Date:	Thu, 16 Apr 2015 20:32:43 +0300
From:	"Ivan.khoronzhuk" <ivan.khoronzhuk@...ballogic.com>
To:	subscivan <subscivan@...il.com>, Jean Delvare <jdelvare@...e.de>
CC:	linux-kernel@...r.kernel.org, matt.fleming@...el.com,
	ard.biesheuvel@...aro.org, grant.likely@...aro.org,
	linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
	mikew@...gle.com, dmidecode-devel@...gnu.org,
	leif.lindholm@...aro.org, msalter@...hat.com, roy.franz@...aro.org
Subject: Re: [Patch 2/3] firmware: dmi_scan: add SBMIOS entry and DMI tables

Sorry, sent it from not original mail.

On 16.04.15 20:27, subscivan wrote:
> Jean,
>
> On 16.04.15 18:44, Jean Delvare wrote:
>> Hi Ivan,
>>
>> Le Thursday 16 April 2015 à 15:56 +0300, Ivan.khoronzhuk a écrit :
>>> On 16.04.15 12:52, Jean Delvare wrote:
>>>> On Thu,  2 Apr 2015 15:57:02 +0300, Ivan Khoronzhuk wrote:
>>>>> +static BIN_ATTR(smbios_entry_point, S_IRUSR, raw_table_read, 
>>>>> NULL, 0);
>>>> This one could be world-readable as it contains no sensitive
>>>> information.
>>> It contains the address of DMI table containing sensitive information.
>>> Who knows which ways can be used to take it. Anyway, no see reasons 
>>> in this
>>> w/o DMI table. But if you insist I can do it "world-readable".
>> OK, you convinced me.
>>
>>>>> +struct bin_attribute bin_attr_dmi_table =
>>>>> +            __BIN_ATTR(DMI, S_IRUSR, raw_table_read, NULL, 0);
>>>> I do not understand why you don't use BIN_ATTR here too? I tried 
>>>> naming
>>>> the attribute bin_attr_DMI and it seems to work just fine, checkpatch
>>>> doesn't even complain!
>>> I dislike upper case in names, at least in such simple names.
>>> It makes me using bin_attr_DMI lower in the code. That's why.
>>> But if you like it, I will name it "bin_attr_DMI"
>> I don't like upper case in names either, but in this specific case, I'd
>> do it for consistency. As you wish though, I really only wanted to know
>> the reason.
>>
>>>>> +
>>>>> +static int __init dmi_init(void)
>>>>> +{
>>>>> +    int ret = -ENOMEM;
>>>>> +    struct kobject *tables_kobj = NULL;
>>>>> +
>>>>> +    if (!dmi_available) {
>>>>> +        ret = -ENOSYS;
>>>>> +        goto err;
>>>>> +    }
>>>> This is weird. Can this actually happen?
>>>>
>>>> We currently have two ways to enter this module: dmi_scan_machine(),
>>>> which is called by the architecture code, and dmi_init(), which is
>>>> called at subsys_initcall time. As far as I can see,
>>>> core/arch_initcalls are guaranteed to be always called before
>>>> subsys_initcalls. If we can rely on that, the test above is not 
>>>> needed.
>>>> If for any reason we can't, that means that dmi_init() should not be a
>>>> subsys_initcall, but should instead be called explicitly at the end of
>>>> dmi_scan_machine().
>>> We cannot be sure that firmware_kobj created at time of dmi_init().
>>> The sources don't oblige you to call it at core level,
>>> for instance like it was done for arm64. For x86, dmi_init() can be 
>>> called
>>> before firmware_kobj is created.
>> Looking at the code, it seems that firmware_kobj is created very, very
>> early in the boot process. In do_basic_setup(), you can see that
>> driver_init() (which in turn calls firmware_init(), creating
>> firmware_kobj) is called before do_initcalls(). So firmware_kobj must be
>> defined before dmi_scan_machine() or dmi_init() is called.
>
> No. Not must, rather should. See below.
>
>>
>> Oh, and this wasn't even my point ;-) I'm fine with you checking if
>> firmware_kobj is defined. My question was about the dmi_available check
>> above. But that question was silly anyway, sorry. I confused
>> dmi_available with dmi_initialized. Checking for dmi_available is
>> perfectly reasonable, please scratch my objection.
>>
>>> And if I call it from dmi_init() I suppose
>>> I would face an error. As I can't call it in dmi_init I can't be 
>>> sure that
>>> DMI is available at all. So, no, we have to check dmi_available here 
>>> and
>>> call it at subsys layer, where it's supposed to be.
>> I can't parse that, I suspect you wrote dmi_init where you actually
>> meant dmi_scan_machine? Given how early firmware_kobj is created, I
>> think the code currently in dmi_init could in fact go at the end of
>> dmi_scan_machine.
>
> Actually, dmi_scan_machine can be called even earlier.
> As I've sad, for x86, it's called before firmware_kobj is created.
>
> kernel_start()
>     setup_arch()
>         dmi_scan_machine()
>
> And for firmware_init(), as you noticed already:
>
> start_kernel()
>     rest_init()
>         kernel_init()
>             kernel_init_freeable()
>                 do_basic_setup()
>                     driver_init()
>                         firmware_init()
>
> Pay attentions that setup_arch() is called much earlier than rest_init().
> So dmi_init couldn't in fact go at the end of dmi_scan_machine.
>
>> But it's not important for the time being, this can be
>> attempted later.
>>
>>>>> (...)
>>>>> +    kobject_del(dmi_kobj);
>>>>> +    kobject_put(dmi_kobj);
>>>>> +    dmi_kobj = NULL;
>>>> I'm wondering, wouldn't it make sense to keep dmi_kobj alive (with an
>>>> appropriate comment), so that dmi-sysfs has a chance to load? As it is
>>>> now, a bug or some unexpected behavior in this new code could cause a
>>>> regression for dmi-sysfs users. Just because I don't like dmi_sysfs
>>>> doesn't mean we can break it ;-)
>>> As I remember it was not so critical for you last time.
>>> "I don't care which way you choose". And I've explained my position.
>>> But it's not very hard to me to change it. Anyway patch requires 
>>> re-push.
>> You're right, I did not remember we had discussed this already,
>> sorry :-(
>>
>> Well, I still agree that it doesn't really matter, but of two acceptable
>> solutions for an event which will most likely never happen, why not go
>> for the ones with the fewer lines of code? ;-)
>
> Ok.

-- 
Regards,
Ivan Khoronzhuk

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