Sorted displaying of the blocking snapshots list

[ghost]

Motivation and Context

When multiple snapshots prevent the destruction/rollback of the respective dataset/snapshot/volume via zfs destroy or zfs rollback, the error message does not list the blocking snapshots sorted according to their order of creation.
This causes inconvenience and can lead to confusion, and also creates a contrast with a returned message from zfs list -t snap function.
#12751

Description

The zfs_iter_snapshots_v2 functions used in these cases are replaced by zfs_iter_snapshots_sorted_v2

Prepare:

sudo zpool create MyPool /tmp/vdev1.img
sudo zfs create MyPool/Test
sudo zfs snap MyPool/Test@Snap1
sudo zfs snap MyPool/Test@Snap2
sudo zfs snap MyPool/Test@Snap3
sudo zfs snap MyPool/Test@Snap4
sudo zfs snap MyPool/Test@Snap5
sudo zfs snap MyPool/Test@Snap6

Before:

sudo zfs destroy MyPool/Test
cannot destroy 'MyPool/Test': filesystem has children
use '-r' to destroy the following datasets:
MyPool/Test@Snap4
MyPool/Test@Snap3
MyPool/Test@Snap2
MyPool/Test@Snap5
MyPool/Test@Snap1
MyPool/Test@Snap6

sudo zfs rollback MyPool/Test@Snap1
cannot rollback to 'MyPool/Test@Snap1': more recent snapshots or bookmarks exist
use '-r' to force deletion of the following snapshots and bookmarks:
MyPool/Test@Snap4
MyPool/Test@Snap3
MyPool/Test@Snap2
MyPool/Test@Snap5
MyPool/Test@Snap6

After:

sudo zfs destroy MyPool/Test
cannot destroy 'MyPool/Test': filesystem has children
use '-r' to destroy the following datasets:
MyPool/Test@Snap1
MyPool/Test@Snap2
MyPool/Test@Snap3
MyPool/Test@Snap4
MyPool/Test@Snap5
MyPool/Test@Snap6

sudo zfs rollback MyPool/Test@Snap1
cannot rollback to 'MyPool/Test@Snap1': more recent snapshots or bookmarks exist
use '-r' to force deletion of the following snapshots and bookmarks:
MyPool/Test@Snap2
MyPool/Test@Snap3
MyPool/Test@Snap4
MyPool/Test@Snap5
MyPool/Test@Snap6

How Has This Been Tested?

Run the commands in the different combinations.

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)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[amotin]

It definitely looks right for the mentioned cases. I just wonder whether you looked in what other cases the code may be used, where sorting could theoretically be a waste.

[tonyhutter]

Could you add the description text from this PR into your commit message, and add a Closes line, like:

Sort the blocking snapshots list

When multiple snapshots prevent the destruction/rollback of the
respective dataset/snapshot/volume via zfs destroy or zfs rollback,
the error message does not list the blocking snapshots sorted
according to their order of creation. This causes inconvenience and can
lead to confusion, and also creates a contrast with a returned message
from zfs list -t snap function.

Closes: #12751
Signed-off-by: Artem-OSSRevival <artem.vlasenko@ossrevival.org>