[PATCH RFC 3/3] btrfs: use latest_bdev in btrfs_show_devname

[Anand Jain <anand.jain@oracle.com>]

latest_bdev is updated according to the changes to the device list.
That means we could use the latest_bdev to show the device name in
/proc/self/mounts. So this patch makes that change.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---

RFC because
1. latest_bdev might not be the lowest devid but, we showed
the lowest devid in /proc/self/mount.
2. The device's path is not shown now but, previously we did.
So does these break ABI? Maybe yes for 2 howabout for 1 above?

 fs/btrfs/super.c | 25 +++----------------------
 1 file changed, 3 insertions(+), 22 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 1f9dd1a4faa3..4ad3fe174c41 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2464,30 +2464,11 @@ static int btrfs_unfreeze(struct super_block *sb)
 static int btrfs_show_devname(struct seq_file *m, struct dentry *root)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(root->d_sb);
-	struct btrfs_device *dev, *first_dev = NULL;
+	char name[BDEVNAME_SIZE];
 
-	/*
-	 * Lightweight locking of the devices. We should not need
-	 * device_list_mutex here as we only read the device data and the list
-	 * is protected by RCU.  Even if a device is deleted during the list
-	 * traversals, we'll get valid data, the freeing callback will wait at
-	 * least until the rcu_read_unlock.
-	 */
-	rcu_read_lock();
-	list_for_each_entry_rcu(dev, &fs_info->fs_devices->devices, dev_list) {
-		if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state))
-			continue;
-		if (!dev->name)
-			continue;
-		if (!first_dev || dev->devid < first_dev->devid)
-			first_dev = dev;
-	}
+	seq_escape(m, bdevname(fs_info->fs_devices->latest_bdev, name),
+		   " \t\n\\");
 
-	if (first_dev)
-		seq_escape(m, rcu_str_deref(first_dev->name), " \t\n\\");
-	else
-		WARN_ON(1);
-	rcu_read_unlock();
 	return 0;
 }
 
-- 
2.31.1