linux-ext4 - Re: [PATCH v5 04/10] fs: Expose name under lookup to d

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Date:   Fri, 11 Aug 2023 19:15:50 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Gabriel Krisman Bertazi <krisman@...e.de>
Cc:     viro@...iv.linux.org.uk, brauner@...nel.org, tytso@....edu,
        jaegeuk@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        Gabriel Krisman Bertazi <krisman@...labora.com>
Subject: Re: [PATCH v5 04/10] fs: Expose name under lookup to d_revalidate
 hooks

On Fri, Aug 11, 2023 at 08:41:40PM -0400, Gabriel Krisman Bertazi wrote:
> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
> index cb2a97e49872..ddd542c2a722 100644
> --- a/Documentation/filesystems/vfs.rst
> +++ b/Documentation/filesystems/vfs.rst
> @@ -1251,7 +1251,8 @@ defined:
>  .. code-block:: c
>  
>  	struct dentry_operations {
> -		int (*d_revalidate)(struct dentry *, unsigned int);
> +		int (*d_revalidate)(struct dentry *, const struct qstr *,
> +				    unsigned int);
>  		int (*d_weak_revalidate)(struct dentry *, unsigned int);
>  		int (*d_hash)(const struct dentry *, struct qstr *);
>  		int (*d_compare)(const struct dentry *,
> @@ -1284,6 +1285,14 @@ defined:
>  	they can change and, in d_inode case, even become NULL under
>  	us).
>  
> +	Filesystems shouldn't rely on the name under lookup, unless
> +	there are particular filename encoding semantics to be handled
> +	during revalidation.  Note the name under lookup can change from
> +	under d_revalidate, so it must be protected with ->d_lock before
> +	accessing.  The exception is when revalidating negative dentries
> +	for creation, in which case the parent inode prevents it from
> +	changing.

Actually, the "name under lookup" can never change.  It's passed as the 'name'
argument, newly added by this patch.  What this paragraph is actually about is
the ->d_name of the dentry being revalidated.  The documentation should make it
clear when it means ->d_name and when it means name, how they differ from each
other, and what the purpose of each is.

- Eric