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SubjectRe: [PATCH net-next 05/10] sysfs: add sysfs_change_owner()
On Wed, Feb 12, 2020 at 11:43:16AM +0100, Christian Brauner wrote:
> Add a helper to change the owner of sysfs objects.

Seems sane, but:

> 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.

A "sysfs object" is a kobject. So I don't understand this sentance,
sorry.

> 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@ubuntu.com>
> ---
> fs/sysfs/file.c | 35 +++++++++++++++++++++++++++++++++++
> include/linux/sysfs.h | 6 ++++++
> 2 files changed, 41 insertions(+)
>
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index 6239d9584f0b..6a0fe88061fd 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -642,3 +642,38 @@ int sysfs_file_change_owner(struct kobject *kobj, const char *name)
> return error;
> }
> EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
> +
> +/**
> + * sysfs_change_owner - change owner of the given object.
> + * @kobj: object.
> + */
> +int sysfs_change_owner(struct kobject *kobj)

What does this change the owner of the given object _to_?

> +{
> + int error;
> + const struct kobj_type *ktype;
> +
> + if (!kobj->state_in_sysfs)
> + return -EINVAL;
> +
> + error = sysfs_file_change_owner(kobj, NULL);

It passes NULL?


> + 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(kobj, (*kattr)->name);
> + if (error)
> + return error;
> + }
> +
> + error = sysfs_groups_change_owner(kobj, ktype->default_groups);
> + if (error)
> + return error;
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(sysfs_change_owner);

I can understand wanting to change owners/groups/whatever of existing
sysfs objects and their files, but I can't figure out how to call this
function to set the attribute I want to change.

With only one parameter, how does this work? It guesses? :)

thanks,

greg k-h

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