Re: [RFC 02/22] configfs: Add struct configfs_item_operations->check_link() in configfs_unlink()

[Konrad Rzeszutek Wilk <konrad@darnok.org>]

On Monday 30 August 2010 05:20:25 Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@linux-iscsi.org>
>
> This patch adds a optional struct configfs_item_operations->check_link()
> check called in fs/configfs/symlink.c:configfs_unlink() that can be used by
> configfs consumers to check for an explict struct config_group dependence
> with active symlink and fail with -EPERM before the unlink(2) syscall is
> allowed to occur.
>
> Currently without this patch, there is not a method that a consumer can
> tell configfs_unlink() that it needs to fail for this particular case. 
> Allowing ->check_link() to propigate up the errno to VFS is also another
> option for the call, but currently for TCM using the existing -EPERM in
> configfs_unlink() is fine here.
>
> Note this patch is used by TCM v4 generic configfs fabric module
> infrastructure to allow  explict Initiator Port MappedLUNs symlinks to
> create a dependency for the fabric TPG Port LUNs living in a configfs group
> that is not a direct struct config_group parent.
>
> Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
> ---
>  fs/configfs/symlink.c    |   13 +++++++++++++
>  include/linux/configfs.h |    1 +
>  2 files changed, 14 insertions(+), 0 deletions(-)
>
> diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
> index 0f3eb41..b8010de 100644
> --- a/fs/configfs/symlink.c
> +++ b/fs/configfs/symlink.c
> @@ -205,6 +205,19 @@ int configfs_unlink(struct inode *dir, struct dentry
> *dentry) parent_item = configfs_get_config_item(dentry->d_parent);
>  	type = parent_item->ci_type;
>
> +	/*
> +	 * See if the underlying struct config_item has dependent
> +	 * symlinks, and should return -EPERM here.
> +	 */
> +	if (type && type->ct_item_ops &&
> +	    type->ct_item_ops->check_link) {
> +		if (type->ct_item_ops->check_link(parent_item,
> +					sl->sl_target) != 0) {
> +			config_item_put(parent_item);
> +			goto out;
> +		}
> +	}
> +
>  	spin_lock(&configfs_dirent_lock);
>  	list_del_init(&sd->s_sibling);
>  	spin_unlock(&configfs_dirent_lock);
> diff --git a/include/linux/configfs.h b/include/linux/configfs.h
> index ddb7a97..7c01d86 100644
> --- a/include/linux/configfs.h
> +++ b/include/linux/configfs.h
> @@ -226,6 +226,7 @@ struct configfs_item_operations {
>  	ssize_t	(*show_attribute)(struct config_item *, struct configfs_attribute
> *,char *); ssize_t	(*store_attribute)(struct config_item *,struct
> configfs_attribute *,const char *, size_t); int (*allow_link)(struct
> config_item *src, struct config_item *target); +	int (*check_link)(struct
> config_item *src, struct config_item *target); int (*drop_link)(struct
> config_item *src, struct config_item *target); };

You might want to copy these folks:

git/linux$ scripts/get_maintainer.pl -f fs/configfs/symlink.c
Joel Becker <joel.becker@oracle.com>
Tejun Heo <tj@kernel.org>
Al Viro <viro@zeniv.linux.org.uk>