netdev - Re: [PATCH net-next v3 4/9] sysfs: add sysfs_change

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Date:   Thu, 20 Feb 2020 12:23:14 +0100
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 v3 4/9] sysfs: add sysfs_change_owner()

On Tue, Feb 18, 2020 at 05:29:38PM +0100, Christian Brauner wrote:
> Add a helper to change the owner of sysfs objects.
> 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>
> ---
> /* v2 */
> -  Greg Kroah-Hartman <gregkh@...uxfoundation.org>:
>    - Add comment how ownership of sysfs object is changed.
> 
> /* v3 */
> -  Greg Kroah-Hartman <gregkh@...uxfoundation.org>:
>    - Add explicit uid/gid parameters.
> ---
>  fs/sysfs/file.c       | 39 +++++++++++++++++++++++++++++++++++++++
>  include/linux/sysfs.h |  6 ++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index df5107d7b3fd..02f7e852aad4 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -665,3 +665,42 @@ int sysfs_file_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
>  	return error;
>  }
>  EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
> +
> +/**
> + *	sysfs_change_owner - change owner of the given object.

"and all of the files associated with this kobject", right?

> + *	@kobj:	object.
> + *	@kuid:	new owner's kuid
> + *	@kgid:	new owner's kgid
> + */
> +int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
> +{
> +	int error;
> +	const struct kobj_type *ktype;
> +
> +	if (!kobj->state_in_sysfs)
> +		return -EINVAL;
> +
> +	error = sysfs_file_change_owner(kobj, kuid, kgid);

Ok, this changes the attributes of the sysfs directory for the kobject
itself.

> +	if (error)
> +		return error;
> +
> +	ktype = get_ktype(kobj);
> +	if (ktype) {
> +		struct attribute **kattr;
> +
> +		for (kattr = ktype->default_attrs; kattr && *kattr; kattr++) {
> +			error = sysfs_file_change_owner_by_name(
> +				kobj, (*kattr)->name, kuid, kgid);
> +			if (error)
> +				return error;
> +		}

And here you change all of the files of the kobject.

But what about files that have a subdir?  Does that also happen here?

> +
> +		error = sysfs_groups_change_owner(kobj, ktype->default_groups,
> +						  kuid, kgid);

Then what are you changing here?

I think the kerneldoc needs a lot more explaination as to what is going
on in this function and why you would call it, and not some of the other
functions you are adding.

thanks,

greg k-h