[PATCH v5] generic: add a test for atomic writes

[PATCH v5] generic: add a test for atomic writes

[Catherine Hoang]

Add a test to validate the new atomic writes feature.

Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Reviewed-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
---
 common/rc             |  51 ++++++++++++
 tests/generic/765     | 188 ++++++++++++++++++++++++++++++++++++++++++
 tests/generic/765.out |   2 +
 3 files changed, 241 insertions(+)
 create mode 100755 tests/generic/765
 create mode 100644 tests/generic/765.out

diff --git a/common/rc b/common/rc
index 16d627e1..25e6a1f7 100644
--- a/common/rc
+++ b/common/rc
@@ -2996,6 +2996,10 @@ _require_xfs_io_command()
 			opts+=" -d"
 			pwrite_opts+="-V 1 -b 4k"
 		fi
+		if [ "$param" == "-A" ]; then
+			opts+=" -d"
+			pwrite_opts+="-D -V 1 -b 4k"
+		fi
 		testio=`$XFS_IO_PROG -f $opts -c \
 		        "pwrite $pwrite_opts $param 0 4k" $testfile 2>&1`
 		param_checked="$pwrite_opts $param"
@@ -5443,6 +5447,53 @@ _require_scratch_btime()
 	_scratch_unmount
 }
 
+_get_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_atomic_write_unit_max()
+{
+	$XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | \
+        grep atomic_write_unit_max | grep -o '[0-9]\+'
+}
+
+_get_atomic_write_segments_max()
+{
+	$XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | \
+        grep atomic_write_segments_max | grep -o '[0-9]\+'
+}
+
+_require_scratch_write_atomic()
+{
+	_require_scratch
+
+	export STATX_WRITE_ATOMIC=0x10000
+
+	awu_min_bdev=$(_get_atomic_write_unit_min $SCRATCH_DEV)
+	awu_max_bdev=$(_get_atomic_write_unit_max $SCRATCH_DEV)
+
+	if [ $awu_min_bdev -eq 0 ] && [ $awu_max_bdev -eq 0 ]; then
+		_notrun "write atomic not supported by this block device"
+	fi
+
+	_scratch_mkfs > /dev/null 2>&1
+	_scratch_mount
+
+	testfile=$SCRATCH_MNT/testfile
+	touch $testfile
+
+	awu_min_fs=$(_get_atomic_write_unit_min $testfile)
+	awu_max_fs=$(_get_atomic_write_unit_max $testfile)
+
+	_scratch_unmount
+
+	if [ $awu_min_fs -eq 0 ] && [ $awu_max_fs -eq 0 ]; then
+		_notrun "write atomic not supported by this filesystem"
+	fi
+}
+
 _require_inode_limits()
 {
 	if [ $(_get_free_inode $TEST_DIR) -eq 0 ]; then
diff --git a/tests/generic/765 b/tests/generic/765
new file mode 100755
index 00000000..9bab3b8a
--- /dev/null
+++ b/tests/generic/765
@@ -0,0 +1,188 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2025 Oracle.  All Rights Reserved.
+#
+# FS QA Test 765
+#
+# Validate atomic write support
+#
+. ./common/preamble
+_begin_fstest auto quick rw
+
+_require_scratch_write_atomic
+_require_xfs_io_command pwrite -A
+
+get_supported_bsize()
+{
+    case "$FSTYP" in
+    "xfs")
+        min_bsize=1024
+        for ((i = 65536; i >= 1024; i /= 2)); do
+            _scratch_mkfs -b size=$i >> $seqres.full || continue
+            if _try_scratch_mount >> $seqres.full 2>&1; then
+                max_bsize=$i
+                _scratch_unmount
+                break;
+            fi
+        done
+        ;;
+    "ext4")
+        min_bsize=1024
+        max_bsize=4096
+        ;;
+    *)
+        _notrun "$FSTYP does not support atomic writes"
+        ;;
+    esac
+}
+
+get_mkfs_opts()
+{
+    local bsize=$1
+
+    case "$FSTYP" in
+    "xfs")
+        mkfs_opts="-b size=$bsize"
+        ;;
+    "ext4")
+        mkfs_opts="-b $bsize"
+        ;;
+    *)
+        _notrun "$FSTYP does not support atomic writes"
+        ;;
+    esac
+}
+
+test_atomic_writes()
+{
+    local bsize=$1
+
+    get_mkfs_opts $bsize
+    _scratch_mkfs $mkfs_opts >> $seqres.full
+    _scratch_mount
+
+    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT
+
+    testfile=$SCRATCH_MNT/testfile
+    touch $testfile
+
+    file_min_write=$(_get_atomic_write_unit_min $testfile)
+    file_max_write=$(_get_atomic_write_unit_max $testfile)
+    file_max_segments=$(_get_atomic_write_segments_max $testfile)
+
+    # 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 -V1 -b $bsize 0 $bsize" $testfile | \
+        grep wrote | awk -F'[/ ]' '{print $2}')
+    test $bytes_written -eq $bsize || echo "atomic write len=$bsize failed"
+
+    # Check that we can perform an atomic single-block cow write
+    if [ "$FSTYP" == "xfs" ]; then
+        testfile_cp=$SCRATCH_MNT/testfile_copy
+        if _xfs_has_feature $SCRATCH_MNT reflink; then
+            cp --reflink $testfile $testfile_cp
+        fi
+        bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile_cp | \
+            grep wrote | awk -F'[/ ]' '{print $2}')
+        test $bytes_written -eq $bsize || echo "atomic write on reflinked file failed"
+    fi
+
+    # 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 -V1 -b $bsize $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 -V1 -b $bsize 0 $bsize" $testfile | \
+        grep wrote | awk -F'[/ ]' '{print $2}')
+    test $bytes_written -eq $bsize || echo "atomic write to sparse hole failed"
+
+    # Check that we can perform an atomic write on a fully mapped block
+    bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile | \
+        grep wrote | awk -F'[/ ]' '{print $2}')
+    test $bytes_written -eq $bsize || echo "atomic write to mapped block failed"
+
+    # Reject atomic write if len is out of bounds
+    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize - 1))" $testfile 2>> $seqres.full && \
+        echo "atomic write len=$((bsize - 1)) should fail"
+    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize + 1))" $testfile 2>> $seqres.full && \
+        echo "atomic write len=$((bsize + 1)) should fail"
+
+    # Reject atomic write when iovecs > 1
+    $XFS_IO_PROG -dc "pwrite -A -D -V2 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
+        echo "atomic write only supports iovec count of 1"
+
+    # Reject atomic write when not using direct I/O
+    $XFS_IO_PROG -c "pwrite -A -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
+        echo "atomic write requires direct I/O"
+
+    # Reject atomic write when offset % bsize != 0
+    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 1 $bsize" $testfile 2>> $seqres.full && \
+        echo "atomic write requires offset to be aligned to bsize"
+
+    _scratch_unmount
+}
+
+test_atomic_write_bounds()
+{
+    local bsize=$1
+
+    get_mkfs_opts $bsize
+    _scratch_mkfs $mkfs_opts >> $seqres.full
+    _scratch_mount
+
+    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT
+
+    testfile=$SCRATCH_MNT/testfile
+    touch $testfile
+
+    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
+        echo "atomic write should fail when bsize is out of bounds"
+
+    _scratch_unmount
+}
+
+sys_min_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_min_bytes")
+sys_max_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_max_bytes")
+
+bdev_min_write=$(_get_atomic_write_unit_min $SCRATCH_DEV)
+bdev_max_write=$(_get_atomic_write_unit_max $SCRATCH_DEV)
+
+# Test that statx atomic values are the same as sysfs values
+if [ "$sys_min_write" -ne "$bdev_min_write" ]; then
+    echo "bdev min write != sys min write"
+fi
+if [ "$sys_max_write" -ne "$bdev_max_write" ]; then
+    echo "bdev max write != sys max write"
+fi
+
+get_supported_bsize
+
+# Test all supported block sizes between bdev min and max
+for ((bsize=$bdev_min_write; bsize<=bdev_max_write; bsize*=2)); do
+    if [ "$bsize" -ge "$min_bsize" ] && [ "$bsize" -le "$max_bsize" ]; then
+        test_atomic_writes $bsize
+    fi
+done;
+
+# Check that atomic write fails if bsize < bdev min or bsize > bdev max
+if [ $((bdev_min_write / 2)) -ge "$min_bsize" ]; then
+    test_atomic_write_bounds $((bdev_min_write / 2))
+fi
+if [ $((bdev_max_write * 2)) -le "$max_bsize" ]; then
+    test_atomic_write_bounds $((bdev_max_write * 2))
+fi
+
+# success, all done
+echo Silence is golden
+status=0
+exit
diff --git a/tests/generic/765.out b/tests/generic/765.out
new file mode 100644
index 00000000..39c254ae
--- /dev/null
+++ b/tests/generic/765.out
@@ -0,0 +1,2 @@
+QA output created by 765
+Silence is golden
-- 
2.34.1

Re: [PATCH v5] generic: add a test for atomic writes

[Ritesh Harjani]

Catherine Hoang <catherine.hoang@oracle.com> writes:

> Add a test to validate the new atomic writes feature.
>
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> Reviewed-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
> Reviewed-by: John Garry <john.g.garry@oracle.com>
> ---
>  common/rc             |  51 ++++++++++++
>  tests/generic/765     | 188 ++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/765.out |   2 +
>  3 files changed, 241 insertions(+)
>  create mode 100755 tests/generic/765
>  create mode 100644 tests/generic/765.out
>
> diff --git a/common/rc b/common/rc
> index 16d627e1..25e6a1f7 100644
> --- a/common/rc
> +++ b/common/rc
> @@ -2996,6 +2996,10 @@ _require_xfs_io_command()
>  			opts+=" -d"
>  			pwrite_opts+="-V 1 -b 4k"
>  		fi
> +		if [ "$param" == "-A" ]; then
> +			opts+=" -d"
> +			pwrite_opts+="-D -V 1 -b 4k"

It's not strictly required for -A to also have -D in pwrite_opts.
We might need to add tests later where we would like to test data
integrity tests with atomic writes, correct? 

So do we really need to add pwrite_opts with -D too?  IMO, we can drop
-D, as the test here suggests that -A can only work with the options
specified in pwrite_opts.

> +		fi
>  		testio=`$XFS_IO_PROG -f $opts -c \
>  		        "pwrite $pwrite_opts $param 0 4k" $testfile 2>&1`
>  		param_checked="$pwrite_opts $param"
> @@ -5443,6 +5447,53 @@ _require_scratch_btime()
>  	_scratch_unmount
>  }
>  
> +_get_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_atomic_write_unit_max()
> +{
> +	$XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | \
> +        grep atomic_write_unit_max | grep -o '[0-9]\+'
> +}
> +
> +_get_atomic_write_segments_max()
> +{
> +	$XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | \
> +        grep atomic_write_segments_max | grep -o '[0-9]\+'
> +}
> +
> +_require_scratch_write_atomic()
> +{
> +	_require_scratch
> +
> +	export STATX_WRITE_ATOMIC=0x10000
> +
> +	awu_min_bdev=$(_get_atomic_write_unit_min $SCRATCH_DEV)
> +	awu_max_bdev=$(_get_atomic_write_unit_max $SCRATCH_DEV)
> +
> +	if [ $awu_min_bdev -eq 0 ] && [ $awu_max_bdev -eq 0 ]; then
> +		_notrun "write atomic not supported by this block device"
> +	fi
> +
> +	_scratch_mkfs > /dev/null 2>&1
> +	_scratch_mount
> +
> +	testfile=$SCRATCH_MNT/testfile
> +	touch $testfile
> +
> +	awu_min_fs=$(_get_atomic_write_unit_min $testfile)
> +	awu_max_fs=$(_get_atomic_write_unit_max $testfile)
> +
> +	_scratch_unmount
> +
> +	if [ $awu_min_fs -eq 0 ] && [ $awu_max_fs -eq 0 ]; then
> +		_notrun "write atomic not supported by this filesystem"
> +	fi
> +}
> +
>  _require_inode_limits()
>  {
>  	if [ $(_get_free_inode $TEST_DIR) -eq 0 ]; then
> diff --git a/tests/generic/765 b/tests/generic/765
> new file mode 100755
> index 00000000..9bab3b8a
> --- /dev/null
> +++ b/tests/generic/765
> @@ -0,0 +1,188 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2025 Oracle.  All Rights Reserved.
> +#
> +# FS QA Test 765
> +#
> +# Validate atomic write support
> +#
> +. ./common/preamble
> +_begin_fstest auto quick rw
> +
> +_require_scratch_write_atomic
> +_require_xfs_io_command pwrite -A
> +
> +get_supported_bsize()
> +{
> +    case "$FSTYP" in
> +    "xfs")
> +        min_bsize=1024
> +        for ((i = 65536; i >= 1024; i /= 2)); do
> +            _scratch_mkfs -b size=$i >> $seqres.full || continue
> +            if _try_scratch_mount >> $seqres.full 2>&1; then
> +                max_bsize=$i
> +                _scratch_unmount
> +                break;
> +            fi
> +        done
> +        ;;
> +    "ext4")
> +        min_bsize=1024
> +        max_bsize=4096

Shouldn't we keep max_bsize as system's pagesize? For systems with 64k
pagesize max_bsize can be 64k.

max_bsize=$(_get_page_size)

> +        ;;
> +    *)
> +        _notrun "$FSTYP does not support atomic writes"
> +        ;;
> +    esac
> +}
> +
> +get_mkfs_opts()
> +{
> +    local bsize=$1
> +
> +    case "$FSTYP" in
> +    "xfs")
> +        mkfs_opts="-b size=$bsize"
> +        ;;
> +    "ext4")
> +        mkfs_opts="-b $bsize"
> +        ;;
> +    *)
> +        _notrun "$FSTYP does not support atomic writes"
> +        ;;
> +    esac
> +}
> +
> +test_atomic_writes()
> +{
> +    local bsize=$1
> +
> +    get_mkfs_opts $bsize
> +    _scratch_mkfs $mkfs_opts >> $seqres.full
> +    _scratch_mount
> +
> +    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT

Ok, this (_xfs_force_bdev()) clears the rtinherit flag on $SCRATCH_MNT
in case if someone is passing that in MKFS_OPTIONS right? But since we
are using our own mkfs_opts, then do we still need this?


> +
> +    testfile=$SCRATCH_MNT/testfile
> +    touch $testfile
> +
> +    file_min_write=$(_get_atomic_write_unit_min $testfile)
> +    file_max_write=$(_get_atomic_write_unit_max $testfile)
> +    file_max_segments=$(_get_atomic_write_segments_max $testfile)
> +
> +    # 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 || \

we should check for $file_max_write here ^^

> +        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 -V1 -b $bsize 0 $bsize" $testfile | \
> +        grep wrote | awk -F'[/ ]' '{print $2}')
> +    test $bytes_written -eq $bsize || echo "atomic write len=$bsize failed"
> +
> +    # Check that we can perform an atomic single-block cow write
> +    if [ "$FSTYP" == "xfs" ]; then
> +        testfile_cp=$SCRATCH_MNT/testfile_copy
> +        if _xfs_has_feature $SCRATCH_MNT reflink; then
> +            cp --reflink $testfile $testfile_cp
> +        fi
> +        bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile_cp | \
> +            grep wrote | awk -F'[/ ]' '{print $2}')
> +        test $bytes_written -eq $bsize || echo "atomic write on reflinked file failed"
> +    fi
> +
> +    # 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 -V1 -b $bsize $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 -V1 -b $bsize 0 $bsize" $testfile | \
> +        grep wrote | awk -F'[/ ]' '{print $2}')
> +    test $bytes_written -eq $bsize || echo "atomic write to sparse hole failed"
> +
> +    # Check that we can perform an atomic write on a fully mapped block
> +    bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile | \
> +        grep wrote | awk -F'[/ ]' '{print $2}')
> +    test $bytes_written -eq $bsize || echo "atomic write to mapped block failed"
> +
> +    # Reject atomic write if len is out of bounds
> +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize - 1))" $testfile 2>> $seqres.full && \
> +        echo "atomic write len=$((bsize - 1)) should fail"
> +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize + 1))" $testfile 2>> $seqres.full && \
> +        echo "atomic write len=$((bsize + 1)) should fail"
> +
> +    # Reject atomic write when iovecs > 1
> +    $XFS_IO_PROG -dc "pwrite -A -D -V2 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> +        echo "atomic write only supports iovec count of 1"
> +
> +    # Reject atomic write when not using direct I/O
> +    $XFS_IO_PROG -c "pwrite -A -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> +        echo "atomic write requires direct I/O"
> +
> +    # Reject atomic write when offset % bsize != 0
> +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 1 $bsize" $testfile 2>> $seqres.full && \
> +        echo "atomic write requires offset to be aligned to bsize"
> +
> +    _scratch_unmount
> +}
> +
> +test_atomic_write_bounds()
> +{
> +    local bsize=$1
> +
> +    get_mkfs_opts $bsize
> +    _scratch_mkfs $mkfs_opts >> $seqres.full
> +    _scratch_mount
> +
> +    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT

ditto

-ritesh

> +
> +    testfile=$SCRATCH_MNT/testfile
> +    touch $testfile
> +
> +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> +        echo "atomic write should fail when bsize is out of bounds"
> +
> +    _scratch_unmount
> +}
> +
> +sys_min_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_min_bytes")
> +sys_max_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_max_bytes")
> +
> +bdev_min_write=$(_get_atomic_write_unit_min $SCRATCH_DEV)
> +bdev_max_write=$(_get_atomic_write_unit_max $SCRATCH_DEV)
> +
> +# Test that statx atomic values are the same as sysfs values
> +if [ "$sys_min_write" -ne "$bdev_min_write" ]; then
> +    echo "bdev min write != sys min write"
> +fi
> +if [ "$sys_max_write" -ne "$bdev_max_write" ]; then
> +    echo "bdev max write != sys max write"
> +fi
> +
> +get_supported_bsize
> +
> +# Test all supported block sizes between bdev min and max
> +for ((bsize=$bdev_min_write; bsize<=bdev_max_write; bsize*=2)); do
> +    if [ "$bsize" -ge "$min_bsize" ] && [ "$bsize" -le "$max_bsize" ]; then
> +        test_atomic_writes $bsize
> +    fi
> +done;
> +
> +# Check that atomic write fails if bsize < bdev min or bsize > bdev max
> +if [ $((bdev_min_write / 2)) -ge "$min_bsize" ]; then
> +    test_atomic_write_bounds $((bdev_min_write / 2))
> +fi
> +if [ $((bdev_max_write * 2)) -le "$max_bsize" ]; then
> +    test_atomic_write_bounds $((bdev_max_write * 2))
> +fi
> +
> +# success, all done
> +echo Silence is golden
> +status=0
> +exit
> diff --git a/tests/generic/765.out b/tests/generic/765.out
> new file mode 100644
> index 00000000..39c254ae
> --- /dev/null
> +++ b/tests/generic/765.out
> @@ -0,0 +1,2 @@
> +QA output created by 765
> +Silence is golden
> -- 
> 2.34.1

Re: [PATCH v5] generic: add a test for atomic writes

[Darrick J. Wong]

On Tue, Apr 15, 2025 at 06:29:11PM +0530, Ritesh Harjani wrote:
> Catherine Hoang <catherine.hoang@oracle.com> writes:
> 
> > Add a test to validate the new atomic writes feature.
> >
> > Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> > Reviewed-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
> > Reviewed-by: John Garry <john.g.garry@oracle.com>
> > ---
> >  common/rc             |  51 ++++++++++++
> >  tests/generic/765     | 188 ++++++++++++++++++++++++++++++++++++++++++
> >  tests/generic/765.out |   2 +
> >  3 files changed, 241 insertions(+)
> >  create mode 100755 tests/generic/765
> >  create mode 100644 tests/generic/765.out
> >
> > diff --git a/common/rc b/common/rc
> > index 16d627e1..25e6a1f7 100644
> > --- a/common/rc
> > +++ b/common/rc
> > @@ -2996,6 +2996,10 @@ _require_xfs_io_command()
> >  			opts+=" -d"
> >  			pwrite_opts+="-V 1 -b 4k"
> >  		fi
> > +		if [ "$param" == "-A" ]; then
> > +			opts+=" -d"
> > +			pwrite_opts+="-D -V 1 -b 4k"
> 
> It's not strictly required for -A to also have -D in pwrite_opts.
> We might need to add tests later where we would like to test data
> integrity tests with atomic writes, correct? 
> 
> So do we really need to add pwrite_opts with -D too?  IMO, we can drop
> -D, as the test here suggests that -A can only work with the options
> specified in pwrite_opts.

pwrite -D sets RWF_DSYNC, doesn't it?  I think you need that to force
all the metadata updates to disk.... but for feature detection, I think
you have a point that it's not needed.

> > +		fi
> >  		testio=`$XFS_IO_PROG -f $opts -c \
> >  		        "pwrite $pwrite_opts $param 0 4k" $testfile 2>&1`
> >  		param_checked="$pwrite_opts $param"
> > @@ -5443,6 +5447,53 @@ _require_scratch_btime()
> >  	_scratch_unmount
> >  }
> >  
> > +_get_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_atomic_write_unit_max()
> > +{
> > +	$XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | \
> > +        grep atomic_write_unit_max | grep -o '[0-9]\+'

Note that this will fail if/when xfs_io starts reporting
atomic_write_unit_max_opt in 6.16.  I think you want to grep for full
words, only:

		grep -w stat.atomic_write_unit_max | awk '{print $3}'

Also: It looks like Zorro merged this patch to for-next, so I guess
subsequent changes should be deltas from this one.

--D

> > +}
> > +
> > +_get_atomic_write_segments_max()
> > +{
> > +	$XFS_IO_PROG -c "statx -r -m $STATX_WRITE_ATOMIC" $1 | \
> > +        grep atomic_write_segments_max | grep -o '[0-9]\+'
> > +}
> > +
> > +_require_scratch_write_atomic()
> > +{
> > +	_require_scratch
> > +
> > +	export STATX_WRITE_ATOMIC=0x10000
> > +
> > +	awu_min_bdev=$(_get_atomic_write_unit_min $SCRATCH_DEV)
> > +	awu_max_bdev=$(_get_atomic_write_unit_max $SCRATCH_DEV)
> > +
> > +	if [ $awu_min_bdev -eq 0 ] && [ $awu_max_bdev -eq 0 ]; then
> > +		_notrun "write atomic not supported by this block device"
> > +	fi
> > +
> > +	_scratch_mkfs > /dev/null 2>&1
> > +	_scratch_mount
> > +
> > +	testfile=$SCRATCH_MNT/testfile
> > +	touch $testfile
> > +
> > +	awu_min_fs=$(_get_atomic_write_unit_min $testfile)
> > +	awu_max_fs=$(_get_atomic_write_unit_max $testfile)
> > +
> > +	_scratch_unmount
> > +
> > +	if [ $awu_min_fs -eq 0 ] && [ $awu_max_fs -eq 0 ]; then
> > +		_notrun "write atomic not supported by this filesystem"
> > +	fi
> > +}
> > +
> >  _require_inode_limits()
> >  {
> >  	if [ $(_get_free_inode $TEST_DIR) -eq 0 ]; then
> > diff --git a/tests/generic/765 b/tests/generic/765
> > new file mode 100755
> > index 00000000..9bab3b8a
> > --- /dev/null
> > +++ b/tests/generic/765
> > @@ -0,0 +1,188 @@
> > +#! /bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Copyright (c) 2025 Oracle.  All Rights Reserved.
> > +#
> > +# FS QA Test 765
> > +#
> > +# Validate atomic write support
> > +#
> > +. ./common/preamble
> > +_begin_fstest auto quick rw
> > +
> > +_require_scratch_write_atomic
> > +_require_xfs_io_command pwrite -A
> > +
> > +get_supported_bsize()
> > +{
> > +    case "$FSTYP" in
> > +    "xfs")
> > +        min_bsize=1024
> > +        for ((i = 65536; i >= 1024; i /= 2)); do
> > +            _scratch_mkfs -b size=$i >> $seqres.full || continue
> > +            if _try_scratch_mount >> $seqres.full 2>&1; then
> > +                max_bsize=$i
> > +                _scratch_unmount
> > +                break;
> > +            fi
> > +        done
> > +        ;;
> > +    "ext4")
> > +        min_bsize=1024
> > +        max_bsize=4096
> 
> Shouldn't we keep max_bsize as system's pagesize? For systems with 64k
> pagesize max_bsize can be 64k.
> 
> max_bsize=$(_get_page_size)
> 
> > +        ;;
> > +    *)
> > +        _notrun "$FSTYP does not support atomic writes"
> > +        ;;
> > +    esac
> > +}
> > +
> > +get_mkfs_opts()
> > +{
> > +    local bsize=$1
> > +
> > +    case "$FSTYP" in
> > +    "xfs")
> > +        mkfs_opts="-b size=$bsize"
> > +        ;;
> > +    "ext4")
> > +        mkfs_opts="-b $bsize"
> > +        ;;
> > +    *)
> > +        _notrun "$FSTYP does not support atomic writes"
> > +        ;;
> > +    esac
> > +}
> > +
> > +test_atomic_writes()
> > +{
> > +    local bsize=$1
> > +
> > +    get_mkfs_opts $bsize
> > +    _scratch_mkfs $mkfs_opts >> $seqres.full
> > +    _scratch_mount
> > +
> > +    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT
> 
> Ok, this (_xfs_force_bdev()) clears the rtinherit flag on $SCRATCH_MNT
> in case if someone is passing that in MKFS_OPTIONS right? But since we
> are using our own mkfs_opts, then do we still need this?
> 
> 
> > +
> > +    testfile=$SCRATCH_MNT/testfile
> > +    touch $testfile
> > +
> > +    file_min_write=$(_get_atomic_write_unit_min $testfile)
> > +    file_max_write=$(_get_atomic_write_unit_max $testfile)
> > +    file_max_segments=$(_get_atomic_write_segments_max $testfile)
> > +
> > +    # 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 || \
> 
> we should check for $file_max_write here ^^
> 
> > +        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 -V1 -b $bsize 0 $bsize" $testfile | \
> > +        grep wrote | awk -F'[/ ]' '{print $2}')
> > +    test $bytes_written -eq $bsize || echo "atomic write len=$bsize failed"
> > +
> > +    # Check that we can perform an atomic single-block cow write
> > +    if [ "$FSTYP" == "xfs" ]; then
> > +        testfile_cp=$SCRATCH_MNT/testfile_copy
> > +        if _xfs_has_feature $SCRATCH_MNT reflink; then
> > +            cp --reflink $testfile $testfile_cp
> > +        fi
> > +        bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile_cp | \
> > +            grep wrote | awk -F'[/ ]' '{print $2}')
> > +        test $bytes_written -eq $bsize || echo "atomic write on reflinked file failed"
> > +    fi
> > +
> > +    # 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 -V1 -b $bsize $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 -V1 -b $bsize 0 $bsize" $testfile | \
> > +        grep wrote | awk -F'[/ ]' '{print $2}')
> > +    test $bytes_written -eq $bsize || echo "atomic write to sparse hole failed"
> > +
> > +    # Check that we can perform an atomic write on a fully mapped block
> > +    bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile | \
> > +        grep wrote | awk -F'[/ ]' '{print $2}')
> > +    test $bytes_written -eq $bsize || echo "atomic write to mapped block failed"
> > +
> > +    # Reject atomic write if len is out of bounds
> > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize - 1))" $testfile 2>> $seqres.full && \
> > +        echo "atomic write len=$((bsize - 1)) should fail"
> > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize + 1))" $testfile 2>> $seqres.full && \
> > +        echo "atomic write len=$((bsize + 1)) should fail"
> > +
> > +    # Reject atomic write when iovecs > 1
> > +    $XFS_IO_PROG -dc "pwrite -A -D -V2 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> > +        echo "atomic write only supports iovec count of 1"
> > +
> > +    # Reject atomic write when not using direct I/O
> > +    $XFS_IO_PROG -c "pwrite -A -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> > +        echo "atomic write requires direct I/O"
> > +
> > +    # Reject atomic write when offset % bsize != 0
> > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 1 $bsize" $testfile 2>> $seqres.full && \
> > +        echo "atomic write requires offset to be aligned to bsize"
> > +
> > +    _scratch_unmount
> > +}
> > +
> > +test_atomic_write_bounds()
> > +{
> > +    local bsize=$1
> > +
> > +    get_mkfs_opts $bsize
> > +    _scratch_mkfs $mkfs_opts >> $seqres.full
> > +    _scratch_mount
> > +
> > +    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT
> 
> ditto
> 
> -ritesh
> 
> > +
> > +    testfile=$SCRATCH_MNT/testfile
> > +    touch $testfile
> > +
> > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> > +        echo "atomic write should fail when bsize is out of bounds"
> > +
> > +    _scratch_unmount
> > +}
> > +
> > +sys_min_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_min_bytes")
> > +sys_max_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_max_bytes")
> > +
> > +bdev_min_write=$(_get_atomic_write_unit_min $SCRATCH_DEV)
> > +bdev_max_write=$(_get_atomic_write_unit_max $SCRATCH_DEV)
> > +
> > +# Test that statx atomic values are the same as sysfs values
> > +if [ "$sys_min_write" -ne "$bdev_min_write" ]; then
> > +    echo "bdev min write != sys min write"
> > +fi
> > +if [ "$sys_max_write" -ne "$bdev_max_write" ]; then
> > +    echo "bdev max write != sys max write"
> > +fi
> > +
> > +get_supported_bsize
> > +
> > +# Test all supported block sizes between bdev min and max
> > +for ((bsize=$bdev_min_write; bsize<=bdev_max_write; bsize*=2)); do
> > +    if [ "$bsize" -ge "$min_bsize" ] && [ "$bsize" -le "$max_bsize" ]; then
> > +        test_atomic_writes $bsize
> > +    fi
> > +done;
> > +
> > +# Check that atomic write fails if bsize < bdev min or bsize > bdev max
> > +if [ $((bdev_min_write / 2)) -ge "$min_bsize" ]; then
> > +    test_atomic_write_bounds $((bdev_min_write / 2))
> > +fi
> > +if [ $((bdev_max_write * 2)) -le "$max_bsize" ]; then
> > +    test_atomic_write_bounds $((bdev_max_write * 2))
> > +fi
> > +
> > +# success, all done
> > +echo Silence is golden
> > +status=0
> > +exit
> > diff --git a/tests/generic/765.out b/tests/generic/765.out
> > new file mode 100644
> > index 00000000..39c254ae
> > --- /dev/null
> > +++ b/tests/generic/765.out
> > @@ -0,0 +1,2 @@
> > +QA output created by 765
> > +Silence is golden
> > -- 
> > 2.34.1
> 

Re: [PATCH v5] generic: add a test for atomic writes

[Darrick J. Wong]

On Tue, Apr 15, 2025 at 11:44:04AM -0700, Darrick J. Wong wrote:

<snip>

> > > +test_atomic_writes()
> > > +{
> > > +    local bsize=$1
> > > +
> > > +    get_mkfs_opts $bsize
> > > +    _scratch_mkfs $mkfs_opts >> $seqres.full
> > > +    _scratch_mount
> > > +
> > > +    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT
> > 
> > Ok, this (_xfs_force_bdev()) clears the rtinherit flag on $SCRATCH_MNT
> > in case if someone is passing that in MKFS_OPTIONS right? But since we
> > are using our own mkfs_opts, then do we still need this?

Yes, we still need this because _scratch_mkfs will try to combine
$MKFS_OPTIONS and the local $mkfs_opts, so rtinherit=1 could still be
set.

--D

> > 
> > > +
> > > +    testfile=$SCRATCH_MNT/testfile
> > > +    touch $testfile
> > > +
> > > +    file_min_write=$(_get_atomic_write_unit_min $testfile)
> > > +    file_max_write=$(_get_atomic_write_unit_max $testfile)
> > > +    file_max_segments=$(_get_atomic_write_segments_max $testfile)
> > > +
> > > +    # 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 || \
> > 
> > we should check for $file_max_write here ^^
> > 
> > > +        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 -V1 -b $bsize 0 $bsize" $testfile | \
> > > +        grep wrote | awk -F'[/ ]' '{print $2}')
> > > +    test $bytes_written -eq $bsize || echo "atomic write len=$bsize failed"
> > > +
> > > +    # Check that we can perform an atomic single-block cow write
> > > +    if [ "$FSTYP" == "xfs" ]; then
> > > +        testfile_cp=$SCRATCH_MNT/testfile_copy
> > > +        if _xfs_has_feature $SCRATCH_MNT reflink; then
> > > +            cp --reflink $testfile $testfile_cp
> > > +        fi
> > > +        bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile_cp | \
> > > +            grep wrote | awk -F'[/ ]' '{print $2}')
> > > +        test $bytes_written -eq $bsize || echo "atomic write on reflinked file failed"
> > > +    fi
> > > +
> > > +    # 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 -V1 -b $bsize $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 -V1 -b $bsize 0 $bsize" $testfile | \
> > > +        grep wrote | awk -F'[/ ]' '{print $2}')
> > > +    test $bytes_written -eq $bsize || echo "atomic write to sparse hole failed"
> > > +
> > > +    # Check that we can perform an atomic write on a fully mapped block
> > > +    bytes_written=$($XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile | \
> > > +        grep wrote | awk -F'[/ ]' '{print $2}')
> > > +    test $bytes_written -eq $bsize || echo "atomic write to mapped block failed"
> > > +
> > > +    # Reject atomic write if len is out of bounds
> > > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize - 1))" $testfile 2>> $seqres.full && \
> > > +        echo "atomic write len=$((bsize - 1)) should fail"
> > > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $((bsize + 1))" $testfile 2>> $seqres.full && \
> > > +        echo "atomic write len=$((bsize + 1)) should fail"
> > > +
> > > +    # Reject atomic write when iovecs > 1
> > > +    $XFS_IO_PROG -dc "pwrite -A -D -V2 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> > > +        echo "atomic write only supports iovec count of 1"
> > > +
> > > +    # Reject atomic write when not using direct I/O
> > > +    $XFS_IO_PROG -c "pwrite -A -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> > > +        echo "atomic write requires direct I/O"
> > > +
> > > +    # Reject atomic write when offset % bsize != 0
> > > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 1 $bsize" $testfile 2>> $seqres.full && \
> > > +        echo "atomic write requires offset to be aligned to bsize"
> > > +
> > > +    _scratch_unmount
> > > +}
> > > +
> > > +test_atomic_write_bounds()
> > > +{
> > > +    local bsize=$1
> > > +
> > > +    get_mkfs_opts $bsize
> > > +    _scratch_mkfs $mkfs_opts >> $seqres.full
> > > +    _scratch_mount
> > > +
> > > +    test "$FSTYP" = "xfs" && _xfs_force_bdev data $SCRATCH_MNT
> > 
> > ditto
> > 
> > -ritesh
> > 
> > > +
> > > +    testfile=$SCRATCH_MNT/testfile
> > > +    touch $testfile
> > > +
> > > +    $XFS_IO_PROG -dc "pwrite -A -D -V1 -b $bsize 0 $bsize" $testfile 2>> $seqres.full && \
> > > +        echo "atomic write should fail when bsize is out of bounds"
> > > +
> > > +    _scratch_unmount
> > > +}
> > > +
> > > +sys_min_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_min_bytes")
> > > +sys_max_write=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/atomic_write_unit_max_bytes")
> > > +
> > > +bdev_min_write=$(_get_atomic_write_unit_min $SCRATCH_DEV)
> > > +bdev_max_write=$(_get_atomic_write_unit_max $SCRATCH_DEV)
> > > +
> > > +# Test that statx atomic values are the same as sysfs values
> > > +if [ "$sys_min_write" -ne "$bdev_min_write" ]; then
> > > +    echo "bdev min write != sys min write"
> > > +fi
> > > +if [ "$sys_max_write" -ne "$bdev_max_write" ]; then
> > > +    echo "bdev max write != sys max write"
> > > +fi
> > > +
> > > +get_supported_bsize
> > > +
> > > +# Test all supported block sizes between bdev min and max
> > > +for ((bsize=$bdev_min_write; bsize<=bdev_max_write; bsize*=2)); do
> > > +    if [ "$bsize" -ge "$min_bsize" ] && [ "$bsize" -le "$max_bsize" ]; then
> > > +        test_atomic_writes $bsize
> > > +    fi
> > > +done;
> > > +
> > > +# Check that atomic write fails if bsize < bdev min or bsize > bdev max
> > > +if [ $((bdev_min_write / 2)) -ge "$min_bsize" ]; then
> > > +    test_atomic_write_bounds $((bdev_min_write / 2))
> > > +fi
> > > +if [ $((bdev_max_write * 2)) -le "$max_bsize" ]; then
> > > +    test_atomic_write_bounds $((bdev_max_write * 2))
> > > +fi
> > > +
> > > +# success, all done
> > > +echo Silence is golden
> > > +status=0
> > > +exit
> > > diff --git a/tests/generic/765.out b/tests/generic/765.out
> > > new file mode 100644
> > > index 00000000..39c254ae
> > > --- /dev/null
> > > +++ b/tests/generic/765.out
> > > @@ -0,0 +1,2 @@
> > > +QA output created by 765
> > > +Silence is golden
> > > -- 
> > > 2.34.1
> > 
> 

Re: [PATCH v5] generic: add a test for atomic writes

[Christoph Hellwig]

This fails in my zoned device tests with;

mkfs.xfs: error - cannot set blocksize 512 on block device /dev/nvme3n1: Invalid argument

that error turns to be because the scratch rtdev /dev/nvme3n1 has a 4k
LBA size, while the main scratch device has a 512 byte sector size,
which is a configuration common for but not exclusive to zoned device,
and which means that we can't use a 512 byte block size for the file
system.

I'm not really sure how to best add the case of a larger LBA size on
the rt device to this test, though.

Re: [PATCH v5] generic: add a test for atomic writes

[Darrick J. Wong]

On Fri, May 02, 2025 at 12:12:12AM -0700, Christoph Hellwig wrote:
> This fails in my zoned device tests with;
> 
> mkfs.xfs: error - cannot set blocksize 512 on block device /dev/nvme3n1: Invalid argument
> 
> that error turns to be because the scratch rtdev /dev/nvme3n1 has a 4k
> LBA size, while the main scratch device has a 512 byte sector size,
> which is a configuration common for but not exclusive to zoned device,
> and which means that we can't use a 512 byte block size for the file
> system.
> 
> I'm not really sure how to best add the case of a larger LBA size on
> the rt device to this test, though.

Me neither.  We can't write 512b blocks to the rt device obviously, but
I think the whole point of the separate "sector" size is that's the
maximum size that the fs knows it can write to the device without
tearing.

Maybe there's a way out of this: the only metadata on the realtime
volume is the rt superblock, whose size is a full fsblock.  Perhaps we
could set/validate the block size of the rt dev with the fsblock size
instead?

--D

Re: [PATCH v5] generic: add a test for atomic writes

[Christoph Hellwig]

On Fri, May 02, 2025 at 12:39:42PM -0700, Darrick J. Wong wrote:
> Me neither.  We can't write 512b blocks to the rt device obviously, but
> I think the whole point of the separate "sector" size is that's the
> maximum size that the fs knows it can write to the device without
> tearing.

The sector size is really the minimum addressable unit.

> Maybe there's a way out of this: the only metadata on the realtime
> volume is the rt superblock, whose size is a full fsblock.  Perhaps we
> could set/validate the block size of the rt dev with the fsblock size
> instead?

We still allow subsector dio to the rt device, so this would be a bit
of a sketchy change.

Re: [PATCH v5] generic: add a test for atomic writes

[Darrick J. Wong]

On Sun, May 04, 2025 at 10:37:07PM -0700, Christoph Hellwig wrote:
> On Fri, May 02, 2025 at 12:39:42PM -0700, Darrick J. Wong wrote:
> > Me neither.  We can't write 512b blocks to the rt device obviously, but
> > I think the whole point of the separate "sector" size is that's the
> > maximum size that the fs knows it can write to the device without
> > tearing.
> 
> The sector size is really the minimum addressable unit.
> 
> > Maybe there's a way out of this: the only metadata on the realtime
> > volume is the rt superblock, whose size is a full fsblock.  Perhaps we
> > could set/validate the block size of the rt dev with the fsblock size
> > instead?
> 
> We still allow subsector dio to the rt device, so this would be a bit
> of a sketchy change.

I don't understand the 'subsector' in this sentence -- we allow
sub-fsblock dio, but not sub-LBA dio, right?

So the only thing we need to validate for the rt device is that
fsblock >= lbasize to avoid confusing the pagecache when it does IO, as
well as user programs that aren't expecting such things.

--D