linux-kernel - Re: [PATCH v5 03/10] kexec_file: factor out arch_kexec_kernel

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Message-ID: <20171011050734.GE6756@linaro.org>
Date:   Wed, 11 Oct 2017 14:07:35 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Julien Thierry <julien.thierry@....com>
Cc:     catalin.marinas@....com, will.deacon@....com,
        bauerman@...ux.vnet.ibm.com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, akpm@...ux-foundation.org, mpe@...erman.id.au,
        dyoung@...hat.com, bhe@...hat.com, arnd@...db.de,
        ard.biesheuvel@...aro.org, kexec@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 03/10] kexec_file: factor out arch_kexec_kernel_*()
 from x86, powerpc

On Tue, Oct 10, 2017 at 12:02:01PM +0100, Julien Thierry wrote:

[snip]

> >--- a/kernel/kexec_file.c
> >+++ b/kernel/kexec_file.c
> >@@ -26,30 +26,79 @@
> >  #include <linux/vmalloc.h>
> >  #include "kexec_internal.h"
> >
> >+const __weak struct kexec_file_ops * const kexec_file_loaders[] = {NULL};
> >+
> >  static int kexec_calculate_store_digests(struct kimage *image);
> >
> >+int _kexec_kernel_image_probe(struct kimage *image, void *buf,
> >+                          unsigned long buf_len)
> >+{
> >+     const struct kexec_file_ops *fops;
> >+     int ret = -ENOEXEC;
> >+
> >+     for (fops = kexec_file_loaders[0]; fops && fops->probe; ++fops) {
> 
> Hmm, that's not gonna work (and I see that what I said in the previous
> patch was not 100% correct either).

Can you elaborate this a bit more?

I'm sure that, with my code, any member of fops, cannot be changed;
"const struct kexec_file_ops *fops" means that fops is a pointer to
"constant sturct kexec_file_ops," while "struct kexec_file_ops *
const kexec_file_loaders[]" means that kexec_file_loaders is a "constant
array" of pointers to "constant struct kexec_file_ops."

Thanks,
-Takahiro AKASHI


> 'fops' should be of type 'const struct kexec_file_ops **', and the loop
> should be:
> 
> for (fops = &kexec_file_loaders[0]; *fops && (*fops)->probe; ++fops)
> 
> With some additional dereferences in the body of the loop.
> 
> Unless you prefer the previous state of the loop (with i and the break
> inside), but I still think this looks better.
> 
> Cheers,
> 
> --
> Julien Thierry
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