Default to zfs_bclone_wait_dirty=1

man/man4/zfs.4

@@ -1399,14 +1399,15 @@ If this setting is 0, then even if feature@block_cloning is enabled,
 using functions and system calls that attempt to clone blocks will act as
 though the feature is disabled.
 .
-.It Sy zfs_bclone_wait_dirty Ns = Ns Sy 0 Ns | Ns 1 Pq int
-When set to 1 the FICLONE and FICLONERANGE ioctls wait for dirty data to be
-written to disk.
-This allows the clone operation to reliably succeed when a file is
+.It Sy zfs_bclone_wait_dirty Ns = Ns Sy 1 Ns | Ns 0 Pq int
+When set to 1 the FICLONE and FICLONERANGE ioctls will wait for any dirty
+data to be written to disk before proceeding.
+This ensures that the clone operation reliably succeeds, even if a file is
 modified and then immediately cloned.
-For small files this may be slower than making a copy of the file.
-Therefore, this setting defaults to 0 which causes a clone operation to
-immediately fail when encountering a dirty block.
+Note that for small files this may be slower than simply copying the file.
+When set to 0 the clone operation will immediately fail if it encounters
+any dirty blocks.
+By default waiting is enabled.
 .
 .It Sy zfs_blake3_impl Ns = Ns Sy fastest Pq string
 Select a BLAKE3 implementation.

module/zfs/zfs_vnops.c

@@ -67,13 +67,14 @@
 int zfs_bclone_enabled = 1;
 
 /*
- * When set zfs_clone_range() waits for dirty data to be written to disk.
- * This allows the clone operation to reliably succeed when a file is modified
- * and then immediately cloned. For small files this may be slower than making
- * a copy of the file and is therefore not the default.  However, in certain
- * scenarios this behavior may be desirable so a tunable is provided.
+ * When set to 1 the FICLONE and FICLONERANGE ioctls will wait for any dirty
+ * data to be written to disk before proceeding. This ensures that the clone
+ * operation reliably succeeds, even if a file is modified and then immediately
+ * cloned. Note that for small files this may be slower than simply copying
+ * the file. When set to 0 the clone operation will immediately fail if it
+ * encounters any dirty blocks. By default waiting is enabled.
  */
-int zfs_bclone_wait_dirty = 0;
+int zfs_bclone_wait_dirty = 1;
 
 /*
  * Enable Direct I/O. If this setting is 0, then all I/O requests will be

tests/zfs-tests/tests/functional/block_cloning/block_cloning_copyfilerange_fallback_same_txg.ksh

@@ -41,16 +41,22 @@ function cleanup
 {
 	datasetexists $TESTPOOL && destroy_pool $TESTPOOL
 	set_tunable64 TXG_TIMEOUT $timeout
+	log_must restore_tunable BCLONE_WAIT_DIRTY
 }
 
 log_onexit cleanup
 
+log_must save_tunable BCLONE_WAIT_DIRTY
+
 log_must set_tunable64 TXG_TIMEOUT 5000
 
 log_must zpool create -o feature@block_cloning=enabled $TESTPOOL $DISKS
 
 log_must sync_pool $TESTPOOL true
 
+# Verify fallback to copy when there are dirty blocks
+log_must set_tunable32 BCLONE_WAIT_DIRTY 0
+
 log_must dd if=/dev/urandom of=/$TESTPOOL/file bs=128K count=4
 log_must clonefile -f /$TESTPOOL/file /$TESTPOOL/clone 0 0 524288
 
@@ -61,5 +67,20 @@ log_must have_same_content /$TESTPOOL/file /$TESTPOOL/clone
 typeset blocks=$(get_same_blocks $TESTPOOL file $TESTPOOL clone)
 log_must [ "$blocks" = "" ]
 
+log_must rm /$TESTPOOL/file /$TESTPOOL/clone
+
+# Verify blocks are cloned even when there are dirty blocks
+log_must set_tunable32 BCLONE_WAIT_DIRTY 1
+
+log_must dd if=/dev/urandom of=/$TESTPOOL/file bs=128K count=4
+log_must clonefile -f /$TESTPOOL/file /$TESTPOOL/clone 0 0 524288
+
+log_must sync_pool $TESTPOOL
+
+log_must have_same_content /$TESTPOOL/file /$TESTPOOL/clone
+
+typeset blocks=$(get_same_blocks $TESTPOOL file $TESTPOOL clone)
+log_must [ "$blocks" = "0 1 2 3" ]
+
 log_pass $claim
 

tests/zfs-tests/tests/functional/cp_files/cp_files_002_pos.ksh

@@ -56,7 +56,7 @@ function cleanup
 {
 	datasetexists $TESTPOOL/cp-reflink && \
 	    destroy_dataset $$TESTPOOL/cp-reflink -f
-	log_must set_tunable32 BCLONE_WAIT_DIRTY 0
+	log_must restore_tunable BCLONE_WAIT_DIRTY
 }
 
 function verify_copy
@@ -81,6 +81,8 @@ SRC_SIZE=$((1024 + $RANDOM % 1024))
 # A smaller recordsize is used merely to speed up the test.
 RECORDSIZE=4096
 
+log_must save_tunable BCLONE_WAIT_DIRTY
+
 log_must zfs create -o recordsize=$RECORDSIZE $TESTPOOL/cp-reflink
 CP_TESTDIR=$(get_prop mountpoint $TESTPOOL/cp-reflink)