linux-kernel - Re: [PATCH net-next 01/10] sysfs: add sysfs_file_change

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Date:   Wed, 12 Feb 2020 05:19:14 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH net-next 01/10] sysfs: add sysfs_file_change_owner()

On Wed, Feb 12, 2020 at 11:43:12AM +0100, Christian Brauner wrote:
> Add a helper to change the owner of a sysfs file.
> The ownership of a sysfs object is determined based on the ownership of
> the corresponding kobject, i.e. only if the ownership of a kobject is
> changed will this function change the ownership of the corresponding
> sysfs entry.
> This function will be used to correctly account for kobject ownership
> changes, e.g. when moving network devices between network namespaces.
> 
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> ---
>  fs/sysfs/file.c       | 46 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/sysfs.h |  7 +++++++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index 130fc6fbcc03..007b97ca8165 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -558,3 +558,49 @@ void sysfs_remove_bin_file(struct kobject *kobj,
>  	kernfs_remove_by_name(kobj->sd, attr->attr.name);
>  }
>  EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
> +
> +static int internal_change_owner(struct kernfs_node *kn, struct kobject *kobj)
> +{
> +	kuid_t uid;
> +	kgid_t gid;
> +	struct iattr newattrs = {
> +		.ia_valid = ATTR_UID | ATTR_GID,
> +	};
> +
> +	kobject_get_ownership(kobj, &uid, &gid);
> +	newattrs.ia_uid = uid;
> +	newattrs.ia_gid = gid;
> +
> +	return kernfs_setattr(kn, &newattrs);
> +}
> +
> +/**
> + *	sysfs_file_change_owner - change owner of a file.
> + *	@kobj:	object.
> + *	@name:	name of the file to change.
> + *	        can be NULL to change current file.
> + */
> +int sysfs_file_change_owner(struct kobject *kobj, const char *name)

Same meta-question I did for the other call, what does this set the file
owner to?  How to you specify this?

I understand your overall goal/need here, I'm just not understanding how
this actually changes anything.

lost,

greg k-h