linux/copy_file_range: properly request a fallback copy on Linux <5.3

Before Linux 5.3, the filesystem's copy_file_range handler had to signal
back to the kernel that we can't fulfill the request and it should
fallback to a content copy. This is done by returning -EOPNOTSUPP.

This commit converts the EXDEV return from zfs_clone_range to
EOPNOTSUPP, to force the kernel to fallback for all the valid reasons it
might be unable to clone. Without it the copy_file_range() syscall will
return EXDEV to userspace, breaking its semantics.

Add test for copy_file_range fallbacks.  copy_file_range should always
fallback to a content copy whenever ZFS can't service the request with
cloning.

Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Kay Pedersen <mail@mkwg.de>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #15131

module/os/linux/zfs/zpl_file_range.c

@@ -106,6 +106,13 @@ zpl_copy_file_range(struct file *src_file, loff_t src_off,
 	if (ret == -EOPNOTSUPP || ret == -EXDEV)
 		ret = generic_copy_file_range(src_file, src_off, dst_file,
 		    dst_off, len, flags);
+#else
+	/*
+	 * Before Linux 5.3 the filesystem has to return -EOPNOTSUPP to signal
+	 * to the kernel that it should fallback to a content copy.
+	 */
+	if (ret == -EXDEV)
+		ret = -EOPNOTSUPP;
 #endif /* HAVE_VFS_GENERIC_COPY_FILE_RANGE */
 
 	return (ret);

tests/runfiles/linux.run

@@ -36,6 +36,7 @@ tags = ['functional', 'atime']
 
 [tests/functional/block_cloning:Linux]
 tests = ['block_cloning_copyfilerange', 'block_cloning_copyfilerange_partial',
+    'block_cloning_copyfilerange_fallback',
     'block_cloning_ficlone', 'block_cloning_ficlonerange',
     'block_cloning_ficlonerange_partial',
     'block_cloning_disabled_copyfilerange', 'block_cloning_disabled_ficlone',

tests/test-runner/bin/zts-report.py.in

@@ -300,6 +300,8 @@ elif sys.platform.startswith('linux'):
             ['SKIP', cfr_reason],
         'block_cloning/block_cloning_copyfilerange_partial':
             ['SKIP', cfr_reason],
+        'block_cloning/block_cloning_copyfilerange_fallback':
+            ['SKIP', cfr_reason],
         'block_cloning/block_cloning_copyfilerange_cross_dataset':
             ['SKIP', cfr_cross_reason],
     })

tests/zfs-tests/tests/Makefile.am

@@ -443,6 +443,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/block_cloning/block_cloning_copyfilerange_cross_dataset.ksh \
 	functional/block_cloning/block_cloning_copyfilerange.ksh \
 	functional/block_cloning/block_cloning_copyfilerange_partial.ksh \
+	functional/block_cloning/block_cloning_copyfilerange_fallback.ksh \
 	functional/block_cloning/block_cloning_disabled_copyfilerange.ksh \
 	functional/block_cloning/block_cloning_disabled_ficlone.ksh \
 	functional/block_cloning/block_cloning_disabled_ficlonerange.ksh \

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

@@ -0,0 +1,86 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2023, Klara Inc.
+# Copyright (c) 2023, Rob Norris <robn@despairlabs.com>
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/block_cloning/block_cloning.kshlib
+
+verify_runnable "global"
+
+if [[ $(linux_version) -lt $(linux_version "4.5") ]]; then
+  log_unsupported "copy_file_range not available before Linux 4.5"
+fi
+
+claim="copy_file_range will fall back to copy when cloning not possible."
+
+log_assert $claim
+
+function cleanup
+{
+	datasetexists $TESTPOOL && destroy_pool $TESTPOOL
+}
+
+log_onexit cleanup
+
+log_must zpool create -o feature@block_cloning=enabled $TESTPOOL $DISKS
+
+log_must dd if=/dev/urandom of=/$TESTPOOL/file bs=128K count=4
+log_must sync_pool $TESTPOOL
+
+
+log_note "Copying entire file with copy_file_range"
+
+log_must clonefile -f /$TESTPOOL/file /$TESTPOOL/clone 0 0 524288
+log_must sync_pool $TESTPOOL
+
+log_must have_same_content /$TESTPOOL/file /$TESTPOOL/clone
+
+typeset blocks=$(unique_blocks $TESTPOOL file $TESTPOOL clone)
+log_must [ "$blocks" = "1 2 3 4" ]
+
+
+log_note "Copying within a block with copy_file_range"
+
+log_must clonefile -f /$TESTPOOL/file /$TESTPOOL/clone 32768 32768 65536
+log_must sync_pool $TESTPOOL
+
+log_must have_same_content /$TESTPOOL/file /$TESTPOOL/clone
+
+typeset blocks=$(unique_blocks $TESTPOOL file $TESTPOOL clone)
+log_must [ "$blocks" = "2 3 4" ]
+
+
+log_note "Copying across a block with copy_file_range"
+
+log_must clonefile -f /$TESTPOOL/file /$TESTPOOL/clone 327680 327680 131072
+log_must sync_pool $TESTPOOL
+
+log_must have_same_content /$TESTPOOL/file /$TESTPOOL/clone
+
+typeset blocks=$(unique_blocks $TESTPOOL file $TESTPOOL clone)
+log_must [ "$blocks" = "2" ]
+
+log_pass $claim