[PATCH v2] fstests: Vertify dir permissions when creating a stub subvolume

[Lee Trager <lee@trager.us>]

btrfs supports creating nesting subvolumes however snapshots are not
recurive. When a snapshot is taken of a volume which contains a subvolume
the subvolume is replaced with a stub subvolume which has the same name and
uses inode number 2. This test validates that the stub volume copies
permissions of the original volume.
Signed-off-by: Lee Trager <lee@trager.us>
---
v2:
- Migrated _require_unshare from overlay/020 into common_rc. Updated the error
  message as most Linux systems should have unshare from util-linux.
- Added note about why the test must be done in one subshell process.
- chown command now uses $qa_user:$qa_group instead of hard coded values.
common/rc           |  6 ++++++
 tests/btrfs/300     | 46 +++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/300.out | 18 ++++++++++++++++++
 tests/overlay/020   |  7 +------
 4 files changed, 71 insertions(+), 6 deletions(-)
 create mode 100755 tests/btrfs/300
 create mode 100644 tests/btrfs/300.out

diff --git a/common/rc b/common/rc
index 5c4429ed..ca7c5c14 100644
--- a/common/rc
+++ b/common/rc
@@ -5224,6 +5224,12 @@ _soak_loop_running() {
 	return 0
 }
 
+
+_require_unshare() {
+	unshare -f -r -m -p -U  true &>/dev/null || \
+		_notrun "unshare $@: not found, should be in util-linux"
+}
+
 init_rc
 
 ################################################################################
diff --git a/tests/btrfs/300 b/tests/btrfs/300
new file mode 100755
index 00000000..c86ed268
--- /dev/null
+++ b/tests/btrfs/300
@@ -0,0 +1,46 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022 Meta Platforms, Inc.  All Rights Reserved.
+#
+# FS QA Test 300
+#
+# Validate that snapshots taken while in a remapped namespace preserve
+# the permissions of the user.
+#
+. ./common/preamble
+_begin_fstest auto quick subvol snapshot
+
+_supported_fs btrfs
+
+_require_test
+_require_user
+_require_group
+_require_unix_perm_checking
+_require_unshare
+_register_cleanup "cleanup"
+
+test_dir="${TEST_DIR}/$(basename $0)"
+cleanup() {
+    [ -d "$test_dir" ] && rm -rf $test_dir
+}
+
+mkdir $test_dir
+chown $qa_user:$qa_group $test_dir
+
+# _user_do executes each command as $qa_user in its own subshell. unshare
+# sets the namespace for the running shell. The test must run in one user
+# subshell to preserve the namespace over multiple commands.
+_user_do "
+cd ${test_dir};
+unshare --user --keep-caps --map-auto --map-root-user;
+$BTRFS_UTIL_PROG subvolume create subvol;
+touch subvol/{1,2,3};
+$BTRFS_UTIL_PROG subvolume create subvol/subsubvol;
+touch subvol/subsubvol/{4,5,6};
+$BTRFS_UTIL_PROG subvolume snapshot subvol snapshot;
+"
+
+find $test_dir -printf "%M %u %g %P\n"
+
+status=0
+exit
diff --git a/tests/btrfs/300.out b/tests/btrfs/300.out
new file mode 100644
index 00000000..33b5fb44
--- /dev/null
+++ b/tests/btrfs/300.out
@@ -0,0 +1,18 @@
+QA output created by 300
+Create subvolume './subvol'
+Create subvolume 'subvol/subsubvol'
+Create a snapshot of 'subvol' in './snapshot'
+drwxr-xr-x fsgqa fsgqa 
+drwxr-xr-x fsgqa fsgqa subvol
+-rw-r--r-- fsgqa fsgqa subvol/1
+-rw-r--r-- fsgqa fsgqa subvol/2
+-rw-r--r-- fsgqa fsgqa subvol/3
+drwxr-xr-x fsgqa fsgqa subvol/subsubvol
+-rw-r--r-- fsgqa fsgqa subvol/subsubvol/4
+-rw-r--r-- fsgqa fsgqa subvol/subsubvol/5
+-rw-r--r-- fsgqa fsgqa subvol/subsubvol/6
+drwxr-xr-x fsgqa fsgqa snapshot
+-rw-r--r-- fsgqa fsgqa snapshot/1
+-rw-r--r-- fsgqa fsgqa snapshot/2
+-rw-r--r-- fsgqa fsgqa snapshot/3
+drwxr-xr-x fsgqa fsgqa snapshot/subsubvol
diff --git a/tests/overlay/020 b/tests/overlay/020
index 98a33aec..9f82da34 100755
--- a/tests/overlay/020
+++ b/tests/overlay/020
@@ -16,18 +16,13 @@ _begin_fstest auto quick copyup perms
 
 # real QA test starts here
 
-require_unshare() {
-	unshare -f -r "$@" true &>/dev/null || \
-		_notrun "unshare $@: not supported"
-}
-
 # Modify as appropriate.
 _supported_fs overlay
 _fixed_by_kernel_commit 3fe6e52f0626 \
 	"ovl: override creds with the ones from the superblock mounter"
 
 _require_scratch
-require_unshare -m -p -U
+_require_unshare
 
 # Remove all files from previous tests
 _scratch_mkfs
-- 
2.34.1