[PATCH RFC v4 3/4] btrfs: use latest_dev in btrfs_show_devname

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

latest_dev is updated according to the changes to the device list.
That means we could use the latest_dev->name 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,
With this patch, /proc/self/mounts might not show the lowest devid
device as we did before.  We show the device that has the greatest
generation and, we used it to build the tree. Are we ok with this change
and, it won't affect the ABI? IMO it should be ok.
 
v2 use latest_dev so that device path is also shown
v3 add missing rcu_lock in show_devname
v4 -

 fs/btrfs/super.c | 24 +++---------------------
 1 file changed, 3 insertions(+), 21 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 64ecbdb50c1a..61682a143bf3 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2464,30 +2464,12 @@ 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;
 
-	/*
-	 * 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;
-	}
-
-	if (first_dev)
-		seq_escape(m, rcu_str_deref(first_dev->name), " \t\n\\");
-	else
-		WARN_ON(1);
+	seq_escape(m, rcu_str_deref(fs_info->fs_devices->latest_dev->name),
+		   " \t\n\\");
 	rcu_read_unlock();
+
 	return 0;
 }
 
-- 
2.31.1