linux-kernel - Re: [PATCH] applesmc: add sysfs file to report OSK

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Message-Id: <4017A6C6-3074-44A5-AAAC-F4246946F151@exactcode.com>
Date:	Mon, 10 Dec 2012 21:43:50 +0100
From:	Rene Rebe <rene@...ctcode.com>
To:	Alexander Graf <agraf@...e.de>
Cc:	Henrik Rydberg <rydberg@...omail.se>,
	Guenter Roeck <groeck-dsl@...global.net>,
	"Gabriel L. Somlo" <somlo@....edu>,
	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"linux@...ck-us.net" <linux@...ck-us.net>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] applesmc: add sysfs file to report OSK


On 10.12.2012, at 21:19, Alexander Graf <agraf@...e.de> wrote:

> 
> On 10.12.2012, at 20:54, Henrik Rydberg wrote:
> 
>> Hi Guenter,
>> 
>>> On Mon, Dec 10, 2012 at 09:51:35AM -0500, Gabriel L. Somlo wrote:
>>>> The AppleSMC contains two char[32] keys, OSK0 and OSK1, which are not
>>>> reported in the key count and index by default. These keys are used by
>>>> the OS X boot sequence, and normally don't matter when running Linux.
>>>> 
>>>> This patch creates a sysfs entry which reports the value of these keys
>>>> as an ASCII string, to help emulators (such as QEMU) load OS X when
>>>> running on genuine Apple hardware.
>>>> 
>>>> Signed-off-by: Gabriel L. Somlo <somlo@....edu>
>>>> ---
>>>> 
>>>> For extra context: To boot OS X as a guest, QEMU must (among others)
>>>> emulate the AppleSMC. To boot successfully, OS X insists on querying
>>>> the (emulated) SMC for the value of OSK0 and OSK1. Currently, these
>>>> values must be supplied on the QEMU command line as
>>>> 
>>>> -device applesmc,osk="...concatenated values of OSK0 and OSK1..."
>>>> 
>>>> With the availability of /sys/devices/platform/applesmc.768/osk, the
>>>> emulated QEMU AppleSMC could acquire this string directly from the
>>>> (Apple-manufactured) host machine.
>>> Hmm ... this is a non-hwmon attribute which doesn't really belong into hwmon
>>> in the first place ... like several other attributes in the same driver.
>>> 
>>> So I'll leave it up to the maintainer to decide if we should accept it. Henrik ?
>> 
>> Indeed, the reaons against this patch are too many. I was just about
>> to reply with the below:
>> 
>> Gabriel,
>> 
>> The OSK string seems constant accross machines, which renders the
>> patch rather pointless, no? And even if the OSK differs between a
>> couple of machines, the emulator could easily handle it gracefully.
> 
> The point is that the return value of the OSK is a copyrighted string, we can not include in any other layer. The only way to make this legally savvy is to read the key from the host.
> 
>> 
>> There are also some technical issues with the patch below, to keep in
>> mind for future submissions.
> 
> Sigh - most of the comments below go back to earlier review from me. He basically had a version almost exactly like what you're asking him to do :). Funny how code style taste differs.

And this is exactly the reason why I'm less and less motivated to waste my lifetime with upstream work ...

> Alex
> 
>> 
>>> drivers/hwmon/applesmc.c |   18 ++++++++++++++++++
>>> 1 files changed, 18 insertions(+), 0 deletions(-)
>>> 
>>> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
>>> index b41baff..0c7cc71 100644
>>> --- a/drivers/hwmon/applesmc.c
>>> +++ b/drivers/hwmon/applesmc.c
>>> @@ -1013,6 +1013,23 @@ static ssize_t applesmc_key_at_index_store(struct device *dev,
>>>    return count;
>>> }
>>> 
>>> +static ssize_t applesmc_osk_show(struct device *dev,
>>> +                struct device_attribute *attr, char *sysfsbuf)
>>> +{
>>> +    int fail;
>> 
>> All other functions use 'ret' here...
>> 
>>> +
>>> +    mutex_lock(&smcreg.mutex);
>>> +    fail = read_smc(APPLESMC_READ_CMD, "OSK0", sysfsbuf, 32) ||
>>> +           read_smc(APPLESMC_READ_CMD, "OSK1", sysfsbuf + 32, 32);
>> 
>> The read function should propagate error messages, i.e., keep the
>> return values here. And please read to buffers instead.
>> 
>>> +    mutex_unlock(&smcreg.mutex);
>>> +    if (fail)
>>> +        return -1;
>> 
>> Return error here.
>> 
>>> +
>>> +    sysfsbuf[64] = '\n';
>>> +    sysfsbuf[65] = '\0';
>>> +    return 65;
>> 
>> A snprintf here, please.
>> 
>>> +}
>>> +
>>> static struct led_classdev applesmc_backlight = {
>>>    .name            = "smc::kbd_backlight",
>>>    .default_trigger    = "nand-disk",
>>> @@ -1027,6 +1044,7 @@ static struct applesmc_node_group info_group[] = {
>>>    { "key_at_index_type", applesmc_key_at_index_type_show },
>>>    { "key_at_index_data_length", applesmc_key_at_index_data_length_show },
>>>    { "key_at_index_data", applesmc_key_at_index_read_show },
>>> +    { "osk", applesmc_osk_show },
>> 
>> Unfortunately this is not a good place to put random things going
>> forward.
>> 
>>>    { }
>>> };
>>> 
>>> -- 
>>> 1.7.7.6
>> 
>> Given the above issues together with the weak rationale for the patch
>> in the first place, this patch will not be applied.
>> 
>> Thanks.
>> Henrik
> 
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