File incorrectly zeroed when receiving incremental stream that toggles -L

Background:

By increasing the recordsize property above the default of 128KB, a
filesystem may have "large" blocks.  By default, a send stream of such a
filesystem does not contain large WRITE records, instead it decreases
objects' block sizes to 128KB and splits the large blocks into 128KB
blocks, allowing the large-block filesystem to be received by a system
that does not support the `large_blocks` feature.  A send stream
generated by `zfs send -L` (or `--large-block`) preserves the large
block size on the receiving system, by using large WRITE records.

When receiving an incremental send stream for a filesystem with large
blocks, if the send stream's -L flag was toggled, a bug is encountered
in which the file's contents are incorrectly zeroed out.  The contents
of any blocks that were not modified by this send stream will be lost.
"Toggled" means that the previous send used `-L`, but this incremental
does not use `-L` (-L to no-L); or that the previous send did not use
`-L`, but this incremental does use `-L` (no-L to -L).

Changes:

This commit addresses the problem with several changes to the semantics
of zfs send/receive:

1. "-L to no-L" incrementals are rejected.  If the previous send used
`-L`, but this incremental does not use `-L`, the `zfs receive` will
fail with this error message:

    incremental send stream requires -L (--large-block), to match
    previous receive.

2. "no-L to -L" incrementals are handled correctly, preserving the
smaller (128KB) block size of any already-received files that used large
blocks on the sending system but were split by `zfs send` without the
`-L` flag.

3. A new send stream format flag is added, `SWITCH_TO_LARGE_BLOCKS`.
This feature indicates that we can correctly handle "no-L to -L"
incrementals.  This flag is currently not set on any send streams.  In
the future, we intend for incremental send streams of snapshots that
have large blocks to use `-L` by default, and these streams will also
have the `SWITCH_TO_LARGE_BLOCKS` feature set. This ensures that streams
from the default use of `zfs send` won't encounter the bug mentioned
above, because they can't be received by software with the bug.

Implementation notes:

To facilitate accessing the ZPL's generation number,
`zfs_space_delta_cb()` has been renamed to `zpl_get_file_info()` and
restructured to fill in a struct with ZPL-specific info including owner
and generation.

In the "no-L to -L" case, if this is a compressed send stream (from
`zfs send -cL`), large WRITE records that are being written to small
(128KB) blocksize files need to be decompressed so that they can be
written split up into multiple blocks.  The zio pipeline will recompress
each smaller block individually.

A new test case, `send-L_toggle`, is added, which tests the "no-L to -L"
case and verifies that we get an error for the "-L to no-L" case.

Reviewed-by: Paul Dagnelie <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Matthew Ahrens <[email protected]>
Closes #6224 
Closes #10383 

3 files changed, 67 insertions, 1 deletions

diff --git a/tests/runfiles/common.run b/tests/runfiles/common.run
index cbad90ad1..d8c109eb7 100644
--- a/tests/runfiles/common.run
+++ b/tests/runfiles/common.run
@@ -781,7 +781,7 @@ tests = ['recv_dedup', 'recv_dedup_encrypted_zvol', 'rsend_001_pos',
     'send-c_lz4_disabled', 'send-c_recv_lz4_disabled',
     'send-c_mixed_compression', 'send-c_stream_size_estimate',
     'send-c_embedded_blocks', 'send-c_resume', 'send-cpL_varied_recsize',
-    'send-c_recv_dedup', 'send_encrypted_hierarchy',
+    'send-c_recv_dedup', 'send-L_toggle', 'send_encrypted_hierarchy',
     'send_encrypted_props', 'send_encrypted_truncated_files',
     'send_freeobjects', 'send_realloc_files',
     'send_realloc_encrypted_files', 'send_spill_block', 'send_holds',
diff --git a/tests/zfs-tests/tests/functional/rsend/Makefile.am b/tests/zfs-tests/tests/functional/rsend/Makefile.am
index 7728a6481..ab3a1c6c3 100644
--- a/tests/zfs-tests/tests/functional/rsend/Makefile.am
+++ b/tests/zfs-tests/tests/functional/rsend/Makefile.am
@@ -41,6 +41,7 @@ dist_pkgdata_SCRIPTS = \
 	send-c_volume.ksh \
 	send-c_zstreamdump.ksh \
 	send-cpL_varied_recsize.ksh \
+	send-L_toggle.ksh \
 	send_freeobjects.ksh \
 	send_partial_dataset.ksh \
 	send_realloc_dnode_size.ksh \
diff --git a/tests/zfs-tests/tests/functional/rsend/send-L_toggle.ksh b/tests/zfs-tests/tests/functional/rsend/send-L_toggle.ksh
new file mode 100755
index 000000000..483efcc60
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/rsend/send-L_toggle.ksh
@@ -0,0 +1,65 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2020 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/rsend/rsend.kshlib
+
+#
+# Description:
+# Verify that send -L can be changed to on in an incremental.
+# Verify that send -L can not be turned off in an incremental.
+#
+
+function cleanup
+{
+	log_must_busy zfs destroy -r $TESTPOOL/fs
+	log_must_busy zfs destroy -r $TESTPOOL/recv
+}
+
+verify_runnable "both"
+
+log_assert "Verify toggling send -L works as expected"
+log_onexit cleanup
+
+log_must zfs create -o compression=on -o recordsize=1m $TESTPOOL/fs
+
+log_must dd if=/dev/urandom of=/$TESTPOOL/fs/file bs=1024 count=1500
+
+log_must zfs snapshot $TESTPOOL/fs@snap
+
+log_must dd if=/dev/urandom of=/$TESTPOOL/fs/file bs=1024 count=1500 conv=notrunc seek=2048
+
+log_must zfs snapshot $TESTPOOL/fs@snap2
+
+log_must zfs create $TESTPOOL/recv
+
+log_must zfs send -c $TESTPOOL/fs@snap | zfs recv $TESTPOOL/recv/noL-noL
+log_must zfs send -c -i @snap $TESTPOOL/fs@snap2| zfs recv $TESTPOOL/recv/noL-noL
+log_must diff /$TESTPOOL/fs/file /$TESTPOOL/recv/noL-noL/file
+
+log_must zfs send -c -L $TESTPOOL/fs@snap | zfs recv $TESTPOOL/recv/L-L
+log_must zfs send -c -L -i @snap $TESTPOOL/fs@snap2 | zfs recv $TESTPOOL/recv/L-L
+log_must diff /$TESTPOOL/fs/file /$TESTPOOL/recv/L-L/file
+
+log_must zfs send -c $TESTPOOL/fs@snap | zfs recv $TESTPOOL/recv/noL-L
+log_must zfs send -c -L -i @snap $TESTPOOL/fs@snap2 | zfs recv $TESTPOOL/recv/noL-L
+log_must diff /$TESTPOOL/fs/file /$TESTPOOL/recv/noL-L/file
+
+log_must zfs send -c -L $TESTPOOL/fs@snap | zfs recv $TESTPOOL/recv/L-noL
+log_mustnot zfs send -c -i @snap $TESTPOOL/fs@snap2 | zfs recv $TESTPOOL/recv/L-noL
+log_must diff /$TESTPOOL/fs/.zfs/snapshot/snap/file /$TESTPOOL/recv/L-noL/file
+
+log_pass "Verify toggling send -L works as expected"