linux-kernel - Re: [PATCH v2 0/2] extend kexec_file

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Date:   Tue, 30 Aug 2016 20:25:08 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     kexec@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, Baoquan He <bhe@...hat.com>,
        David Laight <David.Laight@...lab.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 0/2] extend kexec_file_load system call

Hello Mark,

Sorry for taking this long to respond. I've been focusing on getting my 
kexec_file_load and kexec buffer hand-over series in shape.

Am Donnerstag, 18 August 2016, 11:21:13 schrieb Mark Rutland:
> On Thu, Aug 11, 2016 at 08:03:56PM -0300, Thiago Jung Bauermann wrote:
> > Device tree blob must be passed to a second kernel on DTB-capable
> > archs, like powerpc and arm64, but the current kernel interface
> > lacks this support.
> > 
> > This patch extends kexec_file_load system call by adding an extra
> > argument to this syscall so that an arbitrary number of file descriptors
> > can be handed out from user space to the kernel.
> > 
> > See the background [1].
> > 
> > Please note that the new interface looks quite similar to the current
> > system call, but that it won't always mean that it provides the "binary
> > compatibility."
> > 
> > [1] http://lists.infradead.org/pipermail/kexec/2016-June/016276.html
> 
> As with the original posting, I have a number of concerns, and I'm
> really not keen on this.

Thanks for laying out out the reasons for your objection. That's very 
helpful.

> * For typical usecases, I do not believe that this is necessary (at
>   least for arm64), and generally do not believe that it should be
>   necessary for a user to manipulate the DTB (much like the user need
>   not manipulate ACPI tables or other FW data structures).
> 
>   Other than (potentially) the case of Linux as a flashed-in bootloader,
>   I don't see a compelling case for modifying the DTB that could not be
>   accomplished in-kernel. For that case, if truly necessary, I think
>   that we can get away with something simpler.

Yes, this is the case I am aiming for. I'll experiment with a couple of 
different approaches and see how well they perform.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center