generic: test for seeing unseen fsync errors on newly open files

This adds a regression test for the following kernel patch:

    b4678df184b3 ("errseq: Always report a writeback error once")

This is motivated by some rather odd behavior done by the PostgreSQL
project. The main database writers will offload the fsync calls to a
separate process, which can open files after a writeback error has
already occurred.

This used to work with older kernels that reported the error to only
one fd, but with the errseq_t changes we lost the ability to see
errors that occurred before the open. The above patch restores that
behavior.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/487

@@ -0,0 +1,104 @@
+#! /bin/bash
+# FS QA Test No. 487
+#
+# Open a file several times, write to it, fsync on all fds and make sure that
+# they all return 0. Change the device to start throwing errors. Write again
+# on all fds and fsync on all fds. Ensure that we get errors on all of them.
+# Then fsync on all one last time and verify that all return 0.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2018, Jeff Layton <jlayton@redhat.com>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+
+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.*
+	_dmerror_cleanup
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/dmerror
+
+# real QA test starts here
+_supported_os Linux
+_require_scratch_nocheck
+# This test uses "dm" without taking into account the data could be on
+# realtime subvolume, thus the test will fail with rtinherit=1
+_require_no_rtinherit
+_require_logdev
+
+sflag='-s'
+case $FSTYP in
+        btrfs)
+                _notrun "btrfs has a specialized test for this"
+                ;;
+        *)
+                ;;
+esac
+
+_require_dm_target error
+
+rm -f $seqres.full
+
+echo "Format and mount"
+_scratch_mkfs > $seqres.full 2>&1
+_dmerror_init
+_dmerror_mount
+
+datalen=65536
+_require_fs_space $SCRATCH_MNT $datalen
+
+# use fd 5 to hold file open
+testfile=$SCRATCH_MNT/fsync-open-after-err
+exec 5>$testfile
+
+# write some data to file and fsync it out
+$XFS_IO_PROG -c "pwrite -q 0 $datalen" -c fsync $testfile
+
+# flip device to non-working mode
+_dmerror_load_error_table
+
+# rewrite the data, call sync to ensure it's written back w/o scraping error
+$XFS_IO_PROG -c "pwrite -q 0 $datalen" -c sync $testfile
+
+# heal the device error
+_dmerror_load_working_table
+
+# open again and call fsync
+echo "The following fsync should fail with EIO:"
+$XFS_IO_PROG -c fsync $testfile
+echo "done"
+
+# close file
+exec 5>&-
+
+# success, all done
+_dmerror_cleanup
+
+status=0
+exit

tests/generic/487.out

@@ -0,0 +1,5 @@
+QA output created by 487
+Format and mount
+The following fsync should fail with EIO:
+fsync: Input/output error
+done

tests/generic/group

@@ -489,3 +489,4 @@
 484 auto quick
 485 auto quick insert
 486 auto quick attr
+487 auto quick