dd tool read data from volume snapshot in zfs_rename_006_pos.ksh faild

[liaoyuxiangqin]

Dear All,
When testing zfs_rename group in test suit, i try to open the zfs_rename_006_pos.ksh
to verify rename a volume snapshot and data integrity, and find this script uesd dd tool read
data from voluem snapshot but faild. The detail test case as following description:

setup:

SUCCESS: /home/yuxiang/zfs-master/cmd/zpool/zpool create -f testpool.1321 loop0
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs create testpool.1321/testfs.1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs set mountpoint=/var/tmp/testdir1321 testpool.1321/testfs.1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs create testpool.1321/testctr1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs set canmount=off testpool.1321/testctr1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs create testpool.1321/testctr1321/testfs1.1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs set mountpoint=/var/tmp/testdir11321 testpool.1321/testctr1321/testfs1.1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs create -V 150m testpool.1321/testvol1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs create testpool.1321/datafs.rename
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs set mountpoint=/var/tmp/testdir21321 testpool.1321/datafs.rename
SUCCESS: eval /usr/bin/dd if=/dev/urandom of=/var/tmp/testdir21321/data.rename bs=512 count=2048 >/dev/null 2>&1

zfs_rename_006_pos:
1.Write data to this volume(testvol1321) and create a snapshot(testsnap1321) of volume.

SUCCESS: eval /usr/bin/dd if=/var/tmp/testdir21321/data.rename of=/dev/zvol/testpool.1321/testvol1321 bs=512 count=2048 >/dev/null 2>&1
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs snapshot testpool.1321/testvol1321@testsnap1321

2.Rename volume snapshot to a new one.

SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs rename testpool.1321/testvol1321@testsnap1321 testpool.1321/testvol1321@testsnap1321-new
SUCCESS: datasetexists testpool.1321/testvol1321@testsnap1321 exited 1
SUCCESS: datasetexists testpool.1321/testvol1321@testsnap1321-new

3.Rename volume to a new one.

SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs rename testpool.1321/testvol1321 testpool.1321/testvol1321-new
SUCCESS: datasetexists testpool.1321/testvol1321 exited 1
SUCCESS: datasetexists testpool.1321/testvol1321-new

4.Restore volume and snatshot name to origin.

SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs rename testpool.1321/testvol1321-new@testsnap1321-new testpool.1321/testvol1321-new@testsnap1321
SUCCESS: datasetexists testpool.1321/testvol1321-new@testsnap1321-new exited 1
SUCCESS: datasetexists testpool.1321/testvol1321-new@testsnap1321
SUCCESS: /home/yuxiang/zfs-master/cmd/zfs/zfs rename testpool.1321/testvol1321-new testpool.1321/testvol1321
SUCCESS: datasetexists testpool.1321/testvol1321-new exited 1
SUCCESS: datasetexists testpool.1321/testvol1321

5.Verify data integrity.

SUCCESS: eval dd if=/dev/zvol/testpool.1321/testvol1321 of=/var/tmp/testdir21321/voldata.rename bs=512 count=2048 >/dev/null 2>&1
ERROR: eval dd if=/dev/zvol/testpool.1321/testvol1321@testsnap1321 of=/var/tmp/testdir21321/voldata.rename bs=512 count=2048 >/dev/null 2>&1 exited 1
NOTE: Performing local cleanup via log_onexit (cleanup)

Solution: the above script test fail because used dd tool read data from volume snapshot,
and find that /dev/zvol/testpool.1321/testvol1321@testsnap1321 not exist as a dev in linux,
and i think the volume snapshot don't contains unique bytes in self beacuse the data in vloume don't change. but i also did not find a good way to modify, looking forward to advice, thanks!

[behlendorf]

Duplicate of #5647