* [PATCH fstests v2] overlay: add a test for redirect_dir=followdata
@ 2026-11-09 13:38 Giuseppe Scrivano
2026-11-10 11:43 ` Amir Goldstein
0 siblings, 1 reply; 4+ messages in thread
From: Giuseppe Scrivano @ 2026-11-09 13:38 UTC (permalink / raw)
To: fstests; +Cc: linux-unionfs, amir73il
Test that data-only layers select redirect_dir=followdata, which follows
redirects from lower to lowerdata from any lower layer, with userxattr
and trusted xattrs, and that redirect_dir=nofollow is refused with
data-only layers.
Also test following an absolute redirect past a lower layer that has the
parent directory of the target, which failed with EIO before the fix
"ovl: do not always clear absolute_redirect".
Signed-off-by: Giuseppe Scrivano <giuseppe@scrivano.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
---
common/overlay | 15 +++++
tests/overlay/090 | 149 ++++++++++++++++++++++++++++++++++++++++++
tests/overlay/090.out | 43 ++++++++++++
3 files changed, 207 insertions(+)
create mode 100755 tests/overlay/090
create mode 100644 tests/overlay/090.out
diff --git a/common/overlay b/common/overlay
index 8e89d6e4..382960c3 100644
--- a/common/overlay
+++ b/common/overlay
@@ -286,6 +286,21 @@ _require_scratch_overlay_datadir_without_metacopy()
}
+# Check kernel support for the "redirect_dir=followdata" mount option
+_require_scratch_overlay_redirect_followdata()
+{
+ local lowerdir="$OVL_BASE_SCRATCH_MNT/$OVL_UPPER"
+ local datadir="$OVL_BASE_SCRATCH_MNT/$OVL_LOWER"
+
+ _scratch_mkfs > /dev/null 2>&1
+ _overlay_scratch_mount_opts \
+ -o"lowerdir+=$lowerdir,datadir+=$datadir" \
+ -o"userxattr,redirect_dir=followdata" > /dev/null 2>&1 || \
+ _notrun "overlay redirect_dir=followdata not supported on ${SCRATCH_DEV}"
+
+ _scratch_unmount
+}
+
# Helper function to check underlying dirs of overlay filesystem
_overlay_fsck_dirs()
diff --git a/tests/overlay/090 b/tests/overlay/090
new file mode 100755
index 00000000..6eeeacdf
--- /dev/null
+++ b/tests/overlay/090
@@ -0,0 +1,149 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2026 Giuseppe Scrivano. All Rights Reserved.
+#
+# FS QA Test 090
+#
+# Test the redirect_dir=followdata mount option.
+#
+# Data-only layers select redirect_dir=followdata, which follows redirects
+# from any lower layer to a data-only layer, and cannot be used with
+# redirect_dir=nofollow.
+#
+# Also test following an absolute redirect past a lower layer that has the
+# parent directory of the redirect target, with metacopy=on.
+#
+. ./common/preamble
+_begin_fstest auto quick metacopy redirect attr
+
+# Import common functions.
+. ./common/filter
+. ./common/attr
+
+# We use non-default scratch underlying overlay dirs, we need to check
+# them explicitly after test.
+_require_scratch_nocheck
+_require_attrs user
+_require_attrs trusted
+_require_scratch_overlay_redirect_followdata
+_require_scratch_overlay_features redirect_dir metacopy
+_require_scratch_overlay_lowerdata_layers
+
+data=$OVL_BASE_SCRATCH_MNT/data
+l1=$OVL_BASE_SCRATCH_MNT/lower1
+l2=$OVL_BASE_SCRATCH_MNT/lower2
+l3=$OVL_BASE_SCRATCH_MNT/lower3
+upper=$OVL_BASE_SCRATCH_MNT/upper
+work=$OVL_BASE_SCRATCH_MNT/work
+layers="$l3:$l2:$l1::$data"
+
+# Make a metacopy file <file> with the redirect <redirect>, for both
+# userxattr and trusted xattr mounts
+make_stub()
+{
+ local file=$1 redirect=$2 x
+
+ touch $file
+ for x in user.overlay. ${OVL_XATTR_METACOPY%metacopy}; do
+ $SETFATTR_PROG -n ${x}metacopy $file
+ $SETFATTR_PROG -n ${x}redirect -v $redirect $file
+ done
+ truncate -s 4 $file
+}
+
+# Mount the layers $layers with the options <opts>, print redirect_dir=followdata
+# if the mount shows it and <opts> has userxattr or redirect_dir (otherwise it
+# depends on the kernel config), and the content of each of the following files,
+# or the error reading it
+check()
+{
+ local opts=$1 f
+
+ shift
+ echo "== $opts"
+ _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts
+ case $opts in
+ *userxattr*|*redirect_dir=*)
+ _fs_options $OVL_BASE_SCRATCH_MNT | grep -o redirect_dir=followdata
+ ;;
+ esac
+ for f; do
+ echo "$f: $(cat $SCRATCH_MNT/$f 2>&1 | sed 's/^cat: .*: //')"
+ done
+ _unmount $SCRATCH_MNT
+}
+
+# Mounting the layers $layers with the options <opts> must fail
+check_fail()
+{
+ local opts=$1
+
+ echo "== $opts"
+ _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts \
+ >> $seqres.full 2>&1 && echo "mount succeeded" && \
+ _unmount $SCRATCH_MNT
+}
+
+_scratch_mkfs
+mkdir -p $data/base $l1/base $l2/base $l3 $upper $work
+echo -n "data" > $data/base/file
+
+make_stub $l1/s1 /base/file
+make_stub $l2/s2 /base/file
+make_stub $l3/s3 /base/file
+# The redirect target in a lower layer below s3, which is not looked up
+echo -n "lowr" > $l2/base/file
+# Redirects that are not followed: relative, directory, upper
+echo -n "lowr" > $l2/reltarget
+make_stub $l3/rel reltarget
+mkdir $l3/dir
+$SETFATTR_PROG -n user.overlay.redirect -v /base $l3/dir
+$SETFATTR_PROG -n $OVL_XATTR_REDIRECT -v /base $l3/dir
+make_stub $upper/up /base/file
+
+# followdata is selected by default with userxattr and a data-only layer
+check userxattr s1 s2 s3
+check userxattr,redirect_dir=followdata s1 s2 s3 rel dir up
+# a data-only layer cannot be used without following redirects
+check_fail userxattr,redirect_dir=nofollow
+check_fail userxattr,redirect_dir=off
+echo -n "no data-only layer "
+layers="$l3:$l2:$l1" check userxattr
+
+check metacopy=off s1 s2 s3
+check redirect_dir=followdata s1 s2 s3 rel dir up
+check redirect_dir=follow,metacopy=off s1 s2 s3
+check redirect_dir=on,metacopy=off s1 s2 s3
+check_fail redirect_dir=nofollow
+echo -n "no data-only layer "
+layers="$l3:$l2:$l1" check redirect_dir=nofollow
+
+# An explicit option requires a data-only layer and conflicts with metacopy=on
+_overlay_scratch_mount_dirs "$l3:$l2:$l1" $upper $work \
+ -o userxattr,redirect_dir=followdata >> $seqres.full 2>&1 && \
+ echo "mount redirect_dir=followdata without a data-only layer succeeded"
+_overlay_scratch_mount_dirs "$layers" $upper $work \
+ -o redirect_dir=followdata,metacopy=on >> $seqres.full 2>&1 && \
+ echo "mount with redirect_dir=followdata,metacopy=on succeeded"
+
+# The directory "/base" in a lower layer without a redirect must not make the
+# lookup forget that the redirect of the metacopy file is absolute.
+echo "== metacopy=on,redirect_dir=follow"
+_scratch_mkfs
+mkdir -p $data/base $l1 $l2
+echo -n "data" > $data/base/file
+touch $l1/file
+$SETFATTR_PROG -n $OVL_XATTR_METACOPY $l1/file
+$SETFATTR_PROG -n $OVL_XATTR_REDIRECT -v /base/file $l1/file
+truncate -s 4 $l1/file
+for f in "" base base/file; do
+ [ "$f" = base ] && mkdir $l2/base
+ [ "$f" = base/file ] && echo -n "lowr" > $l2/base/file
+ _overlay_scratch_mount_dirs "$l1:$l2::$data" - - \
+ -o ro,redirect_dir=follow,metacopy=on
+ echo "lower2 /$f: $(cat $SCRATCH_MNT/file 2>&1 | sed 's/^cat: .*: //')"
+ _unmount $SCRATCH_MNT
+done
+
+# success, all done
+_exit 0
diff --git a/tests/overlay/090.out b/tests/overlay/090.out
new file mode 100644
index 00000000..c2f576e2
--- /dev/null
+++ b/tests/overlay/090.out
@@ -0,0 +1,43 @@
+QA output created by 090
+== userxattr
+redirect_dir=followdata
+s1: data
+s2: data
+s3: data
+== userxattr,redirect_dir=followdata
+redirect_dir=followdata
+s1: data
+s2: data
+s3: data
+rel: Operation not permitted
+dir: Operation not permitted
+up: Operation not permitted
+== userxattr,redirect_dir=nofollow
+== userxattr,redirect_dir=off
+no data-only layer == userxattr
+== metacopy=off
+s1: data
+s2: data
+s3: data
+== redirect_dir=followdata
+redirect_dir=followdata
+s1: data
+s2: data
+s3: data
+rel: Operation not permitted
+dir: Operation not permitted
+up: Operation not permitted
+== redirect_dir=follow,metacopy=off
+s1: data
+s2: data
+s3: data
+== redirect_dir=on,metacopy=off
+s1: data
+s2: data
+s3: data
+== redirect_dir=nofollow
+no data-only layer == redirect_dir=nofollow
+== metacopy=on,redirect_dir=follow
+lower2 /: data
+lower2 /base: data
+lower2 /base/file: lowr
--
2.56.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH fstests v2] overlay: add a test for redirect_dir=followdata
2026-11-09 13:38 [PATCH fstests v2] overlay: add a test for redirect_dir=followdata Giuseppe Scrivano
@ 2026-11-10 11:43 ` Amir Goldstein
2026-11-10 14:02 ` Giuseppe Scrivano
0 siblings, 1 reply; 4+ messages in thread
From: Amir Goldstein @ 2026-11-10 11:43 UTC (permalink / raw)
To: Giuseppe Scrivano; +Cc: fstests, linux-unionfs
On Mon, Nov 9, 2026 at 2:40 PM Giuseppe Scrivano <giuseppe@scrivano.org> wrote:
>
> Test that data-only layers select redirect_dir=followdata, which follows
> redirects from lower to lowerdata from any lower layer, with userxattr
> and trusted xattrs, and that redirect_dir=nofollow is refused with
> data-only layers.
>
> Also test following an absolute redirect past a lower layer that has the
> parent directory of the target, which failed with EIO before the fix
> "ovl: do not always clear absolute_redirect".
>
> Signed-off-by: Giuseppe Scrivano <giuseppe@scrivano.org>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> ---
> common/overlay | 15 +++++
> tests/overlay/090 | 149 ++++++++++++++++++++++++++++++++++++++++++
> tests/overlay/090.out | 43 ++++++++++++
> 3 files changed, 207 insertions(+)
> create mode 100755 tests/overlay/090
> create mode 100644 tests/overlay/090.out
>
> diff --git a/common/overlay b/common/overlay
> index 8e89d6e4..382960c3 100644
> --- a/common/overlay
> +++ b/common/overlay
> @@ -286,6 +286,21 @@ _require_scratch_overlay_datadir_without_metacopy()
>
> }
>
> +# Check kernel support for the "redirect_dir=followdata" mount option
> +_require_scratch_overlay_redirect_followdata()
> +{
> + local lowerdir="$OVL_BASE_SCRATCH_MNT/$OVL_UPPER"
> + local datadir="$OVL_BASE_SCRATCH_MNT/$OVL_LOWER"
> +
> + _scratch_mkfs > /dev/null 2>&1
> + _overlay_scratch_mount_opts \
> + -o"lowerdir+=$lowerdir,datadir+=$datadir" \
> + -o"userxattr,redirect_dir=followdata" > /dev/null 2>&1 || \
> + _notrun "overlay redirect_dir=followdata not supported on ${SCRATCH_DEV}"
> +
> + _scratch_unmount
> +}
> +
>
> # Helper function to check underlying dirs of overlay filesystem
> _overlay_fsck_dirs()
> diff --git a/tests/overlay/090 b/tests/overlay/090
> new file mode 100755
> index 00000000..6eeeacdf
> --- /dev/null
> +++ b/tests/overlay/090
> @@ -0,0 +1,149 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 Giuseppe Scrivano. All Rights Reserved.
> +#
> +# FS QA Test 090
> +#
> +# Test the redirect_dir=followdata mount option.
> +#
> +# Data-only layers select redirect_dir=followdata, which follows redirects
> +# from any lower layer to a data-only layer, and cannot be used with
> +# redirect_dir=nofollow.
> +#
> +# Also test following an absolute redirect past a lower layer that has the
> +# parent directory of the redirect target, with metacopy=on.
> +#
> +. ./common/preamble
> +_begin_fstest auto quick metacopy redirect attr
> +
> +# Import common functions.
> +. ./common/filter
> +. ./common/attr
> +
> +# We use non-default scratch underlying overlay dirs, we need to check
> +# them explicitly after test.
> +_require_scratch_nocheck
> +_require_attrs user
> +_require_attrs trusted
> +_require_scratch_overlay_redirect_followdata
> +_require_scratch_overlay_features redirect_dir metacopy
> +_require_scratch_overlay_lowerdata_layers
> +
> +data=$OVL_BASE_SCRATCH_MNT/data
> +l1=$OVL_BASE_SCRATCH_MNT/lower1
> +l2=$OVL_BASE_SCRATCH_MNT/lower2
> +l3=$OVL_BASE_SCRATCH_MNT/lower3
> +upper=$OVL_BASE_SCRATCH_MNT/upper
> +work=$OVL_BASE_SCRATCH_MNT/work
> +layers="$l3:$l2:$l1::$data"
> +
> +# Make a metacopy file <file> with the redirect <redirect>, for both
> +# userxattr and trusted xattr mounts
> +make_stub()
> +{
> + local file=$1 redirect=$2 x
> +
> + touch $file
> + for x in user.overlay. ${OVL_XATTR_METACOPY%metacopy}; do
> + $SETFATTR_PROG -n ${x}metacopy $file
> + $SETFATTR_PROG -n ${x}redirect -v $redirect $file
> + done
> + truncate -s 4 $file
> +}
> +
> +# Mount the layers $layers with the options <opts>, print redirect_dir=followdata
> +# if the mount shows it and <opts> has userxattr or redirect_dir (otherwise it
> +# depends on the kernel config), and the content of each of the following files,
> +# or the error reading it
> +check()
> +{
> + local opts=$1 f
> +
> + shift
> + echo "== $opts"
> + _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts
> + case $opts in
> + *userxattr*|*redirect_dir=*)
> + _fs_options $OVL_BASE_SCRATCH_MNT | grep -o redirect_dir=followdata
> + ;;
> + esac
> + for f; do
> + echo "$f: $(cat $SCRATCH_MNT/$f 2>&1 | sed 's/^cat: .*: //')"
> + done
> + _unmount $SCRATCH_MNT
> +}
> +
> +# Mounting the layers $layers with the options <opts> must fail
> +check_fail()
> +{
> + local opts=$1
> +
> + echo "== $opts"
> + _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts \
> + >> $seqres.full 2>&1 && echo "mount succeeded" && \
> + _unmount $SCRATCH_MNT
> +}
> +
> +_scratch_mkfs
> +mkdir -p $data/base $l1/base $l2/base $l3 $upper $work
> +echo -n "data" > $data/base/file
> +
> +make_stub $l1/s1 /base/file
> +make_stub $l2/s2 /base/file
> +make_stub $l3/s3 /base/file
> +# The redirect target in a lower layer below s3, which is not looked up
> +echo -n "lowr" > $l2/base/file
> +# Redirects that are not followed: relative, directory, upper
> +echo -n "lowr" > $l2/reltarget
> +make_stub $l3/rel reltarget
> +mkdir $l3/dir
> +$SETFATTR_PROG -n user.overlay.redirect -v /base $l3/dir
> +$SETFATTR_PROG -n $OVL_XATTR_REDIRECT -v /base $l3/dir
> +make_stub $upper/up /base/file
> +
> +# followdata is selected by default with userxattr and a data-only layer
> +check userxattr s1 s2 s3
> +check userxattr,redirect_dir=followdata s1 s2 s3 rel dir up
> +# a data-only layer cannot be used without following redirects
> +check_fail userxattr,redirect_dir=nofollow
> +check_fail userxattr,redirect_dir=off
The test looks good but this expectation of failure is problematic.
First of all the test would fail with redirect_always_follow=N
because that makes redirect_dir=off => followdata
But I also think that redirect_dir=off should not fail with
redirect_always_follow=Y.
I will explain with the documentation.
You documentation v2 patch says:
:A data-only layer selects "redirect_dir=followdata", unless
"redirect_dir=follow"
:or "redirect_dir=on" is in effect.
So it implies redirect_dir=off => followdata
All that redirect_dir=off really means is "don't create redirects".
I amended the document as follows to clarify that:
- "redirect_dir=on":
Redirects are created and followed.
- "redirect_dir=follow":
Redirects are not created, but followed.
- "redirect_dir=followdata":
Redirects are not created.
Only redirects from lower to lowerdata are followed.
- "redirect_dir=nofollow":
Redirects are not created and not followed.
- "redirect_dir=off":
Redirects are not created.
Which redirects are followed depends on "redirect_always_follow" in the
kernel/module config, on data-only lower layers and on the "userxattr"
mount option.
Made this off => followdata change in the code and pushed to ovl-fixes:
-static int ovl_redirect_follow_mode(size_t nr_data)
+int ovl_redirect_follow_mode(bool follow_lower, size_t nr_data)
{
- return ovl_redirect_always_follow ? OVL_REDIRECT_FOLLOW :
- ovl_redirect_nofollow_mode(nr_data);
+ if (ovl_redirect_always_follow && follow_lower)
+ return OVL_REDIRECT_FOLLOW;
+
+ /* Data-only layers cannot be used without following redirects
to them */
+ return nr_data ? OVL_REDIRECT_FOLLOWDATA : OVL_REDIRECT_NOFOLLOW;
}
/*
@@ -137,7 +140,7 @@ static int ovl_redirect_follow_mode(size_t nr_data)
static int ovl_redirect_mode_def(void)
{
return ovl_redirect_dir_def ? OVL_REDIRECT_ON :
- ovl_redirect_follow_mode(0);
+ ovl_redirect_follow_mode(true, 0);
}
static const struct constant_table ovl_parameter_verity[] = {
@@ -896,6 +899,9 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
struct ovl_opt_set set = ctx->set;
/* The requested redirect_dir=, for reporting conflicts with it */
int redirect_opt = config->redirect_mode;
+ /* The redirect follow mode for redirect_dir=off and for the default */
+ int follow_mode = ovl_redirect_follow_mode(!config->userxattr,
+ ctx->nr_data);
/* Workdir/index are useless in non-upper mount */
if (!config->upperdir) {
@@ -922,9 +928,12 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
config->uuid = OVL_UUID_NULL;
}
- /* Resolve redirect_dir=off to the default redirect follow mode */
+ /*
+ * Resolve redirect_dir=off to the default redirect follow mode.
+ * With userxattr, redirects are not followed to lower by default.
+ */
if (config->redirect_mode == OVL_REDIRECT_OFF)
- config->redirect_mode = ovl_redirect_follow_mode(ctx->nr_data);
+ config->redirect_mode = follow_mode;
/*
* This is to make the logic below simpler. It doesn't make any other
@@ -1038,7 +1047,7 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
* userxattr.
*/
if (!set.redirect)
- config->redirect_mode =
ovl_redirect_nofollow_mode(ctx->nr_data);
+ config->redirect_mode = follow_mode;
config->metacopy = false;
}
Please amend the test and test with the latest ovl-fixes:
d0d57557b76de ovl: follow lower to lowerdata redirects from any lower layer
Thanks,
Amir.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH fstests v2] overlay: add a test for redirect_dir=followdata
2026-11-10 11:43 ` Amir Goldstein
@ 2026-11-10 14:02 ` Giuseppe Scrivano
2026-11-10 14:27 ` Amir Goldstein
0 siblings, 1 reply; 4+ messages in thread
From: Giuseppe Scrivano @ 2026-11-10 14:02 UTC (permalink / raw)
To: Amir Goldstein; +Cc: fstests, linux-unionfs
Hi Amir,
Amir Goldstein <amir73il@gmail.com> writes:
> On Mon, Nov 9, 2026 at 2:40 PM Giuseppe Scrivano <giuseppe@scrivano.org> wrote:
>>
>> Test that data-only layers select redirect_dir=followdata, which follows
>> redirects from lower to lowerdata from any lower layer, with userxattr
>> and trusted xattrs, and that redirect_dir=nofollow is refused with
>> data-only layers.
>>
>> Also test following an absolute redirect past a lower layer that has the
>> parent directory of the target, which failed with EIO before the fix
>> "ovl: do not always clear absolute_redirect".
>>
>> Signed-off-by: Giuseppe Scrivano <giuseppe@scrivano.org>
>> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
>> ---
>> common/overlay | 15 +++++
>> tests/overlay/090 | 149 ++++++++++++++++++++++++++++++++++++++++++
>> tests/overlay/090.out | 43 ++++++++++++
>> 3 files changed, 207 insertions(+)
>> create mode 100755 tests/overlay/090
>> create mode 100644 tests/overlay/090.out
>>
>> diff --git a/common/overlay b/common/overlay
>> index 8e89d6e4..382960c3 100644
>> --- a/common/overlay
>> +++ b/common/overlay
>> @@ -286,6 +286,21 @@ _require_scratch_overlay_datadir_without_metacopy()
>>
>> }
>>
>> +# Check kernel support for the "redirect_dir=followdata" mount option
>> +_require_scratch_overlay_redirect_followdata()
>> +{
>> + local lowerdir="$OVL_BASE_SCRATCH_MNT/$OVL_UPPER"
>> + local datadir="$OVL_BASE_SCRATCH_MNT/$OVL_LOWER"
>> +
>> + _scratch_mkfs > /dev/null 2>&1
>> + _overlay_scratch_mount_opts \
>> + -o"lowerdir+=$lowerdir,datadir+=$datadir" \
>> + -o"userxattr,redirect_dir=followdata" > /dev/null 2>&1 || \
>> + _notrun "overlay redirect_dir=followdata not supported on ${SCRATCH_DEV}"
>> +
>> + _scratch_unmount
>> +}
>> +
>>
>> # Helper function to check underlying dirs of overlay filesystem
>> _overlay_fsck_dirs()
>> diff --git a/tests/overlay/090 b/tests/overlay/090
>> new file mode 100755
>> index 00000000..6eeeacdf
>> --- /dev/null
>> +++ b/tests/overlay/090
>> @@ -0,0 +1,149 @@
>> +#! /bin/bash
>> +# SPDX-License-Identifier: GPL-2.0
>> +# Copyright (c) 2026 Giuseppe Scrivano. All Rights Reserved.
>> +#
>> +# FS QA Test 090
>> +#
>> +# Test the redirect_dir=followdata mount option.
>> +#
>> +# Data-only layers select redirect_dir=followdata, which follows redirects
>> +# from any lower layer to a data-only layer, and cannot be used with
>> +# redirect_dir=nofollow.
>> +#
>> +# Also test following an absolute redirect past a lower layer that has the
>> +# parent directory of the redirect target, with metacopy=on.
>> +#
>> +. ./common/preamble
>> +_begin_fstest auto quick metacopy redirect attr
>> +
>> +# Import common functions.
>> +. ./common/filter
>> +. ./common/attr
>> +
>> +# We use non-default scratch underlying overlay dirs, we need to check
>> +# them explicitly after test.
>> +_require_scratch_nocheck
>> +_require_attrs user
>> +_require_attrs trusted
>> +_require_scratch_overlay_redirect_followdata
>> +_require_scratch_overlay_features redirect_dir metacopy
>> +_require_scratch_overlay_lowerdata_layers
>> +
>> +data=$OVL_BASE_SCRATCH_MNT/data
>> +l1=$OVL_BASE_SCRATCH_MNT/lower1
>> +l2=$OVL_BASE_SCRATCH_MNT/lower2
>> +l3=$OVL_BASE_SCRATCH_MNT/lower3
>> +upper=$OVL_BASE_SCRATCH_MNT/upper
>> +work=$OVL_BASE_SCRATCH_MNT/work
>> +layers="$l3:$l2:$l1::$data"
>> +
>> +# Make a metacopy file <file> with the redirect <redirect>, for both
>> +# userxattr and trusted xattr mounts
>> +make_stub()
>> +{
>> + local file=$1 redirect=$2 x
>> +
>> + touch $file
>> + for x in user.overlay. ${OVL_XATTR_METACOPY%metacopy}; do
>> + $SETFATTR_PROG -n ${x}metacopy $file
>> + $SETFATTR_PROG -n ${x}redirect -v $redirect $file
>> + done
>> + truncate -s 4 $file
>> +}
>> +
>> +# Mount the layers $layers with the options <opts>, print redirect_dir=followdata
>> +# if the mount shows it and <opts> has userxattr or redirect_dir (otherwise it
>> +# depends on the kernel config), and the content of each of the following files,
>> +# or the error reading it
>> +check()
>> +{
>> + local opts=$1 f
>> +
>> + shift
>> + echo "== $opts"
>> + _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts
>> + case $opts in
>> + *userxattr*|*redirect_dir=*)
>> + _fs_options $OVL_BASE_SCRATCH_MNT | grep -o redirect_dir=followdata
>> + ;;
>> + esac
>> + for f; do
>> + echo "$f: $(cat $SCRATCH_MNT/$f 2>&1 | sed 's/^cat: .*: //')"
>> + done
>> + _unmount $SCRATCH_MNT
>> +}
>> +
>> +# Mounting the layers $layers with the options <opts> must fail
>> +check_fail()
>> +{
>> + local opts=$1
>> +
>> + echo "== $opts"
>> + _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts \
>> + >> $seqres.full 2>&1 && echo "mount succeeded" && \
>> + _unmount $SCRATCH_MNT
>> +}
>> +
>> +_scratch_mkfs
>> +mkdir -p $data/base $l1/base $l2/base $l3 $upper $work
>> +echo -n "data" > $data/base/file
>> +
>> +make_stub $l1/s1 /base/file
>> +make_stub $l2/s2 /base/file
>> +make_stub $l3/s3 /base/file
>> +# The redirect target in a lower layer below s3, which is not looked up
>> +echo -n "lowr" > $l2/base/file
>> +# Redirects that are not followed: relative, directory, upper
>> +echo -n "lowr" > $l2/reltarget
>> +make_stub $l3/rel reltarget
>> +mkdir $l3/dir
>> +$SETFATTR_PROG -n user.overlay.redirect -v /base $l3/dir
>> +$SETFATTR_PROG -n $OVL_XATTR_REDIRECT -v /base $l3/dir
>> +make_stub $upper/up /base/file
>> +
>> +# followdata is selected by default with userxattr and a data-only layer
>> +check userxattr s1 s2 s3
>> +check userxattr,redirect_dir=followdata s1 s2 s3 rel dir up
>> +# a data-only layer cannot be used without following redirects
>> +check_fail userxattr,redirect_dir=nofollow
>> +check_fail userxattr,redirect_dir=off
>
> The test looks good but this expectation of failure is problematic.
>
> First of all the test would fail with redirect_always_follow=N
> because that makes redirect_dir=off => followdata
>
> But I also think that redirect_dir=off should not fail with
> redirect_always_follow=Y.
>
> I will explain with the documentation.
> You documentation v2 patch says:
>
> :A data-only layer selects "redirect_dir=followdata", unless
> "redirect_dir=follow"
> :or "redirect_dir=on" is in effect.
>
> So it implies redirect_dir=off => followdata
>
> All that redirect_dir=off really means is "don't create redirects".
>
> I amended the document as follows to clarify that:
>
> - "redirect_dir=on":
> Redirects are created and followed.
> - "redirect_dir=follow":
> Redirects are not created, but followed.
> - "redirect_dir=followdata":
> Redirects are not created.
> Only redirects from lower to lowerdata are followed.
> - "redirect_dir=nofollow":
> Redirects are not created and not followed.
> - "redirect_dir=off":
> Redirects are not created.
> Which redirects are followed depends on "redirect_always_follow" in the
> kernel/module config, on data-only lower layers and on the "userxattr"
> mount option.
>
> Made this off => followdata change in the code and pushed to ovl-fixes:
>
> -static int ovl_redirect_follow_mode(size_t nr_data)
> +int ovl_redirect_follow_mode(bool follow_lower, size_t nr_data)
> {
> - return ovl_redirect_always_follow ? OVL_REDIRECT_FOLLOW :
> - ovl_redirect_nofollow_mode(nr_data);
> + if (ovl_redirect_always_follow && follow_lower)
> + return OVL_REDIRECT_FOLLOW;
> +
> + /* Data-only layers cannot be used without following redirects
> to them */
> + return nr_data ? OVL_REDIRECT_FOLLOWDATA : OVL_REDIRECT_NOFOLLOW;
> }
>
> /*
> @@ -137,7 +140,7 @@ static int ovl_redirect_follow_mode(size_t nr_data)
> static int ovl_redirect_mode_def(void)
> {
> return ovl_redirect_dir_def ? OVL_REDIRECT_ON :
> - ovl_redirect_follow_mode(0);
> + ovl_redirect_follow_mode(true, 0);
> }
>
> static const struct constant_table ovl_parameter_verity[] = {
> @@ -896,6 +899,9 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> struct ovl_opt_set set = ctx->set;
> /* The requested redirect_dir=, for reporting conflicts with it */
> int redirect_opt = config->redirect_mode;
> + /* The redirect follow mode for redirect_dir=off and for the default */
> + int follow_mode = ovl_redirect_follow_mode(!config->userxattr,
> + ctx->nr_data);
>
> /* Workdir/index are useless in non-upper mount */
> if (!config->upperdir) {
> @@ -922,9 +928,12 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> config->uuid = OVL_UUID_NULL;
> }
>
> - /* Resolve redirect_dir=off to the default redirect follow mode */
> + /*
> + * Resolve redirect_dir=off to the default redirect follow mode.
> + * With userxattr, redirects are not followed to lower by default.
> + */
> if (config->redirect_mode == OVL_REDIRECT_OFF)
> - config->redirect_mode = ovl_redirect_follow_mode(ctx->nr_data);
> + config->redirect_mode = follow_mode;
>
> /*
> * This is to make the logic below simpler. It doesn't make any other
> @@ -1038,7 +1047,7 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> * userxattr.
> */
> if (!set.redirect)
> - config->redirect_mode =
> ovl_redirect_nofollow_mode(ctx->nr_data);
> + config->redirect_mode = follow_mode;
> config->metacopy = false;
> }
>
>
> Please amend the test and test with the latest ovl-fixes:
> d0d57557b76de ovl: follow lower to lowerdata redirects from any lower layer
I've tested this modified version and it works fine. Do you want me to
send a v3 or will you amend it?
Thanks,
Giuseppe
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH fstests v2] overlay: add a test for redirect_dir=followdata
2026-11-10 14:02 ` Giuseppe Scrivano
@ 2026-11-10 14:27 ` Amir Goldstein
0 siblings, 0 replies; 4+ messages in thread
From: Amir Goldstein @ 2026-11-10 14:27 UTC (permalink / raw)
To: Giuseppe Scrivano; +Cc: fstests, linux-unionfs
On Tue, Nov 10, 2026 at 3:02 PM Giuseppe Scrivano <giuseppe@scrivano.org> wrote:
>
> Hi Amir,
>
> Amir Goldstein <amir73il@gmail.com> writes:
>
> > On Mon, Nov 9, 2026 at 2:40 PM Giuseppe Scrivano <giuseppe@scrivano.org> wrote:
> >>
> >> Test that data-only layers select redirect_dir=followdata, which follows
> >> redirects from lower to lowerdata from any lower layer, with userxattr
> >> and trusted xattrs, and that redirect_dir=nofollow is refused with
> >> data-only layers.
> >>
> >> Also test following an absolute redirect past a lower layer that has the
> >> parent directory of the target, which failed with EIO before the fix
> >> "ovl: do not always clear absolute_redirect".
> >>
> >> Signed-off-by: Giuseppe Scrivano <giuseppe@scrivano.org>
> >> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> >> ---
> >> common/overlay | 15 +++++
> >> tests/overlay/090 | 149 ++++++++++++++++++++++++++++++++++++++++++
> >> tests/overlay/090.out | 43 ++++++++++++
> >> 3 files changed, 207 insertions(+)
> >> create mode 100755 tests/overlay/090
> >> create mode 100644 tests/overlay/090.out
> >>
> >> diff --git a/common/overlay b/common/overlay
> >> index 8e89d6e4..382960c3 100644
> >> --- a/common/overlay
> >> +++ b/common/overlay
> >> @@ -286,6 +286,21 @@ _require_scratch_overlay_datadir_without_metacopy()
> >>
> >> }
> >>
> >> +# Check kernel support for the "redirect_dir=followdata" mount option
> >> +_require_scratch_overlay_redirect_followdata()
> >> +{
> >> + local lowerdir="$OVL_BASE_SCRATCH_MNT/$OVL_UPPER"
> >> + local datadir="$OVL_BASE_SCRATCH_MNT/$OVL_LOWER"
> >> +
> >> + _scratch_mkfs > /dev/null 2>&1
> >> + _overlay_scratch_mount_opts \
> >> + -o"lowerdir+=$lowerdir,datadir+=$datadir" \
> >> + -o"userxattr,redirect_dir=followdata" > /dev/null 2>&1 || \
> >> + _notrun "overlay redirect_dir=followdata not supported on ${SCRATCH_DEV}"
> >> +
> >> + _scratch_unmount
> >> +}
> >> +
> >>
> >> # Helper function to check underlying dirs of overlay filesystem
> >> _overlay_fsck_dirs()
> >> diff --git a/tests/overlay/090 b/tests/overlay/090
> >> new file mode 100755
> >> index 00000000..6eeeacdf
> >> --- /dev/null
> >> +++ b/tests/overlay/090
> >> @@ -0,0 +1,149 @@
> >> +#! /bin/bash
> >> +# SPDX-License-Identifier: GPL-2.0
> >> +# Copyright (c) 2026 Giuseppe Scrivano. All Rights Reserved.
> >> +#
> >> +# FS QA Test 090
> >> +#
> >> +# Test the redirect_dir=followdata mount option.
> >> +#
> >> +# Data-only layers select redirect_dir=followdata, which follows redirects
> >> +# from any lower layer to a data-only layer, and cannot be used with
> >> +# redirect_dir=nofollow.
> >> +#
> >> +# Also test following an absolute redirect past a lower layer that has the
> >> +# parent directory of the redirect target, with metacopy=on.
> >> +#
> >> +. ./common/preamble
> >> +_begin_fstest auto quick metacopy redirect attr
> >> +
> >> +# Import common functions.
> >> +. ./common/filter
> >> +. ./common/attr
> >> +
> >> +# We use non-default scratch underlying overlay dirs, we need to check
> >> +# them explicitly after test.
> >> +_require_scratch_nocheck
> >> +_require_attrs user
> >> +_require_attrs trusted
> >> +_require_scratch_overlay_redirect_followdata
> >> +_require_scratch_overlay_features redirect_dir metacopy
> >> +_require_scratch_overlay_lowerdata_layers
> >> +
> >> +data=$OVL_BASE_SCRATCH_MNT/data
> >> +l1=$OVL_BASE_SCRATCH_MNT/lower1
> >> +l2=$OVL_BASE_SCRATCH_MNT/lower2
> >> +l3=$OVL_BASE_SCRATCH_MNT/lower3
> >> +upper=$OVL_BASE_SCRATCH_MNT/upper
> >> +work=$OVL_BASE_SCRATCH_MNT/work
> >> +layers="$l3:$l2:$l1::$data"
> >> +
> >> +# Make a metacopy file <file> with the redirect <redirect>, for both
> >> +# userxattr and trusted xattr mounts
> >> +make_stub()
> >> +{
> >> + local file=$1 redirect=$2 x
> >> +
> >> + touch $file
> >> + for x in user.overlay. ${OVL_XATTR_METACOPY%metacopy}; do
> >> + $SETFATTR_PROG -n ${x}metacopy $file
> >> + $SETFATTR_PROG -n ${x}redirect -v $redirect $file
> >> + done
> >> + truncate -s 4 $file
> >> +}
> >> +
> >> +# Mount the layers $layers with the options <opts>, print redirect_dir=followdata
> >> +# if the mount shows it and <opts> has userxattr or redirect_dir (otherwise it
> >> +# depends on the kernel config), and the content of each of the following files,
> >> +# or the error reading it
> >> +check()
> >> +{
> >> + local opts=$1 f
> >> +
> >> + shift
> >> + echo "== $opts"
> >> + _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts
> >> + case $opts in
> >> + *userxattr*|*redirect_dir=*)
> >> + _fs_options $OVL_BASE_SCRATCH_MNT | grep -o redirect_dir=followdata
> >> + ;;
> >> + esac
> >> + for f; do
> >> + echo "$f: $(cat $SCRATCH_MNT/$f 2>&1 | sed 's/^cat: .*: //')"
> >> + done
> >> + _unmount $SCRATCH_MNT
> >> +}
> >> +
> >> +# Mounting the layers $layers with the options <opts> must fail
> >> +check_fail()
> >> +{
> >> + local opts=$1
> >> +
> >> + echo "== $opts"
> >> + _overlay_scratch_mount_dirs "$layers" $upper $work -o $opts \
> >> + >> $seqres.full 2>&1 && echo "mount succeeded" && \
> >> + _unmount $SCRATCH_MNT
> >> +}
> >> +
> >> +_scratch_mkfs
> >> +mkdir -p $data/base $l1/base $l2/base $l3 $upper $work
> >> +echo -n "data" > $data/base/file
> >> +
> >> +make_stub $l1/s1 /base/file
> >> +make_stub $l2/s2 /base/file
> >> +make_stub $l3/s3 /base/file
> >> +# The redirect target in a lower layer below s3, which is not looked up
> >> +echo -n "lowr" > $l2/base/file
> >> +# Redirects that are not followed: relative, directory, upper
> >> +echo -n "lowr" > $l2/reltarget
> >> +make_stub $l3/rel reltarget
> >> +mkdir $l3/dir
> >> +$SETFATTR_PROG -n user.overlay.redirect -v /base $l3/dir
> >> +$SETFATTR_PROG -n $OVL_XATTR_REDIRECT -v /base $l3/dir
> >> +make_stub $upper/up /base/file
> >> +
> >> +# followdata is selected by default with userxattr and a data-only layer
> >> +check userxattr s1 s2 s3
> >> +check userxattr,redirect_dir=followdata s1 s2 s3 rel dir up
> >> +# a data-only layer cannot be used without following redirects
> >> +check_fail userxattr,redirect_dir=nofollow
> >> +check_fail userxattr,redirect_dir=off
> >
> > The test looks good but this expectation of failure is problematic.
> >
> > First of all the test would fail with redirect_always_follow=N
> > because that makes redirect_dir=off => followdata
> >
> > But I also think that redirect_dir=off should not fail with
> > redirect_always_follow=Y.
> >
> > I will explain with the documentation.
> > You documentation v2 patch says:
> >
> > :A data-only layer selects "redirect_dir=followdata", unless
> > "redirect_dir=follow"
> > :or "redirect_dir=on" is in effect.
> >
> > So it implies redirect_dir=off => followdata
> >
> > All that redirect_dir=off really means is "don't create redirects".
> >
> > I amended the document as follows to clarify that:
> >
> > - "redirect_dir=on":
> > Redirects are created and followed.
> > - "redirect_dir=follow":
> > Redirects are not created, but followed.
> > - "redirect_dir=followdata":
> > Redirects are not created.
> > Only redirects from lower to lowerdata are followed.
> > - "redirect_dir=nofollow":
> > Redirects are not created and not followed.
> > - "redirect_dir=off":
> > Redirects are not created.
> > Which redirects are followed depends on "redirect_always_follow" in the
> > kernel/module config, on data-only lower layers and on the "userxattr"
> > mount option.
> >
> > Made this off => followdata change in the code and pushed to ovl-fixes:
> >
> > -static int ovl_redirect_follow_mode(size_t nr_data)
> > +int ovl_redirect_follow_mode(bool follow_lower, size_t nr_data)
> > {
> > - return ovl_redirect_always_follow ? OVL_REDIRECT_FOLLOW :
> > - ovl_redirect_nofollow_mode(nr_data);
> > + if (ovl_redirect_always_follow && follow_lower)
> > + return OVL_REDIRECT_FOLLOW;
> > +
> > + /* Data-only layers cannot be used without following redirects
> > to them */
> > + return nr_data ? OVL_REDIRECT_FOLLOWDATA : OVL_REDIRECT_NOFOLLOW;
> > }
> >
> > /*
> > @@ -137,7 +140,7 @@ static int ovl_redirect_follow_mode(size_t nr_data)
> > static int ovl_redirect_mode_def(void)
> > {
> > return ovl_redirect_dir_def ? OVL_REDIRECT_ON :
> > - ovl_redirect_follow_mode(0);
> > + ovl_redirect_follow_mode(true, 0);
> > }
> >
> > static const struct constant_table ovl_parameter_verity[] = {
> > @@ -896,6 +899,9 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> > struct ovl_opt_set set = ctx->set;
> > /* The requested redirect_dir=, for reporting conflicts with it */
> > int redirect_opt = config->redirect_mode;
> > + /* The redirect follow mode for redirect_dir=off and for the default */
> > + int follow_mode = ovl_redirect_follow_mode(!config->userxattr,
> > + ctx->nr_data);
> >
> > /* Workdir/index are useless in non-upper mount */
> > if (!config->upperdir) {
> > @@ -922,9 +928,12 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> > config->uuid = OVL_UUID_NULL;
> > }
> >
> > - /* Resolve redirect_dir=off to the default redirect follow mode */
> > + /*
> > + * Resolve redirect_dir=off to the default redirect follow mode.
> > + * With userxattr, redirects are not followed to lower by default.
> > + */
> > if (config->redirect_mode == OVL_REDIRECT_OFF)
> > - config->redirect_mode = ovl_redirect_follow_mode(ctx->nr_data);
> > + config->redirect_mode = follow_mode;
> >
> > /*
> > * This is to make the logic below simpler. It doesn't make any other
> > @@ -1038,7 +1047,7 @@ int ovl_fs_params_verify(const struct ovl_fs_context *ctx,
> > * userxattr.
> > */
> > if (!set.redirect)
> > - config->redirect_mode =
> > ovl_redirect_nofollow_mode(ctx->nr_data);
> > + config->redirect_mode = follow_mode;
> > config->metacopy = false;
> > }
> >
> >
> > Please amend the test and test with the latest ovl-fixes:
> > d0d57557b76de ovl: follow lower to lowerdata redirects from any lower layer
>
> I've tested this modified version and it works fine. Do you want me to
> send a v3 or will you amend it?
Please send v3 to Zoro/fstests because he will be applying it to fstests
after his review, not me.
Please keep my Reviewed-by on v3 I trust that you modified the test case
correctly and fixed the golden output accordingly.
Thanks,
Amir.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2026-11-09 13:38 [PATCH fstests v2] overlay: add a test for redirect_dir=followdata Giuseppe Scrivano
2026-11-10 11:43 ` Amir Goldstein
2026-11-10 14:02 ` Giuseppe Scrivano
2026-11-10 14:27 ` Amir Goldstein
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