linux-kernel - Re: [PATCH 2/2] afs: Make /afs/@...l and /afs/.@...l symlinks

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Message-ID: <20250107152050.GP1977892@ZenIV>
Date: Tue, 7 Jan 2025 15:20:50 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: David Howells <dhowells@...hat.com>
Cc: Marc Dionne <marc.dionne@...istor.com>,
	Christian Brauner <christian@...uner.io>,
	linux-afs@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] afs: Make /afs/@...l and /afs/.@...l symlinks

On Tue, Jan 07, 2025 at 02:25:09PM +0000, David Howells wrote:

> @@ -247,9 +285,13 @@ static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentr
>  		return ERR_PTR(-ENAMETOOLONG);
>  	}
>  
> -	if (dentry->d_name.len == 5 &&
> -	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
> -		return afs_lookup_atcell(dentry);
> +	if (dentry->d_name.len == sizeof(afs_atcell) - 1 &&
> +	    memcmp(dentry->d_name.name, afs_atcell, sizeof(afs_atcell) - 1) == 0)
> +		return afs_lookup_atcell(dentry, false);
> +
> +	if (dentry->d_name.len == sizeof(afs_dotatcell) - 1 &&
> +	    memcmp(dentry->d_name.name, afs_dotatcell, sizeof(afs_dotatcell) - 1) == 0)
> +		return afs_lookup_atcell(dentry, true);

Ow...  That looks just painful.

>  	return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
>  }
> @@ -343,6 +385,40 @@ void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)

> +static int afs_dynroot_symlink(struct afs_net *net)
> +{
> +	struct super_block *sb = net->dynroot_sb;
> +	struct dentry *root, *symlink, *dsymlink;
> +	int ret;
> +
> +	/* Let the ->lookup op do the creation */
> +	root = sb->s_root;
> +	inode_lock(root->d_inode);
> +	symlink = lookup_one_len(afs_atcell, root, sizeof(afs_atcell) - 1);
> +	if (IS_ERR(symlink)) {
> +		ret = PTR_ERR(symlink);
> +		goto unlock;
> +	}
> +
> +	dsymlink = lookup_one_len(afs_dotatcell, root, sizeof(afs_dotatcell) - 1);
> +	if (IS_ERR(dsymlink)) {
> +		ret = PTR_ERR(dsymlink);
> +		dput(symlink);
> +		goto unlock;
> +	}

Just allocate those child dentries and call your afs_lookup_atcell() for them.
No need to keep that mess in ->lookup() - you are keeping those suckers cached
now, so...