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rajputa-deshawandZen Dodd 7998ccfe65 receiver: add --delay-symlinks (#1124)
* Add --delay-symlinks to create symlinks after all files are in place

The generator creates a symlink as soon as it reaches it in the file
list, while regular files arrive later through the sender and receiver
(and, with --delay-updates, are only renamed into place at the end).
For the rest of the transfer a new symlink can point at a file that
isn't there yet, so anything reading the destination during the sync --
e.g. a loader resolving libfoo.so -> libfoo.so.2 -- can fail.

The new --delay-symlinks option makes the generator defer new and
changed symlinks and create them once the receiver reports that every
file, including any --delay-updates renames, is in place.  Each link is
itemized and logged after it has been created, before the generator
ends the delay-updates phase, and the deletion stats are sent after any
directory that a deferred link replaces.

The option implies --no-inc-recursive on the receiving side and is
passed to a remote receiver, which must also support it.  It is an
error to combine it with --remove-source-files, --hard-links,
--compare-dest, --copy-dest, or --link-dest, or to use it with a
protocol older than 29.  support/rrsync accepts the option and refuses
it under -no-overwrite, as it does --delay-updates.

Add delay-symlinks_test.py, which holds a push partway through the
link's target to check that new and changed links aren't created early,
and rrsync-no-overwrite-delay-symlinks_test.py.

* Document --delay-symlinks limits and test how it is passed to the server

The man page now says the option narrows the inconsistency window rather
than making the update atomic, that an interrupted transfer leaves new
symlinks missing and changed ones at their old targets, and that
--delete-before can also remove an old target early.

Add delay-symlinks-remote_test.py.  Through a remote shell that records
the server command, it checks that the option is passed to a remote
receiver on a push but not to a remote sender on a pull, and that
incremental recursion is off in both directions.  It also checks that
--protocol=28 fails with the protocol error, and that a push to an older
rsync (old_versions/rsync_3.4.1) is refused before anything is
transferred while a pull from it works.

* testsuite: seed delay-symlinks fixture with rsync

* NEWS: document --delay-symlinks

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Co-authored-by: Zen Dodd <mail@steadytao.com>
2026-10-11 14:02:12 +10:00
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