btrfs: report filesystem shutdown via fserror

Commit 347b704 ("Merge patch series "fs: generic file IO error
reporting"") has introduced a common framework for reporting errors to
fsnotify in a standard way.

One of the functions being introduced is fserror_report_shutdown() that,
when combined with the experimental support for shutdown in btrfs, it
means that user-space can also easily detect whenever a btrfs filesystem
has been marked as shutdown.

Signed-off-by: Miquel Sabaté Solà <[email protected]>
Reviewed-by: Filipe Manana <[email protected]>
Signed-off-by: Filipe Manana <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: mssola

fs/btrfs/fs.h

@@ -27,6 +27,7 @@
 #include <linux/sched.h>
 #include <linux/rbtree.h>
 #include <linux/xxhash.h>
+#include <linux/fserror.h>
 #include <uapi/linux/btrfs.h>
 #include <uapi/linux/btrfs_tree.h>
 #include "extent-io-tree.h"
@@ -1199,8 +1200,10 @@ static inline void btrfs_force_shutdown(struct btrfs_fs_info *fs_info)
 	 * So here we only mark the fs error without flipping it RO.
 	 */
 	WRITE_ONCE(fs_info->fs_error, -EIO);
-	if (!test_and_set_bit(BTRFS_FS_STATE_EMERGENCY_SHUTDOWN, &fs_info->fs_state))
+	if (!test_and_set_bit(BTRFS_FS_STATE_EMERGENCY_SHUTDOWN, &fs_info->fs_state)) {
 		btrfs_crit(fs_info, "emergency shutdown");
+		fserror_report_shutdown(fs_info->sb, GFP_KERNEL);
+	}
 }
 
 /*