linux-kernel - kernel_thread() for non-GPL drivers

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Message-ID: <CAOxq_8PjG2Hzcdug-G7PJEcP8x02n+ezAw5AiEWpn71RjNt7ww@mail.gmail.com>
Date:	Tue, 2 Jun 2015 12:43:15 -0700
From:	Ani Sinha <ani@...sta.com>
To:	Al Viro <viro@...iv.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	fruggeri <fruggeri@...sta.com>,
	Ivan Delalande <colona@...sta.com>
Subject: kernel_thread() for non-GPL drivers

Hi Al :

I see that there has been some code re-org in linux 3.7 starting with

commit 7076aada1040de4ed79a5977dbabdb5e5ea5e249
Author: Al Viro <viro@...iv.linux.org.uk>
Date:   Mon Sep 10 16:44:54 2012 -0400

    x86: split ret_from_fork

    Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

This removed the kernel_thread() x86 specific function that was
exported to all drivers. Then the following commit added a generic
kernel_thread() function which no longer can be used by modules
because the symbol is not exported anymore :

commit 2aa3a7f8660355c3dddead17e224545c1a3d5a5f
Author: Al Viro <viro@...iv.linux.org.uk>
Date:   Fri Sep 21 19:55:31 2012 -0400

    preparation for generic kernel_thread()

    Let architectures select GENERIC_KERNEL_THREAD and have their copy_thread()
    treat NULL regs as "it came from kernel_thread(), sp argument contains
    the function new thread will be calling and stack_size - the argument for
    that function".  Switching the architectures begins shortly...

    Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

All arch specific code now uses this as all of them has
GENERIC_KERNEL_THREAD turned on and then later eventually this #ifdef
was also removed:

commit ae903caae267154de7cf8576b130ff474630596b
Author: Al Viro <viro@...iv.linux.org.uk>
Date:   Fri Dec 14 12:44:11 2012 -0500

    Bury the conditionals from kernel_thread/kernel_execve series

    All architectures have
        CONFIG_GENERIC_KERNEL_THREAD
        CONFIG_GENERIC_KERNEL_EXECVE
        __ARCH_WANT_SYS_EXECVE
    None of them have __ARCH_WANT_KERNEL_EXECVE and there are only two callers
    of kernel_execve() (which is a trivial wrapper for do_execve() now) left.
    Kill the conditionals and make both callers use do_execve().

    Signed-off-by: Al Viro <viro@...iv.linux.org.uk>


So my question to you is, which api (for x86) are drivers supposed to
use if kernel_thread() is no longer available? It looks to me like
maybe we can use kthread_run() which eventually lazily creates a
kernel thread. Is my understanding correct?

Cheers,
ani
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