[PATCH v3] generic: test fiemap offsets and < 512 byte ranges

[Boris Burkov <boris@bur.io>]

btrfs trims fiemap extents to the inputted offset, which leads to
inconsistent results for most inputs, and downright bizarre outputs like
[7..6] when the trimmed extent is at the end of an extent and shorter
than 512 bytes.

The test writes out one extent of the file system's block size and tries
fiemaps at various offsets. It expects that all the fiemaps return the
full single extent.

I ran it under the following fs, block size combinations:
ext2: 1024, 2048, 4096
ext3: 1024, 2048, 4096
ext4: 1024, 2048, 4096
xfs: 512, 1024, 2048, 4096
f2fs: 4096
btrfs: 4096

This test is fixed for btrfs by:
btrfs: return whole extents in fiemap
(https://lore.kernel.org/linux-btrfs/274e5bcebdb05a8969fc300b4802f33da2fbf218.1617746680.git.boris@bur.io/)

Signed-off-by: Boris Burkov <boris@bur.io>
---
v3: make the block size more generic, use test dev instead of scratch,
cleanup style issues.
v2: fill out copyright and test description
---
 tests/generic/623     | 94 +++++++++++++++++++++++++++++++++++++++++++
 tests/generic/623.out |  2 +
 tests/generic/group   |  1 +
 3 files changed, 97 insertions(+)
 create mode 100755 tests/generic/623
 create mode 100644 tests/generic/623.out

diff --git a/tests/generic/623 b/tests/generic/623
new file mode 100755
index 00000000..a5ef369a
--- /dev/null
+++ b/tests/generic/623
@@ -0,0 +1,94 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Facebook.  All Rights Reserved.
+#
+# FS QA Test 623
+#
+# Test fiemaps with offsets into small parts of extents.
+# Expect to get the whole extent, anyway.
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	rm -f $fiemap_file
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_require_test
+_require_xfs_io_command "fiemap"
+
+rm -f $seqres.full
+
+fiemap_file=$TEST_DIR/foo.$$
+
+do_fiemap() {
+	off=$1
+	len=$2
+	echo $off $len >> $seqres.full
+	$XFS_IO_PROG -c "fiemap $off $len" $fiemap_file | tee -a $seqres.full
+}
+
+check_fiemap() {
+	off=$1
+	len=$2
+	actual=$(do_fiemap $off $len)
+	[ "$actual" == "$expected" ] || _fail "unexpected fiemap on $off $len"
+}
+
+# write a file with one extent
+block_size=$(_get_block_size $TEST_DIR)
+$XFS_IO_PROG -f -s -c "pwrite -S 0xcf 0 $block_size" $fiemap_file >/dev/null
+
+# since the exact extent location is unpredictable especially when
+# varying file systems, just test that they are all equal, which is
+# what we really expect.
+expected=$(do_fiemap)
+
+mid=$((block_size / 2))
+almost=$((block_size - 5))
+past=$((block_size + 1))
+
+check_fiemap 0 $mid
+check_fiemap 0 $block_size
+check_fiemap 0 $past
+check_fiemap $mid $almost
+check_fiemap $mid $block_size
+check_fiemap $mid $past
+check_fiemap $almost 5
+check_fiemap $almost 6
+
+# fiemap output explicitly deals in 512 byte increments,
+# so exercise some cases where len is 512.
+# Naturally, some of these can't work if block size is 512.
+one_short=$((block_size - 512))
+check_fiemap 0 512
+check_fiemap $one_short 512
+check_fiemap $almost 512
+
+_test_unmount
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit
diff --git a/tests/generic/623.out b/tests/generic/623.out
new file mode 100644
index 00000000..6f774f19
--- /dev/null
+++ b/tests/generic/623.out
@@ -0,0 +1,2 @@
+QA output created by 623
+Silence is golden
diff --git a/tests/generic/group b/tests/generic/group
index b10fdea4..39e02383 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -625,3 +625,4 @@
 620 auto mount quick
 621 auto quick encrypt
 622 auto shutdown metadata atime
+623 auto quick
-- 
2.30.2