btrfs: qgroup: use btrfs_qgroup_enabled() in ioctls

We have a publicly exported btrfs_qgroup_enabled() and an ioctl.c private
qgroup_enabled() helper. Both of these test if qgroups are enabled, the
first check if the flag BTRFS_FS_QUOTA_ENABLED is set in fs_info->flags
while the second checks if fs_info->quota_root is not NULL while holding
the mutex fs_info->qgroup_ioctl_lock.

We can get away with the private ioctl.c:qgroup_enabled(), as all entry
points into the qgroup code check if fs_info->quota_root is NULL or not
while holding the mutex fs_info->qgroup_ioctl_lock, and returning the
error -ENOTCONN in case it's NULL.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/ioctl.c

@@ -3711,22 +3711,6 @@ static long btrfs_ioctl_quota_ctl(struct file *file, void __user *arg)
 	return ret;
 }
 
-/*
- * Quick check for ioctl handlers if quotas are enabled. Proper locking must be
- * done before any operations.
- */
-static bool qgroup_enabled(struct btrfs_fs_info *fs_info)
-{
-	bool ret = true;
-
-	mutex_lock(&fs_info->qgroup_ioctl_lock);
-	if (!fs_info->quota_root)
-		ret = false;
-	mutex_unlock(&fs_info->qgroup_ioctl_lock);
-
-	return ret;
-}
-
 static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
 {
 	struct inode *inode = file_inode(file);
@@ -3741,7 +3725,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!qgroup_enabled(root->fs_info))
+	if (!btrfs_qgroup_enabled(fs_info))
 		return -ENOTCONN;
 
 	ret = mnt_want_write_file(file);
@@ -3811,7 +3795,7 @@ static long btrfs_ioctl_qgroup_create(struct file *file, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!qgroup_enabled(root->fs_info))
+	if (!btrfs_qgroup_enabled(root->fs_info))
 		return -ENOTCONN;
 
 	ret = mnt_want_write_file(file);
@@ -3870,7 +3854,7 @@ static long btrfs_ioctl_qgroup_limit(struct file *file, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!qgroup_enabled(root->fs_info))
+	if (!btrfs_qgroup_enabled(root->fs_info))
 		return -ENOTCONN;
 
 	ret = mnt_want_write_file(file);
@@ -3918,7 +3902,7 @@ static long btrfs_ioctl_quota_rescan(struct file *file, void __user *arg)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!qgroup_enabled(fs_info))
+	if (!btrfs_qgroup_enabled(fs_info))
 		return -ENOTCONN;
 
 	ret = mnt_want_write_file(file);