在 2025/7/5 23:52, David Sterba 写道:
On Fri, Jul 04, 2025 at 10:12:33AM +0930, Qu Wenruo wrote:
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@xxxxxxxx>
---
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);
Recently I've looked at scrub blocking filesystem freezing and it does
not work because it blocks on the semaphore taken in mnt_want_write,
also taken in freeze_super().
I have an idea for fix, basically pause scrub, undo mnt_want_write
and then call freeze_super. So we'll need that too for shutdown. Once
implemented the fixup would be to use btrfs_freeze_super callback here.
It may not be that simple.
freeze_super() itself is doing extra works related to the
stage/freeze_owner/etc.
I'm not sure if it's a good idea to completely skip that part.
I'd prefer scrub to check the frozen stage, and if it's already in any
FREEZE stages, exit early.
Thanks,
Qu
+ 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)
{
--- 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)
In XFS it's
#define XFS_IOC_GOINGDOWN _IOR ('X', 125, uint32_t)
It's right to use the same definition and ioctl value as this will
be a generic ioctl eventually, with 3 users at least. I like the name
SHUTDOWN better, ext4 also uses that.
