linux-kernel - Re: [REPOST PATCH v4 1/5] kernfs: move revalidate to be near lookup

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Date:   Thu, 03 Jun 2021 09:50:34 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Ian Kent <raven@...maw.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, Eric Sandeen <sandeen@...deen.net>,
        Fox Chen <foxhlchen@...il.com>,
        Brice Goglin <brice.goglin@...il.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        Rick Lindsley <ricklind@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [REPOST PATCH v4 1/5] kernfs: move revalidate to be near lookup

Ian Kent <raven@...maw.net> writes:

> While the dentry operation kernfs_dop_revalidate() is grouped with
> dentry type functions it also has a strong affinity to the inode
> operation ->lookup().
>
> In order to take advantage of the VFS negative dentry caching that
> can be used to reduce path lookup overhead on non-existent paths it
> will need to call kernfs_find_ns(). So, to avoid a forward declaration,
> move it to be near kernfs_iop_lookup().
>
> There's no functional change from this patch.

Does this patch compile independently?

During the code movement  kernfs_active is replaced
by kernfs_active_read which does not exist yet.

Eric

> Signed-off-by: Ian Kent <raven@...maw.net>
> ---
>  fs/kernfs/dir.c |   86 ++++++++++++++++++++++++++++---------------------------
>  1 file changed, 43 insertions(+), 43 deletions(-)
>
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index 7e0e62deab53c..4c69e2af82dac 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -548,49 +548,6 @@ void kernfs_put(struct kernfs_node *kn)
>  }
>  EXPORT_SYMBOL_GPL(kernfs_put);
>  
> -static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
> -{
> -	struct kernfs_node *kn;
> -
> -	if (flags & LOOKUP_RCU)
> -		return -ECHILD;
> -
> -	/* Always perform fresh lookup for negatives */
> -	if (d_really_is_negative(dentry))
> -		goto out_bad_unlocked;
> -
> -	kn = kernfs_dentry_node(dentry);
> -	mutex_lock(&kernfs_mutex);
> -
> -	/* The kernfs node has been deactivated */
> -	if (!kernfs_active(kn))
> -		goto out_bad;
> -
> -	/* The kernfs node has been moved? */
> -	if (kernfs_dentry_node(dentry->d_parent) != kn->parent)
> -		goto out_bad;
> -
> -	/* The kernfs node has been renamed */
> -	if (strcmp(dentry->d_name.name, kn->name) != 0)
> -		goto out_bad;
> -
> -	/* The kernfs node has been moved to a different namespace */
> -	if (kn->parent && kernfs_ns_enabled(kn->parent) &&
> -	    kernfs_info(dentry->d_sb)->ns != kn->ns)
> -		goto out_bad;
> -
> -	mutex_unlock(&kernfs_mutex);
> -	return 1;
> -out_bad:
> -	mutex_unlock(&kernfs_mutex);
> -out_bad_unlocked:
> -	return 0;
> -}
> -
> -const struct dentry_operations kernfs_dops = {
> -	.d_revalidate	= kernfs_dop_revalidate,
> -};
> -
>  /**
>   * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
>   * @dentry: the dentry in question
> @@ -1073,6 +1030,49 @@ struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
>  	return ERR_PTR(rc);
>  }
>  
> +static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
> +{
> +	struct kernfs_node *kn;
> +
> +	if (flags & LOOKUP_RCU)
> +		return -ECHILD;
> +
> +	/* Always perform fresh lookup for negatives */
> +	if (d_really_is_negative(dentry))
> +		goto out_bad_unlocked;
> +
> +	kn = kernfs_dentry_node(dentry);
> +	mutex_lock(&kernfs_mutex);
> +
> +	/* The kernfs node has been deactivated */
> +	if (!kernfs_active_read(kn))
> +		goto out_bad;
> +
> +	/* The kernfs node has been moved? */
> +	if (kernfs_dentry_node(dentry->d_parent) != kn->parent)
> +		goto out_bad;
> +
> +	/* The kernfs node has been renamed */
> +	if (strcmp(dentry->d_name.name, kn->name) != 0)
> +		goto out_bad;
> +
> +	/* The kernfs node has been moved to a different namespace */
> +	if (kn->parent && kernfs_ns_enabled(kn->parent) &&
> +	    kernfs_info(dentry->d_sb)->ns != kn->ns)
> +		goto out_bad;
> +
> +	mutex_unlock(&kernfs_mutex);
> +	return 1;
> +out_bad:
> +	mutex_unlock(&kernfs_mutex);
> +out_bad_unlocked:
> +	return 0;
> +}
> +
> +const struct dentry_operations kernfs_dops = {
> +	.d_revalidate	= kernfs_dop_revalidate,
> +};
> +
>  static struct dentry *kernfs_iop_lookup(struct inode *dir,
>  					struct dentry *dentry,
>  					unsigned int flags)