Re: [RFC PATCH] kmod: add ability to swap root in usermode helper

From: Oleg Nesterov
Date: Mon May 20 2013 - 10:01:09 EST

On 05/20, Stanislav Kinsbursky wrote:
> Usermode helper executes all binaries in global "init" root context. This
> doesn't allow to call to call the binary from other root (for example in a
> container).
> Currently, containerized NFS server requires an ability to execute a binary in
> a other context, than "init" root (UMH is used for client recovery tracking).
> This patch adds root swap to ____call_usermodehelper(), if non-NULL root was
> passed as a part of subprocess_info data,

Why do we need the new member/arguments?

> @@ -215,6 +216,9 @@ static int ____call_usermodehelper(void *data)
> */
> set_user_nice(current, 0);
> + if (sub_info->root)
> + set_fs_root(current->fs, sub_info->root);

Can't subprocess_info->init() do this? You can pass root as ->data.

IOW, unless I missed something, nfs can do this without any changes
in kmod.c.


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