[PATCH v5 04/10] btrfs: clear oneshot options on mount and remount

From: Boris Burkov <boris@bur.io>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Cc: Boris Burkov <boris@bur.io>
Subject: [PATCH v5 04/10] btrfs: clear oneshot options on mount and remount
Date: Tue, 27 Oct 2020 14:07:58 -0700	[thread overview]
Message-ID: <7b316bb772e15d62df1553c50c8bb4c50cc63c51.1603828718.git.boris@bur.io> (raw)
In-Reply-To: <cover.1603828718.git.boris@bur.io>

Some options only apply during mount time and are cleared at the end
of mount. For now, the example is USEBACKUPROOT, but CLEAR_CACHE also
fits the bill, and this is a preparation patch for also clearing that
option.

One subtlety is that the current code only resets USEBACKUPROOT on rw
mounts, but the option is meaningfully "consumed" by a ro mount, so it
feels appropriate to clear in that case as well. A subsequent read-write
remount would not go through open_ctree, which is the only place that
checks the option, so the change should be benign.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/disk-io.c | 20 +++++++++++++-------
 fs/btrfs/disk-io.h |  1 +
 fs/btrfs/super.c   |  1 +
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5fe0a2640c8a..987e40e12bb4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2814,6 +2814,16 @@ static int btrfs_check_uuid_tree(struct btrfs_fs_info *fs_info)
 	return 0;
 }
 
+/*
+ * Some options only have meaning at mount time and shouldn't persist across
+ * remounts, or be displayed. Clear these at the end of mount and remount
+ * code paths.
+ */
+void btrfs_clear_oneshot_options(struct btrfs_fs_info *fs_info)
+{
+	btrfs_clear_opt(fs_info->mount_opt, USEBACKUPROOT);
+}
+
 /*
  * Mounting logic specific to read-write file systems. Shared by open_ctree
  * and btrfs_remount when remounting from read-only to read-write.
@@ -3293,7 +3303,7 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	}
 
 	if (sb_rdonly(sb))
-		return 0;
+		goto clear_oneshot;
 
 	if (btrfs_test_opt(fs_info, CLEAR_CACHE) &&
 	    btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE)) {
@@ -3337,12 +3347,8 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	}
 	set_bit(BTRFS_FS_OPEN, &fs_info->flags);
 
-	/*
-	 * backuproot only affect mount behavior, and if open_ctree succeeded,
-	 * no need to keep the flag
-	 */
-	btrfs_clear_opt(fs_info->mount_opt, USEBACKUPROOT);
-
+clear_oneshot:
+	btrfs_clear_oneshot_options(fs_info);
 	return 0;
 
 fail_qgroup:
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index b3ee9c19be0c..02bee384f744 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -50,6 +50,7 @@ struct extent_buffer *btrfs_find_create_tree_block(
 						struct btrfs_fs_info *fs_info,
 						u64 bytenr);
 void btrfs_clean_tree_block(struct extent_buffer *buf);
+void btrfs_clear_oneshot_options(struct btrfs_fs_info *fs_info);
 int btrfs_mount_rw(struct btrfs_fs_info *fs_info);
 int __cold open_ctree(struct super_block *sb,
 	       struct btrfs_fs_devices *fs_devices,
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 56bfa23bc52f..85a0cf56cec5 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1945,6 +1945,7 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 
 	wake_up_process(fs_info->transaction_kthread);
 	btrfs_remount_cleanup(fs_info, old_opts);
+	btrfs_clear_oneshot_options(fs_info);
 	clear_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state);
 
 	return 0;
-- 
2.24.1

