linux-kernel - Re: [PATCH] erofs: fix lockdep false positives on initializing erofs_pseudo

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Date: Thu, 7 Mar 2024 07:21:12 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Baokun Li <libaokun1@...wei.com>
Cc: linux-erofs@...ts.ozlabs.org, xiang@...nel.org, chao@...nel.org,
	huyue2@...lpad.com, jefflexu@...ux.alibaba.com,
	linux-kernel@...r.kernel.org, yangerkun@...wei.com,
	houtao1@...wei.com, yukuai3@...wei.com, chengzhihao1@...wei.com
Subject: Re: [PATCH] erofs: fix lockdep false positives on initializing
 erofs_pseudo_mnt

On Thu, Mar 07, 2024 at 03:06:49PM +0800, Baokun Li wrote:
> > > +int erofs_anon_register_fs(void)
> > > +{
> > > +	return register_filesystem(&erofs_anon_fs_type);
> > > +}
> > What for?  The only thing it gives you is an ability to look it up by
> > name.  Which is completely pointless, IMO,
> The helper function here is to avoid extern erofs_anon_fs_type(), because
> we define it in fscache.c, but also use it in super.c. Moreover, we don't
> need
> to register it when CONFIG_EROFS_FS_ONDEMAND is not enabled, so we

You don't need to register it at all.

The one and only effect of register_filesystem() is making file_system_type
instance visible to get_fs_type() (and making it show up in /proc/filesystems).

That's it.  If you want to have it looked up by name (e.g. for userland
mounts), you need to register.  If not, you do not need to do that.

Note that kern_mount() take a pointer to struct file_system_type,
not its (string) name.  So all you get from registration is an extra line
in /proc/filesystems.  What's the point?