[PATCH] fstests: add a test case for btrfs get_subvol_info ioctl

[Qu Wenruo <wqu@suse.com>]

There is a regression caused by upstream kernel commit 538e5bdbc899
("btrfs: add 32-bit compat ioctl for BTRFS_IOC_GET_SUBVOL_INFO"), where
the unprivileged get_subvol_info ioctl is returning incorrect results.

Unfortunately that bug is not covered by fstests, and only exposed by
btrfs-progs libbtrfsutil python tests, which is not a short run.

So add a new test case for such btrfs ioctl:

- Introduce a helper program, btrfs_ioctl
  Which will call the dedicated ioctl, print all of its structure
  members.

  For now only get_subvol_info is supported, but it can be easily
  appended for new ones.

- Mkfs and create a subvolume on btrfs

- Use "_btrfs_get_subvolid()" to grab the subvolid
  That function is utilizing "btrfs subvolume list" to grab the info,
  which is not utilizing the unprivileged ioctl.

- Use "btrfs_ioctl get_subvol_info" to grab the subvolid

- Compare the two subvolids

This should be enough to detect the regression.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 .gitignore          |   1 +
 src/Makefile        |   2 +-
 src/btrfs_ioctl.c   | 103 ++++++++++++++++++++++++++++++++++++++++++++
 tests/btrfs/351     |  47 ++++++++++++++++++++
 tests/btrfs/351.out |   2 +
 5 files changed, 154 insertions(+), 1 deletion(-)
 create mode 100644 src/btrfs_ioctl.c
 create mode 100755 tests/btrfs/351
 create mode 100644 tests/btrfs/351.out

diff --git a/.gitignore b/.gitignore
index dd77ee30..0b6b9452 100644
--- a/.gitignore
+++ b/.gitignore
@@ -215,6 +215,7 @@ tags
 /src/file_attr
 /src/truncate
 /src/t_btrfs_received_uuid_ioctl
+/src/btrfs_ioctl
 
 # Symlinked files
 /tests/generic/035.out
diff --git a/src/Makefile b/src/Makefile
index 31ac43b2..76cf50c3 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -36,7 +36,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
 	fscrypt-crypt-util bulkstat_null_ocount splice-test chprojid_fail \
 	detached_mounts_propagation ext4_resize t_readdir_3 splice2pipe \
 	uuid_ioctl t_snapshot_deleted_subvolume fiemap-fault min_dio_alignment \
-	rw_hint fs-monitor
+	rw_hint fs-monitor btrfs_ioctl
 
 EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
 	      btrfs_crc32c_forged_name.py popdir.pl popattr.py \
diff --git a/src/btrfs_ioctl.c b/src/btrfs_ioctl.c
new file mode 100644
index 00000000..4114fa88
--- /dev/null
+++ b/src/btrfs_ioctl.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) SUSE S.A.
+
+#include <stdio.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <uuid/uuid.h>
+#include <linux/btrfs.h>
+
+#define subvol_info_printf_u64(info, name)	\
+	printf(#name ": %llu\n", (info).name)
+
+#define subvol_info_printf_timestamp(info, name)	\
+	printf(#name ": %llu.%09u\n", (info).name.sec, (info.name.nsec))
+
+#define subvol_info_printf_uuid(info, name)	\
+{						\
+	char uuidbuf[UUID_STR_LEN];		\
+						\
+	uuid_unparse((info).name, uuidbuf);	\
+	printf(#name ": %s\n", (info).name);	\
+}
+
+void get_subvol_info(int fd)
+{
+	struct btrfs_ioctl_get_subvol_info_args info = { 0 };
+	int ret;
+
+	ret = ioctl(fd, BTRFS_IOC_GET_SUBVOL_INFO, &info);
+	if (ret < 0) {
+		fprintf(stderr, "ioctl failed: %m\n");
+		return;
+	}
+
+	subvol_info_printf_u64(info, treeid);
+	printf("name: %.*s\n", BTRFS_VOL_NAME_MAX, info.name);
+	subvol_info_printf_u64(info, parent_id);
+	subvol_info_printf_u64(info, dirid);
+	subvol_info_printf_u64(info, generation);
+	printf("flags: 0x%llx\n", info.flags);
+	subvol_info_printf_uuid(info, uuid);
+	subvol_info_printf_uuid(info, parent_uuid);
+	subvol_info_printf_uuid(info, received_uuid);
+	subvol_info_printf_u64(info, ctransid);
+	subvol_info_printf_u64(info, otransid);
+	subvol_info_printf_u64(info, stransid);
+	subvol_info_printf_u64(info, rtransid);
+	subvol_info_printf_timestamp(info, ctime);
+	subvol_info_printf_timestamp(info, otime);
+	subvol_info_printf_timestamp(info, stime);
+	subvol_info_printf_timestamp(info, rtime);
+}
+
+const struct ioctl {
+	const char *name;
+	void (*func)(int fd);
+} supported_ioctls[] = {
+	{
+		.name = "get_subvol_info",
+		.func = get_subvol_info,
+	},
+};
+
+static void usage()
+{
+	fprintf(stderr, "Usage: btrfs_ioctl <ioctl_name> <path>\n");
+}
+int main(int argc, char **argv)
+{
+	const char *ioctl_name;
+	int done = 0;
+	int fd;
+	int ret = 0;
+
+	if (argc != 3) {
+		usage();
+		return ret;
+	}
+	fd = open(argv[2], O_RDONLY);
+	if (fd < 0) {
+		fprintf(stderr, "failed to open %s: %m", argv[2]);
+		return 1;
+	}
+	ioctl_name = argv[1];
+
+	for (int i = 0; i < sizeof(supported_ioctls) / sizeof(supported_ioctls[0]); i++) {
+		const struct ioctl *ioctl = &supported_ioctls[i];
+
+		if (!strncasecmp(ioctl->name, ioctl_name, strlen(ioctl->name))) {
+			ioctl->func(fd);
+			done = 1;
+			break;
+		}
+	}
+	if (!done) {
+		fprintf(stderr, "ioctl \"%s\" is not recognized\n", ioctl_name);
+		ret = 1;
+	}
+	close(fd);
+	return ret;
+}
diff --git a/tests/btrfs/351 b/tests/btrfs/351
new file mode 100755
index 00000000..e92ddf1b
--- /dev/null
+++ b/tests/btrfs/351
@@ -0,0 +1,47 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2026 SUSE S.A.  All Rights Reserved.
+#
+# FS QA Test 351
+#
+# Make sure the unprivileged get_subvol_info ioctl is providing the correct
+# result.
+#
+. ./common/preamble
+_begin_fstest auto quick
+
+_fixed_by_kernel_commit XXXXXXXXXXXX \
+	"Revert \"btrfs: add 32-bit compat ioctl for BTRFS_IOC_GET_SUBVOL_INFO\""
+
+_require_test_program btrfs_ioctl
+_require_scratch
+
+_scratch_mkfs >> $seqres.full
+_scratch_mount
+
+_btrfs subvolume create $SCRATCH_MNT/subv1
+
+# The id is get through "btrfs subvolume list" command, which doesn't utilize the
+# unprivileged version.
+subvolid=$(_btrfs_get_subvolid $SCRATCH_MNT subv1)
+echo "subvolid=$subvolid" >> $seqres.full
+
+# Do a basic check in case "btrfs subvolume list" doesn't get a correct subvolid
+if [ -z "$subvolid" -o "$subvolid" -lt 256 ]; then
+	_fail "\"btrfs subvolume list\" returned an invalid subvolid"
+fi
+
+# Get the id again through the unprivileged get_subvol_info ioctl
+$here/src/btrfs_ioctl get_subvol_info $SCRATCH_MNT/subv1 >> $tmp.output
+cat $tmp.output >> $seqres.full
+ioctl_subvolid=$(grep treeid: $tmp.output | cut -f 2 -d\ )
+
+if [ "$ioctl_subvolid" -ne "$subvolid" ]; then
+	_fail "get_subvol_info ioctl returned an incorrect treeid"
+fi
+
+_scratch_unmount
+
+echo "Silence is golden"
+# success, all done
+_exit 0
diff --git a/tests/btrfs/351.out b/tests/btrfs/351.out
new file mode 100644
index 00000000..49b14639
--- /dev/null
+++ b/tests/btrfs/351.out
@@ -0,0 +1,2 @@
+QA output created by 351
+Silence is golden
-- 
2.51.2