[PATCH v4 5/6] btrfs: implement shutdown ioctl

Qu Wenruo
2025-07-04T00:43:21Z

The shutdown ioctl should follow the XFS one, which use magic number 'X',
and ioctl number 125, with a u32 as flags.

For now btrfs don't distinguish DEFAULT and LOGFLUSH flags (just like
f2fs), both will freeze the fs first (implies committing the current
transaction), setting the SHUTDOWN flag and finally thaw the fs.

For NOLOGFLUSH flag, the freeze/thaw part is skipped thus the current
transaction is aborted.

The new shutdown ioctl is hidden behind experimental features for more
testing.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/ioctl.c | 40 ++++++++++++++++++++++++++++++++++++++
include/uapi/linux/btrfs.h | 9 +++++++++
2 files changed, 49 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2f3b7be13bea..94eb7a8499db 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -5194,6 +5194,36 @@ static int btrfs_ioctl_subvol_sync(struct btrfs_fs_info *fs_info, void __user *a
return 0;
}

+#ifdef CONFIG_BTRFS_EXPERIMENTAL
+static int btrfs_emergency_shutdown(struct btrfs_fs_info *fs_info, u32 flags)
+{
+ int ret = 0;
+
+ if (flags >= BTRFS_SHUTDOWN_FLAGS_LAST)
+ return -EINVAL;
+
+ if (btrfs_is_shutdown(fs_info))
+ return 0;
+
+ switch (flags) {
+ case BTRFS_SHUTDOWN_FLAGS_LOGFLUSH:
+ case BTRFS_SHUTDOWN_FLAGS_DEFAULT:
+ ret = freeze_super(fs_info->sb, FREEZE_HOLDER_KERNEL, NULL);
+ if (ret)
+ return ret;
+ btrfs_force_shutdown(fs_info);
+ ret = thaw_super(fs_info->sb, FREEZE_HOLDER_KERNEL, NULL);
+ if (ret)
+ return ret;
+ break;
+ case BTRFS_SHUTDOWN_FLAGS_NOLOGFLUSH:
+ btrfs_force_shutdown(fs_info);
+ break;
+ }
+ return ret;
+}
+#endif
+
long btrfs_ioctl(struct file *file, unsigned int
cmd, unsigned long arg)
{
@@ -5201,6 +5231,8 @@ long btrfs_ioctl(struct file *file, unsigned int
struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
struct btrfs_root *root = BTRFS_I(inode)->root;
void __user *argp = (void __user *)arg;
+ /* If @arg is just an unsigned long value. */
+ unsigned long flags;

switch (cmd) {
case FS_IOC_GETVERSION:
@@ -5349,6 +5381,14 @@ long btrfs_ioctl(struct file *file, unsigned int
#endif
case BTRFS_IOC_SUBVOL_SYNC_WAIT:
return btrfs_ioctl_subvol_sync(fs_info, argp);
+#ifdef CONFIG_BTRFS_EXPERIMENTAL
+ case BTRFS_IOC_SHUTDOWN:
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ if (get_user(flags, (__u32 __user *)arg))
+ return -EFAULT;
+ return btrfs_emergency_shutdown(fs_info, flags);
+#endif
}

return -ENOTTY;
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index dd02160015b2..8f6324cf15d9 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -1096,6 +1096,12 @@ enum btrfs_err_code {
BTRFS_ERROR_DEV_RAID1C4_MIN_NOT_MET,
};

+/* Flags for IOC_SHUTDOWN, should match XFS' flags. */
+#define BTRFS_SHUTDOWN_FLAGS_DEFAULT 0x0
+#define BTRFS_SHUTDOWN_FLAGS_LOGFLUSH 0x1
+#define BTRFS_SHUTDOWN_FLAGS_NOLOGFLUSH 0x2
+#define BTRFS_SHUTDOWN_FLAGS_LAST 0x3
+
#define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
struct btrfs_ioctl_vol_args)
#define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
@@ -1217,6 +1223,9 @@ enum btrfs_err_code {
#define BTRFS_IOC_SUBVOL_SYNC_WAIT _IOW(BTRFS_IOCTL_MAGIC, 65, \
struct btrfs_ioctl_subvol_wait)

+/* Shutdown ioctl should follow XFS's interfaces, thus not using btrfs magic. */
+#define BTRFS_IOC_SHUTDOWN _IOR('X', 125, __u32)
+
#ifdef __cplusplus
}
#endif
--
2.50.0