'zfs receive' fails with "dataset is busy"

[loli10K]

Description

Receiving an incremental stream after an interrupted "zfs receive -s" fails with the message "dataset is busy": this is because we still have the hidden clone ../%recv from the resumable receive.

Improve the error message suggesting the existence of a partially complete resumable stream from "zfs receive -s" which can be either aborted ("zfs receive -A") or resumed ("zfs send -t").

Motivation and Context

Fix #7129

How Has This Been Tested?

Local Debian8 worker:

root@linux:/usr/src/zfs# POOLNAME='testpool'
root@linux:/usr/src/zfs# TMPDIR='/var/tmp'
root@linux:/usr/src/zfs# mountpoint -q $TMPDIR || mount -t tmpfs tmpfs $TMPDIR
root@linux:/usr/src/zfs# zpool destroy -f $POOLNAME
root@linux:/usr/src/zfs# rm -f $TMPDIR/zpool_$POOLNAME.dat
root@linux:/usr/src/zfs# truncate -s 128m $TMPDIR/zpool_$POOLNAME.dat
root@linux:/usr/src/zfs# zpool create -f $POOLNAME $TMPDIR/zpool_$POOLNAME.dat
root@linux:/usr/src/zfs# #
root@linux:/usr/src/zfs# zfs create $POOLNAME/sendfs
root@linux:/usr/src/zfs# zfs snap $POOLNAME/sendfs@snap1
root@linux:/usr/src/zfs# dd if=/dev/urandom of=/$POOLNAME/sendfs/file bs=1M count=10 status=none
root@linux:/usr/src/zfs# zfs snap $POOLNAME/sendfs@snap2
root@linux:/usr/src/zfs# #
root@linux:/usr/src/zfs# zfs send $POOLNAME/sendfs@snap1 | zfs recv $POOLNAME/recvfs
root@linux:/usr/src/zfs# zfs send -i $POOLNAME/sendfs@snap1 $POOLNAME/sendfs@snap2 | dd bs=1M count=8 iflag=fullblock status=none | zfs recv -s $POOLNAME/recvfs
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 1-113894673d-e8-789c636064000310a501c49c50360710a715e5e7a69766a6304081e28e29fb8e4bcebfa60064b323a9cb4fca4a4d2e61606082aac3904f4b2b4e2d01c9d4c0e5d990e4932a4b528b81f48fd03aacfa4bf221ae085535f7ff657740d600499e132c9f97989b0aa4538b4b0af2f373f48b53f352d28a1d8af3120b8ca06e02004a9122fd
root@linux:/usr/src/zfs# zfs send -i $POOLNAME/sendfs@snap1 $POOLNAME/sendfs@snap2 | zfs recv $POOLNAME/recvfs
cannot receive incremental stream: destination testpool/recvfs contains partially-complete state from "zfs receive -s".

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[codecov]

Codecov Report

Merging #7154 into master will decrease coverage by 0.09%.
The diff coverage is 42.85%.

@@            Coverage Diff            @@
##           master    #7154     +/-   ##
=========================================
- Coverage   76.29%    76.2%   -0.1%     
=========================================
  Files         324      324             
  Lines      103006   103013      +7     
=========================================
- Hits        78593    78501     -92     
- Misses      24413    24512     +99

Flag	Coverage Δ
#kernel	76.06% <ø> (+0.14%)	⬆️
#user	65.66% <42.85%> (-0.16%)	⬇️

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