Re: [PATCH v2 12/15] xfs: mount-api - add xfs_fc_free()

[Brian Foster <bfoster@redhat.com>]

On Fri, Aug 23, 2019 at 09:00:22AM +0800, Ian Kent wrote:
> Add the fs_context_operations method .free that performs fs
> context cleanup on context release.
> 
> Signed-off-by: Ian Kent <raven@themaw.net>
> ---
>  fs/xfs/xfs_super.c |   22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index aae0098fecab..9976163dc537 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -2129,10 +2129,32 @@ static const struct super_operations xfs_super_operations = {
>  	.free_cached_objects	= xfs_fs_free_cached_objects,
>  };
>  
> +static void xfs_fc_free(struct fs_context *fc)
> +{
> +	struct xfs_fs_context	*ctx = fc->fs_private;
> +	struct xfs_mount	*mp = fc->s_fs_info;
> +
> +	if (mp) {
> +		/*
> +		 * If an error occurs before ownership the xfs_mount
> +		 * info struct is passed to xfs by the VFS (by assigning
> +		 * it to sb->s_fs_info and clearing the corresponding
> +		 * fs_context field, which is done before calling fill
> +		 * super via .get_tree()) there may be some strings to
> +		 * cleanup.
> +		 */

The code looks straightforward but I find the comment confusing. How can
the VFS pass ownership of the xfs_mount if it's an XFS private data
structure?

> +		kfree(mp->m_logname);
> +		kfree(mp->m_rtname);
> +		kfree(mp);
> +	}
> +	kfree(ctx);

Also, should we at least reassign associated fc pointers to NULL if we
have multiple places to free things like ctx or mp?

Brian

> +}
> +
>  static const struct fs_context_operations xfs_context_ops = {
>  	.parse_param = xfs_parse_param,
>  	.get_tree    = xfs_get_tree,
>  	.reconfigure = xfs_reconfigure,
> +	.free	     = xfs_fc_free,
>  };
>  
>  static struct file_system_type xfs_fs_type = {
>