linux-kernel - Re: samples: livepatch: init reloc list and mark as klp module

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Message-ID: <20151112060249.GA5841@packer-debian-8-amd64.digitalocean.com>
Date:	Thu, 12 Nov 2015 01:02:50 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>, linux-api@...r.kernel.org,
	live-patching@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: samples: livepatch: init reloc list and mark as klp module

+++ Petr Mladek [11/11/15 16:42 +0100]:
>On Mon 2015-11-09 23:45:54, Jessica Yu wrote:
>> Intialize the list of relocation sections in the sample
>> klp_object (even if the list will be empty in this case).
>> Also mark module as a livepatch module so that the module
>> loader can appropriately initialize it.
>>
>> Signed-off-by: Jessica Yu <jeyu@...hat.com>
>> ---
>>  samples/livepatch/livepatch-sample.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
>> index fb8c861..2ef9345 100644
>> --- a/samples/livepatch/livepatch-sample.c
>> +++ b/samples/livepatch/livepatch-sample.c
>> @@ -89,3 +90,4 @@ static void livepatch_exit(void)
>>  module_init(livepatch_init);
>>  module_exit(livepatch_exit);
>>  MODULE_LICENSE("GPL");
>> +MODULE_INFO(livepatch, "Y");
>
>This looks a bit error prone. I wonder if we could detect this
>information another way. For example, by a check for the
>livepatch-related elf sections. If it is missing,
>we do not need to preserve struct load_info even
>when it is a livepatch.

Yeah, I agree that it is unnecessary for a livepatch module without
reloc secs to keep a copy of the load_info struct. My justification
for using MODULE_INFO is that I was trying to be consistent with the
way how other module "characteristics" are checked in the module
loader. For example, if the module came from the staging tree, the
module loader simply checks get_modinfo(info, "staging")). If the
module is a livepatch module, we check get_modinfo(info,
"livepatch")). I also thought that it might be useful additional
information for the user to be able to issue the modinfo command on a
module to see if it's a livepatch module or not (but maybe this
information won't be so useful after all, that's quite subjective).
But if we want to do a more thorough check, we could, like you said,
check for the livepatch-related elf sections before copying load_info.

Thanks,
Jessica
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