_size = 512 props = 200000000 salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
FREE object = 32 offset = 512 length = 1024
WRITE object = 33 type = 22 checksum type = 7 compression type = 0
    flags = 0 offset = 0 logical_size = 512 compressed_size = 0 payload_size = 512 props = 200000000 salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
FREE object = 33 offset = 512 length = 1024
WRITE object = 34 type = 20 checksum type = 7 compression type = 0
    flags = 0 offset = 0 logical_size = 512 compressed_size = 0 payload_size = 512 props = 200000000 salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
WRITE object = 35 type = 46 checksum type = 7 compression type = 0
    flags = 0 offset = 0 logical_size = 1536 compressed_size = 0 payload_size = 1536 props = 200020002 salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
FREE object = 35 offset = 1536 length = 3072
WRITE object = 36 type = 47 checksum type = 7 compression type = 0
    flags = 0 offset = 0 logical_size = 16384 compressed_size = 0 payload_size = 16384 props = f0007001f salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
WRITE object = 36 type = 47 checksum type = 7 compression type = 0
    flags = 0 offset = 16384 logical_size = 16384 compressed_size = 0 payload_size = 16384 props = f0007001f salt = 0000000000000000 iv = 000000000000000000000000 mac = 00000000000000000000000000000000
FREE object = 36 offset = 32768 length = 16384
FREEOBJECTS firstobj = 64 numobjs = 0
FREEOBJECTS firstobj = 0 numobjs = 0
END checksum = 198d51e36e9/247a17ad6e271d/781f18ca837018e/21680d7954ed96e8
END checksum = 0/0/0/0
SUMMARY:
        Total DRR_BEGIN records = 2
        Total DRR_END records = 3
        Total DRR_OBJECT records = 6
        Total DRR_FREEOBJECTS records = 5
        Total DRR_WRITE records = 7
        Total DRR_WRITE_BYREF records = 0
        Total DRR_WRITE_EMBEDDED records = 0
        Total DRR_FREE records = 11
        Total DRR_SPILL records = 0
        Total records = 34
        Total write size = 36352 (0x8e00)
        Total stream length = 47712 (0xba60)

[loli10K]

That is indeed the bug, zfs send is doing a full send stream (containing dataset-wide metadata) instead of a no-changes (almost 0 bytes) incremental.

root@linux:~# zfs send -v -R -i $POOLNAME/fs@does-not-exist $POOLNAME/fs@snap2 | zstreamdump -v | grep WRITE
full send of testpool/fs@snap2 estimated size is 12.6K
total estimated size is 12.6K
TIME        SENT   SNAPSHOT
WRITE object = 1 type = 21 checksum type = 7 compression type = 0
WRITE object = 32 type = 45 checksum type = 2 compression type = 0
WRITE object = 33 type = 22 checksum type = 2 compression type = 0
WRITE object = 34 type = 20 checksum type = 2 compression type = 0
WRITE object = 35 type = 46 checksum type = 7 compression type = 0
WRITE object = 36 type = 47 checksum type = 7 compression type = 0
WRITE object = 36 type = 47 checksum type = 7 compression type = 0
	Total DRR_WRITE records = 7
	Total DRR_WRITE_BYREF records = 0
	Total DRR_WRITE_EMBEDDED records = 0
root@linux:~# zdb -dd $POOLNAME/fs
Dataset testpool/fs [ZPL], ID 259, cr_txg 6, 24K, 6 objects

    Object  lvl   iblk   dblk  dsize  dnsize  lsize   %full  type
         0    6   128K    16K    13K     512    32K    9.38  DMU dnode
        -1    1   128K    512      0     512    512  100.00  ZFS user/group/project used
        -2    1   128K    512      0     512    512  100.00  ZFS user/group/project used
        -3    1   128K    512      0     512    512  100.00  ZFS user/group/project used
         1    1   128K    512     1K     512    512  100.00  ZFS master node
        32    1   128K    512      0     512    512  100.00  SA master node
        33    1   128K    512      0     512    512  100.00  ZFS delete queue
        34    1   128K    512      0     512    512  100.00  ZFS directory
        35    1   128K  1.50K     1K     512  1.50K  100.00  SA attr registration
        36    1   128K    16K     8K     512    32K  100.00  SA attr layouts

    Dnode slots:
	Total used:             6
	Max used:              36
	Percent empty:  83.333333

root@linux:~# 

[stale]

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