On Thu, Dec 19, 2024 at 08:43:36PM +0530, Nirjhar Roy wrote:
> On Mon, 2024-12-16 at 18:08 -0800, Catherine Hoang wrote:
> > Add a test to validate the new atomic writes feature.
> >
> > Signed-off-by: Catherine Hoang <catherine.hoang@xxxxxxxxxx>
> > ---
> > common/rc | 14 ++++++++
> > tests/xfs/611 | 81
> > +++++++++++++++++++++++++++++++++++++++++++++++
> > tests/xfs/611.out | 2 ++
> Now that ext4 also has support for block atomic writes, do you think it
> appropritate to put it under generic?
> > 3 files changed, 97 insertions(+)
> > create mode 100755 tests/xfs/611
> > create mode 100644 tests/xfs/611.out
> >
> > diff --git a/common/rc b/common/rc
> > index 2ee46e51..b9da749e 100644
> > --- a/common/rc
> > +++ b/common/rc
> > @@ -5148,6 +5148,20 @@ _require_scratch_btime()
> > _scratch_unmount
> > }
> >
> > +_require_scratch_write_atomic()
> > +{
> > + _require_scratch
> > + _scratch_mkfs > /dev/null 2>&1
> > + _scratch_mount
> Minor: Do we need the _scratch_mount and _scratch_unmount? We can
> directly statx the underlying device too, right?
Yes, we need the scratch fs, because the filesystem might not support
untorn writes even if the underlying block device does. Or it can
decide to constrain the supported io sizes.
> > +
> > + export STATX_WRITE_ATOMIC=0x10000
> > + $XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $SCRATCH_MNT
> > \
> > + | grep atomic >>$seqres.full 2>&1 || \
> > + _notrun "write atomic not supported by this filesystem"
> Are we assuming that the SCRATCH_DEV supports atomic writes here? If
> not, do you think the idea of checking if the underlying device
> supports atomic writes will be appropriate here?
>
> I tried running the test with a loop device (with no atomic writes
> support) and this function did not execute _notrun. The test did fail
> expectedly with "atomic write min 0, should be fs block size 4096".
Oh, yeah, awu_min==awu_max==0 should be an automatic _notrun.
> However, the test shouldn't have begun or reached this stage if the
> underlying device doesn't support atomic writes, right?
_require* helpers decide if the test preconditions have been satisfied,
so this is exactly where the test would bail out.
> Maybe look at how scsi_debug is used? Tests like tests/generic/704 and
> common/scsi_debug?
> > +
> > + _scratch_unmount
> > +}
> > +
> > _require_inode_limits()
> > {
> > if [ $(_get_free_inode $TEST_DIR) -eq 0 ]; then
> > diff --git a/tests/xfs/611 b/tests/xfs/611
> > new file mode 100755
> > index 00000000..a26ec143
> > --- /dev/null
> > +++ b/tests/xfs/611
> > @@ -0,0 +1,81 @@
> > +#! /bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Copyright (c) 2024 Oracle. All Rights Reserved.
> > +#
> > +# FS QA Test 611
> > +#
> > +# Validate atomic write support
> > +#
> > +. ./common/preamble
> > +_begin_fstest auto quick rw
> > +
> > +_supported_fs xfs
> > +_require_scratch
> > +_require_scratch_write_atomic
> > +
> > +test_atomic_writes()
> > +{
> > + local bsize=$1
> > +
> > + _scratch_mkfs_xfs -b size=$bsize >> $seqres.full
> > + _scratch_mount
> > + _xfs_force_bdev data $SCRATCH_MNT
> > +
> > + testfile=$SCRATCH_MNT/testfile
> > + touch $testfile
> > +
> > + file_min_write=$($XFS_IO_PROG -c "statx -r -m
> > $STATX_WRITE_ATOMIC" $testfile | \
> > + grep atomic_write_unit_min | cut -d ' ' -f 3)
> > + file_max_write=$($XFS_IO_PROG -c "statx -r -m
> > $STATX_WRITE_ATOMIC" $testfile | \
> > + grep atomic_write_unit_max | cut -d ' ' -f 3)
> > + file_max_segments=$($XFS_IO_PROG -c "statx -r -m
> > $STATX_WRITE_ATOMIC" $testfile | \
> > + grep atomic_write_segments_max | cut -d ' ' -f 3)
> > +
> Minor: A refactoring suggestion. Can we put the commands to fetch the
> atomic_write_unit_min , atomic_write_unit_max and
> atomic_write_segments_max in a function and re-use them? We are using
> these commands to get bdev_min_write/bdev_max_write as well, so a
> function might make the code look more compact. Some maybe something
> like:
>
> _get_at_wr_unit_min()
Don't reuse another English word ("at") as an abbreviation, please.
_atomic_write_unit_min()
> {
> $XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | grep
> atomic_write_unit_min | \
> grep -o '[0-9]\+'
> }
>
> _get_at_wr_unit_max()
> {
> $XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | grep
> atomic_write_unit_max | \
> grep -o '[0-9]\+'
> }
> and then,
> file_min_write=$(_get_at_wr_unit_min $testfile) and similarly for file_max_write, file_max_segments, bdev_min_write/bdev_max_write
>
>
> > + # Check that atomic min/max = FS block size
> > + test $file_min_write -eq $bsize || \
> > + echo "atomic write min $file_min_write, should be fs block
> > size $bsize"
> > + test $file_min_write -eq $bsize || \
> > + echo "atomic write max $file_max_write, should be fs block
> > size $bsize"
> > + test $file_max_segments -eq 1 || \
> > + echo "atomic write max segments $file_max_segments, should
> > be 1"
> > +
> > + # Check that we can perform an atomic write of len = FS block
> > size
> > + bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D 0 $bsize"
> > $testfile | \
> > + grep wrote | awk -F'[/ ]' '{print $2}')
> is "$XFS_IO_PROG -dc pwrite -A -D 0 $bsize" $testfile actually making a
> pwritev2 syscall?
>
> Let's look at the output below:
> (tested with latest master of xfsprogs-dev (commit 90d6da68) on
> pagesize and block size 4k (x86_64 vm)
>
> mount /dev/sdc /mnt1/test
> touch /mnt1/test/new
> strace -f xfs_io -c "pwrite -A -D 0 4096" /mnt1/test/new
You need to pass -d to xfs_io to get directio mode. The test does that,
but your command line doesn't.
> <last few lines>
> openat(AT_FDCWD, "/mnt1/test/new", O_RDWR) = 3
> ...
> ...
> pwrite64(3,
> "\315\315\315\315\315\315\315\315\315\315\315\315\315\315\315\315\315\3
> 15\315\315\315\315\315\315\315\315\315\315\315\315\315\315"..., 4096,
> 0) = 4096
That seems like a bug though. "pwrite -A -D -V1 0 4096"?
> newfstatat(1, "", {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x1),
> ...}, AT_EMPTY_PATH) = 0
> write(1, "wrote 4096/4096 bytes at offset "..., 34wrote 4096/4096 bytes
> at offset 0
> ) = 34
> write(1, "4 KiB, 1 ops; 0.0001 sec (23.819"..., 644 KiB, 1 ops; 0.0001
> sec (23.819 MiB/sec and 6097.5610 ops/sec)
> ) = 64
> exit_group(0)
>
> So the issues are as follows:
> 1. file /mnt1/test/new is NOT opened with O_DIRECT flag i.e, direct io
> mode which is one of the requirements for atomic write (buffered io
> doesn't support atomic write, correct me if I am wrong).
> 2. pwrite64 doesn't take the RWF_ATOMIC flag and hence I think this
> write is just a non-atomic write with no stdout output difference as
> such.
>
> Also if you look at the function
>
> do_pwrite() in xfsprogs-dev/io/pwrite.c
>
> static ssize_t
> do_pwrite(
> int fd,
> off_t offset,
> long long count,
> size_t buffer_size,
> int pwritev2_flags)
> {
> if (!vectors)
> return pwrite(fd, io_buffer, min(count, buffer_size),
> offset);
>
> return do_pwritev(fd, offset, count, pwritev2_flags);
> }
>
> it will not call pwritev/pwritev2 unless we have vectors for which you
> will need -V parameter with pwrite subcommand of xfs_io.
>
>
> So I think the correct way to do this would be the following:
>
> bytes_written=$($XFS_IO_PROGS -c "open -d $testfile" -c "pwrite -A -D
> -V 1 0 $bsize" | grep wrote | awk -F'[/ ]' '{print $2}').
Agreed.
> This also bring us to 2 more test cases that we can add:
>
> a. Atomic write with vec count > 1
> $XFS_IO_PROGS -c "open -d $testfile" -c "pwrite -A -D -V 2 0 $bsize"
> (This should fail with Invalid argument since currently iovec count is
> restricted to 1)
>
> b.
> Open a file withOUT O_DIRECT and try to perform an atomic write. This
> should fail with Operation not Supported (EOPNOTSUPP). So something
> like
> $XFS_IO_PROGS -c "open -f $testfile" -c "pwrite -A -V 1 0 $bsize"
Yeah, those are good subcases.
> 3. It is better to use -b $bsize with pwrite else, the write might be
> spilitted into multiple atomic writes. For example try the following:
>
> $XFS_IO_PROGS -c "open -fd $testfile" -c "pwrite -A -D -V 1 0 $((
> $bsize * 2 ))"
> The above is expected to fail as the size of the atomic write is
> greater than the limit i.e, 1 block but it will still succeed. Look at
> the strace and you will see 2 pwritev2 system calls. However the
> following will fail expectedly with -EINVAL:
> $XFS_IO_PROGS -c "open -fd $testfile" -c "pwrite -A -D -V 1 -b $((
> $bsize * 2 )) 0 $(( $bsize * 2 ))"
Good catch.
>
>
>
> > + test $bytes_written -eq $bsize || echo "atomic write len=$bsize
> > failed"
> > +
> > + # Check that we can perform an atomic write on an unwritten
> > block
> > + $XFS_IO_PROG -c "falloc $bsize $bsize" $testfile
> > + bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D $bsize $bsize"
> > $testfile | \
> > + grep wrote | awk -F'[/ ]' '{print $2}')
> > + test $bytes_written -eq $bsize || echo "atomic write to
> > unwritten block failed"
> > +
> > + # Check that we can perform an atomic write on a sparse hole
> > + $XFS_IO_PROG -c "fpunch 0 $bsize" $testfile
> > + bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D 0 $bsize"
> > $testfile | \
> > + grep wrote | awk -F'[/ ]' '{print $2}')
> > + test $bytes_written -eq $bsize || echo "atomic write to sparse
> > hole failed"
> > +
> > + # Reject atomic write if len is out of bounds
> > + $XFS_IO_PROG -dc "pwrite -A -D 0 $((bsize - 1))" $testfile 2>>
> > $seqres.full && \
> > + echo "atomic write len=$((bsize - 1)) should fail"
> > + $XFS_IO_PROG -dc "pwrite -A -D 0 $((bsize + 1))" $testfile 2>>
> > $seqres.full && \
> > + echo "atomic write len=$((bsize + 1)) should fail"
> Have we covered the scenario where the offset % len != 0 Should fail -
> Should fail with Invalid arguments -EINVAL.
I think you're right.
> Also do you think adding similar tests with raw writes to the
> underlying devices bypassing the fs layer will add some value? There
> are slight less strict or different rules in the block layer which IMO
> worth to be tested. Please let me know your thoughts.
That should be in blktests.
> > +
> > + _scratch_unmount
> > +}
> > +
> > +bdev_min_write=$($XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC"
> > $SCRATCH_DEV | \
> > + grep atomic_write_unit_min | cut -d ' ' -f 3)
> > +bdev_max_write=$($XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC"
> > $SCRATCH_DEV | \
> > + grep atomic_write_unit_max | cut -d ' ' -f 3)
> > +
> Similar comment before - Refactor this into a function.
> > +for ((bsize=$bdev_min_write; bsize<=bdev_max_write; bsize*=2)); do
> > + _scratch_mkfs_xfs_supported -b size=$bsize >> $seqres.full 2>&1
> > && \
> > + test_atomic_writes $bsize
> > +done;
> Minor: This might fail on some archs(x86_64) if the kernel isn't
> compiled without CONFIG_TRANSPARENT_HUGEPAGE to enable block size
> greater than 4k on x86_64.
Oh, yeah, that's a good catch.
--D
>
> --
> NR
> > +
> > +# success, all done
> > +echo Silence is golden
> > +status=0
> > +exit
> > diff --git a/tests/xfs/611.out b/tests/xfs/611.out
> > new file mode 100644
> > index 00000000..b8a44164
> > --- /dev/null
> > +++ b/tests/xfs/611.out
> > @@ -0,0 +1,2 @@
> > +QA output created by 611
> > +Silence is golden
>
>
