From e8726ce95aa30775f5e1cfe76d8692c97f7fceeb Mon Sep 17 00:00:00 2001
From: Andrea Mazzoleni <amadvance@gmail.com>
Date: Tue, 8 Sep 2026 10:06:11 +0200
Subject: [PATCH] Add regression tests and document parity size requirements
 when adding a parity level

---
 Makefile.am    | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 cmdline/sync.c |  5 +++++
 2 files changed, 52 insertions(+)

diff --git a/Makefile.am b/Makefile.am
index bca4b92e..3200ad63 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1320,6 +1320,53 @@ endif # !HAVE_MEMORY_CHECKER
 	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_SPLIT2) locate > /dev/null
 	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_SPLIT2) sync
 	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_SPLIT2) check
+	$(MSG) Test adding a parity level after an interrupted normal shrink
+	rm -rf bench/realloc-level
+	mkdir -p bench/realloc-level/disk1
+	mkdir -p bench/realloc-level/disk2
+	mkdir -p bench/realloc-level/disk3
+	mkdir -p bench/realloc-level/disk4
+	mkdir -p bench/realloc-level/disk5
+	mkdir -p bench/realloc-level/disk6
+	dd bs=1024 count=1 if=/dev/urandom of=bench/realloc-level/disk1/data
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL1) sync
+	dd bs=1024 count=1 if=/dev/urandom of=bench/realloc-level/disk1/tail
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL1) sync
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) -d 2-parity fix
+	rm bench/realloc-level/disk1/tail
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL1) --test-kill-after-resize sync
+	cp bench/realloc-level/content bench/realloc-level/content.checkpoint
+	$(MSG) Accept the new level initialized at the old logical size
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) sync
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) check
+	cp bench/realloc-level/content.checkpoint bench/realloc-level/content
+	$(MSG) Accept the new level initialized at the checkpoint allocation
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) -d 2-parity fix
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) sync
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) check
+	cp bench/realloc-level/content.checkpoint bench/realloc-level/content
+	$(MSG) Accept the checkpoint allocation after adding files since fix
+	dd bs=1024 count=2 if=/dev/urandom of=bench/realloc-level/disk1/growth
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) sync
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) check
+	$(MSG) Test fix leaving pending parity shorter than the checkpoint allocation
+	cp -p bench/realloc-level/disk1/data bench/realloc-level/disk2/data
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) sync
+	cp -p bench/realloc-level/disk1/growth bench/realloc-level/disk1/tail
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL1) --test-kill-after-sync sync
+	rm bench/realloc-level/disk2/data
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL1) fix
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) fix
+	cp bench/realloc-level/content bench/realloc-level/content.checkpoint
+	$(MSG) Resume after removing the pending additions
+	mv bench/realloc-level/disk1/tail bench/realloc-level/tail
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) sync
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) check
+	$(MSG) Resume with the pending additions still allocated
+	mv bench/realloc-level/tail bench/realloc-level/disk1/tail
+	cp bench/realloc-level/content.checkpoint bench/realloc-level/content
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) sync
+	$(TESTENV) $(SNAPRAID) $(CHECKFLAGS) -c $(REALLOC_LEVEL2) check
 	$(MSG) Test interrupted normal shrink after adding a parity split
 	rm -rf bench/realloc-split
 	mkdir -p bench/realloc-split/disk1
diff --git a/cmdline/sync.c b/cmdline/sync.c
index 51296587..95c9d17f 100644
--- a/cmdline/sync.c
+++ b/cmdline/sync.c
@@ -2031,6 +2031,11 @@ int state_sync(struct snapraid_state* state, block_off_t blockstart, block_off_t
 	 * A full parity rebuild or reallocation from zero reconstructs truncated
 	 * parity. Tail-only reallocation still relies on the existing prefix, so a
 	 * truncation before parity_tail remains fatal.
+	 *
+	 * New levels need the same physical coverage of valid blocks, not an exact
+	 * match with another level or the allocated extent. After an interrupted
+	 * sync, fix leaves pending parity to sync and may truncate its unwritten
+	 * tail. Sync will resize and regenerate that tail if it is still allocated.
 	 */
 	if (!state->opt.force_full && !(state->opt.force_realloc && state->opt.parity_tail == 0)) {
 		/* if the parities are too small */