openzfs/zfs

`zfs diff` shows pathes prefixed by mountpoint path (and sometimes irrelevant)

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#4289 opened on Jan 30, 2016

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Status: InactiveType: Featuregood first issue

Description

Pathes which are printed by zfs diff are not dataset-relative; they include the dataset mountpoint. This creates additional troubles when scripting around zfs diff.

Moreover, if one diffs between two snapshots, output pathes are prefixed by the real dataset mountpoints (and not the relevant snapshot mountpoints). This makes even more troubles as the backup script now needs to have knowledge of completely irrelevant mountpoints. This part is probably related to #3325.

Example:

# mount | grep '^datastore2/Internal[@ ]'
datastore2/Internal@2016-01-24 on /mnt/datastore2@2016-01-24/datastore2-Internal type zfs (ro,relatime,xattr,posixacl)
datastore2/Internal@2016-01-28 on /mnt/datastore2@2016-01-28/datastore2-Internal type zfs (ro,relatime,xattr,posixacl)
datastore2/Internal on /mnt/data/Internal type zfs (ro,relatime,xattr,posixacl)

# zfs diff -FH datastore2/Internal@2016-01-24 datastore2/Internal@2016-01-28 | head -n5
M       /       /mnt/data/Internal/Misc/transmissionbt/.git/objects/eb
M       /       /mnt/data/Internal/Misc/transmissionbt/.git/objects/98
M       /       /mnt/data/Internal/Misc/transmissionbt/.git/objects/4f
M       /       /mnt/data/Internal/Misc/transmissionbt/.git/objects/e6
M       /       /mnt/data/Internal/Misc/transmissionbt/.git/objects/26

That is, pathes printed by mount diff are inside neither of snapshot mountpoints. They reference /mnt/data/Internal (the real dataset mountpoint), which the script knows nothing about.

Contributor guide

Tech stack
c
Domain
cli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C programmingZFS internalsfilesystem mountpoints
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the `zfs diff` command implementation in the OpenZFS codebase. The issue shows that output paths include the dataset mountpoint rather than being relative to the dataset. The fix likely involves changing how the path is determined, possibly by stripping the mountpoint prefix or using snapshot relative paths. Review existing code in `cmd/zfs/zfs diff.c` or similar files. Also consider the related issue #3325 for additional context.