linux-kernel - Re: [PATCH 03/10] sysfs: added __compat_only_sysfs_link_entry_to

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Message-ID: <20151107002356.GA6026@newt.localdomain>
Date:	Fri, 6 Nov 2015 16:23:56 -0800
From:	Jeremiah Mahler <jmmahler@...il.com>
To:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	peterhuewe@....de, gregkh@...uxfoundation.org,
	jgunthorpe@...idianresearch.com, dhowells@...hat.com,
	artem.bityutskiy@...ux.intel.com, Tejun Heo <tj@...nel.org>,
	NeilBrown <neilb@...e.de>, Guenter Roeck <linux@...ck-us.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 03/10] sysfs: added
 __compat_only_sysfs_link_entry_to_kobj()

Jarkko,

On Fri, Oct 16, 2015 at 09:40:22PM +0300, Jarkko Sakkinen wrote:
> Added a new function __compat_only_sysfs_link_group_to_kobj() that adds
> a symlink from attribute or group to a kobject. This needed for
> maintaining backwards compatibility with PPI attributes in the TPM
> driver.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
>  fs/sysfs/group.c      | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/sysfs.h | 11 +++++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> index 39a0199..e123659 100644
> --- a/fs/sysfs/group.c
> +++ b/fs/sysfs/group.c
> @@ -352,3 +352,47 @@ void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
>  	}
>  }
>  EXPORT_SYMBOL_GPL(sysfs_remove_link_from_group);
> +
> +/**
> + * __compat_only_sysfs_link_entry_to_kobj - add a symlink to a kobject pointing
> + * to a group or an attribute
> + * @kobj:		The kobject containing the group.
> + * @target_kobj:	The target kobject.
> + * @target_name:	The name of the target group or attribute.
> + */
> +int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
> +				      struct kobject *target_kobj,
> +				      const char *target_name)
> +{
> +	struct kernfs_node *target;
> +	struct kernfs_node *entry;
> +	struct kernfs_node *link;
> +
> +	/*
> +	 * We don't own @target_kobj and it may be removed at any time.
> +	 * Synchronize using sysfs_symlink_target_lock. See sysfs_remove_dir()
> +	 * for details.
> +	 */
> +	spin_lock(&sysfs_symlink_target_lock);
> +	target = target_kobj->sd;
> +	if (target)
> +		kernfs_get(target);
> +	spin_unlock(&sysfs_symlink_target_lock);
> +	if (!target)
> +		return -ENOENT;
> +
> +	entry = kernfs_find_and_get(target_kobj->sd, target_name);
> +	if (!entry) {
> +		kernfs_put(target);
> +		return -ENOENT;
> +	}
> +
> +	link = kernfs_create_link(kobj->sd, target_name, entry);
> +	if (IS_ERR(link) && PTR_ERR(link) == -EEXIST)
> +		sysfs_warn_dup(kobj->sd, target_name);
> +
> +	kernfs_put(entry);
> +	kernfs_put(target);
> +	return IS_ERR(link) ? PTR_ERR(link) : 0;
> +}
> +EXPORT_SYMBOL_GPL(__compat_only_sysfs_link_entry_to_kobj);
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index 9f65758..ea090ea 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -268,6 +268,9 @@ int sysfs_add_link_to_group(struct kobject *kobj, const char *group_name,
>  			    struct kobject *target, const char *link_name);
>  void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
>  				  const char *link_name);
> +int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
> +				      struct kobject *target_kobj,
> +				      const char *target_name);
>  
>  void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr);
>  
> @@ -451,6 +454,14 @@ static inline void sysfs_remove_link_from_group(struct kobject *kobj,
>  {
>  }
>  
> +static inline int __compat_only_sysfs_link_entry_to_kobj(
> +	struct kobject *kobj,
> +	struct kobject *target_kobj,
> +	const char *target_name)
> +{
> +	return 0;
> +}
> +
>  static inline void sysfs_notify(struct kobject *kobj, const char *dir,
>  				const char *attr)
>  {
> -- 
> 2.5.0
> 
> --
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One problem with this patch is that it adds a bunch of code but none of
it is used.  So if there is a bug, git bisect will point to a later
patch instead of this one.

-- 
- Jeremiah Mahler
--
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